[dev.typeparams] all: merge master (fdab5be) into dev.typeparams

Two non-conflict changes included because they're needed for all.bash: 1. Bump internal/goversion.Version to 18. This will happen eventually anyway (dev.typeparams will not be merged back to Go 1.17), and is needed for cmd/api to allow new API additions. 2. Add fixedbugs/issue46725.go (new test added on master) to the list of known failures for -G=3. This test exercises a bug that was fixed in typecheck, but -G=3 mode has duplicated that code and will need to be fixed as well. That's outside of the scope of a merge. Conflicts: - src/runtime/traceback.go Nearby lines were removed on both master and dev.typeparams. Merge List: + 2021-06-14 fdab5be159 doc/go1.17: further revise OpenBSD release notes + 2021-06-14 326ea438bb cmd/compile: rewrite a, b = f() to use temporaries when type not identical + 2021-06-14 3249b645c9 cmd/compile: factor out rewrite multi-valued f() + 2021-06-13 14305bf0b9 misc/cgo: generate Windows import libraries for clang + 2021-06-13 24cff0f044 cmd/go, misc/cgo: skip test if no .edata + 2021-06-13 67b1b6a2e3 cmd/compile: allow ir.OSLICE2ARRPTR in mayCall + 2021-06-12 1ed0d129e9 runtime: testprogcgo: don't call exported Go functions directly from Go + 2021-06-12 9d46ee5ac4 reflect: handle stack-to-register translation in callMethod + 2021-06-11 e552a6d312 cmd/go: remove hint when no module is suggested + 2021-06-11 16b5d766d8 syscall: do not load native libraries on non-native powershell on arm + 2021-06-11 77aa209b38 runtime: loop on EINTR in macOS sigNoteSleep + 2021-06-11 e2dc6dd5c9 doc/go1.17: clean up formatting of gofmt section + 2021-06-11 2f1128461d cmd/go: match Windows paths in TestScript/mod_invalid_version + 2021-06-11 2721da2608 doc/go1.17: fix formatting near httptest + 2021-06-10 770f1de8c5 net/http: remove test-only private key from production binaries + 2021-06-10 8d11b1d117 cmd/go: report the imports of CompiledGoFiles in ImportMap + 2021-06-10 dc00dc6c6b crypto/tls: let HTTP/1.1 clients connect to servers with NextProtos "h2" + 2021-06-09 27f83723e9 api: promote next to go1.17 + 2021-06-09 182157c81a doc/go1.17: remove lingering TODO + 2021-06-09 a5bc060b42 doc/go1.17: document strconv changes for Go 1.17 + 2021-06-09 1402b27d46 strconv: document parsing of leading +/- + 2021-06-09 df35ade067 doc/go1.17: document //go:build lines + 2021-06-09 e4e7807d24 net/http: add AllowQuerySemicolons + 2021-06-09 ec3026d032 doc/go1.17: remove TODO for ports section + 2021-06-09 e6dda19888 net/url: reject query values with semicolons + 2021-06-09 139e935d3c math/big: comment division + 2021-06-09 aa5540cd82 cmd/compile: make map.zero symbol content-addressable + 2021-06-09 07ca28d529 cmd/link: fix bug in -strictdups checking of BSS symbols + 2021-06-08 bcecae2af6 doc/go1.17: mention new possibility of type conversion panicking + 2021-06-08 63dcab2e91 doc/go1.17: mention new vet checks sigchanyzer and stdmethods. + 2021-06-08 6551763a60 doc/go1.17: mention block profile bias fix + 2021-06-08 cb80937bf6 Revert "doc/go1.17: mention block profile bias fix" + 2021-06-08 d3e3d03666 net: reject leading zeros in IP address parsers + 2021-06-08 da4a640141 doc/go1.17: revise OpenBSD release notes + 2021-06-08 689f4c7415 doc/go1.17: mention block profile bias fix + 2021-06-08 9afe071c60 doc/go1.17: remove TODO for Tools section + 2021-06-08 f753d7223e doc/go1.17: resolve TODO for cmd/cover + 2021-06-08 9498b0155d cmd/go: in Go 1.17+ modules, add indirect go.mod dependencies separately from direct ones + 2021-06-08 949f00cebe doc/go1.17: add release notes for crypto packages + 2021-06-08 0fb3e2c184 doc/go1.17: add a release note for the '-compat' flag to 'go mod tidy' + 2021-06-08 2169deb352 cmd/compile: use t.AllMethods when sorting typesByString + 2021-06-08 c20bcb6488 runtime: remove out-of-date comments about frame skipping + 2021-06-07 39c39ae52f doc: document Go 1.17 language changes + 2021-06-07 dc8b558951 cmd/dist: pass -Wno-lto-type-mismatch in swig_callback_lto + 2021-06-07 909dd5e010 strconv: ParseFloat: always return ErrSyntax for bad syntax Change-Id: Iffdf379d0275bbd12d50149ce38634773ced481d
author: Matthew Dempsky <mdempsky@google.com> 2021-06-14 12:26:41 -0700
committer: Matthew Dempsky <mdempsky@google.com> 2021-06-14 13:24:47 -0700
commit: ea438bda85ed473ecee215b098eba1f19113bc24 (patch)
tree: 78ea8b11917bcdf1e7c78c09c0395c684d55c054
parent: 8eeaf961c50973b0aa2065d2c31dfa5d9949bf93 (diff)
parent: fdab5be159c508c4c1cf5be84119fd2b38403cdf (diff)
download: go-ea438bda85ed473ecee215b098eba1f19113bc24.tar.gz
go-ea438bda85ed473ecee215b098eba1f19113bc24.zip
79 files changed, 2570 insertions, 563 deletions
diff --git a/api/go1.17.txt b/api/go1.17.txt
new file mode 100644
index 0000000000..f054458715
--- /dev/null
+++ b/api/go1.17.txt
@@ -0,0 +1,159 @@
+pkg archive/zip, method (*File) OpenRaw() (io.Reader, error)
+pkg archive/zip, method (*Writer) Copy(*File) error
+pkg archive/zip, method (*Writer) CreateRaw(*FileHeader) (io.Writer, error)
+pkg compress/lzw, method (*Reader) Close() error
+pkg compress/lzw, method (*Reader) Read([]uint8) (int, error)
+pkg compress/lzw, method (*Reader) Reset(io.Reader, Order, int)
+pkg compress/lzw, method (*Writer) Close() error
+pkg compress/lzw, method (*Writer) Reset(io.Writer, Order, int)
+pkg compress/lzw, method (*Writer) Write([]uint8) (int, error)
+pkg compress/lzw, type Reader struct
+pkg compress/lzw, type Writer struct
+pkg crypto/tls, method (*CertificateRequestInfo) Context() context.Context
+pkg crypto/tls, method (*ClientHelloInfo) Context() context.Context
+pkg crypto/tls, method (*Conn) HandshakeContext(context.Context) error
+pkg database/sql, method (*NullByte) Scan(interface{}) error
+pkg database/sql, method (*NullInt16) Scan(interface{}) error
+pkg database/sql, method (NullByte) Value() (driver.Value, error)
+pkg database/sql, method (NullInt16) Value() (driver.Value, error)
+pkg database/sql, type NullByte struct
+pkg database/sql, type NullByte struct, Byte uint8
+pkg database/sql, type NullByte struct, Valid bool
+pkg database/sql, type NullInt16 struct
+pkg database/sql, type NullInt16 struct, Int16 int16
+pkg database/sql, type NullInt16 struct, Valid bool
+pkg debug/elf, const SHT_MIPS_ABIFLAGS = 1879048234
+pkg debug/elf, const SHT_MIPS_ABIFLAGS SectionType
+pkg encoding/csv, method (*Reader) FieldPos(int) (int, int)
+pkg go/build, type Context struct, ToolTags []string
+pkg go/parser, const SkipObjectResolution = 64
+pkg go/parser, const SkipObjectResolution Mode
+pkg io/fs, func FileInfoToDirEntry(FileInfo) DirEntry
+pkg math, const MaxFloat64 = 1.79769e+308  // 179769313486231570814527423731704356798070567525844996598917476803157260780028538760589558632766878171540458953514382464234321326889464182768467546703537516986049910576551282076245490090389328944075868508455133942304583236903222948165808559332123348274797826204144723168738177180919299881250404026184124858368
+pkg math, const MaxInt = 9223372036854775807
+pkg math, const MaxInt ideal-int
+pkg math, const MaxUint = 18446744073709551615
+pkg math, const MaxUint ideal-int
+pkg math, const MinInt = -9223372036854775808
+pkg math, const MinInt ideal-int
+pkg math, const SmallestNonzeroFloat32 = 1.4013e-45  // 1/713623846352979940529142984724747568191373312
+pkg math, const SmallestNonzeroFloat64 = 4.94066e-324  // 1/202402253307310618352495346718917307049556649764142118356901358027430339567995346891960383701437124495187077864316811911389808737385793476867013399940738509921517424276566361364466907742093216341239767678472745068562007483424692698618103355649159556340810056512358769552333414615230502532186327508646006263307707741093494784
+pkg net, method (*ParseError) Temporary() bool
+pkg net, method (*ParseError) Timeout() bool
+pkg net, method (IP) IsPrivate() bool
+pkg net/http, func AllowQuerySemicolons(Handler) Handler
+pkg net/url, method (Values) Has(string) bool
+pkg reflect, func VisibleFields(Type) []StructField
+pkg reflect, method (Method) IsExported() bool
+pkg reflect, method (StructField) IsExported() bool
+pkg runtime/cgo (darwin-amd64-cgo), func NewHandle(interface{}) Handle
+pkg runtime/cgo (darwin-amd64-cgo), method (Handle) Delete()
+pkg runtime/cgo (darwin-amd64-cgo), method (Handle) Value() interface{}
+pkg runtime/cgo (darwin-amd64-cgo), type Handle uintptr
+pkg runtime/cgo (freebsd-386-cgo), func NewHandle(interface{}) Handle
+pkg runtime/cgo (freebsd-386-cgo), method (Handle) Delete()
+pkg runtime/cgo (freebsd-386-cgo), method (Handle) Value() interface{}
+pkg runtime/cgo (freebsd-386-cgo), type Handle uintptr
+pkg runtime/cgo (freebsd-amd64-cgo), func NewHandle(interface{}) Handle
+pkg runtime/cgo (freebsd-amd64-cgo), method (Handle) Delete()
+pkg runtime/cgo (freebsd-amd64-cgo), method (Handle) Value() interface{}
+pkg runtime/cgo (freebsd-amd64-cgo), type Handle uintptr
+pkg runtime/cgo (freebsd-arm-cgo), func NewHandle(interface{}) Handle
+pkg runtime/cgo (freebsd-arm-cgo), method (Handle) Delete()
+pkg runtime/cgo (freebsd-arm-cgo), method (Handle) Value() interface{}
+pkg runtime/cgo (freebsd-arm-cgo), type Handle uintptr
+pkg runtime/cgo (linux-386-cgo), func NewHandle(interface{}) Handle
+pkg runtime/cgo (linux-386-cgo), method (Handle) Delete()
+pkg runtime/cgo (linux-386-cgo), method (Handle) Value() interface{}
+pkg runtime/cgo (linux-386-cgo), type Handle uintptr
+pkg runtime/cgo (linux-amd64-cgo), func NewHandle(interface{}) Handle
+pkg runtime/cgo (linux-amd64-cgo), method (Handle) Delete()
+pkg runtime/cgo (linux-amd64-cgo), method (Handle) Value() interface{}
+pkg runtime/cgo (linux-amd64-cgo), type Handle uintptr
+pkg runtime/cgo (linux-arm-cgo), func NewHandle(interface{}) Handle
+pkg runtime/cgo (linux-arm-cgo), method (Handle) Delete()
+pkg runtime/cgo (linux-arm-cgo), method (Handle) Value() interface{}
+pkg runtime/cgo (linux-arm-cgo), type Handle uintptr
+pkg runtime/cgo (netbsd-386-cgo), func NewHandle(interface{}) Handle
+pkg runtime/cgo (netbsd-386-cgo), method (Handle) Delete()
+pkg runtime/cgo (netbsd-386-cgo), method (Handle) Value() interface{}
+pkg runtime/cgo (netbsd-386-cgo), type Handle uintptr
+pkg runtime/cgo (netbsd-amd64-cgo), func NewHandle(interface{}) Handle
+pkg runtime/cgo (netbsd-amd64-cgo), method (Handle) Delete()
+pkg runtime/cgo (netbsd-amd64-cgo), method (Handle) Value() interface{}
+pkg runtime/cgo (netbsd-amd64-cgo), type Handle uintptr
+pkg runtime/cgo (netbsd-arm-cgo), func NewHandle(interface{}) Handle
+pkg runtime/cgo (netbsd-arm-cgo), method (Handle) Delete()
+pkg runtime/cgo (netbsd-arm-cgo), method (Handle) Value() interface{}
+pkg runtime/cgo (netbsd-arm-cgo), type Handle uintptr
+pkg runtime/cgo (netbsd-arm64-cgo), func NewHandle(interface{}) Handle
+pkg runtime/cgo (netbsd-arm64-cgo), method (Handle) Delete()
+pkg runtime/cgo (netbsd-arm64-cgo), method (Handle) Value() interface{}
+pkg runtime/cgo (netbsd-arm64-cgo), type Handle uintptr
+pkg runtime/cgo (openbsd-386-cgo), func NewHandle(interface{}) Handle
+pkg runtime/cgo (openbsd-386-cgo), method (Handle) Delete()
+pkg runtime/cgo (openbsd-386-cgo), method (Handle) Value() interface{}
+pkg runtime/cgo (openbsd-386-cgo), type Handle uintptr
+pkg runtime/cgo (openbsd-amd64-cgo), func NewHandle(interface{}) Handle
+pkg runtime/cgo (openbsd-amd64-cgo), method (Handle) Delete()
+pkg runtime/cgo (openbsd-amd64-cgo), method (Handle) Value() interface{}
+pkg runtime/cgo (openbsd-amd64-cgo), type Handle uintptr
+pkg strconv, func QuotedPrefix(string) (string, error)
+pkg sync/atomic, method (*Value) CompareAndSwap(interface{}, interface{}) bool
+pkg sync/atomic, method (*Value) Swap(interface{}) interface{}
+pkg syscall (netbsd-386), const SYS_WAIT6 = 481
+pkg syscall (netbsd-386), const SYS_WAIT6 ideal-int
+pkg syscall (netbsd-386), const WEXITED = 32
+pkg syscall (netbsd-386), const WEXITED ideal-int
+pkg syscall (netbsd-386-cgo), const SYS_WAIT6 = 481
+pkg syscall (netbsd-386-cgo), const SYS_WAIT6 ideal-int
+pkg syscall (netbsd-386-cgo), const WEXITED = 32
+pkg syscall (netbsd-386-cgo), const WEXITED ideal-int
+pkg syscall (netbsd-amd64), const SYS_WAIT6 = 481
+pkg syscall (netbsd-amd64), const SYS_WAIT6 ideal-int
+pkg syscall (netbsd-amd64), const WEXITED = 32
+pkg syscall (netbsd-amd64), const WEXITED ideal-int
+pkg syscall (netbsd-amd64-cgo), const SYS_WAIT6 = 481
+pkg syscall (netbsd-amd64-cgo), const SYS_WAIT6 ideal-int
+pkg syscall (netbsd-amd64-cgo), const WEXITED = 32
+pkg syscall (netbsd-amd64-cgo), const WEXITED ideal-int
+pkg syscall (netbsd-arm), const SYS_WAIT6 = 481
+pkg syscall (netbsd-arm), const SYS_WAIT6 ideal-int
+pkg syscall (netbsd-arm), const WEXITED = 32
+pkg syscall (netbsd-arm), const WEXITED ideal-int
+pkg syscall (netbsd-arm-cgo), const SYS_WAIT6 = 481
+pkg syscall (netbsd-arm-cgo), const SYS_WAIT6 ideal-int
+pkg syscall (netbsd-arm-cgo), const WEXITED = 32
+pkg syscall (netbsd-arm-cgo), const WEXITED ideal-int
+pkg syscall (netbsd-arm64), const SYS_WAIT6 = 481
+pkg syscall (netbsd-arm64), const SYS_WAIT6 ideal-int
+pkg syscall (netbsd-arm64), const WEXITED = 32
+pkg syscall (netbsd-arm64), const WEXITED ideal-int
+pkg syscall (netbsd-arm64-cgo), const SYS_WAIT6 = 481
+pkg syscall (netbsd-arm64-cgo), const SYS_WAIT6 ideal-int
+pkg syscall (netbsd-arm64-cgo), const WEXITED = 32
+pkg syscall (netbsd-arm64-cgo), const WEXITED ideal-int
+pkg syscall (openbsd-386), const MSG_CMSG_CLOEXEC = 2048
+pkg syscall (openbsd-386), const MSG_CMSG_CLOEXEC ideal-int
+pkg syscall (openbsd-386-cgo), const MSG_CMSG_CLOEXEC = 2048
+pkg syscall (openbsd-386-cgo), const MSG_CMSG_CLOEXEC ideal-int
+pkg syscall (openbsd-amd64), const MSG_CMSG_CLOEXEC = 2048
+pkg syscall (openbsd-amd64), const MSG_CMSG_CLOEXEC ideal-int
+pkg syscall (openbsd-amd64-cgo), const MSG_CMSG_CLOEXEC = 2048
+pkg syscall (openbsd-amd64-cgo), const MSG_CMSG_CLOEXEC ideal-int
+pkg syscall (windows-386), type SysProcAttr struct, AdditionalInheritedHandles []Handle
+pkg syscall (windows-386), type SysProcAttr struct, ParentProcess Handle
+pkg syscall (windows-amd64), type SysProcAttr struct, AdditionalInheritedHandles []Handle
+pkg syscall (windows-amd64), type SysProcAttr struct, ParentProcess Handle
+pkg testing, method (*B) Setenv(string, string)
+pkg testing, method (*T) Setenv(string, string)
+pkg text/template/parse, const SkipFuncCheck = 2
+pkg text/template/parse, const SkipFuncCheck Mode
+pkg time, const Layout = "01/02 03:04:05PM '06 -0700"
+pkg time, const Layout ideal-string
+pkg time, func UnixMicro(int64) Time
+pkg time, func UnixMilli(int64) Time
+pkg time, method (*Time) IsDST() bool
+pkg time, method (Time) GoString() string
+pkg time, method (Time) UnixMicro() int64
+pkg time, method (Time) UnixMilli() int64
diff --git a/api/next.txt b/api/next.txt
index 9e996005c6..e69de29bb2 100644
--- a/api/next.txt
+++ b/api/next.txt
@@ -1,99 +0,0 @@
-pkg compress/lzw, method (*Reader) Close() error
-pkg compress/lzw, method (*Reader) Read([]uint8) (int, error)
-pkg compress/lzw, method (*Reader) Reset(io.Reader, Order, int)
-pkg compress/lzw, method (*Writer) Close() error
-pkg compress/lzw, method (*Writer) Reset(io.Writer, Order, int)
-pkg compress/lzw, method (*Writer) Write([]uint8) (int, error)
-pkg compress/lzw, type Reader struct
-pkg compress/lzw, type Writer struct
-pkg crypto/tls, method (*CertificateRequestInfo) Context() context.Context
-pkg crypto/tls, method (*ClientHelloInfo) Context() context.Context
-pkg crypto/tls, method (*Conn) HandshakeContext(context.Context) error
-pkg debug/elf, const SHT_MIPS_ABIFLAGS = 1879048234
-pkg debug/elf, const SHT_MIPS_ABIFLAGS SectionType
-pkg encoding/csv, method (*Reader) FieldPos(int) (int, int)
-pkg go/ast, method (*FuncDecl) IsMethod() bool
-pkg go/build, type Context struct, ToolTags []string
-pkg go/parser, const SkipObjectResolution = 64
-pkg go/parser, const SkipObjectResolution Mode
-pkg go/types, type Config struct, GoVersion string
-pkg io/fs, func FileInfoToDirEntry(FileInfo) DirEntry
-pkg net, method (*ParseError) Temporary() bool
-pkg net, method (*ParseError) Timeout() bool
-pkg net, method (IP) IsPrivate() bool
-pkg reflect, func VisibleFields(Type) []StructField
-pkg reflect, method (Method) IsExported() bool
-pkg reflect, method (StructField) IsExported() bool
-pkg runtime/cgo (darwin-amd64-cgo), func NewHandle(interface{}) Handle
-pkg runtime/cgo (darwin-amd64-cgo), method (Handle) Delete()
-pkg runtime/cgo (darwin-amd64-cgo), method (Handle) Value() interface{}
-pkg runtime/cgo (darwin-amd64-cgo), type Handle uintptr
-pkg runtime/cgo (freebsd-386-cgo), func NewHandle(interface{}) Handle
-pkg runtime/cgo (freebsd-386-cgo), method (Handle) Delete()
-pkg runtime/cgo (freebsd-386-cgo), method (Handle) Value() interface{}
-pkg runtime/cgo (freebsd-386-cgo), type Handle uintptr
-pkg runtime/cgo (freebsd-amd64-cgo), func NewHandle(interface{}) Handle
-pkg runtime/cgo (freebsd-amd64-cgo), method (Handle) Delete()
-pkg runtime/cgo (freebsd-amd64-cgo), method (Handle) Value() interface{}
-pkg runtime/cgo (freebsd-amd64-cgo), type Handle uintptr
-pkg runtime/cgo (freebsd-arm-cgo), func NewHandle(interface{}) Handle
-pkg runtime/cgo (freebsd-arm-cgo), method (Handle) Delete()
-pkg runtime/cgo (freebsd-arm-cgo), method (Handle) Value() interface{}
-pkg runtime/cgo (freebsd-arm-cgo), type Handle uintptr
-pkg runtime/cgo (linux-386-cgo), func NewHandle(interface{}) Handle
-pkg runtime/cgo (linux-386-cgo), method (Handle) Delete()
-pkg runtime/cgo (linux-386-cgo), method (Handle) Value() interface{}
-pkg runtime/cgo (linux-386-cgo), type Handle uintptr
-pkg runtime/cgo (linux-amd64-cgo), func NewHandle(interface{}) Handle
-pkg runtime/cgo (linux-amd64-cgo), method (Handle) Delete()
-pkg runtime/cgo (linux-amd64-cgo), method (Handle) Value() interface{}
-pkg runtime/cgo (linux-amd64-cgo), type Handle uintptr
-pkg runtime/cgo (linux-arm-cgo), func NewHandle(interface{}) Handle
-pkg runtime/cgo (linux-arm-cgo), method (Handle) Delete()
-pkg runtime/cgo (linux-arm-cgo), method (Handle) Value() interface{}
-pkg runtime/cgo (linux-arm-cgo), type Handle uintptr
-pkg runtime/cgo (netbsd-386-cgo), func NewHandle(interface{}) Handle
-pkg runtime/cgo (netbsd-386-cgo), method (Handle) Delete()
-pkg runtime/cgo (netbsd-386-cgo), method (Handle) Value() interface{}
-pkg runtime/cgo (netbsd-386-cgo), type Handle uintptr
-pkg runtime/cgo (netbsd-amd64-cgo), func NewHandle(interface{}) Handle
-pkg runtime/cgo (netbsd-amd64-cgo), method (Handle) Delete()
-pkg runtime/cgo (netbsd-amd64-cgo), method (Handle) Value() interface{}
-pkg runtime/cgo (netbsd-amd64-cgo), type Handle uintptr
-pkg runtime/cgo (netbsd-arm-cgo), func NewHandle(interface{}) Handle
-pkg runtime/cgo (netbsd-arm-cgo), method (Handle) Delete()
-pkg runtime/cgo (netbsd-arm-cgo), method (Handle) Value() interface{}
-pkg runtime/cgo (netbsd-arm-cgo), type Handle uintptr
-pkg runtime/cgo (netbsd-arm64-cgo), func NewHandle(interface{}) Handle
-pkg runtime/cgo (netbsd-arm64-cgo), method (Handle) Delete()
-pkg runtime/cgo (netbsd-arm64-cgo), method (Handle) Value() interface{}
-pkg runtime/cgo (netbsd-arm64-cgo), type Handle uintptr
-pkg runtime/cgo (openbsd-386-cgo), func NewHandle(interface{}) Handle
-pkg runtime/cgo (openbsd-386-cgo), method (Handle) Delete()
-pkg runtime/cgo (openbsd-386-cgo), method (Handle) Value() interface{}
-pkg runtime/cgo (openbsd-386-cgo), type Handle uintptr
-pkg runtime/cgo (openbsd-amd64-cgo), func NewHandle(interface{}) Handle
-pkg runtime/cgo (openbsd-amd64-cgo), method (Handle) Delete()
-pkg runtime/cgo (openbsd-amd64-cgo), method (Handle) Value() interface{}
-pkg runtime/cgo (openbsd-amd64-cgo), type Handle uintptr
-pkg syscall (openbsd-386), const MSG_CMSG_CLOEXEC = 2048
-pkg syscall (openbsd-386), const MSG_CMSG_CLOEXEC ideal-int
-pkg syscall (openbsd-386-cgo), const MSG_CMSG_CLOEXEC = 2048
-pkg syscall (openbsd-386-cgo), const MSG_CMSG_CLOEXEC ideal-int
-pkg syscall (openbsd-amd64), const MSG_CMSG_CLOEXEC = 2048
-pkg syscall (openbsd-amd64), const MSG_CMSG_CLOEXEC ideal-int
-pkg syscall (openbsd-amd64-cgo), const MSG_CMSG_CLOEXEC = 2048
-pkg syscall (openbsd-amd64-cgo), const MSG_CMSG_CLOEXEC ideal-int
-pkg syscall (windows-386), type SysProcAttr struct, AdditionalInheritedHandles []Handle
-pkg syscall (windows-386), type SysProcAttr struct, ParentProcess Handle
-pkg syscall (windows-amd64), type SysProcAttr struct, AdditionalInheritedHandles []Handle
-pkg syscall (windows-amd64), type SysProcAttr struct, ParentProcess Handle
-pkg testing, method (*B) Setenv(string, string)
-pkg testing, method (*T) Setenv(string, string)
-pkg text/template/parse, const SkipFuncCheck = 2
-pkg text/template/parse, const SkipFuncCheck Mode
-pkg time, func UnixMicro(int64) Time
-pkg time, func UnixMilli(int64) Time
-pkg time, method (*Time) IsDST() bool
-pkg time, method (Time) UnixMicro() int64
-pkg time, method (Time) UnixMilli() int64
diff --git a/doc/go1.17.html b/doc/go1.17.html
index 7438d894fe..35d0f97450 100644
--- a/doc/go1.17.html
+++ b/doc/go1.17.html
@@ -25,12 +25,54 @@ Do not send CLs removing the interior tags from such phrases.
 
 <h2 id="language">Changes to the language</h2>
 
-<p><!-- CL 216424 -->
-  TODO: <a href="https://golang.org/cl/216424">https://golang.org/cl/216424</a>: allow conversion from slice to array ptr
+<p>
+  Go 1.17 includes three small enhancements to the language.
+</p>
+
+<ul>
+  <li><!-- CL 216424; issue 395 -->
+    <a href="/ref/spec#Conversions_from_slice_to_array_pointer">Conversions
+    from slice to array pointer</a>: An expression <code>s</code> of
+    type <code>[]T</code> may now be converted to array pointer type
+    <code>*[N]T</code>. If <code>a</code> is the result of such a
+    conversion, then corresponding indices that are in range refer to
+    the same underlying elements: <code>&amp;a[i] == &amp;s[i]</code>
+    for <code>0 &lt;= i &lt; N</code>. The conversion panics if
+    <code>len(s)</code> is less than <code>N</code>.
+  </li>
+
+  <li><!-- CL 312212; issue 40481 -->
+    <a href="/pkg/unsafe#Add"><code>unsafe.Add</code></a>:
+    <code>unsafe.Add(ptr, len)</code> adds <code>len</code>
+    to <code>ptr</code> and returns the updated pointer
+    <code>unsafe.Pointer(uintptr(ptr) + uintptr(len))</code>.
+  </li>
+
+  <li><!-- CL 312212; issue 19367 -->
+    <a href="/pkg/unsafe#Slice"><code>unsafe.Slice</code></a>:
+    For expression <code>ptr</code> of type <code>*T</code>,
+    <code>unsafe.Slice(ptr, len)</code> returns a slice of
+    type <code>[]T</code> whose underlying array starts
+    at <code>ptr</code> and whose length and capacity
+    are <code>len</code>.
+  </li>
+</ul>
+
+<p>
+  These enhancements were added to simplify writing code that conforms
+  to <code>unsafe.Pointer</code>'s <a href="/pkg/unsafe/#Pointer">safety
+  rules</a>, but the rules remain unchanged. In particular, existing
+  programs that correctly use <code>unsafe.Pointer</code> remain
+  valid, and new programs must still follow the rules when
+  using <code>unsafe.Add</code> or <code>unsafe.Slice</code>.
 </p>
 
-<p><!-- CL 312212 -->
-  TODO: <a href="https://golang.org/cl/312212">https://golang.org/cl/312212</a>: add unsafe.Add and unsafe.Slice
+
+<p>
+  Note that the new conversion from slice to array pointer is the
+  first case in which a type conversion can panic at run time.
+  Analysis tools that assume type conversions can never panic
+  should be updated to consider this possibility.
 </p>
 
 <h2 id="ports">Ports</h2>
@@ -61,11 +103,12 @@ Do not send CLs removing the interior tags from such phrases.
   In Go 1.16, on the 64-bit x86 and 64-bit ARM architectures on
   OpenBSD (the <code>openbsd/amd64</code> and <code>openbsd/arm64</code>
   ports) system calls are made through <code>libc</code>, instead
-  of directly using the machine instructions. In Go 1.17, this is
-  also done on the 32-bit x86 and 32-bit ARM architectures on OpenBSD
+  of directly using machine instructions. In Go 1.17, this is also
+  done on the 32-bit x86 and 32-bit ARM architectures on OpenBSD
   (the <code>openbsd/386</code> and <code>openbsd/arm</code> ports).
-  This ensures forward-compatibility with future versions of
-  OpenBSD.
+  This ensures compatibility with OpenBSD 6.9 onwards, which require
+  system calls to be made through <code>libc</code> for non-static
+  Go binaries.
 </p>
 
 <h3 id="arm64">ARM64</h3>
@@ -76,16 +119,8 @@ Do not send CLs removing the interior tags from such phrases.
   stack frame pointers only on Linux, macOS, and iOS.
 </p>
 
-<p>
-  TODO: complete the Ports section
-</p>
-
 <h2 id="tools">Tools</h2>
 
-<p>
-  TODO: complete the Tools section
-</p>
-
 <h3 id="go-command">Go command</h3>
 
 <h4 id="lazy-loading">Lazy module loading</h4>
@@ -103,8 +138,17 @@ Do not send CLs removing the interior tags from such phrases.
   <!-- TODO(bcmills): replace the design-doc link with proper documentation. -->
 </p>
 
-<p><!-- golang.org/issue/45094 --> To facilitate the upgrade to lazy loading,
-  the <code>go</code> <code>mod</code> <code>tidy</code> subcommand now supports
+<p><!-- golang.org/issue/45965 -->
+  Because the number of additional explicit requirements in the go.mod file may
+  be substantial, in a Go 1.17 module the newly-added requirements
+  on <em>indirect</em> dependencies are maintained in a
+  separate <code>require</code> block from the block containing direct
+  dependencies.
+</p>
+
+<p><!-- golang.org/issue/45094 -->
+  To facilitate the upgrade to lazy loading, the
+  <code>go</code> <code>mod</code> <code>tidy</code> subcommand now supports
   a <code>-go</code> flag to set or change the <code>go</code> version in
   the <code>go.mod</code> file. To enable lazy loading for an existing module
   without changing the selected versions of its dependencies, run:
@@ -115,8 +159,32 @@ Do not send CLs removing the interior tags from such phrases.
 </pre>
 
 <p><!-- golang.org/issue/46141 -->
-  TODO: Describe the <code>-compat</code> flag
-  for <code>go</code> <code>mod</code> <code>tidy</code>.
+  By default, <code>go</code> <code>mod</code> <code>tidy</code> verifies that
+  the selected versions of dependencies relevant to the main module are the same
+  versions that would be used by the prior Go release (Go 1.16 for a module that
+  spsecifies <code>go</code> <code>1.17</code>), and preserves
+  the <code>go.sum</code> entries needed by that release even for dependencies
+  that are not normally needed by other commands.
+</p>
+
+<p>
+  The <code>-compat</code> flag allows that version to be overridden to support
+  older (or only newer) versions, up to the version specified by
+  the <code>go</code> directive in the <code>go.mod</code> file. To tidy
+  a <code>go</code> <code>1.17</code> module for Go 1.17 only, without saving
+  checksums for (or checking for consistency with) Go 1.16:
+</p>
+
+<pre>
+  go mod tidy -compat=1.17
+</pre>
+
+<p>
+  Note that even if the main module is tidied with <code>-compat=1.17</code>,
+  users who <code>require</code> the module from a
+  <code>go</code> <code>1.16</code> or earlier module will still be able to
+  use it, provided that the packages use only compatible language and library
+  features.
 </p>
 
 <h4 id="module-deprecation-comments">Module deprecation comments</h4>
@@ -210,18 +278,94 @@ Do not send CLs removing the interior tags from such phrases.
   <code>mod</code> <code>download</code> <code>all</code>.
 </p>
 
-<p><!-- CL 249759 -->
-  TODO: <a href="https://golang.org/cl/249759">https://golang.org/cl/249759</a>: cmd/cover: replace code using optimized golang.org/x/tools/cover
+<h4 id="build-lines"><code>//go:build</code> lines</h4>
+
+<p>
+  The <code>go</code> command now understands <code>//go:build</code> lines
+  and prefers them over <code>// +build</code> lines. The new syntax uses
+  boolean expressions, just like Go, and should be less error-prone.
+  As of this release, the new syntax is fully supported, and all Go files
+  should be updated to have both forms with the same meaning. To aid in
+  migration, <a href="#gofmt"><code>gofmt</code></a> now automatically
+  synchronizes the two forms. For more details on the syntax and migration plan,
+  see
+  <a href="https://golang.org/design/draft-gobuild">https://golang.org/design/draft-gobuild</a>.
+</p>
+
+<h3 id="gofmt">Gofmt</h3>
+
+<p>
+  <code>gofmt</code> (and <code>go</code> <code>fmt</code>) now synchronizes
+  <code>//go:build</code> lines with <code>// +build</code> lines. If a file
+  only has <code>// +build</code> lines, they will be moved to the appropriate
+  location in the file, and matching <code>//go:build</code> lines will be
+  added. Otherwise, <code>// +build</code> lines will be overwritten based on
+  any existing <code>//go:build</code> lines. For more information, see
+  <a href="https://golang.org/design/draft-gobuild">https://golang.org/design/draft-gobuild</a>.
 </p>
 
 <h3 id="vet">Vet</h3>
 
+<h4 id="vet-buildtags">New warning for mismatched <code>//go:build</code> and <code>// +build</code> lines</h4>
+
+<p><!-- CL 240609 -->
+  The <code>vet</code> tool now verifies that <code>//go:build</code> and
+  <code>// +build</code> lines are in the correct part of the file and
+  synchronized with each other. If they aren't,
+  <a href="#gofmt"><code>gofmt</code></a> can be used to fix them. For more
+  information, see
+  <a href="https://golang.org/design/draft-gobuild">https://golang.org/design/draft-gobuild</a>.
+</p>
+
+<h4 id="vet-sigchanyzer">New warning for calling <code>signal.Notify</code> on unbuffered channels</h4>
+
 <p><!-- CL 299532 -->
-  TODO: <a href="https://golang.org/cl/299532">https://golang.org/cl/299532</a>: cmd/vet: bring in sigchanyzer to report unbuffered channels to signal.Notify
+  The vet tool now warns about calls to <a href="/pkg/os/signal/#Notify">signal.Notify</a>
+  with incoming signals being sent to an unbuffered channel. Using an unbuffered channel
+  risks missing signals sent on them as <code>signal.Notify</code> does not block when
+  sending to a channel. For example:
 </p>
 
+<pre>
+c := make(chan os.Signal)
+// signals are sent on c before the channel is read from.
+// This signal may be dropped as c is unbuffered.
+signal.Notify(c, os.Interrupt)
+</pre>
+
 <p>
-  TODO: complete the Vet section
+  Users of <code>signal.Notify</code> should use channels with sufficient buffer space to keep up with the
+  expected signal rate.
+</p>
+
+<h4 id="vet-error-stdmethods">New warnings for Is, As and Unwrap methods</h4>
+
+<p><!-- CL 321389 -->
+  The vet tool now warns about methods named <code>As</code>, <code>Is</code> or <code>Unwrap</code>
+  on types implementing the <code>error</code> interface that have a different signature than the
+  one expected by the <code>errors</code> package. The <code>errors.{As,Is,Unwrap}</code> functions
+  expect such methods to implement either <code>Is(error)</code> <code>bool</code>,
+  <code>As(interface{})</code> <code>bool</code>, or <code>Unwrap()</code> <code>error</code>
+  respectively. The functions <code>errors.{As,Is,Unwrap}</code> will ignore methods with the same
+  names but a different signature. For example:
+</p>
+
+<pre>
+type MyError struct { hint string }
+func (m MyError) Error() string { ... } // MyError implements error.
+func (MyError) Is(target interface{}) bool { ... } // target is interface{} instead of error.
+func Foo() bool {
+	x, y := MyError{"A"}, MyError{"B"}
+	return errors.Is(x, y) // returns false as x != y and MyError does not have an `Is(error) bool` function.
+}
+</pre>
+
+<h3 id="cover">Cover</h3>
+
+<p><!-- CL 249759 -->
+  The <code>cover</code> tool now uses an optimized parser
+  from <code>golang.org/x/tools/cover</code>, which may be noticeably faster
+  when parsing large coverage profiles.
 </p>
 
 <h2 id="compiler">Compiler</h2>
@@ -275,34 +419,6 @@ Do not send CLs removing the interior tags from such phrases.
 
 <h2 id="library">Core library</h2>
 
-<p>
-  TODO: complete the Core library section
-</p>
-
-<h3 id="crypto/tls"><a href="/pkg/crypto/tls">crypto/tls</a></h3>
-
-<p><!-- CL 295370 -->
-  <a href="/pkg/crypto/tls#Conn.HandshakeContext">(*Conn).HandshakeContext</a> was added to
-  allow the user to control cancellation of an in-progress TLS Handshake.
-  The context provided is propagated into the
-  <a href="/pkg/crypto/tls#ClientHelloInfo">ClientHelloInfo</a>
-  and <a href="/pkg/crypto/tls#CertificateRequestInfo">CertificateRequestInfo</a>
-  structs and accessible through the new
-  <a href="/pkg/crypto/tls#ClientHelloInfo.Context">(*ClientHelloInfo).Context</a>
-  and
-  <a href="/pkg/crypto/tls#CertificateRequestInfo.Context">
-      (*CertificateRequestInfo).Context
-  </a> methods respectively. Canceling the context after the handshake has finished
-  has no effect.
-</p>
-
-<p><!-- CL 289209 -->
-  When <a href="/pkg/crypto/tls#Config">Config.NextProtos</a> is set, servers now
-  enforce that there is an overlap between the configured protocols and the protocols
-  advertised by the client, if any. If there is no overlap the connection is closed
-  with the <code>no_application_protocol</code> alert, as required by RFC 7301.
-</p>
-
 <h3 id="runtime/cgo"><a href="/pkg/runtime/cgo">Cgo</a></h3>
 
 <p>
@@ -365,13 +481,117 @@ Do not send CLs removing the interior tags from such phrases.
   </dd>
 </dl><!-- compress/lzw -->
 
-<dl id="crypto/rsa"><dt><a href="/pkg/crypto/rsa/">crypto/rsa</a></dt>
+<dl id="crypto/ed25519"><dt><a href="/pkg/crypto/ed25519/">crypto/ed25519</a></dt>
+  <dd>
+    <p><!-- CL 276272 -->
+      The <code>crypto/ed25519</code> package has been rewritten, and all
+      operations are now approximately twice as fast on amd64 and arm64.
+      The observable behavior has not otherwise changed.
+    </p>
+  </dd>
+</dl><!-- crypto/ed25519 -->
+
+<dl id="crypto/elliptic"><dt><a href="/pkg/crypto/elliptic/">crypto/elliptic</a></dt>
+  <dd>
+    <p><!-- CL 233939 -->
+      <a href="/pkg/crypto/elliptic#CurveParams"><code>CurveParams</code></a>
+      methods now automatically invoke faster and safer dedicated
+      implementations for known curves (P-224, P-256, and P-521) when
+      available. Note that this is a best-effort approach and applications
+      should avoid using the generic, not constant-time <code>CurveParams</code>
+      methods and instead use dedicated
+      <a href="/pkg/crypto/elliptic#Curve"><code>Curve</code></a> implementations
+      such as <a href="/pkg/crypto/elliptic#P256"><code>P256</code></a>.
+    </p>
+
+    <p><!-- CL 315271, CL 315274 -->
+      The <a href="/pkg/crypto/elliptic#P521"><code>P521</code></a> curve
+      implementation has been rewritten using code generated by the
+      <a href="https://github.com/mit-plv/fiat-crypto">fiat-crypto project</a>,
+      which is based on a formally-verified model of the arithmetic
+      operations. It is now constant-time and three times faster on amd64 and
+      arm64. The observable behavior has not otherwise changed.
+    </p>
+  </dd>
+</dl><!-- crypto/elliptic -->
+
+<dl id="crypto/rand"><dt><a href="/pkg/crypto/rand/">crypto/rand</a></dt>
+  <dd>
+    <p><!-- CL 302489, CL 299134, CL 269999 -->
+      The <code>crypto/rand</code> package now uses the <code>getentropy</code>
+      syscall on macOS and the <code>getrandom</code> syscall on Solaris,
+      Illumos, and DragonFlyBSD.
+    </p>
+  </dd>
+</dl><!-- crypto/rand -->
+
+<dl id="crypto/tls"><dt><a href="/pkg/crypto/tls/">crypto/tls</a></dt>
+  <dd>
+    <p><!-- CL 295370 -->
+      The new <a href="/pkg/crypto/tls#Conn.HandshakeContext"><code>Conn.HandshakeContext</code></a>
+      method allows the user to control cancellation of an in-progress TLS
+      handshake. The provided context is accessible from various callbacks through the new
+      <a href="/pkg/crypto/tls#ClientHelloInfo.Context"><code>ClientHelloInfo.Context</code></a> and
+      <a href="/pkg/crypto/tls#CertificateRequestInfo.Context"><code>CertificateRequestInfo.Context</code></a>
+      methods. Canceling the context after the handshake has finished has no effect.
+    </p>
+
+    <p><!-- CL 289209 -->
+      When <a href="/pkg/crypto/tls#Config.NextProtos"><code>Config.NextProtos</code></a>
+      is set, servers now enforce that there is an overlap between the
+      configured protocols and the protocols advertised by the client, if any.
+      If there is no overlap the connection is closed with the
+      <code>no_application_protocol</code> alert, as required by RFC 7301.
+    </p>
+
+    <p><!-- CL 314609 -->
+      Cipher suite ordering is now handled entirely by the
+      <code>crypto/tls</code> package. Currently, cipher suites are sorted based
+      on their security, performance, and hardware support taking into account
+      both the local and peer's hardware. The order of the
+      <a href="/pkg/crypto/tls#Config.CipherSuites"><code>Config.CipherSuites</code></a>
+      field is now ignored, as well as the
+      <a href="/pkg/crypto/tls#Config.PreferServerCipherSuites"><code>Config.PreferServerCipherSuites</code></a>
+      field. Note that <code>Config.CipherSuites</code> still allows
+      applications to choose what TLS 1.0–1.2 cipher suites to enable.
+    </p>
+
+    <p>
+      The 3DES cipher suites have been moved to
+      <a href="/pkg/crypto/tls#InsecureCipherSuites"><code>InsecureCipherSuites</code></a>
+      due to <a href="https://sweet32.info/">fundamental block size-related
+      weakness</a>. They are still enabled by default but only as a last resort,
+      thanks to the cipher suite ordering change above.
+    </p>
+  </dd>
+</dl><!-- crypto/tls -->
+
+<dl id="crypto/x509"><dt><a href="/pkg/crypto/x509/">crypto/x509</a></dt>
   <dd>
-    <p><!-- CL 302230 -->
-      TODO: <a href="https://golang.org/cl/302230">https://golang.org/cl/302230</a>: fix salt length calculation with PSSSaltLengthAuto
+    <p><!-- CL 224157 -->
+      <a href="/pkg/crypto/x509/#CreateCertificate"><code>CreateCertificate</code></a>
+      now returns an error if the provided private key doesn't match the
+      parent's public key, if any. The resulting certificate would have failed
+      to verify.
+    </p>
+
+    <p><!-- CL 315209 -->
+      The temporary <code>GODEBUG=x509ignoreCN=0</code> flag has been removed.
+    </p>
+
+    <p><!-- CL 274234 -->
+      <a href="/pkg/crypto/x509/#ParseCertificate"><code>ParseCertificate</code></a>
+      has been rewritten, and now consumes ~70% fewer resources. The observable
+      behavior has not otherwise changed, except for error messages.
+    </p>
+
+    <p><!-- CL 321190 -->
+      On BSD systems, <code>/etc/ssl/certs</code> is now searched for trusted
+      roots. This adds support for the new system trusted certificate store in
+      FreeBSD 12.2+.
     </p>
   </dd>
-</dl><!-- crypto/rsa -->
+</dl><!-- crypto/x509 -->
 
 <dl id="database/sql"><dt><a href="/pkg/database/sql/">database/sql</a></dt>
   <dd>
@@ -444,6 +664,22 @@ Do not send CLs removing the interior tags from such phrases.
   </dd>
 </dl><!-- go/build -->
 
+<dl id="go/format"><dt><a href="/pkg/go/format/">go/format</a></dt>
+  <dd>
+    <p>
+      The <a href="/pkg/go/format/#Source"><code>Source</code></a> and
+      <a href="/pkg/go/format/#Node"><code>Node</code></a> functions now
+      synchronize <code>//go:build</code> lines with <code>// +build</code>
+      lines. If a file only has <code>// +build</code> lines, they will be
+      moved to the appropriate location in the file, and matching
+      <code>//go:build</code> lines will be added. Otherwise,
+      <code>// +build</code> lines will be overwritten based on any existing
+      <code>//go:build</code> lines. For more information, see
+      <a href="https://golang.org/design/draft-gobuild">https://golang.org/design/draft-gobuild</a>.
+    </p>
+  </dd>
+</dl><!-- go/format -->
+
 <dl id="io/fs"><dt><a href="/pkg/io/fs/">io/fs</a></dt>
   <dd>
     <p><!-- CL 293649 -->
@@ -490,6 +726,16 @@ Do not send CLs removing the interior tags from such phrases.
       <a href="/pkg/net/#ParseError"><code>ParseError</code></a> error type now implement
       the <a href="/pkg/net/#Error"><code>net.Error</code></a> interface.
     </p>
+
+    <p><!-- CL325829 -->
+      The <a href="/pkg/net/#ParseIP"><code>ParseIP</code></a> and <a href="/pkg/net/#ParseCIDR"><code>ParseCIDR</code></a>
+      functions now reject IPv4 addresses which contain decimal components with leading zeros.
+
+      These components were always interpreted as decimal, but some operating systems treat them as octal.
+      This mismatch could hypothetically lead to security issues if a Go application was used to validate IP addresses
+      which were then used in their original form with non-Go applications which interpreted components as octal. Generally,
+      it is advisable to always re-encoded values after validation, which avoids this class of parser misalignment issues.
+    </p>
   </dd>
 </dl><!-- net -->
 
@@ -518,9 +764,9 @@ Do not send CLs removing the interior tags from such phrases.
 <dl id="net/http/httptest"><dt><a href="/pkg/net/http/httptest/">net/http/httptest</a></dt>
   <dd>
     <p><!-- CL 308950 -->
-      <a href="/pkg/net/http/httptest/#ResponseRecorder.WriteHeader"><code>ResponseRecorder.WriteHeader></code></a>
+      <a href="/pkg/net/http/httptest/#ResponseRecorder.WriteHeader"><code>ResponseRecorder.WriteHeader</code></a>
       now panics when the provided code is not a valid three-digit HTTP status code.
-      This matches the behavior of <a href="/pkg/net/http/#ResponseWriter"><code>ResponseWriter></code></a>
+      This matches the behavior of <a href="/pkg/net/http/#ResponseWriter"><code>ResponseWriter</code></a>
       implementations in the <a href="/pkg/net/http/"><code>net/http</code></a> package.
     </p>
   </dd>
@@ -578,14 +824,20 @@ Do not send CLs removing the interior tags from such phrases.
   </dd>
 </dl><!-- runtime/metrics -->
 
-<dl id="strconv"><dt><a href="/pkg/strconv/">strconv</a></dt>
+<dl id="runtime/pprof"><dt><a href="/pkg/runtime/pprof">runtime/pprof</a></dt>
   <dd>
-    <p><!-- CL 170079 -->
-      TODO: <a href="https://golang.org/cl/170079">https://golang.org/cl/170079</a>: implement Ryū-like algorithm for fixed precision ftoa
+    <p><!-- CL 299991 -->
+      Block profiles are no longer biased to favor infrequent long events over
+      frequent short events.
     </p>
+  </dd>
+</dl><!-- runtime/pprof -->
 
-    <p><!-- CL 170080 -->
-      TODO: <a href="https://golang.org/cl/170080">https://golang.org/cl/170080</a>: Implement Ryū algorithm for ftoa shortest mode
+<dl id="strconv"><dt><a href="/pkg/strconv/">strconv</a></dt>
+  <dd>
+    <p><!-- CL 170079, CL 170080 -->
+      The <code>strconv</code> package now uses Ulf Adams's Ryū algorithm for formatting floating-point numbers.
+      This algorithm improves performance on most inputs, and is more than 99% faster on worst-case inputs.
     </p>
 
     <p><!-- CL 314775 -->
diff --git a/misc/cgo/testcshared/cshared_test.go b/misc/cgo/testcshared/cshared_test.go
index 90d8c365e6..19ad8c76a8 100644
--- a/misc/cgo/testcshared/cshared_test.go
+++ b/misc/cgo/testcshared/cshared_test.go
@@ -292,11 +292,60 @@ func createHeaders() error {
 		"-installsuffix", "testcshared",
 		"-o", libgoname,
 		filepath.Join(".", "libgo", "libgo.go")}
+	if GOOS == "windows" && strings.HasSuffix(args[6], ".a") {
+		args[6] = strings.TrimSuffix(args[6], ".a") + ".dll"
+	}
 	cmd = exec.Command(args[0], args[1:]...)
 	out, err = cmd.CombinedOutput()
 	if err != nil {
 		return fmt.Errorf("command failed: %v\n%v\n%s\n", args, err, out)
 	}
+	if GOOS == "windows" {
+		// We can't simply pass -Wl,--out-implib, because this relies on having imports from multiple packages,
+		// which results in the linkers output implib getting overwritten at each step. So instead build the
+		// import library the traditional way, using a def file.
+		err = os.WriteFile("libgo.def",
+			[]byte("LIBRARY libgo.dll\nEXPORTS\n\tDidInitRun\n\tDidMainRun\n\tDivu\n\tFromPkg\n\t_cgo_dummy_export\n"),
+			0644)
+		if err != nil {
+			return fmt.Errorf("unable to write def file: %v", err)
+		}
+		out, err = exec.Command(cc[0], append(cc[1:], "-print-prog-name=dlltool")...).CombinedOutput()
+		if err != nil {
+			return fmt.Errorf("unable to find dlltool path: %v\n%s\n", err, out)
+		}
+		args := []string{strings.TrimSpace(string(out)), "-D", args[6], "-l", libgoname, "-d", "libgo.def"}
+
+		// This is an unfortunate workaround for https://github.com/mstorsjo/llvm-mingw/issues/205 in which
+		// we basically reimplement the contents of the dlltool.sh wrapper: https://git.io/JZFlU
+		dlltoolContents, err := os.ReadFile(args[0])
+		if err != nil {
+			return fmt.Errorf("unable to read dlltool: %v\n", err)
+		}
+		if bytes.HasPrefix(dlltoolContents, []byte("#!/bin/sh")) && bytes.Contains(dlltoolContents, []byte("llvm-dlltool")) {
+			base, name := filepath.Split(args[0])
+			args[0] = filepath.Join(base, "llvm-dlltool")
+			var machine string
+			switch strings.SplitN(name, "-", 2)[0] {
+			case "i686":
+				machine = "i386"
+			case "x86_64":
+				machine = "i386:x86-64"
+			case "armv7":
+				machine = "arm"
+			case "aarch64":
+				machine = "arm64"
+			}
+			if len(machine) > 0 {
+				args = append(args, "-m", machine)
+			}
+		}
+
+		out, err = exec.Command(args[0], args[1:]...).CombinedOutput()
+		if err != nil {
+			return fmt.Errorf("unable to run dlltool to create import library: %v\n%s\n", err, out)
+		}
+	}
 
 	if runtime.GOOS != GOOS && GOOS == "android" {
 		args = append(adbCmd(), "push", libgoname, fmt.Sprintf("%s/%s", androiddir, libgoname))
@@ -400,7 +449,7 @@ func main() {
 	defer f.Close()
 	section := f.Section(".edata")
 	if section == nil {
-		t.Fatalf(".edata section is not present")
+		t.Skip(".edata section is not present")
 	}
 
 	// TODO: deduplicate this struct from cmd/link/internal/ld/pe.go
@@ -749,7 +798,12 @@ func TestGo2C2Go(t *testing.T) {
 	defer os.RemoveAll(tmpdir)
 
 	lib := filepath.Join(tmpdir, "libtestgo2c2go."+libSuffix)
-	run(t, nil, "go", "build", "-buildmode=c-shared", "-o", lib, "./go2c2go/go")
+	var env []string
+	if GOOS == "windows" && strings.HasSuffix(lib, ".a") {
+		env = append(env, "CGO_LDFLAGS=-Wl,--out-implib,"+lib, "CGO_LDFLAGS_ALLOW=.*")
+		lib = strings.TrimSuffix(lib, ".a") + ".dll"
+	}
+	run(t, env, "go", "build", "-buildmode=c-shared", "-o", lib, "./go2c2go/go")
 
 	cgoCflags := os.Getenv("CGO_CFLAGS")
 	if cgoCflags != "" {
diff --git a/src/cmd/compile/internal/gc/obj.go b/src/cmd/compile/internal/gc/obj.go
index a52696fbb6..8a2ff75583 100644
--- a/src/cmd/compile/internal/gc/obj.go
+++ b/src/cmd/compile/internal/gc/obj.go
@@ -149,6 +149,7 @@ func dumpdata() {
 	if reflectdata.ZeroSize > 0 {
 		zero := base.PkgLinksym("go.map", "zero", obj.ABI0)
 		objw.Global(zero, int32(reflectdata.ZeroSize), obj.DUPOK|obj.RODATA)
+		zero.Set(obj.AttrContentAddressable, true)
 	}
 
 	staticdata.WriteFuncSyms()
diff --git a/src/cmd/compile/internal/reflectdata/reflect.go b/src/cmd/compile/internal/reflectdata/reflect.go
index bdc3527011..f16034ea70 100644
--- a/src/cmd/compile/internal/reflectdata/reflect.go
+++ b/src/cmd/compile/internal/reflectdata/reflect.go
@@ -1472,8 +1472,8 @@ func (a typesByString) Less(i, j int) bool {
 	// will be equal for the above checks, but different in DWARF output.
 	// Sort by source position to ensure deterministic order.
 	// See issues 27013 and 30202.
-	if a[i].t.Kind() == types.TINTER && a[i].t.Methods().Len() > 0 {
-		return a[i].t.Methods().Index(0).Pos.Before(a[j].t.Methods().Index(0).Pos)
+	if a[i].t.Kind() == types.TINTER && a[i].t.AllMethods().Len() > 0 {
+		return a[i].t.AllMethods().Index(0).Pos.Before(a[j].t.AllMethods().Index(0).Pos)
 	}
 	return false
 }
diff --git a/src/cmd/compile/internal/typecheck/stmt.go b/src/cmd/compile/internal/typecheck/stmt.go
index 175216f279..922a01bfbe 100644
--- a/src/cmd/compile/internal/typecheck/stmt.go
+++ b/src/cmd/compile/internal/typecheck/stmt.go
@@ -204,8 +204,20 @@ assignOK:
 		r.Use = ir.CallUseList
 		rtyp := r.Type()
 
+		mismatched := false
+		failed := false
 		for i := range lhs {
-			assignType(i, rtyp.Field(i).Type)
+			result := rtyp.Field(i).Type
+			assignType(i, result)
+
+			if lhs[i].Type() == nil || result == nil {
+				failed = true
+			} else if lhs[i] != ir.BlankNode && !types.Identical(lhs[i].Type(), result) {
+				mismatched = true
+			}
+		}
+		if mismatched && !failed {
+			rewriteMultiValueCall(stmt, r)
 		}
 		return
 	}
diff --git a/src/cmd/compile/internal/typecheck/typecheck.go b/src/cmd/compile/internal/typecheck/typecheck.go
index a6b21f948a..8454b8d5b3 100644
--- a/src/cmd/compile/internal/typecheck/typecheck.go
+++ b/src/cmd/compile/internal/typecheck/typecheck.go
@@ -941,16 +941,18 @@ func typecheckargs(n ir.InitNode) {
 		return
 	}
 
-	// Rewrite f(g()) into t1, t2, ... = g(); f(t1, t2, ...).
-
 	// Save n as n.Orig for fmt.go.
 	if ir.Orig(n) == n {
 		n.(ir.OrigNode).SetOrig(ir.SepCopy(n))
 	}
 
-	as := ir.NewAssignListStmt(base.Pos, ir.OAS2, nil, nil)
-	as.Rhs.Append(list...)
+	// Rewrite f(g()) into t1, t2, ... = g(); f(t1, t2, ...).
+	rewriteMultiValueCall(n, list[0])
+}
 
+// rewriteMultiValueCall rewrites multi-valued f() to use temporaries,
+// so the backend wouldn't need to worry about tuple-valued expressions.
+func rewriteMultiValueCall(n ir.InitNode, call ir.Node) {
 	// If we're outside of function context, then this call will
 	// be executed during the generated init function. However,
 	// init.go hasn't yet created it. Instead, associate the
@@ -960,25 +962,40 @@ func typecheckargs(n ir.InitNode) {
 	if static {
 		ir.CurFunc = InitTodoFunc
 	}
-	list = nil
-	for _, f := range t.FieldSlice() {
-		t := Temp(f.Type)
-		as.PtrInit().Append(ir.NewDecl(base.Pos, ir.ODCL, t))
-		as.Lhs.Append(t)
-		list = append(list, t)
+
+	as := ir.NewAssignListStmt(base.Pos, ir.OAS2, nil, []ir.Node{call})
+	results := call.Type().FieldSlice()
+	list := make([]ir.Node, len(results))
+	for i, result := range results {
+		tmp := Temp(result.Type)
+		as.PtrInit().Append(ir.NewDecl(base.Pos, ir.ODCL, tmp))
+		as.Lhs.Append(tmp)
+		list[i] = tmp
 	}
 	if static {
 		ir.CurFunc = nil
 	}
 
+	n.PtrInit().Append(Stmt(as))
+
 	switch n := n.(type) {
+	default:
+		base.Fatalf("rewriteMultiValueCall %+v", n.Op())
 	case *ir.CallExpr:
 		n.Args = list
 	case *ir.ReturnStmt:
 		n.Results = list
+	case *ir.AssignListStmt:
+		if n.Op() != ir.OAS2FUNC {
+			base.Fatalf("rewriteMultiValueCall: invalid op %v", n.Op())
+		}
+		as.SetOp(ir.OAS2FUNC)
+		n.SetOp(ir.OAS2)
+		n.Rhs = make([]ir.Node, len(list))
+		for i, tmp := range list {
+			n.Rhs[i] = AssignConv(tmp, n.Lhs[i].Type(), "assignment")
+		}
 	}
-
-	n.PtrInit().Append(Stmt(as))
 }
 
 func checksliceindex(l ir.Node, r ir.Node, tp *types.Type) bool {
diff --git a/src/cmd/compile/internal/walk/walk.go b/src/cmd/compile/internal/walk/walk.go
index fe2c62cd4f..26da6e3145 100644
--- a/src/cmd/compile/internal/walk/walk.go
+++ b/src/cmd/compile/internal/walk/walk.go
@@ -313,7 +313,7 @@ func mayCall(n ir.Node) bool {
 			return true
 
 		case ir.OINDEX, ir.OSLICE, ir.OSLICEARR, ir.OSLICE3, ir.OSLICE3ARR, ir.OSLICESTR,
-			ir.ODEREF, ir.ODOTPTR, ir.ODOTTYPE, ir.ODIV, ir.OMOD:
+			ir.ODEREF, ir.ODOTPTR, ir.ODOTTYPE, ir.ODIV, ir.OMOD, ir.OSLICE2ARRPTR:
 			// These ops might panic, make sure they are done
 			// before we start marshaling args for a call. See issue 16760.
 			return true
diff --git a/src/cmd/dist/test.go b/src/cmd/dist/test.go
index bc49c6d804..1ed2c0f631 100644
--- a/src/cmd/dist/test.go
+++ b/src/cmd/dist/test.go
@@ -737,9 +737,9 @@ func (t *tester) registerTests() {
 						fn: func(dt *distTest) error {
 							cmd := t.addCmd(dt, "misc/swig/callback", t.goTest())
 							cmd.Env = append(os.Environ(),
-								"CGO_CFLAGS=-flto",
-								"CGO_CXXFLAGS=-flto",
-								"CGO_LDFLAGS=-flto",
+								"CGO_CFLAGS=-flto -Wno-lto-type-mismatch",
+								"CGO_CXXFLAGS=-flto -Wno-lto-type-mismatch",
+								"CGO_LDFLAGS=-flto -Wno-lto-type-mismatch",
 							)
 							return nil
 						},
diff --git a/src/cmd/go.mod b/src/cmd/go.mod
index 1aa0320d07..cd03968eed 100644
--- a/src/cmd/go.mod
+++ b/src/cmd/go.mod
@@ -7,7 +7,7 @@ require (
 	github.com/ianlancetaylor/demangle v0.0.0-20200824232613-28f6c0f3b639 // indirect
 	golang.org/x/arch v0.0.0-20210502124803-cbf565b21d1e
 	golang.org/x/crypto v0.0.0-20210503195802-e9a32991a82e // indirect
-	golang.org/x/mod v0.4.3-0.20210512182355-6088ed88cecd
+	golang.org/x/mod v0.4.3-0.20210608190319-0f08993efd8a
 	golang.org/x/sys v0.0.0-20210511113859-b0526f3d8744 // indirect
 	golang.org/x/term v0.0.0-20210503060354-a79de5458b56
 	golang.org/x/tools v0.1.2-0.20210519160823-49064d2332f9
diff --git a/src/cmd/go.sum b/src/cmd/go.sum
index eeb625fcf8..d728acaec9 100644
--- a/src/cmd/go.sum
+++ b/src/cmd/go.sum
@@ -13,8 +13,8 @@ golang.org/x/crypto v0.0.0-20191011191535-87dc89f01550/go.mod h1:yigFU9vqHzYiE8U
 golang.org/x/crypto v0.0.0-20210503195802-e9a32991a82e h1:8foAy0aoO5GkqCvAEJ4VC4P3zksTg4X4aJCDpZzmgQI=
 golang.org/x/crypto v0.0.0-20210503195802-e9a32991a82e/go.mod h1:P+XmwS30IXTQdn5tA2iutPOUgjI07+tq3H3K9MVA1s8=
 golang.org/x/mod v0.4.2/go.mod h1:s0Qsj1ACt9ePp/hMypM3fl4fZqREWJwdYDEqhRiZZUA=
-golang.org/x/mod v0.4.3-0.20210512182355-6088ed88cecd h1:CuRnpyMrCCBulv0d/y0CswR4K0vGydgE3DZ2wYPIOo8=
-golang.org/x/mod v0.4.3-0.20210512182355-6088ed88cecd/go.mod h1:5OXOZSfqPIIbmVBIIKWRFfZjPR0E5r58TLhUjH0a2Ro=
+golang.org/x/mod v0.4.3-0.20210608190319-0f08993efd8a h1:e8qnjKz4EE6OjRki9wTadWSIogINvq10sMcuBRORxMY=
+golang.org/x/mod v0.4.3-0.20210608190319-0f08993efd8a/go.mod h1:5OXOZSfqPIIbmVBIIKWRFfZjPR0E5r58TLhUjH0a2Ro=
 golang.org/x/net v0.0.0-20190404232315-eb5bcb51f2a3/go.mod h1:t9HGtf8HONx5eT2rtn7q6eTqICYqUVnKs3thJo3Qplg=
 golang.org/x/net v0.0.0-20190620200207-3b0461eec859/go.mod h1:z5CRVTTTmAJ677TzLLGU+0bjPO0LkuOLi4/5GtJWs/s=
 golang.org/x/net v0.0.0-20210226172049-e18ecbb05110/go.mod h1:m0MpNAwzfU5UDzcl9v0D8zg8gWTRqZa9RBIspLL5mdg=
diff --git a/src/cmd/go/go_test.go b/src/cmd/go/go_test.go
index a059a6dd90..c0c86ab9f5 100644
--- a/src/cmd/go/go_test.go
+++ b/src/cmd/go/go_test.go
@@ -72,7 +72,6 @@ func tooSlow(t *testing.T) {
 // (temp) directory.
 var testGOROOT string
 
-var testCC string
 var testGOCACHE string
 
 var testGo string
@@ -179,13 +178,6 @@ func TestMain(m *testing.M) {
 			os.Exit(2)
 		}
 
-		out, err = exec.Command(gotool, "env", "CC").CombinedOutput()
-		if err != nil {
-			fmt.Fprintf(os.Stderr, "could not find testing CC: %v\n%s", err, out)
-			os.Exit(2)
-		}
-		testCC = strings.TrimSpace(string(out))
-
 		cmd := exec.Command(testGo, "env", "CGO_ENABLED")
 		cmd.Stderr = new(strings.Builder)
 		if out, err := cmd.Output(); err != nil {
@@ -2185,7 +2177,7 @@ func testBuildmodePIE(t *testing.T, useCgo, setBuildmodeToPIE bool) {
 			// See https://sourceware.org/bugzilla/show_bug.cgi?id=19011
 			section := f.Section(".edata")
 			if section == nil {
-				t.Fatalf(".edata section is not present")
+				t.Skip(".edata section is not present")
 			}
 			// TODO: deduplicate this struct from cmd/link/internal/ld/pe.go
 			type IMAGE_EXPORT_DIRECTORY struct {
diff --git a/src/cmd/go/internal/list/list.go b/src/cmd/go/internal/list/list.go
index 53aaf311ec..7cb9ec6d94 100644
--- a/src/cmd/go/internal/list/list.go
+++ b/src/cmd/go/internal/list/list.go
@@ -724,8 +724,18 @@ func runList(ctx context.Context, cmd *base.Command, args []string) {
 
 	// Record non-identity import mappings in p.ImportMap.
 	for _, p := range pkgs {
-		for i, srcPath := range p.Internal.RawImports {
-			path := p.Imports[i]
+		nRaw := len(p.Internal.RawImports)
+		for i, path := range p.Imports {
+			var srcPath string
+			if i < nRaw {
+				srcPath = p.Internal.RawImports[i]
+			} else {
+				// This path is not within the raw imports, so it must be an import
+				// found only within CompiledGoFiles. Those paths are found in
+				// CompiledImports.
+				srcPath = p.Internal.CompiledImports[i-nRaw]
+			}
+
 			if path != srcPath {
 				if p.ImportMap == nil {
 					p.ImportMap = make(map[string]string)
diff --git a/src/cmd/go/internal/load/pkg.go b/src/cmd/go/internal/load/pkg.go
index 738904865e..a83cc9a812 100644
--- a/src/cmd/go/internal/load/pkg.go
+++ b/src/cmd/go/internal/load/pkg.go
@@ -194,8 +194,8 @@ type PackageInternal struct {
 	// Unexported fields are not part of the public API.
 	Build             *build.Package
 	Imports           []*Package           // this package's direct imports
-	CompiledImports   []string             // additional Imports necessary when using CompiledGoFiles (all from standard library)
-	RawImports        []string             // this package's original imports as they appear in the text of the program
+	CompiledImports   []string             // additional Imports necessary when using CompiledGoFiles (all from standard library); 1:1 with the end of PackagePublic.Imports
+	RawImports        []string             // this package's original imports as they appear in the text of the program; 1:1 with the end of PackagePublic.Imports
 	ForceLibrary      bool                 // this package is a library (even if named "main")
 	CmdlineFiles      bool                 // package built from files listed on command line
 	CmdlinePkg        bool                 // package listed on command line
diff --git a/src/cmd/go/internal/modload/import.go b/src/cmd/go/internal/modload/import.go
index f76befcfe3..60bd26fb22 100644
--- a/src/cmd/go/internal/modload/import.go
+++ b/src/cmd/go/internal/modload/import.go
@@ -178,11 +178,13 @@ func (e *ImportMissingSumError) Error() string {
 		// Importing package is unknown, or the missing package was named on the
 		// command line. Recommend 'go mod download' for the modules that could
 		// provide the package, since that shouldn't change go.mod.
-		args := make([]string, len(e.mods))
-		for i, mod := range e.mods {
-			args[i] = mod.Path
+		if len(e.mods) > 0 {
+			args := make([]string, len(e.mods))
+			for i, mod := range e.mods {
+				args[i] = mod.Path
+			}
+			hint = fmt.Sprintf("; to add:\n\tgo mod download %s", strings.Join(args, " "))
 		}
-		hint = fmt.Sprintf("; to add:\n\tgo mod download %s", strings.Join(args, " "))
 	} else {
 		// Importing package is known (common case). Recommend 'go get' on the
 		// current version of the importing package.
diff --git a/src/cmd/go/internal/modload/init.go b/src/cmd/go/internal/modload/init.go
index ea404b9f78..eb9cfe629b 100644
--- a/src/cmd/go/internal/modload/init.go
+++ b/src/cmd/go/internal/modload/init.go
@@ -999,10 +999,14 @@ func commitRequirements(ctx context.Context, goVersion string, rs *Requirements)
 			Indirect: !rs.direct[m.Path],
 		})
 	}
-	modFile.SetRequire(list)
 	if goVersion != "" {
 		modFile.AddGoStmt(goVersion)
 	}
+	if semver.Compare("v"+modFileGoVersion(), separateIndirectVersionV) < 0 {
+		modFile.SetRequire(list)
+	} else {
+		modFile.SetRequireSeparateIndirect(list)
+	}
 	modFile.Cleanup()
 
 	dirty := index.modFileIsDirty(modFile)
diff --git a/src/cmd/go/internal/modload/modfile.go b/src/cmd/go/internal/modload/modfile.go
index a9c3a91d35..1145ac4ba5 100644
--- a/src/cmd/go/internal/modload/modfile.go
+++ b/src/cmd/go/internal/modload/modfile.go
@@ -35,6 +35,11 @@ const (
 	// module's go.mod file is expected to list explicit requirements on every
 	// module that provides any package transitively imported by that module.
 	lazyLoadingVersionV = "v1.17"
+
+	// separateIndirectVersionV is the Go version (plus leading "v") at which
+	// "// indirect" dependencies are added in a block separate from the direct
+	// ones. See https://golang.org/issue/45965.
+	separateIndirectVersionV = "v1.17"
 )
 
 const (
diff --git a/src/cmd/go/testdata/script/list_cgo_compiled_importmap.txt b/src/cmd/go/testdata/script/list_cgo_compiled_importmap.txt
new file mode 100644
index 0000000000..3d68ef3055
--- /dev/null
+++ b/src/cmd/go/testdata/script/list_cgo_compiled_importmap.txt
@@ -0,0 +1,38 @@
+# Regression test for https://golang.org/issue/46462.
+#
+# The "runtime/cgo" import found in synthesized .go files (reported in
+# the CompiledGoFiles field) should have a corresponding entry in the
+# ImportMap field when a runtime/cgo variant (such as a test variant)
+# will be used.
+
+[short] skip  # -compiled can be slow (because it compiles things)
+[!cgo] skip
+
+env CGO_ENABLED=1
+env GOFLAGS=-tags=netcgo  # Force net to use cgo even on Windows.
+
+
+# "runtime/cgo [runtime.test]" appears in the the test dependencies of "runtime",
+# because "runtime/cgo" itself depends on "runtime"
+
+go list -deps -test -compiled -f '{{if eq .ImportPath "net [runtime.test]"}}{{printf "%q" .Imports}}{{end}}' runtime
+
+	# Control case: the explicitly-imported package "sync" is a test variant,
+	# because "sync" depends on "runtime".
+stdout '"sync \[runtime\.test\]"'
+! stdout '"sync"'
+
+	# Experiment: the implicitly-imported package "runtime/cgo" is also a test variant,
+	# because "runtime/cgo" also depends on "runtime".
+stdout '"runtime/cgo \[runtime\.test\]"'
+! stdout '"runtime/cgo"'
+
+
+# Because the import of "runtime/cgo" in the cgo-generated file actually refers
+# to "runtime/cgo [runtime.test]", the latter should be listed in the ImportMap.
+# BUG(#46462): Today, it is not.
+
+go list -deps -test -compiled -f '{{if eq .ImportPath "net [runtime.test]"}}{{printf "%q" .ImportMap}}{{end}}' runtime
+
+stdout '"sync":"sync \[runtime\.test\]"'                # control
+stdout '"runtime/cgo":"runtime/cgo \[runtime\.test\]"'  # experiment
diff --git a/src/cmd/go/testdata/script/mod_go_version_missing.txt b/src/cmd/go/testdata/script/mod_go_version_missing.txt
index aca36a0450..d704816729 100644
--- a/src/cmd/go/testdata/script/mod_go_version_missing.txt
+++ b/src/cmd/go/testdata/script/mod_go_version_missing.txt
@@ -73,10 +73,9 @@ module example.com/m
 
 go $goversion
 
-require (
-	example.com/dep v0.1.0
-	example.com/testdep v0.1.0 // indirect
-)
+require example.com/dep v0.1.0
+
+require example.com/testdep v0.1.0 // indirect
 
 replace (
 	example.com/dep v0.1.0 => ./dep
diff --git a/src/cmd/go/testdata/script/mod_install_hint.txt b/src/cmd/go/testdata/script/mod_install_hint.txt
new file mode 100644
index 0000000000..ab02840eb8
--- /dev/null
+++ b/src/cmd/go/testdata/script/mod_install_hint.txt
@@ -0,0 +1,5 @@
+# Module is replaced but not required. No hint appears as no module is suggested.
+go mod init m
+go mod edit -replace=github.com/notrequired@v0.5.0=github.com/doesnotexist@v0.5.0
+! go install github.com/notrequired
+! stderr 'to add it:'
+\ No newline at end of file
diff --git a/src/cmd/go/testdata/script/mod_invalid_version.txt b/src/cmd/go/testdata/script/mod_invalid_version.txt
index 34d9c47674..6846a792a5 100644
--- a/src/cmd/go/testdata/script/mod_invalid_version.txt
+++ b/src/cmd/go/testdata/script/mod_invalid_version.txt
@@ -19,7 +19,7 @@ cp go.mod.orig go.mod
 go mod edit -require golang.org/x/text@14c0d48ead0c
 cd outside
 ! go list -m golang.org/x/text
-stderr 'go list -m: example.com@v0.0.0 \(replaced by \./\..\): parsing ../go.mod: '$WORK'/gopath/src/go.mod:5: require golang.org/x/text: version "14c0d48ead0c" invalid: must be of the form v1.2.3'
+stderr 'go list -m: example.com@v0.0.0 \(replaced by \./\.\.\): parsing ..[/\\]go.mod: '$WORK'[/\\]gopath[/\\]src[/\\]go.mod:5: require golang.org/x/text: version "14c0d48ead0c" invalid: must be of the form v1.2.3'
 cd ..
 go list -m golang.org/x/text
 stdout 'golang.org/x/text v0.1.1-0.20170915032832-14c0d48ead0c'
@@ -47,10 +47,10 @@ cp go.mod.orig go.mod
 go mod edit -require golang.org/x/text@v2.1.1-0.20170915032832-14c0d48ead0c
 cd outside
 ! go list -m golang.org/x/text
-stderr 'go list -m: example.com@v0.0.0 \(replaced by \./\.\.\): parsing ../go.mod: '$WORK'/gopath/src/go.mod:5: require golang.org/x/text: version "v2.1.1-0.20170915032832-14c0d48ead0c" invalid: should be v0 or v1, not v2'
+stderr 'go list -m: example.com@v0.0.0 \(replaced by \./\.\.\): parsing ..[/\\]go.mod: '$WORK'[/\\]gopath[/\\]src[/\\]go.mod:5: require golang.org/x/text: version "v2.1.1-0.20170915032832-14c0d48ead0c" invalid: should be v0 or v1, not v2'
 cd ..
 ! go list -m golang.org/x/text
-stderr $WORK'/gopath/src/go.mod:5: require golang.org/x/text: version "v2.1.1-0.20170915032832-14c0d48ead0c" invalid: should be v0 or v1, not v2'
+stderr $WORK'[/\\]gopath[/\\]src[/\\]go.mod:5: require golang.org/x/text: version "v2.1.1-0.20170915032832-14c0d48ead0c" invalid: should be v0 or v1, not v2'
 
 # A pseudo-version with fewer than 12 digits of SHA-1 prefix is invalid.
 cp go.mod.orig go.mod
diff --git a/src/cmd/go/testdata/script/mod_lazy_import_allmod.txt b/src/cmd/go/testdata/script/mod_lazy_import_allmod.txt
index 3dc1515df2..97718c4513 100644
--- a/src/cmd/go/testdata/script/mod_lazy_import_allmod.txt
+++ b/src/cmd/go/testdata/script/mod_lazy_import_allmod.txt
@@ -139,9 +139,10 @@ go 1.17
 require (
 	a v0.1.0
 	b v0.1.0
-	c v0.1.0 // indirect
 )
 
+require c v0.1.0 // indirect
+
 replace (
 	a v0.1.0 => ./a1
 	b v0.1.0 => ./b1
diff --git a/src/cmd/go/testdata/script/mod_lazy_new_import.txt b/src/cmd/go/testdata/script/mod_lazy_new_import.txt
index 86b14b64b6..4272a52de1 100644
--- a/src/cmd/go/testdata/script/mod_lazy_new_import.txt
+++ b/src/cmd/go/testdata/script/mod_lazy_new_import.txt
@@ -78,10 +78,9 @@ module example.com/lazy
 
 go 1.17
 
-require (
-	example.com/a v0.1.0
-	example.com/b v0.1.0 // indirect
-)
+require example.com/a v0.1.0
+
+require example.com/b v0.1.0 // indirect
 
 replace (
 	example.com/a v0.1.0 => ./a
@@ -94,8 +93,9 @@ module example.com/lazy
 
 go 1.17
 
+require example.com/a v0.1.0
+
 require (
-	example.com/a v0.1.0
 	example.com/b v0.1.0 // indirect
 	example.com/c v0.1.0 // indirect
 )
diff --git a/src/cmd/go/testdata/script/mod_lazy_test_of_test_dep.txt b/src/cmd/go/testdata/script/mod_lazy_test_of_test_dep.txt
index 722712d1f2..68a5b6dca2 100644
--- a/src/cmd/go/testdata/script/mod_lazy_test_of_test_dep.txt
+++ b/src/cmd/go/testdata/script/mod_lazy_test_of_test_dep.txt
@@ -148,10 +148,9 @@ module example.com/lazy
 
 go 1.17
 
-require (
-	example.com/a v0.1.0
-	example.com/b v0.1.0 // indirect
-)
+require example.com/a v0.1.0
+
+require example.com/b v0.1.0 // indirect
 
 replace (
 	example.com/a v0.1.0 => ./a
diff --git a/src/cmd/go/testdata/script/mod_retention.txt b/src/cmd/go/testdata/script/mod_retention.txt
index 0e639db551..7a371b1806 100644
--- a/src/cmd/go/testdata/script/mod_retention.txt
+++ b/src/cmd/go/testdata/script/mod_retention.txt
@@ -140,8 +140,9 @@ module m
 go $goversion
 
 require (
-	golang.org/x/text v0.0.0-20170915032832-14c0d48ead0c // indirect
 	rsc.io/quote v1.5.2
 	rsc.io/sampler v1.3.0 // indirect
 	rsc.io/testonly v1.0.0 // indirect
 )
+
+require golang.org/x/text v0.0.0-20170915032832-14c0d48ead0c // indirect
diff --git a/src/cmd/go/testdata/script/mod_tidy_convergence.txt b/src/cmd/go/testdata/script/mod_tidy_convergence.txt
index 22c8fc66c5..09c46f764b 100644
--- a/src/cmd/go/testdata/script/mod_tidy_convergence.txt
+++ b/src/cmd/go/testdata/script/mod_tidy_convergence.txt
@@ -90,7 +90,6 @@ cmp go.mod go.mod.postget
 cp go.mod.orig go.mod
 go mod edit -go=1.17 go.mod
 go mod edit -go=1.17 go.mod.tidye
-go mod edit -go=1.17 go.mod.postget
 
 go mod tidy -e
 cmp go.mod go.mod.tidye
@@ -99,7 +98,7 @@ stderr '^example\.net/m imports\n\texample\.net/x: package example\.net/x provid
 
 go get -d example.net/x@v0.1.0 example.net/y@v0.1.0
 go mod tidy
-cmp go.mod go.mod.postget
+cmp go.mod go.mod.postget-117
 
 
 -- go.mod --
@@ -144,6 +143,21 @@ require (
 	example.net/x v0.1.0
 	example.net/y v0.1.0 // indirect
 )
+-- go.mod.postget-117 --
+module example.net/m
+
+go 1.17
+
+replace (
+	example.net/x v0.1.0 => ./x1
+	example.net/x v0.2.0-pre => ./x2-pre
+	example.net/y v0.1.0 => ./y1
+	example.net/y v0.2.0 => ./y2
+)
+
+require example.net/x v0.1.0
+
+require example.net/y v0.1.0 // indirect
 -- m.go --
 package m
 
diff --git a/src/cmd/go/testdata/script/mod_tidy_version.txt b/src/cmd/go/testdata/script/mod_tidy_version.txt
index eaa6ee7b0d..3bc97bcb1e 100644
--- a/src/cmd/go/testdata/script/mod_tidy_version.txt
+++ b/src/cmd/go/testdata/script/mod_tidy_version.txt
@@ -92,8 +92,9 @@ cmpenv go.mod go.mod.latest
 -- go.mod --
 module example.com/m
 
+require example.net/a v0.1.0
+
 require (
-	example.net/a v0.1.0
 	example.net/c v0.1.0 // indirect
 	example.net/d v0.1.0 // indirect
 )
@@ -118,8 +119,9 @@ module example.com/m
 
 go 1.15
 
+require example.net/a v0.1.0
+
 require (
-	example.net/a v0.1.0
 	example.net/c v0.1.0 // indirect
 	example.net/d v0.1.0 // indirect
 )
@@ -139,8 +141,9 @@ module example.com/m
 
 go 1.15
 
+require example.net/a v0.1.0
+
 require (
-	example.net/a v0.1.0
 	example.net/c v0.1.0 // indirect
 	example.net/d v0.2.0 // indirect
 )
@@ -160,10 +163,9 @@ module example.com/m
 
 go 1.16
 
-require (
-	example.net/a v0.1.0
-	example.net/c v0.1.0 // indirect
-)
+require example.net/a v0.1.0
+
+require example.net/c v0.1.0 // indirect
 
 replace (
 	example.net/a v0.1.0 => ./a
@@ -180,8 +182,9 @@ module example.com/m
 
 go 1.17
 
+require example.net/a v0.1.0
+
 require (
-	example.net/a v0.1.0
 	example.net/b v0.1.0 // indirect
 	example.net/c v0.1.0 // indirect
 )
@@ -201,8 +204,9 @@ module example.com/m
 
 go $goversion
 
+require example.net/a v0.1.0
+
 require (
-	example.net/a v0.1.0
 	example.net/b v0.1.0 // indirect
 	example.net/c v0.1.0 // indirect
 )
diff --git a/src/cmd/link/internal/loader/loader.go b/src/cmd/link/internal/loader/loader.go
index 1b71a66c6f..efca824d98 100644
--- a/src/cmd/link/internal/loader/loader.go
+++ b/src/cmd/link/internal/loader/loader.go
@@ -699,12 +699,18 @@ func (l *Loader) checkdup(name string, r *oReader, li uint32, dup Sym) {
 	p := r.Data(li)
 	rdup, ldup := l.toLocal(dup)
 	pdup := rdup.Data(ldup)
-	if bytes.Equal(p, pdup) {
-		return
-	}
 	reason := "same length but different contents"
 	if len(p) != len(pdup) {
 		reason = fmt.Sprintf("new length %d != old length %d", len(p), len(pdup))
+	} else if bytes.Equal(p, pdup) {
+		// For BSS symbols, we need to check size as well, see issue 46653.
+		szdup := l.SymSize(dup)
+		sz := int64(r.Sym(li).Siz())
+		if szdup == sz {
+			return
+		}
+		reason = fmt.Sprintf("different sizes: new size %d != old size %d",
+			sz, szdup)
 	}
 	fmt.Fprintf(os.Stderr, "cmd/link: while reading object for '%v': duplicate symbol '%s', previous def at '%v', with mismatched payload: %s\n", r.unit.Lib, name, rdup.unit.Lib, reason)
 
diff --git a/src/cmd/link/link_test.go b/src/cmd/link/link_test.go
index 4a580991ef..fed9c7bc3f 100644
--- a/src/cmd/link/link_test.go
+++ b/src/cmd/link/link_test.go
@@ -470,10 +470,30 @@ TEXT	·f(SB), NOSPLIT|DUPOK, $0-0
 	JMP	0(PC)
 `
 
+const testStrictDupAsmSrc3 = `
+#include "textflag.h"
+GLOBL ·rcon(SB), RODATA|DUPOK, $64
+`
+
+const testStrictDupAsmSrc4 = `
+#include "textflag.h"
+GLOBL ·rcon(SB), RODATA|DUPOK, $32
+`
+
 func TestStrictDup(t *testing.T) {
 	// Check that -strictdups flag works.
 	testenv.MustHaveGoBuild(t)
 
+	asmfiles := []struct {
+		fname   string
+		payload string
+	}{
+		{"a", testStrictDupAsmSrc1},
+		{"b", testStrictDupAsmSrc2},
+		{"c", testStrictDupAsmSrc3},
+		{"d", testStrictDupAsmSrc4},
+	}
+
 	t.Parallel()
 
 	tmpdir := t.TempDir()
@@ -483,15 +503,12 @@ func TestStrictDup(t *testing.T) {
 	if err != nil {
 		t.Fatal(err)
 	}
-	src = filepath.Join(tmpdir, "a.s")
-	err = ioutil.WriteFile(src, []byte(testStrictDupAsmSrc1), 0666)
-	if err != nil {
-		t.Fatal(err)
-	}
-	src = filepath.Join(tmpdir, "b.s")
-	err = ioutil.WriteFile(src, []byte(testStrictDupAsmSrc2), 0666)
-	if err != nil {
-		t.Fatal(err)
+	for _, af := range asmfiles {
+		src = filepath.Join(tmpdir, af.fname+".s")
+		err = ioutil.WriteFile(src, []byte(af.payload), 0666)
+		if err != nil {
+			t.Fatal(err)
+		}
 	}
 	src = filepath.Join(tmpdir, "go.mod")
 	err = ioutil.WriteFile(src, []byte("module teststrictdup\n"), 0666)
@@ -503,7 +520,7 @@ func TestStrictDup(t *testing.T) {
 	cmd.Dir = tmpdir
 	out, err := cmd.CombinedOutput()
 	if err != nil {
-		t.Errorf("linking with -strictdups=1 failed: %v", err)
+		t.Errorf("linking with -strictdups=1 failed: %v\n%s", err, string(out))
 	}
 	if !bytes.Contains(out, []byte("mismatched payload")) {
 		t.Errorf("unexpected output:\n%s", out)
@@ -515,7 +532,11 @@ func TestStrictDup(t *testing.T) {
 	if err == nil {
 		t.Errorf("linking with -strictdups=2 did not fail")
 	}
-	if !bytes.Contains(out, []byte("mismatched payload")) {
+	// NB: on amd64 we get the 'new length' error, on arm64 the 'different
+	// contents' error.
+	if !(bytes.Contains(out, []byte("mismatched payload: new length")) ||
+		bytes.Contains(out, []byte("mismatched payload: same length but different contents"))) ||
+		!bytes.Contains(out, []byte("mismatched payload: different sizes")) {
 		t.Errorf("unexpected output:\n%s", out)
 	}
 }
diff --git a/src/cmd/vendor/golang.org/x/mod/modfile/read.go b/src/cmd/vendor/golang.org/x/mod/modfile/read.go
index 2a961ca81c..956f30cbb3 100644
--- a/src/cmd/vendor/golang.org/x/mod/modfile/read.go
+++ b/src/cmd/vendor/golang.org/x/mod/modfile/read.go
@@ -194,12 +194,15 @@ func (x *FileSyntax) updateLine(line *Line, tokens ...string) {
 	line.Token = tokens
 }
 
-func (x *FileSyntax) removeLine(line *Line) {
+// markRemoved modifies line so that it (and its end-of-line comment, if any)
+// will be dropped by (*FileSyntax).Cleanup.
+func (line *Line) markRemoved() {
 	line.Token = nil
+	line.Comments.Suffix = nil
 }
 
 // Cleanup cleans up the file syntax x after any edit operations.
-// To avoid quadratic behavior, removeLine marks the line as dead
+// To avoid quadratic behavior, (*Line).markRemoved marks the line as dead
 // by setting line.Token = nil but does not remove it from the slice
 // in which it appears. After edits have all been indicated,
 // calling Cleanup cleans out the dead lines.
diff --git a/src/cmd/vendor/golang.org/x/mod/modfile/rule.go b/src/cmd/vendor/golang.org/x/mod/modfile/rule.go
index 7299e15500..78f83fa714 100644
--- a/src/cmd/vendor/golang.org/x/mod/modfile/rule.go
+++ b/src/cmd/vendor/golang.org/x/mod/modfile/rule.go
@@ -58,13 +58,6 @@ type Go struct {
 	Syntax  *Line
 }
 
-// A Require is a single require statement.
-type Require struct {
-	Mod      module.Version
-	Indirect bool // has "// indirect" comment
-	Syntax   *Line
-}
-
 // An Exclude is a single exclude statement.
 type Exclude struct {
 	Mod    module.Version
@@ -93,6 +86,93 @@ type VersionInterval struct {
 	Low, High string
 }
 
+// A Require is a single require statement.
+type Require struct {
+	Mod      module.Version
+	Indirect bool // has "// indirect" comment
+	Syntax   *Line
+}
+
+func (r *Require) markRemoved() {
+	r.Syntax.markRemoved()
+	*r = Require{}
+}
+
+func (r *Require) setVersion(v string) {
+	r.Mod.Version = v
+
+	if line := r.Syntax; len(line.Token) > 0 {
+		if line.InBlock {
+			// If the line is preceded by an empty line, remove it; see
+			// https://golang.org/issue/33779.
+			if len(line.Comments.Before) == 1 && len(line.Comments.Before[0].Token) == 0 {
+				line.Comments.Before = line.Comments.Before[:0]
+			}
+			if len(line.Token) >= 2 { // example.com v1.2.3
+				line.Token[1] = v
+			}
+		} else {
+			if len(line.Token) >= 3 { // require example.com v1.2.3
+				line.Token[2] = v
+			}
+		}
+	}
+}
+
+// setIndirect sets line to have (or not have) a "// indirect" comment.
+func (r *Require) setIndirect(indirect bool) {
+	r.Indirect = indirect
+	line := r.Syntax
+	if isIndirect(line) == indirect {
+		return
+	}
+	if indirect {
+		// Adding comment.
+		if len(line.Suffix) == 0 {
+			// New comment.
+			line.Suffix = []Comment{{Token: "// indirect", Suffix: true}}
+			return
+		}
+
+		com := &line.Suffix[0]
+		text := strings.TrimSpace(strings.TrimPrefix(com.Token, string(slashSlash)))
+		if text == "" {
+			// Empty comment.
+			com.Token = "// indirect"
+			return
+		}
+
+		// Insert at beginning of existing comment.
+		com.Token = "// indirect; " + text
+		return
+	}
+
+	// Removing comment.
+	f := strings.TrimSpace(strings.TrimPrefix(line.Suffix[0].Token, string(slashSlash)))
+	if f == "indirect" {
+		// Remove whole comment.
+		line.Suffix = nil
+		return
+	}
+
+	// Remove comment prefix.
+	com := &line.Suffix[0]
+	i := strings.Index(com.Token, "indirect;")
+	com.Token = "//" + com.Token[i+len("indirect;"):]
+}
+
+// isIndirect reports whether line has a "// indirect" comment,
+// meaning it is in go.mod only for its effect on indirect dependencies,
+// so that it can be dropped entirely once the effective version of the
+// indirect dependency reaches the given minimum version.
+func isIndirect(line *Line) bool {
+	if len(line.Suffix) == 0 {
+		return false
+	}
+	f := strings.Fields(strings.TrimPrefix(line.Suffix[0].Token, string(slashSlash)))
+	return (len(f) == 1 && f[0] == "indirect" || len(f) > 1 && f[0] == "indirect;")
+}
+
 func (f *File) AddModuleStmt(path string) error {
 	if f.Syntax == nil {
 		f.Syntax = new(FileSyntax)
@@ -476,58 +556,6 @@ func (f *File) fixRetract(fix VersionFixer, errs *ErrorList) {
 	}
 }
 
-// isIndirect reports whether line has a "// indirect" comment,
-// meaning it is in go.mod only for its effect on indirect dependencies,
-// so that it can be dropped entirely once the effective version of the
-// indirect dependency reaches the given minimum version.
-func isIndirect(line *Line) bool {
-	if len(line.Suffix) == 0 {
-		return false
-	}
-	f := strings.Fields(strings.TrimPrefix(line.Suffix[0].Token, string(slashSlash)))
-	return (len(f) == 1 && f[0] == "indirect" || len(f) > 1 && f[0] == "indirect;")
-}
-
-// setIndirect sets line to have (or not have) a "// indirect" comment.
-func setIndirect(line *Line, indirect bool) {
-	if isIndirect(line) == indirect {
-		return
-	}
-	if indirect {
-		// Adding comment.
-		if len(line.Suffix) == 0 {
-			// New comment.
-			line.Suffix = []Comment{{Token: "// indirect", Suffix: true}}
-			return
-		}
-
-		com := &line.Suffix[0]
-		text := strings.TrimSpace(strings.TrimPrefix(com.Token, string(slashSlash)))
-		if text == "" {
-			// Empty comment.
-			com.Token = "// indirect"
-			return
-		}
-
-		// Insert at beginning of existing comment.
-		com.Token = "// indirect; " + text
-		return
-	}
-
-	// Removing comment.
-	f := strings.TrimSpace(strings.TrimPrefix(line.Suffix[0].Token, string(slashSlash)))
-	if f == "indirect" {
-		// Remove whole comment.
-		line.Suffix = nil
-		return
-	}
-
-	// Remove comment prefix.
-	com := &line.Suffix[0]
-	i := strings.Index(com.Token, "indirect;")
-	com.Token = "//" + com.Token[i+len("indirect;"):]
-}
-
 // IsDirectoryPath reports whether the given path should be interpreted
 // as a directory path. Just like on the go command line, relative paths
 // and rooted paths are directory paths; the rest are module paths.
@@ -835,6 +863,12 @@ func (f *File) AddGoStmt(version string) error {
 	return nil
 }
 
+// AddRequire sets the first require line for path to version vers,
+// preserving any existing comments for that line and removing all
+// other lines for path.
+//
+// If no line currently exists for path, AddRequire adds a new line
+// at the end of the last require block.
 func (f *File) AddRequire(path, vers string) error {
 	need := true
 	for _, r := range f.Require {
@@ -844,7 +878,7 @@ func (f *File) AddRequire(path, vers string) error {
 				f.Syntax.updateLine(r.Syntax, "require", AutoQuote(path), vers)
 				need = false
 			} else {
-				f.Syntax.removeLine(r.Syntax)
+				r.Syntax.markRemoved()
 				*r = Require{}
 			}
 		}
@@ -856,69 +890,235 @@ func (f *File) AddRequire(path, vers string) error {
 	return nil
 }
 
+// AddNewRequire adds a new require line for path at version vers at the end of
+// the last require block, regardless of any existing require lines for path.
 func (f *File) AddNewRequire(path, vers string, indirect bool) {
 	line := f.Syntax.addLine(nil, "require", AutoQuote(path), vers)
-	setIndirect(line, indirect)
-	f.Require = append(f.Require, &Require{module.Version{Path: path, Version: vers}, indirect, line})
+	r := &Require{
+		Mod:    module.Version{Path: path, Version: vers},
+		Syntax: line,
+	}
+	r.setIndirect(indirect)
+	f.Require = append(f.Require, r)
 }
 
+// SetRequire updates the requirements of f to contain exactly req, preserving
+// the existing block structure and line comment contents (except for 'indirect'
+// markings) for the first requirement on each named module path.
+//
+// The Syntax field is ignored for the requirements in req.
+//
+// Any requirements not already present in the file are added to the block
+// containing the last require line.
+//
+// The requirements in req must specify at most one distinct version for each
+// module path.
+//
+// If any existing requirements may be removed, the caller should call Cleanup
+// after all edits are complete.
 func (f *File) SetRequire(req []*Require) {
-	need := make(map[string]string)
-	indirect := make(map[string]bool)
+	type elem struct {
+		version  string
+		indirect bool
+	}
+	need := make(map[string]elem)
 	for _, r := range req {
-		need[r.Mod.Path] = r.Mod.Version
-		indirect[r.Mod.Path] = r.Indirect
+		if prev, dup := need[r.Mod.Path]; dup && prev.version != r.Mod.Version {
+			panic(fmt.Errorf("SetRequire called with conflicting versions for path %s (%s and %s)", r.Mod.Path, prev.version, r.Mod.Version))
+		}
+		need[r.Mod.Path] = elem{r.Mod.Version, r.Indirect}
 	}
 
+	// Update or delete the existing Require entries to preserve
+	// only the first for each module path in req.
 	for _, r := range f.Require {
-		if v, ok := need[r.Mod.Path]; ok {
-			r.Mod.Version = v
-			r.Indirect = indirect[r.Mod.Path]
+		e, ok := need[r.Mod.Path]
+		if ok {
+			r.setVersion(e.version)
+			r.setIndirect(e.indirect)
 		} else {
-			*r = Require{}
+			r.markRemoved()
+		}
+		delete(need, r.Mod.Path)
+	}
+
+	// Add new entries in the last block of the file for any paths that weren't
+	// already present.
+	//
+	// This step is nondeterministic, but the final result will be deterministic
+	// because we will sort the block.
+	for path, e := range need {
+		f.AddNewRequire(path, e.version, e.indirect)
+	}
+
+	f.SortBlocks()
+}
+
+// SetRequireSeparateIndirect updates the requirements of f to contain the given
+// requirements. Comment contents (except for 'indirect' markings) are retained
+// from the first existing requirement for each module path, and block structure
+// is maintained as long as the indirect markings match.
+//
+// Any requirements on paths not already present in the file are added. Direct
+// requirements are added to the last block containing *any* other direct
+// requirement. Indirect requirements are added to the last block containing
+// *only* other indirect requirements. If no suitable block exists, a new one is
+// added, with the last block containing a direct dependency (if any)
+// immediately before the first block containing only indirect dependencies.
+//
+// The Syntax field is ignored for requirements in the given blocks.
+func (f *File) SetRequireSeparateIndirect(req []*Require) {
+	type modKey struct {
+		path     string
+		indirect bool
+	}
+	need := make(map[modKey]string)
+	for _, r := range req {
+		need[modKey{r.Mod.Path, r.Indirect}] = r.Mod.Version
+	}
+
+	comments := make(map[string]Comments)
+	for _, r := range f.Require {
+		v, ok := need[modKey{r.Mod.Path, r.Indirect}]
+		if !ok {
+			if _, ok := need[modKey{r.Mod.Path, !r.Indirect}]; ok {
+				if _, dup := comments[r.Mod.Path]; !dup {
+					comments[r.Mod.Path] = r.Syntax.Comments
+				}
+			}
+			r.markRemoved()
+			continue
 		}
+		r.setVersion(v)
+		delete(need, modKey{r.Mod.Path, r.Indirect})
 	}
 
-	var newStmts []Expr
+	var (
+		lastDirectOrMixedBlock Expr
+		firstIndirectOnlyBlock Expr
+		lastIndirectOnlyBlock  Expr
+	)
 	for _, stmt := range f.Syntax.Stmt {
 		switch stmt := stmt.(type) {
+		case *Line:
+			if len(stmt.Token) == 0 || stmt.Token[0] != "require" {
+				continue
+			}
+			if isIndirect(stmt) {
+				lastIndirectOnlyBlock = stmt
+			} else {
+				lastDirectOrMixedBlock = stmt
+			}
 		case *LineBlock:
-			if len(stmt.Token) > 0 && stmt.Token[0] == "require" {
-				var newLines []*Line
+			if len(stmt.Token) == 0 || stmt.Token[0] != "require" {
+				continue
+			}
+			indirectOnly := true
+			for _, line := range stmt.Line {
+				if len(line.Token) == 0 {
+					continue
+				}
+				if !isIndirect(line) {
+					indirectOnly = false
+					break
+				}
+			}
+			if indirectOnly {
+				lastIndirectOnlyBlock = stmt
+				if firstIndirectOnlyBlock == nil {
+					firstIndirectOnlyBlock = stmt
+				}
+			} else {
+				lastDirectOrMixedBlock = stmt
+			}
+		}
+	}
+
+	isOrContainsStmt := func(stmt Expr, target Expr) bool {
+		if stmt == target {
+			return true
+		}
+		if stmt, ok := stmt.(*LineBlock); ok {
+			if target, ok := target.(*Line); ok {
 				for _, line := range stmt.Line {
-					if p, err := parseString(&line.Token[0]); err == nil && need[p] != "" {
-						if len(line.Comments.Before) == 1 && len(line.Comments.Before[0].Token) == 0 {
-							line.Comments.Before = line.Comments.Before[:0]
-						}
-						line.Token[1] = need[p]
-						delete(need, p)
-						setIndirect(line, indirect[p])
-						newLines = append(newLines, line)
+					if line == target {
+						return true
 					}
 				}
-				if len(newLines) == 0 {
-					continue // drop stmt
-				}
-				stmt.Line = newLines
 			}
+		}
+		return false
+	}
 
-		case *Line:
-			if len(stmt.Token) > 0 && stmt.Token[0] == "require" {
-				if p, err := parseString(&stmt.Token[1]); err == nil && need[p] != "" {
-					stmt.Token[2] = need[p]
-					delete(need, p)
-					setIndirect(stmt, indirect[p])
+	addRequire := func(path, vers string, indirect bool, comments Comments) {
+		var line *Line
+		if indirect {
+			if lastIndirectOnlyBlock != nil {
+				line = f.Syntax.addLine(lastIndirectOnlyBlock, "require", path, vers)
+			} else {
+				// Add a new require block after the last direct-only or mixed "require"
+				// block (if any).
+				//
+				// (f.Syntax.addLine would add the line to an existing "require" block if
+				// present, but here the existing "require" blocks are all direct-only, so
+				// we know we need to add a new block instead.)
+				line = &Line{Token: []string{"require", path, vers}}
+				lastIndirectOnlyBlock = line
+				firstIndirectOnlyBlock = line // only block implies first block
+				if lastDirectOrMixedBlock == nil {
+					f.Syntax.Stmt = append(f.Syntax.Stmt, line)
 				} else {
-					continue // drop stmt
+					for i, stmt := range f.Syntax.Stmt {
+						if isOrContainsStmt(stmt, lastDirectOrMixedBlock) {
+							f.Syntax.Stmt = append(f.Syntax.Stmt, nil)     // increase size
+							copy(f.Syntax.Stmt[i+2:], f.Syntax.Stmt[i+1:]) // shuffle elements up
+							f.Syntax.Stmt[i+1] = line
+							break
+						}
+					}
+				}
+			}
+		} else {
+			if lastDirectOrMixedBlock != nil {
+				line = f.Syntax.addLine(lastDirectOrMixedBlock, "require", path, vers)
+			} else {
+				// Add a new require block before the first indirect block (if any).
+				//
+				// That way if the file initially contains only indirect lines,
+				// the direct lines still appear before it: we preserve existing
+				// structure, but only to the extent that that structure already
+				// reflects the direct/indirect split.
+				line = &Line{Token: []string{"require", path, vers}}
+				lastDirectOrMixedBlock = line
+				if firstIndirectOnlyBlock == nil {
+					f.Syntax.Stmt = append(f.Syntax.Stmt, line)
+				} else {
+					for i, stmt := range f.Syntax.Stmt {
+						if isOrContainsStmt(stmt, firstIndirectOnlyBlock) {
+							f.Syntax.Stmt = append(f.Syntax.Stmt, nil)   // increase size
+							copy(f.Syntax.Stmt[i+1:], f.Syntax.Stmt[i:]) // shuffle elements up
+							f.Syntax.Stmt[i] = line
+							break
+						}
+					}
 				}
 			}
 		}
-		newStmts = append(newStmts, stmt)
+
+		line.Comments.Before = commentsAdd(line.Comments.Before, comments.Before)
+		line.Comments.Suffix = commentsAdd(line.Comments.Suffix, comments.Suffix)
+
+		r := &Require{
+			Mod:      module.Version{Path: path, Version: vers},
+			Indirect: indirect,
+			Syntax:   line,
+		}
+		r.setIndirect(indirect)
+		f.Require = append(f.Require, r)
 	}
-	f.Syntax.Stmt = newStmts
 
-	for path, vers := range need {
-		f.AddNewRequire(path, vers, indirect[path])
+	for k, vers := range need {
+		addRequire(k.path, vers, k.indirect, comments[k.path])
 	}
 	f.SortBlocks()
 }
@@ -926,7 +1126,7 @@ func (f *File) SetRequire(req []*Require) {
 func (f *File) DropRequire(path string) error {
 	for _, r := range f.Require {
 		if r.Mod.Path == path {
-			f.Syntax.removeLine(r.Syntax)
+			r.Syntax.markRemoved()
 			*r = Require{}
 		}
 	}
@@ -957,7 +1157,7 @@ func (f *File) AddExclude(path, vers string) error {
 func (f *File) DropExclude(path, vers string) error {
 	for _, x := range f.Exclude {
 		if x.Mod.Path == path && x.Mod.Version == vers {
-			f.Syntax.removeLine(x.Syntax)
+			x.Syntax.markRemoved()
 			*x = Exclude{}
 		}
 	}
@@ -988,7 +1188,7 @@ func (f *File) AddReplace(oldPath, oldVers, newPath, newVers string) error {
 				continue
 			}
 			// Already added; delete other replacements for same.
-			f.Syntax.removeLine(r.Syntax)
+			r.Syntax.markRemoved()
 			*r = Replace{}
 		}
 		if r.Old.Path == oldPath {
@@ -1004,7 +1204,7 @@ func (f *File) AddReplace(oldPath, oldVers, newPath, newVers string) error {
 func (f *File) DropReplace(oldPath, oldVers string) error {
 	for _, r := range f.Replace {
 		if r.Old.Path == oldPath && r.Old.Version == oldVers {
-			f.Syntax.removeLine(r.Syntax)
+			r.Syntax.markRemoved()
 			*r = Replace{}
 		}
 	}
@@ -1045,7 +1245,7 @@ func (f *File) AddRetract(vi VersionInterval, rationale string) error {
 func (f *File) DropRetract(vi VersionInterval) error {
 	for _, r := range f.Retract {
 		if r.VersionInterval == vi {
-			f.Syntax.removeLine(r.Syntax)
+			r.Syntax.markRemoved()
 			*r = Retract{}
 		}
 	}
diff --git a/src/cmd/vendor/modules.txt b/src/cmd/vendor/modules.txt
index 9a1723d32c..34dbdaf5dd 100644
--- a/src/cmd/vendor/modules.txt
+++ b/src/cmd/vendor/modules.txt
@@ -28,7 +28,7 @@ golang.org/x/arch/x86/x86asm
 ## explicit; go 1.17
 golang.org/x/crypto/ed25519
 golang.org/x/crypto/ed25519/internal/edwards25519
-# golang.org/x/mod v0.4.3-0.20210512182355-6088ed88cecd
+# golang.org/x/mod v0.4.3-0.20210608190319-0f08993efd8a
 ## explicit; go 1.17
 golang.org/x/mod/internal/lazyregexp
 golang.org/x/mod/modfile
diff --git a/src/crypto/tls/handshake_client.go b/src/crypto/tls/handshake_client.go
index 13a7f3442c..4af3d998a3 100644
--- a/src/crypto/tls/handshake_client.go
+++ b/src/crypto/tls/handshake_client.go
@@ -711,17 +711,11 @@ func (hs *clientHandshakeState) processServerHello() (bool, error) {
 		}
 	}
 
-	if hs.serverHello.alpnProtocol != "" {
-		if len(hs.hello.alpnProtocols) == 0 {
-			c.sendAlert(alertUnsupportedExtension)
-			return false, errors.New("tls: server advertised unrequested ALPN extension")
-		}
-		if mutualProtocol([]string{hs.serverHello.alpnProtocol}, hs.hello.alpnProtocols) == "" {
-			c.sendAlert(alertUnsupportedExtension)
-			return false, errors.New("tls: server selected unadvertised ALPN protocol")
-		}
-		c.clientProtocol = hs.serverHello.alpnProtocol
+	if err := checkALPN(hs.hello.alpnProtocols, hs.serverHello.alpnProtocol); err != nil {
+		c.sendAlert(alertUnsupportedExtension)
+		return false, err
 	}
+	c.clientProtocol = hs.serverHello.alpnProtocol
 
 	c.scts = hs.serverHello.scts
 
@@ -753,6 +747,23 @@ func (hs *clientHandshakeState) processServerHello() (bool, error) {
 	return true, nil
 }
 
+// checkALPN ensure that the server's choice of ALPN protocol is compatible with
+// the protocols that we advertised in the Client Hello.
+func checkALPN(clientProtos []string, serverProto string) error {
+	if serverProto == "" {
+		return nil
+	}
+	if len(clientProtos) == 0 {
+		return errors.New("tls: server advertised unrequested ALPN extension")
+	}
+	for _, proto := range clientProtos {
+		if proto == serverProto {
+			return nil
+		}
+	}
+	return errors.New("tls: server selected unadvertised ALPN protocol")
+}
+
 func (hs *clientHandshakeState) readFinished(out []byte) error {
 	c := hs.c
 
@@ -979,19 +990,6 @@ func clientSessionCacheKey(serverAddr net.Addr, config *Config) string {
 	return serverAddr.String()
 }
 
-// mutualProtocol finds the mutual ALPN protocol given list of possible
-// protocols and a list of the preference order.
-func mutualProtocol(protos, preferenceProtos []string) string {
-	for _, s := range preferenceProtos {
-		for _, c := range protos {
-			if s == c {
-				return s
-			}
-		}
-	}
-	return ""
-}
-
 // hostnameInSNI converts name into an appropriate hostname for SNI.
 // Literal IP addresses and absolute FQDNs are not permitted as SNI values.
 // See RFC 6066, Section 3.
diff --git a/src/crypto/tls/handshake_client_tls13.go b/src/crypto/tls/handshake_client_tls13.go
index be37c681c6..eb59ac90d1 100644
--- a/src/crypto/tls/handshake_client_tls13.go
+++ b/src/crypto/tls/handshake_client_tls13.go
@@ -396,17 +396,11 @@ func (hs *clientHandshakeStateTLS13) readServerParameters() error {
 	}
 	hs.transcript.Write(encryptedExtensions.marshal())
 
-	if encryptedExtensions.alpnProtocol != "" {
-		if len(hs.hello.alpnProtocols) == 0 {
-			c.sendAlert(alertUnsupportedExtension)
-			return errors.New("tls: server advertised unrequested ALPN extension")
-		}
-		if mutualProtocol([]string{encryptedExtensions.alpnProtocol}, hs.hello.alpnProtocols) == "" {
-			c.sendAlert(alertUnsupportedExtension)
-			return errors.New("tls: server selected unadvertised ALPN protocol")
-		}
-		c.clientProtocol = encryptedExtensions.alpnProtocol
+	if err := checkALPN(hs.hello.alpnProtocols, encryptedExtensions.alpnProtocol); err != nil {
+		c.sendAlert(alertUnsupportedExtension)
+		return err
 	}
+	c.clientProtocol = encryptedExtensions.alpnProtocol
 
 	return nil
 }
diff --git a/src/crypto/tls/handshake_server.go b/src/crypto/tls/handshake_server.go
index b231981e09..43f30e2fef 100644
--- a/src/crypto/tls/handshake_server.go
+++ b/src/crypto/tls/handshake_server.go
@@ -217,15 +217,13 @@ func (hs *serverHandshakeState) processClientHello() error {
 		c.serverName = hs.clientHello.serverName
 	}
 
-	if len(c.config.NextProtos) > 0 && len(hs.clientHello.alpnProtocols) > 0 {
-		selectedProto := mutualProtocol(hs.clientHello.alpnProtocols, c.config.NextProtos)
-		if selectedProto == "" {
-			c.sendAlert(alertNoApplicationProtocol)
-			return fmt.Errorf("tls: client requested unsupported application protocols (%s)", hs.clientHello.alpnProtocols)
-		}
-		hs.hello.alpnProtocol = selectedProto
-		c.clientProtocol = selectedProto
+	selectedProto, err := negotiateALPN(c.config.NextProtos, hs.clientHello.alpnProtocols)
+	if err != nil {
+		c.sendAlert(alertNoApplicationProtocol)
+		return err
 	}
+	hs.hello.alpnProtocol = selectedProto
+	c.clientProtocol = selectedProto
 
 	hs.cert, err = c.config.getCertificate(clientHelloInfo(hs.ctx, c, hs.clientHello))
 	if err != nil {
@@ -277,6 +275,34 @@ func (hs *serverHandshakeState) processClientHello() error {
 	return nil
 }
 
+// negotiateALPN picks a shared ALPN protocol that both sides support in server
+// preference order. If ALPN is not configured or the peer doesn't support it,
+// it returns "" and no error.
+func negotiateALPN(serverProtos, clientProtos []string) (string, error) {
+	if len(serverProtos) == 0 || len(clientProtos) == 0 {
+		return "", nil
+	}
+	var http11fallback bool
+	for _, s := range serverProtos {
+		for _, c := range clientProtos {
+			if s == c {
+				return s, nil
+			}
+			if s == "h2" && c == "http/1.1" {
+				http11fallback = true
+			}
+		}
+	}
+	// As a special case, let http/1.1 clients connect to h2 servers as if they
+	// didn't support ALPN. We used not to enforce protocol overlap, so over
+	// time a number of HTTP servers were configured with only "h2", but
+	// expected to accept connections from "http/1.1" clients. See Issue 46310.
+	if http11fallback {
+		return "", nil
+	}
+	return "", fmt.Errorf("tls: client requested unsupported application protocols (%s)", clientProtos)
+}
+
 // supportsECDHE returns whether ECDHE key exchanges can be used with this
 // pre-TLS 1.3 client.
 func supportsECDHE(c *Config, supportedCurves []CurveID, supportedPoints []uint8) bool {
diff --git a/src/crypto/tls/handshake_server_test.go b/src/crypto/tls/handshake_server_test.go
index 4483838045..f61b4c88ef 100644
--- a/src/crypto/tls/handshake_server_test.go
+++ b/src/crypto/tls/handshake_server_test.go
@@ -949,6 +949,27 @@ func TestHandshakeServerALPNNotConfigured(t *testing.T) {
 	runServerTestTLS13(t, test)
 }
 
+func TestHandshakeServerALPNFallback(t *testing.T) {
+	config := testConfig.Clone()
+	config.NextProtos = []string{"proto1", "h2", "proto2"}
+
+	test := &serverTest{
+		name: "ALPN-Fallback",
+		// Note that this needs OpenSSL 1.0.2 because that is the first
+		// version that supports the -alpn flag.
+		command: []string{"openssl", "s_client", "-alpn", "proto3,http/1.1,proto4", "-cipher", "ECDHE-RSA-CHACHA20-POLY1305", "-ciphersuites", "TLS_CHACHA20_POLY1305_SHA256"},
+		config:  config,
+		validate: func(state ConnectionState) error {
+			if state.NegotiatedProtocol != "" {
+				return fmt.Errorf("Got protocol %q, wanted nothing", state.NegotiatedProtocol)
+			}
+			return nil
+		},
+	}
+	runServerTestTLS12(t, test)
+	runServerTestTLS13(t, test)
+}
+
 // TestHandshakeServerSNI involves a client sending an SNI extension of
 // "snitest.com", which happens to match the CN of testSNICertificate. The test
 // verifies that the server correctly selects that certificate.
diff --git a/src/crypto/tls/handshake_server_tls13.go b/src/crypto/tls/handshake_server_tls13.go
index c375ec4246..08251b84de 100644
--- a/src/crypto/tls/handshake_server_tls13.go
+++ b/src/crypto/tls/handshake_server_tls13.go
@@ -11,7 +11,6 @@ import (
 	"crypto/hmac"
 	"crypto/rsa"
 	"errors"
-	"fmt"
 	"hash"
 	"io"
 	"sync/atomic"
@@ -551,15 +550,13 @@ func (hs *serverHandshakeStateTLS13) sendServerParameters() error {
 
 	encryptedExtensions := new(encryptedExtensionsMsg)
 
-	if len(c.config.NextProtos) > 0 && len(hs.clientHello.alpnProtocols) > 0 {
-		selectedProto := mutualProtocol(hs.clientHello.alpnProtocols, c.config.NextProtos)
-		if selectedProto == "" {
-			c.sendAlert(alertNoApplicationProtocol)
-			return fmt.Errorf("tls: client requested unsupported application protocols (%s)", hs.clientHello.alpnProtocols)
-		}
-		encryptedExtensions.alpnProtocol = selectedProto
-		c.clientProtocol = selectedProto
+	selectedProto, err := negotiateALPN(c.config.NextProtos, hs.clientHello.alpnProtocols)
+	if err != nil {
+		c.sendAlert(alertNoApplicationProtocol)
+		return err
 	}
+	encryptedExtensions.alpnProtocol = selectedProto
+	c.clientProtocol = selectedProto
 
 	hs.transcript.Write(encryptedExtensions.marshal())
 	if _, err := c.writeRecord(recordTypeHandshake, encryptedExtensions.marshal()); err != nil {
diff --git a/src/crypto/tls/testdata/Server-TLSv12-ALPN-Fallback b/src/crypto/tls/testdata/Server-TLSv12-ALPN-Fallback
new file mode 100644
index 0000000000..4fadf39062
--- /dev/null
+++ b/src/crypto/tls/testdata/Server-TLSv12-ALPN-Fallback
@@ -0,0 +1,91 @@
+>>> Flow 1 (client to server)
+00000000  16 03 01 00 a6 01 00 00  a2 03 03 b5 c9 ab 32 7f  |..............2.|
+00000010  e1 af 3f f2 ac 2a 11 dd  33 f9 b5 21 88 0d e4 29  |..?..*..3..!...)|
+00000020  e2 47 49 dc c7 31 a8 a5  25 81 0c 00 00 04 cc a8  |.GI..1..%.......|
+00000030  00 ff 01 00 00 75 00 0b  00 04 03 00 01 02 00 0a  |.....u..........|
+00000040  00 0c 00 0a 00 1d 00 17  00 1e 00 19 00 18 00 23  |...............#|
+00000050  00 00 00 10 00 19 00 17  06 70 72 6f 74 6f 33 08  |.........proto3.|
+00000060  68 74 74 70 2f 31 2e 31  06 70 72 6f 74 6f 34 00  |http/1.1.proto4.|
+00000070  16 00 00 00 17 00 00 00  0d 00 30 00 2e 04 03 05  |..........0.....|
+00000080  03 06 03 08 07 08 08 08  09 08 0a 08 0b 08 04 08  |................|
+00000090  05 08 06 04 01 05 01 06  01 03 03 02 03 03 01 02  |................|
+000000a0  01 03 02 02 02 04 02 05  02 06 02                 |...........|
+>>> Flow 2 (server to client)
+00000000  16 03 03 00 3b 02 00 00  37 03 03 00 00 00 00 00  |....;...7.......|
+00000010  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
+00000020  00 00 00 44 4f 57 4e 47  52 44 01 00 cc a8 00 00  |...DOWNGRD......|
+00000030  0f 00 23 00 00 ff 01 00  01 00 00 0b 00 02 01 00  |..#.............|
+00000040  16 03 03 02 59 0b 00 02  55 00 02 52 00 02 4f 30  |....Y...U..R..O0|
+00000050  82 02 4b 30 82 01 b4 a0  03 02 01 02 02 09 00 e8  |..K0............|
+00000060  f0 9d 3f e2 5b ea a6 30  0d 06 09 2a 86 48 86 f7  |..?.[..0...*.H..|
+00000070  0d 01 01 0b 05 00 30 1f  31 0b 30 09 06 03 55 04  |......0.1.0...U.|
+00000080  0a 13 02 47 6f 31 10 30  0e 06 03 55 04 03 13 07  |...Go1.0...U....|
+00000090  47 6f 20 52 6f 6f 74 30  1e 17 0d 31 36 30 31 30  |Go Root0...16010|
+000000a0  31 30 30 30 30 30 30 5a  17 0d 32 35 30 31 30 31  |1000000Z..250101|
+000000b0  30 30 30 30 30 30 5a 30  1a 31 0b 30 09 06 03 55  |000000Z0.1.0...U|
+000000c0  04 0a 13 02 47 6f 31 0b  30 09 06 03 55 04 03 13  |....Go1.0...U...|
+000000d0  02 47 6f 30 81 9f 30 0d  06 09 2a 86 48 86 f7 0d  |.Go0..0...*.H...|
+000000e0  01 01 01 05 00 03 81 8d  00 30 81 89 02 81 81 00  |.........0......|
+000000f0  db 46 7d 93 2e 12 27 06  48 bc 06 28 21 ab 7e c4  |.F}...'.H..(!.~.|
+00000100  b6 a2 5d fe 1e 52 45 88  7a 36 47 a5 08 0d 92 42  |..]..RE.z6G....B|
+00000110  5b c2 81 c0 be 97 79 98  40 fb 4f 6d 14 fd 2b 13  |[.....y.@.Om..+.|
+00000120  8b c2 a5 2e 67 d8 d4 09  9e d6 22 38 b7 4a 0b 74  |....g....."8.J.t|
+00000130  73 2b c2 34 f1 d1 93 e5  96 d9 74 7b f3 58 9f 6c  |s+.4......t{.X.l|
+00000140  61 3c c0 b0 41 d4 d9 2b  2b 24 23 77 5b 1c 3b bd  |a<..A..++$#w[.;.|
+00000150  75 5d ce 20 54 cf a1 63  87 1d 1e 24 c4 f3 1d 1a  |u]. T..c...$....|
+00000160  50 8b aa b6 14 43 ed 97  a7 75 62 f4 14 c8 52 d7  |P....C...ub...R.|
+00000170  02 03 01 00 01 a3 81 93  30 81 90 30 0e 06 03 55  |........0..0...U|
+00000180  1d 0f 01 01 ff 04 04 03  02 05 a0 30 1d 06 03 55  |...........0...U|
+00000190  1d 25 04 16 30 14 06 08  2b 06 01 05 05 07 03 01  |.%..0...+.......|
+000001a0  06 08 2b 06 01 05 05 07  03 02 30 0c 06 03 55 1d  |..+.......0...U.|
+000001b0  13 01 01 ff 04 02 30 00  30 19 06 03 55 1d 0e 04  |......0.0...U...|
+000001c0  12 04 10 9f 91 16 1f 43  43 3e 49 a6 de 6d b6 80  |.......CC>I..m..|
+000001d0  d7 9f 60 30 1b 06 03 55  1d 23 04 14 30 12 80 10  |..`0...U.#..0...|
+000001e0  48 13 49 4d 13 7e 16 31  bb a3 01 d5 ac ab 6e 7b  |H.IM.~.1......n{|
+000001f0  30 19 06 03 55 1d 11 04  12 30 10 82 0e 65 78 61  |0...U....0...exa|
+00000200  6d 70 6c 65 2e 67 6f 6c  61 6e 67 30 0d 06 09 2a  |mple.golang0...*|
+00000210  86 48 86 f7 0d 01 01 0b  05 00 03 81 81 00 9d 30  |.H.............0|
+00000220  cc 40 2b 5b 50 a0 61 cb  ba e5 53 58 e1 ed 83 28  |.@+[P.a...SX...(|
+00000230  a9 58 1a a9 38 a4 95 a1  ac 31 5a 1a 84 66 3d 43  |.X..8....1Z..f=C|
+00000240  d3 2d d9 0b f2 97 df d3  20 64 38 92 24 3a 00 bc  |.-...... d8.$:..|
+00000250  cf 9c 7d b7 40 20 01 5f  aa d3 16 61 09 a2 76 fd  |..}.@ ._...a..v.|
+00000260  13 c3 cc e1 0c 5c ee b1  87 82 f1 6c 04 ed 73 bb  |.....\.....l..s.|
+00000270  b3 43 77 8d 0c 1c f1 0f  a1 d8 40 83 61 c9 4c 72  |.Cw.......@.a.Lr|
+00000280  2b 9d ae db 46 06 06 4d  f4 c1 b3 3e c0 d1 bd 42  |+...F..M...>...B|
+00000290  d4 db fe 3d 13 60 84 5c  21 d3 3b e9 fa e7 16 03  |...=.`.\!.;.....|
+000002a0  03 00 ac 0c 00 00 a8 03  00 1d 20 2f e5 7d a3 47  |.......... /.}.G|
+000002b0  cd 62 43 15 28 da ac 5f  bb 29 07 30 ff f6 84 af  |.bC.(.._.).0....|
+000002c0  c4 cf c2 ed 90 99 5f 58  cb 3b 74 08 04 00 80 5f  |......_X.;t...._|
+000002d0  37 27 84 58 1e ea 1e 40  1b de a9 8f 04 d4 94 64  |7'.X...@.......d|
+000002e0  4e 27 c7 f1 b3 30 d0 53  f5 3d 57 50 d2 17 97 c8  |N'...0.S.=WP....|
+000002f0  3d 61 af a6 21 ab 1c 34  47 70 f8 b1 3b 9c 06 86  |=a..!..4Gp..;...|
+00000300  87 00 e2 13 50 83 91 ad  bc 84 bd b4 7b f3 4b ed  |....P.......{.K.|
+00000310  ca 81 0c 94 37 a8 ec 67  ca 9c f3 00 f6 af c2 92  |....7..g........|
+00000320  c4 8c 78 07 18 0e 43 24  1b 98 16 50 5c 2b 75 0e  |..x...C$...P\+u.|
+00000330  40 66 dc 40 cd 10 1a 51  25 f3 96 25 1a 3e 70 af  |@f.@...Q%..%.>p.|
+00000340  16 24 d0 1c 0e 33 f9 c1  74 cf b7 e2 28 ac 60 16  |.$...3..t...(.`.|
+00000350  03 03 00 04 0e 00 00 00                           |........|
+>>> Flow 3 (client to server)
+00000000  16 03 03 00 25 10 00 00  21 20 30 f2 bb f7 a7 ac  |....%...! 0.....|
+00000010  23 20 22 ee 73 0d 49 9c  b3 7b c1 9a db 2c 85 f3  |# ".s.I..{...,..|
+00000020  c0 82 31 60 bd 8b 14 4e  73 43 14 03 03 00 01 01  |..1`...NsC......|
+00000030  16 03 03 00 20 09 8d c7  86 ee cc f4 c7 36 a3 49  |.... ........6.I|
+00000040  d3 f7 a1 4a 68 a2 1e b4  fc cc a2 15 cb 01 92 d8  |...Jh...........|
+00000050  72 b0 d1 6f eb                                    |r..o.|
+>>> Flow 4 (server to client)
+00000000  16 03 03 00 8b 04 00 00  87 00 00 00 00 00 81 50  |...............P|
+00000010  46 ad c1 db a8 38 86 7b  2b bb fd d0 c3 42 3e 00  |F....8.{+....B>.|
+00000020  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 94  |................|
+00000030  6f e0 18 83 51 ed 14 ef  68 ca 42 c5 4c a2 ac 05  |o...Q...h.B.L...|
+00000040  9c 69 69 99 08 9f de a4  d4 e7 37 ab 14 38 4c 47  |.ii.......7..8LG|
+00000050  70 f0 97 1d db 2d 0a 14  c2 1e f0 16 9f 6d 37 02  |p....-.......m7.|
+00000060  4b f1 16 be 98 3f df 74  83 7c 19 85 61 49 38 16  |K....?.t.|..aI8.|
+00000070  ee 35 7a e2 3f 74 fe 8d  e3 07 93 a1 5e fa f2 02  |.5z.?t......^...|
+00000080  e5 c8 60 3f 11 83 8b 0e  32 52 f1 aa 52 b7 0a 89  |..`?....2R..R...|
+00000090  14 03 03 00 01 01 16 03  03 00 20 9e 65 15 cf 45  |.......... .e..E|
+000000a0  a5 03 69 c9 b1 d8 9e 92  a3 a2 b0 df 2e 62 b1 3a  |..i..........b.:|
+000000b0  17 78 cd e5 1d f3 51 42  7e 4e 25 17 03 03 00 1d  |.x....QB~N%.....|
+000000c0  d9 ae d0 fa b7 90 a9 2f  28 8d 1d 6f 54 1f c0 1e  |......./(..oT...|
+000000d0  4d ae b6 91 f0 e8 84 cf  86 11 22 25 ea 15 03 03  |M........."%....|
+000000e0  00 12 0e 71 f2 11 9e 9f  58 ad c0 d8 fc fa 34 bc  |...q....X.....4.|
+000000f0  02 5a 60 00                                       |.Z`.|
diff --git a/src/crypto/tls/testdata/Server-TLSv13-ALPN-Fallback b/src/crypto/tls/testdata/Server-TLSv13-ALPN-Fallback
new file mode 100644
index 0000000000..6203e6877c
--- /dev/null
+++ b/src/crypto/tls/testdata/Server-TLSv13-ALPN-Fallback
@@ -0,0 +1,100 @@
+>>> Flow 1 (client to server)
+00000000  16 03 01 00 eb 01 00 00  e7 03 03 1c d3 8e 3b d9  |..............;.|
+00000010  fe 7d e7 f9 9f fa c6 51  c3 8c 1b dd dc 87 95 f4  |.}.....Q........|
+00000020  39 23 67 e4 d6 bd 94 93  fc 88 4e 20 c3 c0 e2 c1  |9#g.......N ....|
+00000030  3d 12 ec 4c 0a 3f 40 51  13 24 61 11 c0 5d 09 f9  |=..L.?@Q.$a..]..|
+00000040  08 d6 3e cd e7 b3 51 c3  06 8f b4 42 00 04 13 03  |..>...Q....B....|
+00000050  00 ff 01 00 00 9a 00 0b  00 04 03 00 01 02 00 0a  |................|
+00000060  00 0c 00 0a 00 1d 00 17  00 1e 00 19 00 18 00 23  |...............#|
+00000070  00 00 00 10 00 19 00 17  06 70 72 6f 74 6f 33 08  |.........proto3.|
+00000080  68 74 74 70 2f 31 2e 31  06 70 72 6f 74 6f 34 00  |http/1.1.proto4.|
+00000090  16 00 00 00 17 00 00 00  0d 00 1e 00 1c 04 03 05  |................|
+000000a0  03 06 03 08 07 08 08 08  09 08 0a 08 0b 08 04 08  |................|
+000000b0  05 08 06 04 01 05 01 06  01 00 2b 00 03 02 03 04  |..........+.....|
+000000c0  00 2d 00 02 01 01 00 33  00 26 00 24 00 1d 00 20  |.-.....3.&.$... |
+000000d0  f4 05 eb 4a 7a 73 20 18  74 aa 14 2a 0c 35 63 29  |...Jzs .t..*.5c)|
+000000e0  cb f2 ad d1 a2 3d bd 9d  02 b4 62 00 bc eb 10 58  |.....=....b....X|
+>>> Flow 2 (server to client)
+00000000  16 03 03 00 7a 02 00 00  76 03 03 00 00 00 00 00  |....z...v.......|
+00000010  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
+00000020  00 00 00 00 00 00 00 00  00 00 00 20 c3 c0 e2 c1  |........... ....|
+00000030  3d 12 ec 4c 0a 3f 40 51  13 24 61 11 c0 5d 09 f9  |=..L.?@Q.$a..]..|
+00000040  08 d6 3e cd e7 b3 51 c3  06 8f b4 42 13 03 00 00  |..>...Q....B....|
+00000050  2e 00 2b 00 02 03 04 00  33 00 24 00 1d 00 20 2f  |..+.....3.$... /|
+00000060  e5 7d a3 47 cd 62 43 15  28 da ac 5f bb 29 07 30  |.}.G.bC.(.._.).0|
+00000070  ff f6 84 af c4 cf c2 ed  90 99 5f 58 cb 3b 74 14  |.........._X.;t.|
+00000080  03 03 00 01 01 17 03 03  00 17 fb 75 d8 5c 50 35  |...........u.\P5|
+00000090  55 82 ba 65 1e 63 73 b8  c1 e9 d7 f5 28 68 3c c1  |U..e.cs.....(h<.|
+000000a0  5d 17 03 03 02 6d 56 c9  a9 09 73 6a bc fd 1a 3c  |]....mV...sj...<|
+000000b0  6a f8 3e 32 99 83 e8 f6  01 9e 5e 30 e8 53 7f 72  |j.>2......^0.S.r|
+000000c0  fd 86 72 a8 9e 47 25 67  c1 f1 9a 03 c0 9d 6f 9d  |..r..G%g......o.|
+000000d0  bd ed 29 30 8f 3c 01 ce  49 bb 5f dd 58 9a ae 80  |..)0.<..I._.X...|
+000000e0  5c 2d 81 fc ea 7b 03 03  3d 5d bb 92 23 73 67 89  |\-...{..=]..#sg.|
+000000f0  2e f0 ec 08 20 8a 36 eb  43 a6 a1 68 d0 39 95 37  |.... .6.C..h.9.7|
+00000100  6b 15 a9 0e 46 20 92 51  9c 04 bf 3b 07 97 84 cb  |k...F .Q...;....|
+00000110  1f 30 38 37 2e ff e7 0f  f5 14 93 5a 84 f1 f7 10  |.087.......Z....|
+00000120  c2 a5 0d bb 97 96 ef 4a  e0 13 c0 63 72 2b 60 f3  |.......J...cr+`.|
+00000130  59 b5 57 aa 5f d1 da a9  0e dd 9c dd c2 cb 61 fe  |Y.W._.........a.|
+00000140  e2 69 8e db 5d 70 6c 3a  33 e0 9e db 9a 31 26 6a  |.i..]pl:3....1&j|
+00000150  2b 9e 19 8e bb 5d 06 48  ea c0 a1 c6 11 24 fb c4  |+....].H.....$..|
+00000160  ce ae 48 54 64 81 d1 84  38 a6 e0 7a 7b 74 2b bc  |..HTd...8..z{t+.|
+00000170  ce 07 8b b6 04 1f 5b 4c  36 29 68 0c 8c c7 32 15  |......[L6)h...2.|
+00000180  93 e0 10 52 c2 27 23 96  c5 0c 9c e9 e2 a9 08 7d  |...R.'#........}|
+00000190  25 68 65 f5 4e 44 eb a9  85 78 13 e1 0d 86 5e dc  |%he.ND...x....^.|
+000001a0  fd e5 c6 dd 65 46 8e 2f  32 82 83 0b dd 67 f8 42  |....eF./2....g.B|
+000001b0  65 87 3b 08 fe b1 f5 12  e9 74 21 04 12 6d 75 35  |e.;......t!..mu5|
+000001c0  b2 eb 93 95 72 10 fa 56  96 77 c3 0c 17 8c 9e f6  |....r..V.w......|
+000001d0  77 19 28 37 96 3e 73 98  f4 d2 91 4f 40 db 76 56  |w.(7.>s....O@.vV|
+000001e0  ce b5 a8 7a b8 86 d0 9a  ba b5 8b 40 c2 63 e1 cf  |...z.......@.c..|
+000001f0  49 29 2c 5d 1a 9b 8b 56  cb 93 ca 2c c0 d0 15 b7  |I),]...V...,....|
+00000200  8a f1 6a d5 0a a8 81 57  b1 6e 10 cd a5 ff b1 4d  |..j....W.n.....M|
+00000210  47 c6 9b 35 f1 5f 83 91  22 f6 88 68 65 b3 b9 c9  |G..5._.."..he...|
+00000220  02 dc 4b f7 13 39 06 e6  3a ec 94 ef 51 15 05 72  |..K..9..:...Q..r|
+00000230  1d f4 9d 3b da ca 8d 2c  64 be 9b 45 99 2c 63 cc  |...;...,d..E.,c.|
+00000240  22 b3 8b 93 ad f6 2c f0  d2 d9 11 3f 5b c0 40 fa  |".....,....?[.@.|
+00000250  90 6e a0 76 b2 43 b9 4c  72 c4 24 28 a2 bf 56 d6  |.n.v.C.Lr.$(..V.|
+00000260  d2 a7 2a d1 8c 5e 1d eb  f8 be d0 43 da 7a c7 88  |..*..^.....C.z..|
+00000270  61 67 a2 69 85 23 43 3e  d4 88 f2 33 c3 5b 38 0a  |ag.i.#C>...3.[8.|
+00000280  1e de 28 3b 3b 19 de 95  2f 84 c0 37 88 80 59 2f  |..(;;.../..7..Y/|
+00000290  a6 ee 93 1a 69 08 c3 df  7c cf da c3 9b 96 70 d9  |....i...|.....p.|
+000002a0  60 c5 e9 0f 42 f6 1a f2  58 5e f2 32 61 6a b2 a3  |`...B...X^.2aj..|
+000002b0  1f 97 fa 08 6c 3f 4b 83  1f 04 66 80 8a 26 3a 7f  |....l?K...f..&:.|
+000002c0  24 30 ec 10 ae 7d 19 ff  39 91 ca 97 4e ed 0a d7  |$0...}..9...N...|
+000002d0  64 3b 6b 50 29 33 0d b2  10 bc 83 63 3c fb 9a 82  |d;kP)3.....c<...|
+000002e0  3b 7f bc 04 40 f1 33 64  4a 80 cd 01 f9 f4 c6 89  |;...@.3dJ.......|
+000002f0  65 27 25 f9 cf 4f 7e c8  6e d9 0e ec 47 4a 51 29  |e'%..O~.n...GJQ)|
+00000300  2f be 34 50 bd 9b d2 d8  b7 ea bb 0b a1 e0 20 1b  |/.4P.......... .|
+00000310  02 9c f2 17 03 03 00 99  61 dc 0b 3a 30 de 39 f6  |........a..:0.9.|
+00000320  f3 db f8 6c 3b fa 4e 1e  7e 62 a5 ae 73 ba e1 41  |...l;.N.~b..s..A|
+00000330  58 77 2a c1 7a 0c 50 bb  0c 57 b4 c4 25 bf 2f 9f  |Xw*.z.P..W..%./.|
+00000340  38 91 e2 65 22 9d ca ac  18 58 7e 81 2d fd 74 24  |8..e"....X~.-.t$|
+00000350  28 69 76 11 df 9d 23 b8  be ae 8b e0 93 8e 5d df  |(iv...#.......].|
+00000360  0a 64 d0 b7 02 68 aa 86  01 0d 55 11 3b 76 70 c6  |.d...h....U.;vp.|
+00000370  83 0c 5e 0a e3 37 a5 8b  ad 25 50 b9 e8 5c 6b 04  |..^..7...%P..\k.|
+00000380  b4 51 ec 9c d3 fa c6 b7  9c f0 46 aa 73 da 3c 0d  |.Q........F.s.<.|
+00000390  d3 bd 32 81 d4 d2 f1 1a  b0 92 f3 73 3e 54 2b 05  |..2........s>T+.|
+000003a0  92 24 34 75 df d6 18 a0  6a 82 95 4c 9b fc 7e b6  |.$4u....j..L..~.|
+000003b0  8e 17 03 03 00 35 8f 34  0e 3b 91 d8 e7 74 24 71  |.....5.4.;...t$q|
+000003c0  0e 7b f3 12 bb 76 2f 31  12 17 b8 9e 24 ce f9 2f  |.{...v/1....$../|
+000003d0  3f 5d f2 13 4b 2e 9b 1e  c4 78 03 a6 c8 07 11 a3  |?]..K....x......|
+000003e0  98 79 61 6e 4f 44 6e 18  ee c4 9b 17 03 03 00 93  |.yanODn.........|
+000003f0  64 dd 52 a9 d9 51 63 6a  a0 a3 c2 75 6b 5d 1d 54  |d.R..Qcj...uk].T|
+00000400  ce d4 53 7e 14 8e d9 26  93 28 78 65 16 1b 95 77  |..S~...&.(xe...w|
+00000410  68 0a 46 f1 82 36 bb 8a  fa 0d df 54 8c 3d 83 e0  |h.F..6.....T.=..|
+00000420  d7 de 2d 96 e9 c4 d7 22  d3 97 8e ae 90 f8 fc e6  |..-...."........|
+00000430  a6 4b 78 98 4c c5 28 87  91 46 fa f4 1c 8d 0e ec  |.Kx.L.(..F......|
+00000440  0d 71 40 9a 04 49 b4 e8  5b 62 6f cd 16 c1 d5 fb  |.q@..I..[bo.....|
+00000450  73 2a 96 8f e5 a2 f4 11  1e df 2d 40 45 6b d5 a9  |s*........-@Ek..|
+00000460  e4 e3 f7 93 fc fa d7 20  af d5 f7 b4 0e 09 ad d5  |....... ........|
+00000470  26 87 b8 6c e2 20 95 fb  c0 70 3e 38 be b7 b1 9f  |&..l. ...p>8....|
+00000480  70 da c1                                          |p..|
+>>> Flow 3 (client to server)
+00000000  14 03 03 00 01 01 17 03  03 00 35 29 d2 b9 bb 9b  |..........5)....|
+00000010  de 6c 5d 22 23 c1 fe 99  4c c5 33 bf fd 70 36 6b  |.l]"#...L.3..p6k|
+00000020  f1 a5 92 e8 bf 7c 3d 6e  ef 6a 44 73 bc cb 27 1c  |.....|=n.jDs..'.|
+00000030  09 5d bf 99 4c 19 24 c3  3b 30 91 b5 e3 b6 63 45  |.]..L.$.;0....cE|
+>>> Flow 4 (server to client)
+00000000  17 03 03 00 1e 52 55 85  7c b8 87 dd c7 b2 d9 5b  |.....RU.|......[|
+00000010  18 1d bb ac bf b6 ab 76  82 be 64 0e b2 7b 2c 0f  |.......v..d..{,.|
+00000020  aa 17 92 17 03 03 00 13  79 0a 60 b1 46 20 33 74  |........y.`.F 3t|
+00000030  ed 12 a0 23 de 68 88 fc  6f dd 8e                 |...#.h..o..|
diff --git a/src/go/build/deps_test.go b/src/go/build/deps_test.go
index 5d1cf7f4c9..45e2f25df7 100644
--- a/src/go/build/deps_test.go
+++ b/src/go/build/deps_test.go
@@ -440,7 +440,8 @@ var depsRules = `
 	# HTTP, King of Dependencies.
 
 	FMT
-	< golang.org/x/net/http2/hpack, net/http/internal, net/http/internal/ascii;
+	< golang.org/x/net/http2/hpack
+	< net/http/internal, net/http/internal/ascii, net/http/internal/testcert;
 
 	FMT, NET, container/list, encoding/binary, log
 	< golang.org/x/text/transform
@@ -459,6 +460,7 @@ var depsRules = `
 	golang.org/x/net/http2/hpack,
 	net/http/internal,
 	net/http/internal/ascii,
+	net/http/internal/testcert,
 	net/http/httptrace,
 	mime/multipart,
 	log
diff --git a/src/internal/goversion/goversion.go b/src/internal/goversion/goversion.go
index 4cc15688c0..8fcea100dc 100644
--- a/src/internal/goversion/goversion.go
+++ b/src/internal/goversion/goversion.go
@@ -9,4 +9,4 @@ package goversion
 //
 // It should be updated at the start of each development cycle to be
 // the version of the next Go 1.x release. See golang.org/issue/40705.
-const Version = 17
+const Version = 18
diff --git a/src/math/big/natdiv.go b/src/math/big/natdiv.go
index 1330990c2c..882bb6d3ba 100644
--- a/src/math/big/natdiv.go
+++ b/src/math/big/natdiv.go
@@ -2,10 +2,506 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+/*
+
+Multi-precision division. Here be dragons.
+
+Given u and v, where u is n+m digits, and v is n digits (with no leading zeros),
+the goal is to return quo, rem such that u = quo*v + rem, where 0 ≤ rem < v.
+That is, quo = ⌊u/v⌋ where ⌊x⌋ denotes the floor (truncation to integer) of x,
+and rem = u - quo·v.
+
+
+Long Division
+
+Division in a computer proceeds the same as long division in elementary school,
+but computers are not as good as schoolchildren at following vague directions,
+so we have to be much more precise about the actual steps and what can happen.
+
+We work from most to least significant digit of the quotient, doing:
+
+ • Guess a digit q, the number of v to subtract from the current
+   section of u to zero out the topmost digit.
+ • Check the guess by multiplying q·v and comparing it against
+   the current section of u, adjusting the guess as needed.
+ • Subtract q·v from the current section of u.
+ • Add q to the corresponding section of the result quo.
+
+When all digits have been processed, the final remainder is left in u
+and returned as rem.
+
+For example, here is a sketch of dividing 5 digits by 3 digits (n=3, m=2).
+
+	                 q₂ q₁ q₀
+	         _________________
+	v₂ v₁ v₀ ) u₄ u₃ u₂ u₁ u₀
+	           ↓  ↓  ↓  |  |
+	          [u₄ u₃ u₂]|  |
+	        - [  q₂·v  ]|  |
+	        ----------- ↓  |
+	          [  rem  | u₁]|
+	        - [    q₁·v   ]|
+	           ----------- ↓
+	             [  rem  | u₀]
+	           - [    q₀·v   ]
+	              ------------
+	                [  rem   ]
+
+Instead of creating new storage for the remainders and copying digits from u
+as indicated by the arrows, we use u's storage directly as both the source
+and destination of the subtractions, so that the remainders overwrite
+successive overlapping sections of u as the division proceeds, using a slice
+of u to identify the current section. This avoids all the copying as well as
+shifting of remainders.
+
+Division of u with n+m digits by v with n digits (in base B) can in general
+produce at most m+1 digits, because:
+
+  • u < B^(n+m)               [B^(n+m) has n+m+1 digits]
+  • v ≥ B^(n-1)               [B^(n-1) is the smallest n-digit number]
+  • u/v < B^(n+m) / B^(n-1)   [divide bounds for u, v]
+  • u/v < B^(m+1)             [simplify]
+
+The first step is special: it takes the top n digits of u and divides them by
+the n digits of v, producing the first quotient digit and an n-digit remainder.
+In the example, q₂ = ⌊u₄u₃u₂ / v⌋.
+
+The first step divides n digits by n digits to ensure that it produces only a
+single digit.
+
+Each subsequent step appends the next digit from u to the remainder and divides
+those n+1 digits by the n digits of v, producing another quotient digit and a
+new n-digit remainder.
+
+Subsequent steps divide n+1 digits by n digits, an operation that in general
+might produce two digits. However, as used in the algorithm, that division is
+guaranteed to produce only a single digit. The dividend is of the form
+rem·B + d, where rem is a remainder from the previous step and d is a single
+digit, so:
+
+ • rem ≤ v - 1                 [rem is a remainder from dividing by v]
+ • rem·B ≤ v·B - B             [multiply by B]
+ • d ≤ B - 1                   [d is a single digit]
+ • rem·B + d ≤ v·B - 1         [add]
+ • rem·B + d < v·B             [change ≤ to <]
+ • (rem·B + d)/v < B           [divide by v]
+
+
+Guess and Check
+
+At each step we need to divide n+1 digits by n digits, but this is for the
+implementation of division by n digits, so we can't just invoke a division
+routine: we _are_ the division routine. Instead, we guess at the answer and
+then check it using multiplication. If the guess is wrong, we correct it.
+
+How can this guessing possibly be efficient? It turns out that the following
+statement (let's call it the Good Guess Guarantee) is true.
+
+If
+
+ • q = ⌊u/v⌋ where u is n+1 digits and v is n digits,
+ • q < B, and
+ • the topmost digit of v = vₙ₋₁ ≥ B/2,
+
+then q̂ = ⌊uₙuₙ₋₁ / vₙ₋₁⌋ satisfies q ≤ q̂ ≤ q+2. (Proof below.)
+
+That is, if we know the answer has only a single digit and we guess an answer
+by ignoring the bottom n-1 digits of u and v, using a 2-by-1-digit division,
+then that guess is at least as large as the correct answer. It is also not
+too much larger: it is off by at most two from the correct answer.
+
+Note that in the first step of the overall division, which is an n-by-n-digit
+division, the 2-by-1 guess uses an implicit uₙ = 0.
+
+Note that using a 2-by-1-digit division here does not mean calling ourselves
+recursively. Instead, we use an efficient direct hardware implementation of
+that operation.
+
+Note that because q is u/v rounded down, q·v must not exceed u: u ≥ q·v.
+If a guess q̂ is too big, it will not satisfy this test. Viewed a different way,
+the remainder r̂ for a given q̂ is u - q̂·v, which must be positive. If it is
+negative, then the guess q̂ is too big.
+
+This gives us a way to compute q. First compute q̂ with 2-by-1-digit division.
+Then, while u < q̂·v, decrement q̂; this loop executes at most twice, because
+q̂ ≤ q+2.
+
+
+Scaling Inputs
+
+The Good Guess Guarantee requires that the top digit of v (vₙ₋₁) be at least B/2.
+For example in base 10, ⌊172/19⌋ = 9, but ⌊18/1⌋ = 18: the guess is wildly off
+because the first digit 1 is smaller than B/2 = 5.
+
+We can ensure that v has a large top digit by multiplying both u and v by the
+right amount. Continuing the example, if we multiply both 172 and 19 by 3, we
+now have ⌊516/57⌋, the leading digit of v is now ≥ 5, and sure enough
+⌊51/5⌋ = 10 is much closer to the correct answer 9. It would be easier here
+to multiply by 4, because that can be done with a shift. Specifically, we can
+always count the number of leading zeros i in the first digit of v and then
+shift both u and v left by i bits.
+
+Having scaled u and v, the value ⌊u/v⌋ is unchanged, but the remainder will
+be scaled: 172 mod 19 is 1, but 516 mod 57 is 3. We have to divide the remainder
+by the scaling factor (shifting right i bits) when we finish.
+
+Note that these shifts happen before and after the entire division algorithm,
+not at each step in the per-digit iteration.
+
+Note the effect of scaling inputs on the size of the possible quotient.
+In the scaled u/v, u can gain a digit from scaling; v never does, because we
+pick the scaling factor to make v's top digit larger but without overflowing.
+If u and v have n+m and n digits after scaling, then:
+
+  • u < B^(n+m)               [B^(n+m) has n+m+1 digits]
+  • v ≥ B^n / 2               [vₙ₋₁ ≥ B/2, so vₙ₋₁·B^(n-1) ≥ B^n/2]
+  • u/v < B^(n+m) / (B^n / 2) [divide bounds for u, v]
+  • u/v < 2 B^m               [simplify]
+
+The quotient can still have m+1 significant digits, but if so the top digit
+must be a 1. This provides a different way to handle the first digit of the
+result: compare the top n digits of u against v and fill in either a 0 or a 1.
+
+
+Refining Guesses
+
+Before we check whether u < q̂·v, we can adjust our guess to change it from
+q̂ = ⌊uₙuₙ₋₁ / vₙ₋₁⌋ into the refined guess ⌊uₙuₙ₋₁uₙ₋₂ / vₙ₋₁vₙ₋₂⌋.
+Although not mentioned above, the Good Guess Guarantee also promises that this
+3-by-2-digit division guess is more precise and at most one away from the real
+answer q. The improvement from the 2-by-1 to the 3-by-2 guess can also be done
+without n-digit math.
+
+If we have a guess q̂ = ⌊uₙuₙ₋₁ / vₙ₋₁⌋ and we want to see if it also equal to
+⌊uₙuₙ₋₁uₙ₋₂ / vₙ₋₁vₙ₋₂⌋, we can use the same check we would for the full division:
+if uₙuₙ₋₁uₙ₋₂ < q̂·vₙ₋₁vₙ₋₂, then the guess is too large and should be reduced.
+
+Checking uₙuₙ₋₁uₙ₋₂ < q̂·vₙ₋₁vₙ₋₂ is the same as uₙuₙ₋₁uₙ₋₂ - q̂·vₙ₋₁vₙ₋₂ < 0,
+and
+
+	uₙuₙ₋₁uₙ₋₂ - q̂·vₙ₋₁vₙ₋₂ = (uₙuₙ₋₁·B + uₙ₋₂) - q̂·(vₙ₋₁·B + vₙ₋₂)
+	                          [splitting off the bottom digit]
+	                      = (uₙuₙ₋₁ - q̂·vₙ₋₁)·B + uₙ₋₂ - q̂·vₙ₋₂
+	                          [regrouping]
+
+The expression (uₙuₙ₋₁ - q̂·vₙ₋₁) is the remainder of uₙuₙ₋₁ / vₙ₋₁.
+If the initial guess returns both q̂ and its remainder r̂, then checking
+whether uₙuₙ₋₁uₙ₋₂ < q̂·vₙ₋₁vₙ₋₂ is the same as checking r̂·B + uₙ₋₂ < q̂·vₙ₋₂.
+
+If we find that r̂·B + uₙ₋₂ < q̂·vₙ₋₂, then we can adjust the guess by
+decrementing q̂ and adding vₙ₋₁ to r̂. We repeat until r̂·B + uₙ₋₂ ≥ q̂·vₙ₋₂.
+(As before, this fixup is only needed at most twice.)
+
+Now that q̂ = ⌊uₙuₙ₋₁uₙ₋₂ / vₙ₋₁vₙ₋₂⌋, as mentioned above it is at most one
+away from the correct q, and we've avoided doing any n-digit math.
+(If we need the new remainder, it can be computed as r̂·B + uₙ₋₂ - q̂·vₙ₋₂.)
+
+The final check u < q̂·v and the possible fixup must be done at full precision.
+For random inputs, a fixup at this step is exceedingly rare: the 3-by-2 guess
+is not often wrong at all. But still we must do the check. Note that since the
+3-by-2 guess is off by at most 1, it can be convenient to perform the final
+u < q̂·v as part of the computation of the remainder r = u - q̂·v. If the
+subtraction underflows, decremeting q̂ and adding one v back to r is enough to
+arrive at the final q, r.
+
+That's the entirety of long division: scale the inputs, and then loop over
+each output position, guessing, checking, and correcting the next output digit.
+
+For a 2n-digit number divided by an n-digit number (the worst size-n case for
+division complexity), this algorithm uses n+1 iterations, each of which must do
+at least the 1-by-n-digit multiplication q̂·v. That's O(n) iterations of
+O(n) time each, so O(n²) time overall.
+
+
+Recursive Division
+
+For very large inputs, it is possible to improve on the O(n²) algorithm.
+Let's call a group of n/2 real digits a (very) “wide digit”. We can run the
+standard long division algorithm explained above over the wide digits instead of
+the actual digits. This will result in many fewer steps, but the math involved in
+each step is more work.
+
+Where basic long division uses a 2-by-1-digit division to guess the initial q̂,
+the new algorithm must use a 2-by-1-wide-digit division, which is of course
+really an n-by-n/2-digit division. That's OK: if we implement n-digit division
+in terms of n/2-digit division, the recursion will terminate when the divisor
+becomes small enough to handle with standard long division or even with the
+2-by-1 hardware instruction.
+
+For example, here is a sketch of dividing 10 digits by 4, proceeding with
+wide digits corresponding to two regular digits. The first step, still special,
+must leave off a (regular) digit, dividing 5 by 4 and producing a 4-digit
+remainder less than v. The middle steps divide 6 digits by 4, guaranteed to
+produce two output digits each (one wide digit) with 4-digit remainders.
+The final step must use what it has: the 4-digit remainder plus one more,
+5 digits to divide by 4.
+
+	                       q₆ q₅ q₄ q₃ q₂ q₁ q₀
+	            _______________________________
+	v₃ v₂ v₁ v₀ ) u₉ u₈ u₇ u₆ u₅ u₄ u₃ u₂ u₁ u₀
+	              ↓  ↓  ↓  ↓  ↓  |  |  |  |  |
+	             [u₉ u₈ u₇ u₆ u₅]|  |  |  |  |
+	           - [    q₆q₅·v    ]|  |  |  |  |
+	           ----------------- ↓  ↓  |  |  |
+	                [    rem    |u₄ u₃]|  |  |
+	              - [     q₄q₃·v      ]|  |  |
+	              -------------------- ↓  ↓  |
+	                      [    rem    |u₂ u₁]|
+	                    - [     q₂q₁·v      ]|
+	                    -------------------- ↓
+	                            [    rem    |u₀]
+	                          - [     q₀·v     ]
+	                          ------------------
+	                               [    rem    ]
+
+An alternative would be to look ahead to how well n/2 divides into n+m and
+adjust the first step to use fewer digits as needed, making the first step
+more special to make the last step not special at all. For example, using the
+same input, we could choose to use only 4 digits in the first step, leaving
+a full wide digit for the last step:
+
+	                       q₆ q₅ q₄ q₃ q₂ q₁ q₀
+	            _______________________________
+	v₃ v₂ v₁ v₀ ) u₉ u₈ u₇ u₆ u₅ u₄ u₃ u₂ u₁ u₀
+	              ↓  ↓  ↓  ↓  |  |  |  |  |  |
+	             [u₉ u₈ u₇ u₆]|  |  |  |  |  |
+	           - [    q₆·v   ]|  |  |  |  |  |
+	           -------------- ↓  ↓  |  |  |  |
+	             [    rem    |u₅ u₄]|  |  |  |
+	           - [     q₅q₄·v      ]|  |  |  |
+	           -------------------- ↓  ↓  |  |
+	                   [    rem    |u₃ u₂]|  |
+	                 - [     q₃q₂·v      ]|  |
+	                 -------------------- ↓  ↓
+	                         [    rem    |u₁ u₀]
+	                       - [     q₁q₀·v      ]
+	                       ---------------------
+	                               [    rem    ]
+
+Today, the code in divRecursiveStep works like the first example. Perhaps in
+the future we will make it work like the alternative, to avoid a special case
+in the final iteration.
+
+Either way, each step is a 3-by-2-wide-digit division approximated first by
+a 2-by-1-wide-digit division, just as we did for regular digits in long division.
+Because the actual answer we want is a 3-by-2-wide-digit division, instead of
+multiplying q̂·v directly during the fixup, we can use the quick refinement
+from long division (an n/2-by-n/2 multiply) to correct q to its actual value
+and also compute the remainder (as mentioned above), and then stop after that,
+never doing a full n-by-n multiply.
+
+Instead of using an n-by-n/2-digit division to produce n/2 digits, we can add
+(not discard) one more real digit, doing an (n+1)-by-(n/2+1)-digit division that
+produces n/2+1 digits. That single extra digit tightens the Good Guess Guarantee
+to q ≤ q̂ ≤ q+1 and lets us drop long division's special treatment of the first
+digit. These benefits are discussed more after the Good Guess Guarantee proof
+below.
+
+
+How Fast is Recursive Division?
+
+For a 2n-by-n-digit division, this algorithm runs a 4-by-2 long division over
+wide digits, producing two wide digits plus a possible leading regular digit 1,
+which can be handled without a recursive call. That is, the algorithm uses two
+full iterations, each using an n-by-n/2-digit division and an n/2-by-n/2-digit
+multiplication, along with a few n-digit additions and subtractions. The standard
+n-by-n-digit multiplication algorithm requires O(n²) time, making the overall
+algorithm require time T(n) where
+
+	T(n) = 2T(n/2) + O(n) + O(n²)
+
+which, by the Bentley-Haken-Saxe theorem, ends up reducing to T(n) = O(n²).
+This is not an improvement over regular long division.
+
+When the number of digits n becomes large enough, Karatsuba's algorithm for
+multiplication can be used instead, which takes O(n^log₂3) = O(n^1.6) time.
+(Karatsuba multiplication is implemented in func karatsuba in nat.go.)
+That makes the overall recursive division algorithm take O(n^1.6) time as well,
+which is an improvement, but again only for large enough numbers.
+
+It is not critical to make sure that every recursion does only two recursive
+calls. While in general the number of recursive calls can change the time
+analysis, in this case doing three calls does not change the analysis:
+
+	T(n) = 3T(n/2) + O(n) + O(n^log₂3)
+
+ends up being T(n) = O(n^log₂3). Because the Karatsuba multiplication taking
+time O(n^log₂3) is itself doing 3 half-sized recursions, doing three for the
+division does not hurt the asymptotic performance. Of course, it is likely
+still faster in practice to do two.
+
+
+Proof of the Good Guess Guarantee
+
+Given numbers x, y, let us break them into the quotients and remainders when
+divided by some scaling factor S, with the added constraints that the quotient
+x/y and the high part of y are both less than some limit T, and that the high
+part of y is at least half as big as T.
+
+	x₁ = ⌊x/S⌋        y₁ = ⌊y/S⌋
+	x₀ = x mod S      y₀ = y mod S
+
+	x  = x₁·S + x₀    0 ≤ x₀ < S    x/y < T
+	y  = y₁·S + y₀    0 ≤ y₀ < S    T/2 ≤ y₁ < T
+
+And consider the two truncated quotients:
+
+	q = ⌊x/y⌋
+	q̂ = ⌊x₁/y₁⌋
+
+We will prove that q ≤ q̂ ≤ q+2.
+
+The guarantee makes no real demands on the scaling factor S: it is simply the
+magnitude of the digits cut from both x and y to produce x₁ and y₁.
+The guarantee makes only limited demands on T: it must be large enough to hold
+the quotient x/y, and y₁ must have roughly the same size.
+
+To apply to the earlier discussion of 2-by-1 guesses in long division,
+we would choose:
+
+	S  = Bⁿ⁻¹
+	T  = B
+	x  = u
+	x₁ = uₙuₙ₋₁
+	x₀ = uₙ₋₂...u₀
+	y  = v
+	y₁ = vₙ₋₁
+	y₀ = vₙ₋₂...u₀
+
+These simpler variables avoid repeating those longer expressions in the proof.
+
+Note also that, by definition, truncating division ⌊x/y⌋ satisfies
+
+	x/y - 1 < ⌊x/y⌋ ≤ x/y.
+
+This fact will be used a few times in the proofs.
+
+Proof that q ≤ q̂:
+
+	q̂·y₁ = ⌊x₁/y₁⌋·y₁                      [by definition, q̂ = ⌊x₁/y₁⌋]
+	     > (x₁/y₁ - 1)·y₁                  [x₁/y₁ - 1 < ⌊x₁/y₁⌋]
+	     = x₁ - y₁                         [distribute y₁]
+
+	So q̂·y₁ > x₁ - y₁.
+	Since q̂·y₁ is an integer, q̂·y₁ ≥ x₁ - y₁ + 1.
+
+	q̂ - q = q̂ - ⌊x/y⌋                      [by definition, q = ⌊x/y⌋]
+	      ≥ q̂ - x/y                        [⌊x/y⌋ < x/y]
+	      = (1/y)·(q̂·y - x)                [factor out 1/y]
+	      ≥ (1/y)·(q̂·y₁·S - x)             [y = y₁·S + y₀ ≥ y₁·S]
+	      ≥ (1/y)·((x₁ - y₁ + 1)·S - x)    [above: q̂·y₁ ≥ x₁ - y₁ + 1]
+	      = (1/y)·(x₁·S - y₁·S + S - x)    [distribute S]
+	      = (1/y)·(S - x₀ - y₁·S)          [-x = -x₁·S - x₀]
+	      > -y₁·S / y                      [x₀ < S, so S - x₀ < 0; drop it]
+	      ≥ -1                             [y₁·S ≤ y]
+
+	So q̂ - q > -1.
+	Since q̂ - q is an integer, q̂ - q ≥ 0, or equivalently q ≤ q̂.
+
+Proof that q̂ ≤ q+2:
+
+	x₁/y₁ - x/y = x₁·S/y₁·S - x/y          [multiply left term by S/S]
+	            ≤ x/y₁·S - x/y             [x₁S ≤ x]
+	            = (x/y)·(y/y₁·S - 1)       [factor out x/y]
+	            = (x/y)·((y - y₁·S)/y₁·S)  [move -1 into y/y₁·S fraction]
+	            = (x/y)·(y₀/y₁·S)          [y - y₁·S = y₀]
+	            = (x/y)·(1/y₁)·(y₀/S)      [factor out 1/y₁]
+	            < (x/y)·(1/y₁)             [y₀ < S, so y₀/S < 1]
+	            ≤ (x/y)·(2/T)              [y₁ ≥ T/2, so 1/y₁ ≤ 2/T]
+	            < T·(2/T)                  [x/y < T]
+	            = 2                        [T·(2/T) = 2]
+
+	So x₁/y₁ - x/y < 2.
+
+	q̂ - q = ⌊x₁/y₁⌋ - q                    [by definition, q̂ = ⌊x₁/y₁⌋]
+	      = ⌊x₁/y₁⌋ - ⌊x/y⌋                [by definition, q = ⌊x/y⌋]
+	      ≤ x₁/y₁ - ⌊x/y⌋                  [⌊x₁/y₁⌋ ≤ x₁/y₁]
+	      < x₁/y₁ - (x/y - 1)              [⌊x/y⌋ > x/y - 1]
+	      = (x₁/y₁ - x/y) + 1              [regrouping]
+	      < 2 + 1                          [above: x₁/y₁ - x/y < 2]
+	      = 3
+
+	So q̂ - q < 3.
+	Since q̂ - q is an integer, q̂ - q ≤ 2.
+
+Note that when x/y < T/2, the bounds tighten to x₁/y₁ - x/y < 1 and therefore
+q̂ - q ≤ 1.
+
+Note also that in the general case 2n-by-n division where we don't know that
+x/y < T, we do know that x/y < 2T, yielding the bound q̂ - q ≤ 4. So we could
+remove the special case first step of long division as long as we allow the
+first fixup loop to run up to four times. (Using a simple comparison to decide
+whether the first digit is 0 or 1 is still more efficient, though.)
+
+Finally, note that when dividing three leading base-B digits by two (scaled),
+we have T = B² and x/y < B = T/B, a much tighter bound than x/y < T.
+This in turn yields the much tighter bound x₁/y₁ - x/y < 2/B. This means that
+⌊x₁/y₁⌋ and ⌊x/y⌋ can only differ when x/y is less than 2/B greater than an
+integer. For random x and y, the chance of this is 2/B, or, for large B,
+approximately zero. This means that after we produce the 3-by-2 guess in the
+long division algorithm, the fixup loop essentially never runs.
+
+In the recursive algorithm, the extra digit in (2·⌊n/2⌋+1)-by-(⌊n/2⌋+1)-digit
+division has exactly the same effect: the probability of needing a fixup is the
+same 2/B. Even better, we can allow the general case x/y < 2T and the fixup
+probability only grows to 4/B, still essentially zero.
+
+
+References
+
+There are no great references for implementing long division; thus this comment.
+Here are some notes about what to expect from the obvious references.
+
+Knuth Volume 2 (Seminumerical Algorithms) section 4.3.1 is the usual canonical
+reference for long division, but that entire series is highly compressed, never
+repeating a necessary fact and leaving important insights to the exercises.
+For example, no rationale whatsoever is given for the calculation that extends
+q̂ from a 2-by-1 to a 3-by-2 guess, nor why it reduces the error bound.
+The proof that the calculation even has the desired effect is left to exercises.
+The solutions to those exercises provided at the back of the book are entirely
+calculations, still with no explanation as to what is going on or how you would
+arrive at the idea of doing those exact calculations. Nowhere is it mentioned
+that this test extends the 2-by-1 guess into a 3-by-2 guess. The proof of the
+Good Guess Guarantee is only for the 2-by-1 guess and argues by contradiction,
+making it difficult to understand how modifications like adding another digit
+or adjusting the quotient range affects the overall bound.
+
+All that said, Knuth remains the canonical reference. It is dense but packed
+full of information and references, and the proofs are simpler than many other
+presentations. The proofs above are reworkings of Knuth's to remove the
+arguments by contradiction and add explanations or steps that Knuth omitted.
+But beware of errors in older printings. Take the published errata with you.
+
+Brinch Hansen's “Multiple-length Division Revisited: a Tour of the Minefield”
+starts with a blunt critique of Knuth's presentation (among others) and then
+presents a more detailed and easier to follow treatment of long division,
+including an implementation in Pascal. But the algorithm and implementation
+work entirely in terms of 3-by-2 division, which is much less useful on modern
+hardware than an algorithm using 2-by-1 division. The proofs are a bit too
+focused on digit counting and seem needlessly complex, especially compared to
+the ones given above.
+
+Burnikel and Ziegler's “Fast Recursive Division” introduced the key insight of
+implementing division by an n-digit divisor using recursive calls to division
+by an n/2-digit divisor, relying on Karatsuba multiplication to yield a
+sub-quadratic run time. However, the presentation decisions are made almost
+entirely for the purpose of simplifying the run-time analysis, rather than
+simplifying the presentation. Instead of a single algorithm that loops over
+quotient digits, the paper presents two mutually-recursive algorithms, for
+2n-by-n and 3n-by-2n. The paper also does not present any general (n+m)-by-n
+algorithm.
+
+The proofs in the paper are remarkably complex, especially considering that
+the algorithm is at its core just long division on wide digits, so that the
+usual long division proofs apply essentially unaltered.
+*/
+
 package big
 
 import "math/bits"
 
+// div returns q, r such that q = ⌊u/v⌋ and r = u%v = u - q·v.
+// It uses z and z2 as the storage for q and r.
 func (z nat) div(z2, u, v nat) (q, r nat) {
 	if len(v) == 0 {
 		panic("division by zero")
@@ -18,6 +514,8 @@ func (z nat) div(z2, u, v nat) (q, r nat) {
 	}
 
 	if len(v) == 1 {
+		// Short division: long optimized for a single-word divisor.
+		// In that case, the 2-by-1 guess is all we need at each step.
 		var r2 Word
 		q, r2 = z.divW(u, v[0])
 		r = z2.setWord(r2)
@@ -28,7 +526,9 @@ func (z nat) div(z2, u, v nat) (q, r nat) {
 	return
 }
 
-// q = (x-r)/y, with 0 <= r < y
+// divW returns q, r such that q = ⌊x/y⌋ and r = x%y = x - q·y.
+// It uses z as the storage for q.
+// Note that y is a single digit (Word), not a big number.
 func (z nat) divW(x nat, y Word) (q nat, r Word) {
 	m := len(x)
 	switch {
@@ -56,6 +556,8 @@ func (x nat) modW(d Word) (r Word) {
 	return divWVW(q, 0, x, d)
 }
 
+// divWVW overwrites z with ⌊x/y⌋, returning the remainder r.
+// The caller must ensure that len(z) = len(x).
 func divWVW(z []Word, xn Word, x []Word, y Word) (r Word) {
 	r = xn
 	if len(x) == 1 {
@@ -70,34 +572,33 @@ func divWVW(z []Word, xn Word, x []Word, y Word) (r Word) {
 	return r
 }
 
-// q = (uIn-r)/vIn, with 0 <= r < vIn
-// Uses z as storage for q, and u as storage for r if possible.
-// See Knuth, Volume 2, section 4.3.1, Algorithm D.
-// Preconditions:
-//    len(vIn) >= 2
-//    len(uIn) >= len(vIn)
-//    u must not alias z
+// div returns q, r such that q = ⌊uIn/vIn⌋ and r = uIn%vIn = uIn - q·vIn.
+// It uses z and u as the storage for q and r.
+// The caller must ensure that len(vIn) ≥ 2 (use divW otherwise)
+// and that len(uIn) ≥ len(vIn) (the answer is 0, uIn otherwise).
 func (z nat) divLarge(u, uIn, vIn nat) (q, r nat) {
 	n := len(vIn)
 	m := len(uIn) - n
 
-	// D1.
+	// Scale the inputs so vIn's top bit is 1 (see “Scaling Inputs” above).
+	// vIn is treated as a read-only input (it may be in use by another
+	// goroutine), so we must make a copy.
+	// uIn is copied to u.
 	shift := nlz(vIn[n-1])
-	// do not modify vIn, it may be used by another goroutine simultaneously
 	vp := getNat(n)
 	v := *vp
 	shlVU(v, vIn, shift)
-
-	// u may safely alias uIn or vIn, the value of uIn is used to set u and vIn was already used
 	u = u.make(len(uIn) + 1)
 	u[len(uIn)] = shlVU(u[0:len(uIn)], uIn, shift)
 
-	// z may safely alias uIn or vIn, both values were used already
+	// The caller should not pass aliased z and u, since those are
+	// the two different outputs, but correct just in case.
 	if alias(z, u) {
-		z = nil // z is an alias for u - cannot reuse
+		z = nil
 	}
 	q = z.make(m + 1)
 
+	// Use basic or recursive long division depending on size.
 	if n < divRecursiveThreshold {
 		q.divBasic(u, v)
 	} else {
@@ -106,19 +607,17 @@ func (z nat) divLarge(u, uIn, vIn nat) (q, r nat) {
 	putNat(vp)
 
 	q = q.norm()
+
+	// Undo scaling of remainder.
 	shrVU(u, u, shift)
 	r = u.norm()
 
 	return q, r
 }
 
-// divBasic performs word-by-word division of u by v.
-// The quotient is written in pre-allocated q.
-// The remainder overwrites input u.
-//
-// Precondition:
-// - q is large enough to hold the quotient u / v
-//   which has a maximum length of len(u)-len(v)+1.
+// divBasic implements long division as described above.
+// It overwrites q with ⌊u/v⌋ and overwrites u with the remainder r.
+// q must be large enough to hold ⌊u/v⌋.
 func (q nat) divBasic(u, v nat) {
 	n := len(v)
 	m := len(u) - n
@@ -126,45 +625,56 @@ func (q nat) divBasic(u, v nat) {
 	qhatvp := getNat(n + 1)
 	qhatv := *qhatvp
 
-	// D2.
+	// Set up for divWW below, precomputing reciprocal argument.
 	vn1 := v[n-1]
 	rec := reciprocalWord(vn1)
+
+	// Compute each digit of quotient.
 	for j := m; j >= 0; j-- {
-		// D3.
+		// Compute the 2-by-1 guess q̂.
+		// The first iteration must invent a leading 0 for u.
 		qhat := Word(_M)
 		var ujn Word
 		if j+n < len(u) {
 			ujn = u[j+n]
 		}
+
+		// ujn ≤ vn1, or else q̂ would be more than one digit.
+		// For ujn == vn1, we set q̂ to the max digit M above.
+		// Otherwise, we compute the 2-by-1 guess.
 		if ujn != vn1 {
 			var rhat Word
 			qhat, rhat = divWW(ujn, u[j+n-1], vn1, rec)
 
-			// x1 | x2 = q̂v_{n-2}
+			// Refine q̂ to a 3-by-2 guess. See “Refining Guesses” above.
 			vn2 := v[n-2]
 			x1, x2 := mulWW(qhat, vn2)
-			// test if q̂v_{n-2} > br̂ + u_{j+n-2}
 			ujn2 := u[j+n-2]
-			for greaterThan(x1, x2, rhat, ujn2) {
+			for greaterThan(x1, x2, rhat, ujn2) { // x1x2 > r̂ u[j+n-2]
 				qhat--
 				prevRhat := rhat
 				rhat += vn1
-				// v[n-1] >= 0, so this tests for overflow.
+				// If r̂  overflows, then
+				// r̂ u[j+n-2]v[n-1] is now definitely > x1 x2.
 				if rhat < prevRhat {
 					break
 				}
+				// TODO(rsc): No need for a full mulWW.
+				// x2 += vn2; if x2 overflows, x1++
 				x1, x2 = mulWW(qhat, vn2)
 			}
 		}
 
-		// D4.
-		// Compute the remainder u - (q̂*v) << (_W*j).
-		// The subtraction may overflow if q̂ estimate was off by one.
+		// Compute q̂·v.
 		qhatv[n] = mulAddVWW(qhatv[0:n], v, qhat, 0)
 		qhl := len(qhatv)
 		if j+qhl > len(u) && qhatv[n] == 0 {
 			qhl--
 		}
+
+		// Subtract q̂·v from the current section of u.
+		// If it underflows, q̂·v > u, which we fix up
+		// by decrementing q̂ and adding v back.
 		c := subVV(u[j:j+qhl], u[j:], qhatv)
 		if c != 0 {
 			c := addVV(u[j:j+n], u[j:], v)
@@ -176,6 +686,8 @@ func (q nat) divBasic(u, v nat) {
 			qhat--
 		}
 
+		// Save quotient digit.
+		// Caller may know the top digit is zero and not leave room for it.
 		if j == m && m == len(q) && qhat == 0 {
 			continue
 		}
@@ -185,30 +697,34 @@ func (q nat) divBasic(u, v nat) {
 	putNat(qhatvp)
 }
 
-// greaterThan reports whether (x1<<_W + x2) > (y1<<_W + y2)
+// greaterThan reports whether the two digit numbers x1 x2 > y1 y2.
+// TODO(rsc): In contradiction to most of this file, x1 is the high
+// digit and x2 is the low digit. This should be fixed.
 func greaterThan(x1, x2, y1, y2 Word) bool {
 	return x1 > y1 || x1 == y1 && x2 > y2
 }
 
+// divRecursiveThreshold is the number of divisor digits
+// at which point divRecursive is faster than divBasic.
 const divRecursiveThreshold = 100
 
-// divRecursive performs word-by-word division of u by v.
-// The quotient is written in pre-allocated z.
-// The remainder overwrites input u.
-//
-// Precondition:
-// - len(z) >= len(u)-len(v)
-//
-// See Burnikel, Ziegler, "Fast Recursive Division", Algorithm 1 and 2.
+// divRecursive implements recursive division as described above.
+// It overwrites z with ⌊u/v⌋ and overwrites u with the remainder r.
+// z must be large enough to hold ⌊u/v⌋.
+// This function is just for allocating and freeing temporaries
+// around divRecursiveStep, the real implementation.
 func (z nat) divRecursive(u, v nat) {
-	// Recursion depth is less than 2 log2(len(v))
-	// Allocate a slice of temporaries to be reused across recursion.
+	// Recursion depth is (much) less than 2 log₂(len(v)).
+	// Allocate a slice of temporaries to be reused across recursion,
+	// plus one extra temporary not live across the recursion.
 	recDepth := 2 * bits.Len(uint(len(v)))
-	// large enough to perform Karatsuba on operands as large as v
 	tmp := getNat(3 * len(v))
 	temps := make([]*nat, recDepth)
+
 	z.clear()
 	z.divRecursiveStep(u, v, 0, tmp, temps)
+
+	// Free temporaries.
 	for _, n := range temps {
 		if n != nil {
 			putNat(n)
@@ -217,72 +733,92 @@ func (z nat) divRecursive(u, v nat) {
 	putNat(tmp)
 }
 
-// divRecursiveStep computes the division of u by v.
-// - z must be large enough to hold the quotient
-// - the quotient will overwrite z
-// - the remainder will overwrite u
+// divRecursiveStep is the actual implementation of recursive division.
+// It adds ⌊u/v⌋ to z and overwrites u with the remainder r.
+// z must be large enough to hold ⌊u/v⌋.
+// It uses temps[depth] (allocating if needed) as a temporary live across
+// the recursive call. It also uses tmp, but not live across the recursion.
 func (z nat) divRecursiveStep(u, v nat, depth int, tmp *nat, temps []*nat) {
+	// u is a subsection of the original and may have leading zeros.
+	// TODO(rsc): The v = v.norm() is useless and should be removed.
+	// We know (and require) that v's top digit is ≥ B/2.
 	u = u.norm()
 	v = v.norm()
-
 	if len(u) == 0 {
 		z.clear()
 		return
 	}
+
+	// Fall back to basic division if the problem is now small enough.
 	n := len(v)
 	if n < divRecursiveThreshold {
 		z.divBasic(u, v)
 		return
 	}
+
+	// Nothing to do if u is shorter than v (implies u < v).
 	m := len(u) - n
 	if m < 0 {
 		return
 	}
 
-	// Produce the quotient by blocks of B words.
-	// Division by v (length n) is done using a length n/2 division
-	// and a length n/2 multiplication for each block. The final
-	// complexity is driven by multiplication complexity.
+	// We consider B digits in a row as a single wide digit.
+	// (See “Recursive Division” above.)
+	//
+	// TODO(rsc): rename B to Wide, to avoid confusion with _B,
+	// which is something entirely different.
+	// TODO(rsc): Look into whether using ⌈n/2⌉ is better than ⌊n/2⌋.
 	B := n / 2
 
 	// Allocate a nat for qhat below.
 	if temps[depth] == nil {
-		temps[depth] = getNat(n)
+		temps[depth] = getNat(n) // TODO(rsc): Can be just B+1.
 	} else {
 		*temps[depth] = temps[depth].make(B + 1)
 	}
 
+	// Compute each wide digit of the quotient.
+	//
+	// TODO(rsc): Change the loop to be
+	//	for j := (m+B-1)/B*B; j > 0; j -= B {
+	// which will make the final step a regular step, letting us
+	// delete what amounts to an extra copy of the loop body below.
 	j := m
 	for j > B {
-		// Divide u[j-B:j+n] by vIn. Keep remainder in u
-		// for next block.
-		//
-		// The following property will be used (Lemma 2):
-		// if u = u1 << s + u0
-		//    v = v1 << s + v0
-		// then floor(u1/v1) >= floor(u/v)
+		// Divide u[j-B:j+n] (3 wide digits) by v (2 wide digits).
+		// First make the 2-by-1-wide-digit guess using a recursive call.
+		// Then extend the guess to the full 3-by-2 (see “Refining Guesses”).
 		//
-		// Moreover, the difference is at most 2 if len(v1) >= len(u/v)
-		// We choose s = B-1 since len(v)-s >= B+1 >= len(u/v)
+		// For the 2-by-1-wide-digit guess, instead of doing 2B-by-B-digit,
+		// we use a (2B+1)-by-(B+1) digit, which handles the possibility that
+		// the result has an extra leading 1 digit as well as guaranteeing
+		// that the computed q̂ will be off by at most 1 instead of 2.
+
+		// s is the number of digits to drop from the 3B- and 2B-digit chunks.
+		// We drop B-1 to be left with 2B+1 and B+1.
 		s := (B - 1)
-		// Except for the first step, the top bits are always
-		// a division remainder, so the quotient length is <= n.
+
+		// uu is the up-to-3B-digit section of u we are working on.
 		uu := u[j-B:]
 
+		// Compute the 2-by-1 guess q̂, leaving r̂ in uu[s:B+n].
 		qhat := *temps[depth]
 		qhat.clear()
 		qhat.divRecursiveStep(uu[s:B+n], v[s:], depth+1, tmp, temps)
 		qhat = qhat.norm()
-		// Adjust the quotient:
-		//    u = u_h << s + u_l
-		//    v = v_h << s + v_l
-		//  u_h = q̂ v_h + rh
-		//    u = q̂ (v - v_l) + rh << s + u_l
-		// After the above step, u contains a remainder:
-		//    u = rh << s + u_l
-		// and we need to subtract q̂ v_l
-		//
-		// But it may be a bit too large, in which case q̂ needs to be smaller.
+
+		// Extend to a 3-by-2 quotient and remainder.
+		// Because divRecursiveStep overwrote the top part of uu with
+		// the remainder r̂, the full uu already contains the equivalent
+		// of r̂·B + uₙ₋₂ from the “Refining Guesses” discussion.
+		// Subtracting q̂·vₙ₋₂ from it will compute the full-length remainder.
+		// If that subtraction underflows, q̂·v > u, which we fix up
+		// by decrementing q̂ and adding v back, same as in long division.
+
+		// TODO(rsc): Instead of subtract and fix-up, this code is computing
+		// q̂·vₙ₋₂ and decrementing q̂ until that product is ≤ u.
+		// But we can do the subtraction directly, as in the comment above
+		// and in long division, because we know that q̂ is wrong by at most one.
 		qhatv := tmp.make(3 * n)
 		qhatv.clear()
 		qhatv = qhatv.mul(qhat, v[:s])
@@ -309,6 +845,8 @@ func (z nat) divRecursiveStep(u, v nat, depth int, tmp *nat, temps []*nat) {
 		j -= B
 	}
 
+	// TODO(rsc): Rewrite loop as described above and delete all this code.
+
 	// Now u < (v<<B), compute lower bits in the same way.
 	// Choose shift = B-1 again.
 	s := B - 1
diff --git a/src/net/hosts_test.go b/src/net/hosts_test.go
index f850e2fccf..19c43999f9 100644
--- a/src/net/hosts_test.go
+++ b/src/net/hosts_test.go
@@ -36,7 +36,7 @@ var lookupStaticHostTests = []struct {
 		},
 	},
 	{
-		"testdata/ipv4-hosts", // see golang.org/issue/8996
+		"testdata/ipv4-hosts",
 		[]staticHostEntry{
 			{"localhost", []string{"127.0.0.1", "127.0.0.2", "127.0.0.3"}},
 			{"localhost.localdomain", []string{"127.0.0.3"}},
@@ -102,7 +102,7 @@ var lookupStaticAddrTests = []struct {
 		},
 	},
 	{
-		"testdata/ipv4-hosts", // see golang.org/issue/8996
+		"testdata/ipv4-hosts",
 		[]staticHostEntry{
 			{"127.0.0.1", []string{"localhost"}},
 			{"127.0.0.2", []string{"localhost"}},
diff --git a/src/net/http/httptest/server.go b/src/net/http/httptest/server.go
index a02a6d64c3..4f85ff55d8 100644
--- a/src/net/http/httptest/server.go
+++ b/src/net/http/httptest/server.go
@@ -14,7 +14,7 @@ import (
 	"log"
 	"net"
 	"net/http"
-	"net/http/internal"
+	"net/http/internal/testcert"
 	"os"
 	"strings"
 	"sync"
@@ -144,7 +144,7 @@ func (s *Server) StartTLS() {
 	if s.client == nil {
 		s.client = &http.Client{Transport: &http.Transport{}}
 	}
-	cert, err := tls.X509KeyPair(internal.LocalhostCert, internal.LocalhostKey)
+	cert, err := tls.X509KeyPair(testcert.LocalhostCert, testcert.LocalhostKey)
 	if err != nil {
 		panic(fmt.Sprintf("httptest: NewTLSServer: %v", err))
 	}
diff --git a/src/net/http/internal/testcert.go b/src/net/http/internal/testcert/testcert.go
index 2284a836fb..5f94704ef5 100644
--- a/src/net/http/internal/testcert.go
+++ b/src/net/http/internal/testcert/testcert.go
@@ -2,7 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-package internal
+// Package testcert contains a test-only localhost certificate.
+package testcert
 
 import "strings"
 
@@ -25,7 +26,7 @@ h1fIw3cSS2OolhloGw/XM6RWPWtPAlGykKLciQrBru5NAPvCMsb/I1DAceTiotQM
 fblo6RBxUQ==
 -----END CERTIFICATE-----`)
 
-// LocalhostKey is the private key for localhostCert.
+// LocalhostKey is the private key for LocalhostCert.
 var LocalhostKey = []byte(testingKey(`-----BEGIN RSA TESTING KEY-----
 MIICXgIBAAKBgQDuLnQAI3mDgey3VBzWnB2L39JUU4txjeVE6myuDqkM/uGlfjb9
 SjY1bIw4iA5sBBZzHi3z0h1YV8QPuxEbi4nW91IJm2gsvvZhIrCHS3l6afab4pZB
diff --git a/src/net/http/request.go b/src/net/http/request.go
index 7895417af5..09cb0c7f56 100644
--- a/src/net/http/request.go
+++ b/src/net/http/request.go
@@ -1293,16 +1293,18 @@ func (r *Request) ParseForm() error {
 // its file parts are stored in memory, with the remainder stored on
 // disk in temporary files.
 // ParseMultipartForm calls ParseForm if necessary.
+// If ParseForm returns an error, ParseMultipartForm returns it but also
+// continues parsing the request body.
 // After one call to ParseMultipartForm, subsequent calls have no effect.
 func (r *Request) ParseMultipartForm(maxMemory int64) error {
 	if r.MultipartForm == multipartByReader {
 		return errors.New("http: multipart handled by MultipartReader")
 	}
+	var parseFormErr error
 	if r.Form == nil {
-		err := r.ParseForm()
-		if err != nil {
-			return err
-		}
+		// Let errors in ParseForm fall through, and just
+		// return it at the end.
+		parseFormErr = r.ParseForm()
 	}
 	if r.MultipartForm != nil {
 		return nil
@@ -1329,7 +1331,7 @@ func (r *Request) ParseMultipartForm(maxMemory int64) error {
 
 	r.MultipartForm = f
 
-	return nil
+	return parseFormErr
 }
 
 // FormValue returns the first value for the named component of the query.
diff --git a/src/net/http/request_test.go b/src/net/http/request_test.go
index 952828b395..4e0c4ba207 100644
--- a/src/net/http/request_test.go
+++ b/src/net/http/request_test.go
@@ -32,9 +32,26 @@ func TestQuery(t *testing.T) {
 	}
 }
 
+// Issue #25192: Test that ParseForm fails but still parses the form when an URL
+// containing a semicolon is provided.
+func TestParseFormSemicolonSeparator(t *testing.T) {
+	for _, method := range []string{"POST", "PATCH", "PUT", "GET"} {
+		req, _ := NewRequest(method, "http://www.google.com/search?q=foo;q=bar&a=1",
+			strings.NewReader("q"))
+		err := req.ParseForm()
+		if err == nil {
+			t.Fatalf(`for method %s, ParseForm expected an error, got success`, method)
+		}
+		wantForm := url.Values{"a": []string{"1"}}
+		if !reflect.DeepEqual(req.Form, wantForm) {
+			t.Fatalf("for method %s, ParseForm expected req.Form = %v, want %v", method, req.Form, wantForm)
+		}
+	}
+}
+
 func TestParseFormQuery(t *testing.T) {
 	req, _ := NewRequest("POST", "http://www.google.com/search?q=foo&q=bar&both=x&prio=1&orphan=nope&empty=not",
-		strings.NewReader("z=post&both=y&prio=2&=nokey&orphan;empty=&"))
+		strings.NewReader("z=post&both=y&prio=2&=nokey&orphan&empty=&"))
 	req.Header.Set("Content-Type", "application/x-www-form-urlencoded; param=value")
 
 	if q := req.FormValue("q"); q != "foo" {
@@ -365,6 +382,18 @@ func TestMultipartRequest(t *testing.T) {
 	validateTestMultipartContents(t, req, false)
 }
 
+// Issue #25192: Test that ParseMultipartForm fails but still parses the
+// multi-part form when an URL containing a semicolon is provided.
+func TestParseMultipartFormSemicolonSeparator(t *testing.T) {
+	req := newTestMultipartRequest(t)
+	req.URL = &url.URL{RawQuery: "q=foo;q=bar"}
+	if err := req.ParseMultipartForm(25); err == nil {
+		t.Fatal("ParseMultipartForm expected error due to invalid semicolon, got nil")
+	}
+	defer req.MultipartForm.RemoveAll()
+	validateTestMultipartContents(t, req, false)
+}
+
 func TestMultipartRequestAuto(t *testing.T) {
 	// Test that FormValue and FormFile automatically invoke
 	// ParseMultipartForm and return the right values.
diff --git a/src/net/http/serve_test.go b/src/net/http/serve_test.go
index a9714682c7..6394da3bb7 100644
--- a/src/net/http/serve_test.go
+++ b/src/net/http/serve_test.go
@@ -25,6 +25,7 @@ import (
 	"net/http/httptest"
 	"net/http/httputil"
 	"net/http/internal"
+	"net/http/internal/testcert"
 	"net/url"
 	"os"
 	"os/exec"
@@ -1475,7 +1476,7 @@ func TestServeTLS(t *testing.T) {
 	defer afterTest(t)
 	defer SetTestHookServerServe(nil)
 
-	cert, err := tls.X509KeyPair(internal.LocalhostCert, internal.LocalhostKey)
+	cert, err := tls.X509KeyPair(testcert.LocalhostCert, testcert.LocalhostKey)
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -1599,7 +1600,7 @@ func TestAutomaticHTTP2_Serve_WithTLSConfig(t *testing.T) {
 }
 
 func TestAutomaticHTTP2_ListenAndServe(t *testing.T) {
-	cert, err := tls.X509KeyPair(internal.LocalhostCert, internal.LocalhostKey)
+	cert, err := tls.X509KeyPair(testcert.LocalhostCert, testcert.LocalhostKey)
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -1609,7 +1610,7 @@ func TestAutomaticHTTP2_ListenAndServe(t *testing.T) {
 }
 
 func TestAutomaticHTTP2_ListenAndServe_GetCertificate(t *testing.T) {
-	cert, err := tls.X509KeyPair(internal.LocalhostCert, internal.LocalhostKey)
+	cert, err := tls.X509KeyPair(testcert.LocalhostCert, testcert.LocalhostKey)
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -6524,3 +6525,87 @@ func TestMuxRedirectRelative(t *testing.T) {
 		t.Errorf("Expected response code %d; got %d", want, got)
 	}
 }
+
+// TestQuerySemicolon tests the behavior of semicolons in queries. See Issue 25192.
+func TestQuerySemicolon(t *testing.T) {
+	t.Cleanup(func() { afterTest(t) })
+
+	tests := []struct {
+		query           string
+		xNoSemicolons   string
+		xWithSemicolons string
+		warning         bool
+	}{
+		{"?a=1;x=bad&x=good", "good", "bad", true},
+		{"?a=1;b=bad&x=good", "good", "good", true},
+		{"?a=1%3Bx=bad&x=good%3B", "good;", "good;", false},
+		{"?a=1;x=good;x=bad", "", "good", true},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.query+"/allow=false", func(t *testing.T) {
+			allowSemicolons := false
+			testQuerySemicolon(t, tt.query, tt.xNoSemicolons, allowSemicolons, tt.warning)
+		})
+		t.Run(tt.query+"/allow=true", func(t *testing.T) {
+			allowSemicolons, expectWarning := true, false
+			testQuerySemicolon(t, tt.query, tt.xWithSemicolons, allowSemicolons, expectWarning)
+		})
+	}
+}
+
+func testQuerySemicolon(t *testing.T, query string, wantX string, allowSemicolons, expectWarning bool) {
+	setParallel(t)
+
+	writeBackX := func(w ResponseWriter, r *Request) {
+		x := r.URL.Query().Get("x")
+		if expectWarning {
+			if err := r.ParseForm(); err == nil || !strings.Contains(err.Error(), "semicolon") {
+				t.Errorf("expected error mentioning semicolons from ParseForm, got %v", err)
+			}
+		} else {
+			if err := r.ParseForm(); err != nil {
+				t.Errorf("expected no error from ParseForm, got %v", err)
+			}
+		}
+		if got := r.FormValue("x"); x != got {
+			t.Errorf("got %q from FormValue, want %q", got, x)
+		}
+		fmt.Fprintf(w, "%s", x)
+	}
+
+	h := Handler(HandlerFunc(writeBackX))
+	if allowSemicolons {
+		h = AllowQuerySemicolons(h)
+	}
+
+	ts := httptest.NewUnstartedServer(h)
+	logBuf := &bytes.Buffer{}
+	ts.Config.ErrorLog = log.New(logBuf, "", 0)
+	ts.Start()
+	defer ts.Close()
+
+	req, _ := NewRequest("GET", ts.URL+query, nil)
+	res, err := ts.Client().Do(req)
+	if err != nil {
+		t.Fatal(err)
+	}
+	slurp, _ := io.ReadAll(res.Body)
+	res.Body.Close()
+	if got, want := res.StatusCode, 200; got != want {
+		t.Errorf("Status = %d; want = %d", got, want)
+	}
+	if got, want := string(slurp), wantX; got != want {
+		t.Errorf("Body = %q; want = %q", got, want)
+	}
+
+	if expectWarning {
+		if !strings.Contains(logBuf.String(), "semicolon") {
+			t.Errorf("got %q from ErrorLog, expected a mention of semicolons", logBuf.String())
+		}
+	} else {
+		if strings.Contains(logBuf.String(), "semicolon") {
+			t.Errorf("got %q from ErrorLog, expected no mention of semicolons", logBuf.String())
+		}
+	}
+}
diff --git a/src/net/http/server.go b/src/net/http/server.go
index 430019de50..50fab4520d 100644
--- a/src/net/http/server.go
+++ b/src/net/http/server.go
@@ -2862,9 +2862,51 @@ func (sh serverHandler) ServeHTTP(rw ResponseWriter, req *Request) {
 	if req.RequestURI == "*" && req.Method == "OPTIONS" {
 		handler = globalOptionsHandler{}
 	}
+
+	if req.URL != nil && strings.Contains(req.URL.RawQuery, ";") {
+		var allowQuerySemicolonsInUse int32
+		req = req.WithContext(context.WithValue(req.Context(), silenceSemWarnContextKey, func() {
+			atomic.StoreInt32(&allowQuerySemicolonsInUse, 1)
+		}))
+		defer func() {
+			if atomic.LoadInt32(&allowQuerySemicolonsInUse) == 0 {
+				sh.srv.logf("http: URL query contains semicolon, which is no longer a supported separator; parts of the query may be stripped when parsed; see golang.org/issue/25192")
+			}
+		}()
+	}
+
 	handler.ServeHTTP(rw, req)
 }
 
+var silenceSemWarnContextKey = &contextKey{"silence-semicolons"}
+
+// AllowQuerySemicolons returns a handler that serves requests by converting any
+// unescaped semicolons in the URL query to ampersands, and invoking the handler h.
+//
+// This restores the pre-Go 1.17 behavior of splitting query parameters on both
+// semicolons and ampersands. (See golang.org/issue/25192). Note that this
+// behavior doesn't match that of many proxies, and the mismatch can lead to
+// security issues.
+//
+// AllowQuerySemicolons should be invoked before Request.ParseForm is called.
+func AllowQuerySemicolons(h Handler) Handler {
+	return HandlerFunc(func(w ResponseWriter, r *Request) {
+		if silenceSemicolonsWarning, ok := r.Context().Value(silenceSemWarnContextKey).(func()); ok {
+			silenceSemicolonsWarning()
+		}
+		if strings.Contains(r.URL.RawQuery, ";") {
+			r2 := new(Request)
+			*r2 = *r
+			r2.URL = new(url.URL)
+			*r2.URL = *r.URL
+			r2.URL.RawQuery = strings.ReplaceAll(r.URL.RawQuery, ";", "&")
+			h.ServeHTTP(w, r2)
+		} else {
+			h.ServeHTTP(w, r)
+		}
+	})
+}
+
 // ListenAndServe listens on the TCP network address srv.Addr and then
 // calls Serve to handle requests on incoming connections.
 // Accepted connections are configured to enable TCP keep-alives.
diff --git a/src/net/http/transport_internal_test.go b/src/net/http/transport_internal_test.go
index 1097ffd173..1cce27235d 100644
--- a/src/net/http/transport_internal_test.go
+++ b/src/net/http/transport_internal_test.go
@@ -12,7 +12,7 @@ import (
 	"errors"
 	"io"
 	"net"
-	"net/http/internal"
+	"net/http/internal/testcert"
 	"strings"
 	"testing"
 )
@@ -191,7 +191,7 @@ func (f roundTripFunc) RoundTrip(r *Request) (*Response, error) {
 
 // Issue 25009
 func TestTransportBodyAltRewind(t *testing.T) {
-	cert, err := tls.X509KeyPair(internal.LocalhostCert, internal.LocalhostKey)
+	cert, err := tls.X509KeyPair(testcert.LocalhostCert, testcert.LocalhostKey)
 	if err != nil {
 		t.Fatal(err)
 	}
diff --git a/src/net/http/transport_test.go b/src/net/http/transport_test.go
index dcaacece61..690e0c299d 100644
--- a/src/net/http/transport_test.go
+++ b/src/net/http/transport_test.go
@@ -30,7 +30,7 @@ import (
 	"net/http/httptest"
 	"net/http/httptrace"
 	"net/http/httputil"
-	"net/http/internal"
+	"net/http/internal/testcert"
 	"net/textproto"
 	"net/url"
 	"os"
@@ -4299,7 +4299,7 @@ func TestTransportReuseConnEmptyResponseBody(t *testing.T) {
 
 // Issue 13839
 func TestNoCrashReturningTransportAltConn(t *testing.T) {
-	cert, err := tls.X509KeyPair(internal.LocalhostCert, internal.LocalhostKey)
+	cert, err := tls.X509KeyPair(testcert.LocalhostCert, testcert.LocalhostKey)
 	if err != nil {
 		t.Fatal(err)
 	}
diff --git a/src/net/ip.go b/src/net/ip.go
index 0477269761..38e1aa2247 100644
--- a/src/net/ip.go
+++ b/src/net/ip.go
@@ -574,6 +574,10 @@ func parseIPv4(s string) IP {
 		if !ok || n > 0xFF {
 			return nil
 		}
+		if c > 1 && s[0] == '0' {
+			// Reject non-zero components with leading zeroes.
+			return nil
+		}
 		s = s[c:]
 		p[i] = byte(n)
 	}
diff --git a/src/net/ip_test.go b/src/net/ip_test.go
index 3af5e41ceb..5bbda6024d 100644
--- a/src/net/ip_test.go
+++ b/src/net/ip_test.go
@@ -21,9 +21,7 @@ var parseIPTests = []struct {
 }{
 	{"127.0.1.2", IPv4(127, 0, 1, 2)},
 	{"127.0.0.1", IPv4(127, 0, 0, 1)},
-	{"127.001.002.003", IPv4(127, 1, 2, 3)},
 	{"::ffff:127.1.2.3", IPv4(127, 1, 2, 3)},
-	{"::ffff:127.001.002.003", IPv4(127, 1, 2, 3)},
 	{"::ffff:7f01:0203", IPv4(127, 1, 2, 3)},
 	{"0:0:0:0:0000:ffff:127.1.2.3", IPv4(127, 1, 2, 3)},
 	{"0:0:0:0:000000:ffff:127.1.2.3", IPv4(127, 1, 2, 3)},
@@ -43,6 +41,11 @@ var parseIPTests = []struct {
 	{"fe80::1%911", nil},
 	{"", nil},
 	{"a1:a2:a3:a4::b1:b2:b3:b4", nil}, // Issue 6628
+	{"127.001.002.003", nil},
+	{"::ffff:127.001.002.003", nil},
+	{"123.000.000.000", nil},
+	{"1.2..4", nil},
+	{"0123.0.0.1", nil},
 }
 
 func TestParseIP(t *testing.T) {
@@ -358,6 +361,7 @@ var parseCIDRTests = []struct {
 	{"0.0.-2.0/32", nil, nil, &ParseError{Type: "CIDR address", Text: "0.0.-2.0/32"}},
 	{"0.0.0.-3/32", nil, nil, &ParseError{Type: "CIDR address", Text: "0.0.0.-3/32"}},
 	{"0.0.0.0/-0", nil, nil, &ParseError{Type: "CIDR address", Text: "0.0.0.0/-0"}},
+	{"127.000.000.001/32", nil, nil, &ParseError{Type: "CIDR address", Text: "127.000.000.001/32"}},
 	{"", nil, nil, &ParseError{Type: "CIDR address", Text: ""}},
 }
 
diff --git a/src/net/testdata/ipv4-hosts b/src/net/testdata/ipv4-hosts
index 5208bb44ac..6b99675dfc 100644
--- a/src/net/testdata/ipv4-hosts
+++ b/src/net/testdata/ipv4-hosts
@@ -1,12 +1,8 @@
 # See https://tools.ietf.org/html/rfc1123.
-#
-# The literal IPv4 address parser in the net package is a relaxed
-# one. It may accept a literal IPv4 address in dotted-decimal notation
-# with leading zeros such as "001.2.003.4".
 
 # internet address and host name
 127.0.0.1	localhost	# inline comment separated by tab
-127.000.000.002	localhost       # inline comment separated by space
+127.0.0.2	localhost   # inline comment separated by space
 
 # internet address, host name and aliases
-127.000.000.003	localhost	localhost.localdomain
+127.0.0.3	localhost	localhost.localdomain
diff --git a/src/net/url/example_test.go b/src/net/url/example_test.go
index cb9e8922a2..476132a1c9 100644
--- a/src/net/url/example_test.go
+++ b/src/net/url/example_test.go
@@ -72,13 +72,13 @@ func ExampleURL_ResolveReference() {
 }
 
 func ExampleParseQuery() {
-	m, err := url.ParseQuery(`x=1&y=2&y=3;z`)
+	m, err := url.ParseQuery(`x=1&y=2&y=3`)
 	if err != nil {
 		log.Fatal(err)
 	}
 	fmt.Println(toJSON(m))
 	// Output:
-	// {"x":["1"], "y":["2", "3"], "z":[""]}
+	// {"x":["1"], "y":["2", "3"]}
 }
 
 func ExampleURL_EscapedPath() {
diff --git a/src/net/url/url.go b/src/net/url/url.go
index 73bef22e45..20de0f6f51 100644
--- a/src/net/url/url.go
+++ b/src/net/url/url.go
@@ -921,9 +921,10 @@ func (v Values) Has(key string) bool {
 // valid query parameters found; err describes the first decoding error
 // encountered, if any.
 //
-// Query is expected to be a list of key=value settings separated by
-// ampersands or semicolons. A setting without an equals sign is
-// interpreted as a key set to an empty value.
+// Query is expected to be a list of key=value settings separated by ampersands.
+// A setting without an equals sign is interpreted as a key set to an empty
+// value.
+// Settings containing a non-URL-encoded semicolon are considered invalid.
 func ParseQuery(query string) (Values, error) {
 	m := make(Values)
 	err := parseQuery(m, query)
@@ -933,11 +934,15 @@ func ParseQuery(query string) (Values, error) {
 func parseQuery(m Values, query string) (err error) {
 	for query != "" {
 		key := query
-		if i := strings.IndexAny(key, "&;"); i >= 0 {
+		if i := strings.IndexAny(key, "&"); i >= 0 {
 			key, query = key[:i], key[i+1:]
 		} else {
 			query = ""
 		}
+		if strings.Contains(key, ";") {
+			err = fmt.Errorf("invalid semicolon separator in query")
+			continue
+		}
 		if key == "" {
 			continue
 		}
diff --git a/src/net/url/url_test.go b/src/net/url/url_test.go
index 55348c4a7d..63c8e695af 100644
--- a/src/net/url/url_test.go
+++ b/src/net/url/url_test.go
@@ -1334,57 +1334,125 @@ func TestQueryValues(t *testing.T) {
 type parseTest struct {
 	query string
 	out   Values
+	ok    bool
 }
 
 var parseTests = []parseTest{
 	{
+		query: "a=1",
+		out:   Values{"a": []string{"1"}},
+		ok:    true,
+	},
+	{
 		query: "a=1&b=2",
 		out:   Values{"a": []string{"1"}, "b": []string{"2"}},
+		ok:    true,
 	},
 	{
 		query: "a=1&a=2&a=banana",
 		out:   Values{"a": []string{"1", "2", "banana"}},
+		ok:    true,
 	},
 	{
 		query: "ascii=%3Ckey%3A+0x90%3E",
 		out:   Values{"ascii": []string{"<key: 0x90>"}},
+		ok:    true,
+	}, {
+		query: "a=1;b=2",
+		out:   Values{},
+		ok:    false,
+	}, {
+		query: "a;b=1",
+		out:   Values{},
+		ok:    false,
+	}, {
+		query: "a=%3B", // hex encoding for semicolon
+		out:   Values{"a": []string{";"}},
+		ok:    true,
 	},
 	{
-		query: "a=1;b=2",
-		out:   Values{"a": []string{"1"}, "b": []string{"2"}},
+		query: "a%3Bb=1",
+		out:   Values{"a;b": []string{"1"}},
+		ok:    true,
 	},
 	{
 		query: "a=1&a=2;a=banana",
-		out:   Values{"a": []string{"1", "2", "banana"}},
+		out:   Values{"a": []string{"1"}},
+		ok:    false,
+	},
+	{
+		query: "a;b&c=1",
+		out:   Values{"c": []string{"1"}},
+		ok:    false,
+	},
+	{
+		query: "a=1&b=2;a=3&c=4",
+		out:   Values{"a": []string{"1"}, "c": []string{"4"}},
+		ok:    false,
+	},
+	{
+		query: "a=1&b=2;c=3",
+		out:   Values{"a": []string{"1"}},
+		ok:    false,
+	},
+	{
+		query: ";",
+		out:   Values{},
+		ok:    false,
+	},
+	{
+		query: "a=1;",
+		out:   Values{},
+		ok:    false,
+	},
+	{
+		query: "a=1&;",
+		out:   Values{"a": []string{"1"}},
+		ok:    false,
+	},
+	{
+		query: ";a=1&b=2",
+		out:   Values{"b": []string{"2"}},
+		ok:    false,
+	},
+	{
+		query: "a=1&b=2;",
+		out:   Values{"a": []string{"1"}},
+		ok:    false,
 	},
 }
 
 func TestParseQuery(t *testing.T) {
-	for i, test := range parseTests {
-		form, err := ParseQuery(test.query)
-		if err != nil {
-			t.Errorf("test %d: Unexpected error: %v", i, err)
-			continue
-		}
-		if len(form) != len(test.out) {
-			t.Errorf("test %d: len(form) = %d, want %d", i, len(form), len(test.out))
-		}
-		for k, evs := range test.out {
-			vs, ok := form[k]
-			if !ok {
-				t.Errorf("test %d: Missing key %q", i, k)
-				continue
+	for _, test := range parseTests {
+		t.Run(test.query, func(t *testing.T) {
+			form, err := ParseQuery(test.query)
+			if test.ok != (err == nil) {
+				want := "<error>"
+				if test.ok {
+					want = "<nil>"
+				}
+				t.Errorf("Unexpected error: %v, want %v", err, want)
 			}
-			if len(vs) != len(evs) {
-				t.Errorf("test %d: len(form[%q]) = %d, want %d", i, k, len(vs), len(evs))
-				continue
+			if len(form) != len(test.out) {
+				t.Errorf("len(form) = %d, want %d", len(form), len(test.out))
 			}
-			for j, ev := range evs {
-				if v := vs[j]; v != ev {
-					t.Errorf("test %d: form[%q][%d] = %q, want %q", i, k, j, v, ev)
+			for k, evs := range test.out {
+				vs, ok := form[k]
+				if !ok {
+					t.Errorf("Missing key %q", k)
+					continue
+				}
+				if len(vs) != len(evs) {
+					t.Errorf("len(form[%q]) = %d, want %d", k, len(vs), len(evs))
+					continue
+				}
+				for j, ev := range evs {
+					if v := vs[j]; v != ev {
+						t.Errorf("form[%q][%d] = %q, want %q", k, j, v, ev)
+					}
 				}
 			}
-		}
+		})
 	}
 }
 
diff --git a/src/reflect/abi_test.go b/src/reflect/abi_test.go
index 26e77f14dd..2b247d1d79 100644
--- a/src/reflect/abi_test.go
+++ b/src/reflect/abi_test.go
@@ -79,7 +79,34 @@ func TestMethodValueCallABI(t *testing.T) {
 		t.Errorf("bad method value call: got %#v, want %#v", r2, a2)
 	}
 	if s.Value != 3 {
-		t.Errorf("bad method value call: failed to set s.Value: got %d, want %d", s.Value, 1)
+		t.Errorf("bad method value call: failed to set s.Value: got %d, want %d", s.Value, 3)
+	}
+
+	s, i = makeMethodValue("ValueRegMethodSpillInt")
+	f3 := i.(func(StructFillRegs, int, MagicLastTypeNameForTestingRegisterABI) (StructFillRegs, int))
+	r3a, r3b := f3(a2, 42, MagicLastTypeNameForTestingRegisterABI{})
+	if r3a != a2 {
+		t.Errorf("bad method value call: got %#v, want %#v", r3a, a2)
+	}
+	if r3b != 42 {
+		t.Errorf("bad method value call: got %#v, want %#v", r3b, 42)
+	}
+	if s.Value != 4 {
+		t.Errorf("bad method value call: failed to set s.Value: got %d, want %d", s.Value, 4)
+	}
+
+	s, i = makeMethodValue("ValueRegMethodSpillPtr")
+	f4 := i.(func(StructFillRegs, *byte, MagicLastTypeNameForTestingRegisterABI) (StructFillRegs, *byte))
+	vb := byte(10)
+	r4a, r4b := f4(a2, &vb, MagicLastTypeNameForTestingRegisterABI{})
+	if r4a != a2 {
+		t.Errorf("bad method value call: got %#v, want %#v", r4a, a2)
+	}
+	if r4b != &vb {
+		t.Errorf("bad method value call: got %#v, want %#v", r4b, &vb)
+	}
+	if s.Value != 5 {
+		t.Errorf("bad method value call: failed to set s.Value: got %d, want %d", s.Value, 5)
 	}
 }
 
@@ -112,6 +139,20 @@ func (m *StructWithMethods) SpillStructCall(s StructFillRegs, _ MagicLastTypeNam
 	return s
 }
 
+// When called as a method value, i is passed on the stack.
+// When called as a method, i is passed in a register.
+func (m *StructWithMethods) ValueRegMethodSpillInt(s StructFillRegs, i int, _ MagicLastTypeNameForTestingRegisterABI) (StructFillRegs, int) {
+	m.Value = 4
+	return s, i
+}
+
+// When called as a method value, i is passed on the stack.
+// When called as a method, i is passed in a register.
+func (m *StructWithMethods) ValueRegMethodSpillPtr(s StructFillRegs, i *byte, _ MagicLastTypeNameForTestingRegisterABI) (StructFillRegs, *byte) {
+	m.Value = 5
+	return s, i
+}
+
 func TestReflectCallABI(t *testing.T) {
 	// Enable register-based reflect.Call and ensure we don't
 	// use potentially incorrect cached versions by clearing
diff --git a/src/reflect/value.go b/src/reflect/value.go
index 418dff781f..c963a407bc 100644
--- a/src/reflect/value.go
+++ b/src/reflect/value.go
@@ -952,25 +952,47 @@ func callMethod(ctxt *methodValue, frame unsafe.Pointer, retValid *bool, regs *a
 			continue
 		}
 
-		// There are three cases to handle in translating each
+		// There are four cases to handle in translating each
 		// argument:
 		// 1. Stack -> stack translation.
-		// 2. Registers -> stack translation.
-		// 3. Registers -> registers translation.
-		// The fourth cases can't happen, because a method value
-		// call uses strictly fewer registers than a method call.
+		// 2. Stack -> registers translation.
+		// 3. Registers -> stack translation.
+		// 4. Registers -> registers translation.
+		// TODO(mknyszek): Cases 2 and 3 below only work on little endian
+		// architectures. This is OK for now, but this needs to be fixed
+		// before supporting the register ABI on big endian architectures.
 
 		// If the value ABI passes the value on the stack,
 		// then the method ABI does too, because it has strictly
 		// fewer arguments. Simply copy between the two.
 		if vStep := valueSteps[0]; vStep.kind == abiStepStack {
 			mStep := methodSteps[0]
-			if mStep.kind != abiStepStack || vStep.size != mStep.size {
-				panic("method ABI and value ABI do not align")
+			// Handle stack -> stack translation.
+			if mStep.kind == abiStepStack {
+				if vStep.size != mStep.size {
+					panic("method ABI and value ABI do not align")
+				}
+				typedmemmove(t,
+					add(methodFrame, mStep.stkOff, "precomputed stack offset"),
+					add(valueFrame, vStep.stkOff, "precomputed stack offset"))
+				continue
+			}
+			// Handle stack -> register translation.
+			for _, mStep := range methodSteps {
+				from := add(valueFrame, vStep.stkOff+mStep.offset, "precomputed stack offset")
+				switch mStep.kind {
+				case abiStepPointer:
+					// Do the pointer copy directly so we get a write barrier.
+					methodRegs.Ptrs[mStep.ireg] = *(*unsafe.Pointer)(from)
+					fallthrough // We need to make sure this ends up in Ints, too.
+				case abiStepIntReg:
+					memmove(unsafe.Pointer(&methodRegs.Ints[mStep.ireg]), from, mStep.size)
+				case abiStepFloatReg:
+					memmove(unsafe.Pointer(&methodRegs.Floats[mStep.freg]), from, mStep.size)
+				default:
+					panic("unexpected method step")
+				}
 			}
-			typedmemmove(t,
-				add(methodFrame, mStep.stkOff, "precomputed stack offset"),
-				add(valueFrame, vStep.stkOff, "precomputed stack offset"))
 			continue
 		}
 		// Handle register -> stack translation.
diff --git a/src/runtime/os_darwin.go b/src/runtime/os_darwin.go
index df2c0ff4a5..ca61f20e8a 100644
--- a/src/runtime/os_darwin.go
+++ b/src/runtime/os_darwin.go
@@ -118,10 +118,15 @@ func sigNoteWakeup(*note) {
 
 // sigNoteSleep waits for a note created by sigNoteSetup to be woken.
 func sigNoteSleep(*note) {
-	entersyscallblock()
-	var b byte
-	read(sigNoteRead, unsafe.Pointer(&b), 1)
-	exitsyscall()
+	for {
+		var b byte
+		entersyscallblock()
+		n := read(sigNoteRead, unsafe.Pointer(&b), 1)
+		exitsyscall()
+		if n != -_EINTR {
+			return
+		}
+	}
 }
 
 // BSD interface for threading.
diff --git a/src/runtime/testdata/testprogcgo/aprof.go b/src/runtime/testdata/testprogcgo/aprof.go
index aabca9e1eb..44a15b0865 100644
--- a/src/runtime/testdata/testprogcgo/aprof.go
+++ b/src/runtime/testdata/testprogcgo/aprof.go
@@ -10,7 +10,7 @@ package main
 // The test fails when the function is the first C function.
 // The exported functions are the first C functions, so we use that.
 
-// extern void GoNop();
+// extern void CallGoNop();
 import "C"
 
 import (
@@ -38,7 +38,7 @@ func CgoCCodeSIGPROF() {
 					break
 				}
 			}
-			C.GoNop()
+			C.CallGoNop()
 		}
 		c <- true
 	}()
diff --git a/src/runtime/testdata/testprogcgo/aprof_c.c b/src/runtime/testdata/testprogcgo/aprof_c.c
new file mode 100644
index 0000000000..d588e13045
--- /dev/null
+++ b/src/runtime/testdata/testprogcgo/aprof_c.c
@@ -0,0 +1,9 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+#include "_cgo_export.h"
+
+void CallGoNop() {
+	GoNop();
+}
diff --git a/src/runtime/testdata/testprogcgo/bigstack1_windows.c b/src/runtime/testdata/testprogcgo/bigstack1_windows.c
new file mode 100644
index 0000000000..551fb68309
--- /dev/null
+++ b/src/runtime/testdata/testprogcgo/bigstack1_windows.c
@@ -0,0 +1,12 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// This is not in bigstack_windows.c because it needs to be part of
+// testprogcgo but is not part of the DLL built from bigstack_windows.c.
+
+#include "_cgo_export.h"
+
+void CallGoBigStack1(char* p) {
+	goBigStack1(p);
+}
diff --git a/src/runtime/testdata/testprogcgo/bigstack_windows.go b/src/runtime/testdata/testprogcgo/bigstack_windows.go
index f58fcf993f..135b5fcfe0 100644
--- a/src/runtime/testdata/testprogcgo/bigstack_windows.go
+++ b/src/runtime/testdata/testprogcgo/bigstack_windows.go
@@ -6,7 +6,7 @@ package main
 
 /*
 typedef void callback(char*);
-extern void goBigStack1(char*);
+extern void CallGoBigStack1(char*);
 extern void bigStack(callback*);
 */
 import "C"
@@ -18,7 +18,7 @@ func init() {
 func BigStack() {
 	// Create a large thread stack and call back into Go to test
 	// if Go correctly determines the stack bounds.
-	C.bigStack((*C.callback)(C.goBigStack1))
+	C.bigStack((*C.callback)(C.CallGoBigStack1))
 }
 
 //export goBigStack1
diff --git a/src/runtime/traceback.go b/src/runtime/traceback.go
index 3fc9d07fc5..fa41fdfe2d 100644
--- a/src/runtime/traceback.go
+++ b/src/runtime/traceback.go
@@ -21,8 +21,6 @@ import (
 
 const usesLR = sys.MinFrameSize > 0
 
-const sizeofSkipFunction = 256
-
 // Generic traceback. Handles runtime stack prints (pcbuf == nil),
 // the runtime.Callers function (pcbuf != nil), as well as the garbage
 // collector (callback != nil).  A little clunky to merge these, but avoids
@@ -30,9 +28,7 @@ const sizeofSkipFunction = 256
 //
 // The skip argument is only valid with pcbuf != nil and counts the number
 // of logical frames to skip rather than physical frames (with inlining, a
-// PC in pcbuf can represent multiple calls). If a PC is partially skipped
-// and max > 1, pcbuf[1] will be runtime.skipPleaseUseCallersFrames+N where
-// N indicates the number of logical frames to skip in pcbuf[0].
+// PC in pcbuf can represent multiple calls).
 func gentraceback(pc0, sp0, lr0 uintptr, gp *g, skip int, pcbuf *uintptr, max int, callback func(*stkframe, unsafe.Pointer) bool, v unsafe.Pointer, flags uint) int {
 	if skip > 0 && callback != nil {
 		throw("gentraceback callback cannot be used with non-zero skip")
diff --git a/src/strconv/atof.go b/src/strconv/atof.go
index 9010a66ca8..57556c7047 100644
--- a/src/strconv/atof.go
+++ b/src/strconv/atof.go
@@ -689,7 +689,7 @@ func atof64(s string) (f float64, n int, err error) {
 // as their respective special floating point values. It ignores case when matching.
 func ParseFloat(s string, bitSize int) (float64, error) {
 	f, n, err := parseFloatPrefix(s, bitSize)
-	if err == nil && n != len(s) {
+	if n != len(s) && (err == nil || err.(*NumError).Err != ErrSyntax) {
 		return 0, syntaxError(fnParseFloat, s)
 	}
 	return f, err
diff --git a/src/strconv/atof_test.go b/src/strconv/atof_test.go
index 3c058b9be5..aa587a473c 100644
--- a/src/strconv/atof_test.go
+++ b/src/strconv/atof_test.go
@@ -342,6 +342,9 @@ var atoftests = []atofTest{
 	{"0x12.345p-_12", "0", ErrSyntax},
 	{"0x12.345p+1__2", "0", ErrSyntax},
 	{"0x12.345p+12_", "0", ErrSyntax},
+
+	{"1e100x", "0", ErrSyntax},
+	{"1e1000x", "0", ErrSyntax},
 }
 
 var atof32tests = []atofTest{
diff --git a/src/strconv/atoi.go b/src/strconv/atoi.go
index c9ba0383b3..631b487d97 100644
--- a/src/strconv/atoi.go
+++ b/src/strconv/atoi.go
@@ -57,6 +57,8 @@ const IntSize = intSize
 const maxUint64 = 1<<64 - 1
 
 // ParseUint is like ParseInt but for unsigned numbers.
+//
+// A sign prefix is not permitted.
 func ParseUint(s string, base int, bitSize int) (uint64, error) {
 	const fnParseUint = "ParseUint"
 
@@ -159,10 +161,13 @@ func ParseUint(s string, base int, bitSize int) (uint64, error) {
 // ParseInt interprets a string s in the given base (0, 2 to 36) and
 // bit size (0 to 64) and returns the corresponding value i.
 //
+// The string may begin with a leading sign: "+" or "-".
+//
 // If the base argument is 0, the true base is implied by the string's
-// prefix: 2 for "0b", 8 for "0" or "0o", 16 for "0x", and 10 otherwise.
-// Also, for argument base 0 only, underscore characters are permitted
-// as defined by the Go syntax for integer literals.
+// prefix following the sign (if present): 2 for "0b", 8 for "0" or "0o",
+// 16 for "0x", and 10 otherwise. Also, for argument base 0 only,
+// underscore characters are permitted as defined by the Go syntax for
+// integer literals.
 //
 // The bitSize argument specifies the integer type
 // that the result must fit into. Bit sizes 0, 8, 16, 32, and 64
diff --git a/src/strconv/atoi_test.go b/src/strconv/atoi_test.go
index 178fb01ea7..867fa66a14 100644
--- a/src/strconv/atoi_test.go
+++ b/src/strconv/atoi_test.go
@@ -33,6 +33,9 @@ var parseUint64Tests = []parseUint64Test{
 	{"_12345", 0, ErrSyntax},
 	{"1__2345", 0, ErrSyntax},
 	{"12345_", 0, ErrSyntax},
+	{"-0", 0, ErrSyntax},
+	{"-1", 0, ErrSyntax},
+	{"+1", 0, ErrSyntax},
 }
 
 type parseUint64BaseTest struct {
@@ -140,8 +143,10 @@ var parseInt64Tests = []parseInt64Test{
 	{"", 0, ErrSyntax},
 	{"0", 0, nil},
 	{"-0", 0, nil},
+	{"+0", 0, nil},
 	{"1", 1, nil},
 	{"-1", -1, nil},
+	{"+1", 1, nil},
 	{"12345", 12345, nil},
 	{"-12345", -12345, nil},
 	{"012345", 12345, nil},
@@ -236,6 +241,11 @@ var parseInt64BaseTests = []parseInt64BaseTest{
 	{"0__12345", 0, 0, ErrSyntax},
 	{"01234__5", 0, 0, ErrSyntax},
 	{"012345_", 0, 0, ErrSyntax},
+
+	{"+0xf", 0, 0xf, nil},
+	{"-0xf", 0, -0xf, nil},
+	{"0x+f", 0, 0, ErrSyntax},
+	{"0x-f", 0, 0, ErrSyntax},
 }
 
 type parseUint32Test struct {
diff --git a/src/syscall/syscall_windows_test.go b/src/syscall/syscall_windows_test.go
index ea8fa191dc..3243952ded 100644
--- a/src/syscall/syscall_windows_test.go
+++ b/src/syscall/syscall_windows_test.go
@@ -10,6 +10,7 @@ import (
 	"os"
 	"os/exec"
 	"path/filepath"
+	"runtime"
 	"strings"
 	"syscall"
 	"testing"
@@ -79,6 +80,9 @@ func TestTOKEN_ALL_ACCESS(t *testing.T) {
 func TestStdioAreInheritable(t *testing.T) {
 	testenv.MustHaveGoBuild(t)
 	testenv.MustHaveExecPath(t, "gcc")
+	if runtime.GOARCH == "arm64" || runtime.GOARCH == "arm" {
+		t.Skip("Powershell is not native on ARM; see golang.org/issues/46701")
+	}
 
 	tmpdir := t.TempDir()
 
diff --git a/test/declbad.go b/test/declbad.go
index 728eceb7f1..b978652a2b 100644
--- a/test/declbad.go
+++ b/test/declbad.go
@@ -23,13 +23,13 @@ func main() {
 	{
 		// change of type for f
 		i, f, s := f3()
-		f, g, t := f3() // ERROR "redeclared|cannot assign|incompatible"
+		f, g, t := f3() // ERROR "redeclared|cannot assign|incompatible|cannot use"
 		_, _, _, _, _ = i, f, s, g, t
 	}
 	{
 		// change of type for i
 		i, f, s := f3()
-		j, i, t := f3() // ERROR "redeclared|cannot assign|incompatible"
+		j, i, t := f3() // ERROR "redeclared|cannot assign|incompatible|cannot use"
 		_, _, _, _, _ = i, f, s, j, t
 	}
 	{
diff --git a/test/fixedbugs/issue46386.go b/test/fixedbugs/issue46386.go
new file mode 100644
index 0000000000..89dea8abf3
--- /dev/null
+++ b/test/fixedbugs/issue46386.go
@@ -0,0 +1,32 @@
+// compile -p=main
+
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+type I interface {
+	M() interface{}
+}
+
+type S1 struct{}
+
+func (S1) M() interface{} {
+	return nil
+}
+
+type EI interface{}
+
+type S struct{}
+
+func (S) M(as interface{ I }) {}
+
+func f() interface{ EI } {
+	return &S1{}
+}
+
+func main() {
+	var i interface{ I }
+	(&S{}).M(i)
+}
diff --git a/test/fixedbugs/issue46653.dir/bad/bad.go b/test/fixedbugs/issue46653.dir/bad/bad.go
new file mode 100644
index 0000000000..c1611b8347
--- /dev/null
+++ b/test/fixedbugs/issue46653.dir/bad/bad.go
@@ -0,0 +1,64 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package a
+
+func Bad() {
+	m := make(map[int64]A)
+	a := m[0]
+	if len(a.B.C1.D2.E2.F1) != 0 ||
+		len(a.B.C1.D2.E2.F2) != 0 ||
+		len(a.B.C1.D2.E2.F3) != 0 ||
+		len(a.B.C1.D2.E2.F4) != 0 ||
+		len(a.B.C1.D2.E2.F5) != 0 ||
+		len(a.B.C1.D2.E2.F6) != 0 ||
+		len(a.B.C1.D2.E2.F7) != 0 ||
+		len(a.B.C1.D2.E2.F8) != 0 ||
+		len(a.B.C1.D2.E2.F9) != 0 ||
+		len(a.B.C1.D2.E2.F10) != 0 ||
+		len(a.B.C1.D2.E2.F11) != 0 ||
+		len(a.B.C1.D2.E2.F16) != 0 {
+		panic("bad")
+	}
+}
+
+type A struct {
+	B
+}
+
+type B struct {
+	C1 C
+	C2 C
+}
+
+type C struct {
+	D1 D
+	D2 D
+}
+
+type D struct {
+	E1 E
+	E2 E
+	E3 E
+	E4 E
+}
+
+type E struct {
+	F1  string
+	F2  string
+	F3  string
+	F4  string
+	F5  string
+	F6  string
+	F7  string
+	F8  string
+	F9  string
+	F10 string
+	F11 string
+	F12 string
+	F13 string
+	F14 string
+	F15 string
+	F16 string
+}
diff --git a/test/fixedbugs/issue46653.dir/main.go b/test/fixedbugs/issue46653.dir/main.go
new file mode 100644
index 0000000000..e2a96e54ec
--- /dev/null
+++ b/test/fixedbugs/issue46653.dir/main.go
@@ -0,0 +1,27 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+import (
+	bad "issue46653.dir/bad"
+)
+
+func main() {
+	bad.Bad()
+}
+
+func neverCalled() L {
+	m := make(map[string]L)
+	return m[""]
+}
+
+type L struct {
+	A Data
+	B Data
+}
+
+type Data struct {
+	F1 [22][]string
+}
diff --git a/test/fixedbugs/issue46653.go b/test/fixedbugs/issue46653.go
new file mode 100644
index 0000000000..e6283b1de5
--- /dev/null
+++ b/test/fixedbugs/issue46653.go
@@ -0,0 +1,10 @@
+// runindir
+
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Test to verify compiler and linker handling of multiple
+// competing map.zero symbol definitions.
+
+package ignored
diff --git a/test/fixedbugs/issue46720.go b/test/fixedbugs/issue46720.go
new file mode 100644
index 0000000000..3b0151ae84
--- /dev/null
+++ b/test/fixedbugs/issue46720.go
@@ -0,0 +1,15 @@
+// compile
+
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package p
+
+func f() {
+	nonce := make([]byte, 24)
+	g((*[24]byte)(nonce))
+}
+
+//go:noinline
+func g(*[24]byte) {}
diff --git a/test/fixedbugs/issue46725.go b/test/fixedbugs/issue46725.go
new file mode 100644
index 0000000000..29799c7d7e
--- /dev/null
+++ b/test/fixedbugs/issue46725.go
@@ -0,0 +1,48 @@
+// run
+
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+import "runtime"
+
+type T [4]int
+
+//go:noinline
+func g(x []*T) ([]*T, []*T) { return x, x }
+
+func main() {
+	const Jenny = 8675309
+	s := [10]*T{{Jenny}}
+
+	done := make(chan struct{})
+	runtime.SetFinalizer(s[0], func(p *T) { close(done) })
+
+	var h, _ interface{} = g(s[:])
+
+	if wait(done) {
+		panic("GC'd early")
+	}
+
+	if h.([]*T)[0][0] != Jenny {
+		panic("lost Jenny's number")
+	}
+
+	if !wait(done) {
+		panic("never GC'd")
+	}
+}
+
+func wait(done <-chan struct{}) bool {
+	for i := 0; i < 10; i++ {
+		runtime.GC()
+		select {
+		case <-done:
+			return true
+		default:
+		}
+	}
+	return false
+}
diff --git a/test/run.go b/test/run.go
index ca6a0f5c29..656519e301 100644
--- a/test/run.go
+++ b/test/run.go
@@ -2079,6 +2079,7 @@ var excludedFiles = map[string]bool{
 	"fixedbugs/issue33460.go":  true, // types2 reports alternative positions in separate error
 	"fixedbugs/issue42058a.go": true, // types2 doesn't report "channel element type too large"
 	"fixedbugs/issue42058b.go": true, // types2 doesn't report "channel element type too large"
+	"fixedbugs/issue46725.go":  true, // fix applied to typecheck needs to be ported to irgen/transform
 	"fixedbugs/issue4232.go":   true, // types2 reports (correct) extra errors
 	"fixedbugs/issue4452.go":   true, // types2 reports (correct) extra errors
 	"fixedbugs/issue4510.go":   true, // types2 reports different (but ok) line numbers
author	Matthew Dempsky <mdempsky@google.com>	2021-06-14 12:26:41 -0700
committer	Matthew Dempsky <mdempsky@google.com>	2021-06-14 13:24:47 -0700
commit	ea438bda85ed473ecee215b098eba1f19113bc24 (patch)
tree	78ea8b11917bcdf1e7c78c09c0395c684d55c054
parent	8eeaf961c50973b0aa2065d2c31dfa5d9949bf93 (diff)
parent	fdab5be159c508c4c1cf5be84119fd2b38403cdf (diff)
download	go-ea438bda85ed473ecee215b098eba1f19113bc24.tar.gz go-ea438bda85ed473ecee215b098eba1f19113bc24.zip