cmd: move GOEXPERIMENT knob from make.bash to cmd/go

This CL changes GOEXPERIMENT to act like other GO[CONFIG] environment
variables. Namely, that it can be set at make.bash time to provide a
default value used by the toolchain, but then can be manually set when
running either cmd/go or the individual tools (compiler, assembler,
linker).

For example, it's now possible to test rsc.io/tmp/fieldtrack by simply
running:

GOEXPERIMENT=fieldtrack go test -gcflags=-l rsc.io/tmp/fieldtrack \
  -ldflags=-k=rsc.io/tmp/fieldtrack.tracked

without needing to re-run make.bash. (-gcflags=-l is needed because
the compiler's inlining abilities have improved, so calling a function
with a for loop is no longer sufficient to suppress inlining.)

Fixes #42681.

Change-Id: I2cf8995d5d0d05f6785a2ee1d3b54b2cfb3331ca
Reviewed-on: https://go-review.googlesource.com/c/go/+/300991
Trust: Matthew Dempsky <mdempsky@google.com>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Bryan C. Mills <bcmills@google.com>

12 files changed, 51 insertions, 48 deletions

diff --git a/src/cmd/asm/internal/lex/input.go b/src/cmd/asm/internal/lex/input.go
index da4ebe6d6e..1d4d4be7bd 100644
--- a/src/cmd/asm/internal/lex/input.go
+++ b/src/cmd/asm/internal/lex/input.go
@@ -45,6 +45,16 @@ func NewInput(name string) *Input {
 // predefine installs the macros set by the -D flag on the command line.
 func predefine(defines flags.MultiFlag) map[string]*Macro {
 	macros := make(map[string]*Macro)
+
+	if *flags.CompilingRuntime && objabi.Regabi_enabled != 0 {
+		const name = "GOEXPERIMENT_REGABI"
+		macros[name] = &Macro{
+			name:   name,
+			args:   nil,
+			tokens: Tokenize("1"),
+		}
+	}
+
 	for _, name := range defines {
 		value := "1"
 		i := strings.IndexRune(name, '=')
diff --git a/src/cmd/dist/build.go b/src/cmd/dist/build.go
index 158cedbadc..b2d13e7db4 100644
--- a/src/cmd/dist/build.go
+++ b/src/cmd/dist/build.go
@@ -39,6 +39,7 @@ var (
 	goextlinkenabled string
 	gogcflags        string // For running built compiler
 	goldflags        string
+	goexperiment     string
 	workdir          string
 	tooldir          string
 	oldgoos          string
@@ -194,6 +195,9 @@ func xinit() {
 		goextlinkenabled = b
 	}
 
+	goexperiment = os.Getenv("GOEXPERIMENT")
+	// TODO(mdempsky): Validate known experiments?
+
 	gogcflags = os.Getenv("BOOT_GO_GCFLAGS")
 	goldflags = os.Getenv("BOOT_GO_LDFLAGS")
 
@@ -834,18 +838,6 @@ func runInstall(pkg string, ch chan struct{}) {
 	goasmh := pathf("%s/go_asm.h", workdir)
 	if IsRuntimePackagePath(pkg) {
 		asmArgs = append(asmArgs, "-compiling-runtime")
-		if os.Getenv("GOEXPERIMENT") == "regabi" {
-			// In order to make it easier to port runtime assembly
-			// to the register ABI, we introduce a macro
-			// indicating the experiment is enabled.
-			//
-			// Note: a similar change also appears in
-			// cmd/go/internal/work/gc.go.
-			//
-			// TODO(austin): Remove this once we commit to the
-			// register ABI (#40724).
-			asmArgs = append(asmArgs, "-D=GOEXPERIMENT_REGABI=1")
-		}
 	}
 
 	// Collect symabis from assembly code.
diff --git a/src/cmd/dist/buildruntime.go b/src/cmd/dist/buildruntime.go
index 2744951597..e0a101a353 100644
--- a/src/cmd/dist/buildruntime.go
+++ b/src/cmd/dist/buildruntime.go
@@ -20,7 +20,6 @@ import (
 //	package sys
 //
 //	const TheVersion = <version>
-//	const Goexperiment = <goexperiment>
 //	const StackGuardMultiplier = <multiplier value>
 //
 func mkzversion(dir, file string) {
@@ -30,7 +29,6 @@ func mkzversion(dir, file string) {
 	fmt.Fprintf(&buf, "package sys\n")
 	fmt.Fprintln(&buf)
 	fmt.Fprintf(&buf, "const TheVersion = `%s`\n", findgoversion())
-	fmt.Fprintf(&buf, "const Goexperiment = `%s`\n", os.Getenv("GOEXPERIMENT"))
 	fmt.Fprintf(&buf, "const StackGuardMultiplierDefault = %d\n", stackGuardMultiplierDefault())
 
 	writefile(buf.String(), file, writeSkipSame)
@@ -48,10 +46,10 @@ func mkzversion(dir, file string) {
 //	const defaultGOPPC64 = <goppc64>
 //	const defaultGOOS = runtime.GOOS
 //	const defaultGOARCH = runtime.GOARCH
+//	const defaultGOEXPERIMENT = <goexperiment>
 //	const defaultGO_EXTLINK_ENABLED = <goextlinkenabled>
 //	const version = <version>
 //	const stackGuardMultiplierDefault = <multiplier value>
-//	const goexperiment = <goexperiment>
 //
 // The use of runtime.GOOS and runtime.GOARCH makes sure that
 // a cross-compiled compiler expects to compile for its own target
@@ -77,11 +75,11 @@ func mkzbootstrap(file string) {
 	fmt.Fprintf(&buf, "const defaultGOPPC64 = `%s`\n", goppc64)
 	fmt.Fprintf(&buf, "const defaultGOOS = runtime.GOOS\n")
 	fmt.Fprintf(&buf, "const defaultGOARCH = runtime.GOARCH\n")
+	fmt.Fprintf(&buf, "const defaultGOEXPERIMENT = `%s`\n", goexperiment)
 	fmt.Fprintf(&buf, "const defaultGO_EXTLINK_ENABLED = `%s`\n", goextlinkenabled)
 	fmt.Fprintf(&buf, "const defaultGO_LDSO = `%s`\n", defaultldso)
 	fmt.Fprintf(&buf, "const version = `%s`\n", findgoversion())
 	fmt.Fprintf(&buf, "const stackGuardMultiplierDefault = %d\n", stackGuardMultiplierDefault())
-	fmt.Fprintf(&buf, "const goexperiment = `%s`\n", os.Getenv("GOEXPERIMENT"))
 
 	writefile(buf.String(), file, writeSkipSame)
 }
diff --git a/src/cmd/go/internal/cfg/cfg.go b/src/cmd/go/internal/cfg/cfg.go
index 810189c15d..a91b6a57b9 100644
--- a/src/cmd/go/internal/cfg/cfg.go
+++ b/src/cmd/go/internal/cfg/cfg.go
@@ -252,12 +252,13 @@ var (
 	GOMODCACHE   = envOr("GOMODCACHE", gopathDir("pkg/mod"))
 
 	// Used in envcmd.MkEnv and build ID computations.
-	GOARM    = envOr("GOARM", fmt.Sprint(objabi.GOARM))
-	GO386    = envOr("GO386", objabi.GO386)
-	GOMIPS   = envOr("GOMIPS", objabi.GOMIPS)
-	GOMIPS64 = envOr("GOMIPS64", objabi.GOMIPS64)
-	GOPPC64  = envOr("GOPPC64", fmt.Sprintf("%s%d", "power", objabi.GOPPC64))
-	GOWASM   = envOr("GOWASM", fmt.Sprint(objabi.GOWASM))
+	GOARM        = envOr("GOARM", fmt.Sprint(objabi.GOARM))
+	GO386        = envOr("GO386", objabi.GO386)
+	GOMIPS       = envOr("GOMIPS", objabi.GOMIPS)
+	GOMIPS64     = envOr("GOMIPS64", objabi.GOMIPS64)
+	GOPPC64      = envOr("GOPPC64", fmt.Sprintf("%s%d", "power", objabi.GOPPC64))
+	GOWASM       = envOr("GOWASM", fmt.Sprint(objabi.GOWASM))
+	GOEXPERIMENT = envOr("GOEXPERIMENT", objabi.GOEXPERIMENT)
 
 	GOPROXY    = envOr("GOPROXY", "https://proxy.golang.org,direct")
 	GOSUMDB    = envOr("GOSUMDB", "sum.golang.org")
diff --git a/src/cmd/go/internal/work/exec.go b/src/cmd/go/internal/work/exec.go
index 3980c5f898..bd5ae46739 100644
--- a/src/cmd/go/internal/work/exec.go
+++ b/src/cmd/go/internal/work/exec.go
@@ -276,6 +276,10 @@ func (b *Builder) buildActionID(a *Action) cache.ActionID {
 		key, val := cfg.GetArchEnv()
 		fmt.Fprintf(h, "%s=%s\n", key, val)
 
+		if exp := cfg.Getenv("GOEXPERIMENT"); exp != "" {
+			fmt.Fprintf(h, "GOEXPERIMENT=%q\n", exp)
+		}
+
 		// TODO(rsc): Convince compiler team not to add more magic environment variables,
 		// or perhaps restrict the environment variables passed to subprocesses.
 		// Because these are clumsy, undocumented special-case hacks
@@ -1246,6 +1250,10 @@ func (b *Builder) printLinkerConfig(h io.Writer, p *load.Package) {
 		key, val := cfg.GetArchEnv()
 		fmt.Fprintf(h, "%s=%s\n", key, val)
 
+		if exp := cfg.Getenv("GOEXPERIMENT"); exp != "" {
+			fmt.Fprintf(h, "GOEXPERIMENT=%q\n", exp)
+		}
+
 		// The linker writes source file paths that say GOROOT_FINAL, but
 		// only if -trimpath is not specified (see ld() in gc.go).
 		gorootFinal := cfg.GOROOT_FINAL
diff --git a/src/cmd/go/internal/work/gc.go b/src/cmd/go/internal/work/gc.go
index 2087855b3c..3cb7c5aff3 100644
--- a/src/cmd/go/internal/work/gc.go
+++ b/src/cmd/go/internal/work/gc.go
@@ -343,18 +343,6 @@ func asmArgs(a *Action, p *load.Package) []interface{} {
 	}
 	if objabi.IsRuntimePackagePath(pkgpath) {
 		args = append(args, "-compiling-runtime")
-		if objabi.Regabi_enabled != 0 {
-			// In order to make it easier to port runtime assembly
-			// to the register ABI, we introduce a macro
-			// indicating the experiment is enabled.
-			//
-			// Note: a similar change also appears in
-			// cmd/dist/build.go.
-			//
-			// TODO(austin): Remove this once we commit to the
-			// register ABI (#40724).
-			args = append(args, "-D=GOEXPERIMENT_REGABI=1")
-		}
 	}
 
 	if cfg.Goarch == "mips" || cfg.Goarch == "mipsle" {
diff --git a/src/cmd/internal/objabi/util.go b/src/cmd/internal/objabi/util.go
index 1f99f8ed5d..de8e6de4e6 100644
--- a/src/cmd/internal/objabi/util.go
+++ b/src/cmd/internal/objabi/util.go
@@ -21,17 +21,18 @@ func envOr(key, value string) string {
 var (
 	defaultGOROOT string // set by linker
 
-	GOROOT   = envOr("GOROOT", defaultGOROOT)
-	GOARCH   = envOr("GOARCH", defaultGOARCH)
-	GOOS     = envOr("GOOS", defaultGOOS)
-	GO386    = envOr("GO386", defaultGO386)
-	GOARM    = goarm()
-	GOMIPS   = gomips()
-	GOMIPS64 = gomips64()
-	GOPPC64  = goppc64()
-	GOWASM   = gowasm()
-	GO_LDSO  = defaultGO_LDSO
-	Version  = version
+	GOROOT       = envOr("GOROOT", defaultGOROOT)
+	GOARCH       = envOr("GOARCH", defaultGOARCH)
+	GOOS         = envOr("GOOS", defaultGOOS)
+	GOEXPERIMENT = envOr("GOEXPERIMENT", defaultGOEXPERIMENT)
+	GO386        = envOr("GO386", defaultGO386)
+	GOARM        = goarm()
+	GOMIPS       = gomips()
+	GOMIPS64     = gomips64()
+	GOPPC64      = goppc64()
+	GOWASM       = gowasm()
+	GO_LDSO      = defaultGO_LDSO
+	Version      = version
 )
 
 const (
@@ -124,7 +125,7 @@ func Getgoextlinkenabled() string {
 }
 
 func init() {
-	for _, f := range strings.Split(goexperiment, ",") {
+	for _, f := range strings.Split(GOEXPERIMENT, ",") {
 		if f != "" {
 			addexp(f)
 		}
diff --git a/src/cmd/link/internal/ld/main.go b/src/cmd/link/internal/ld/main.go
index 68dee18598..8e9a9b9207 100644
--- a/src/cmd/link/internal/ld/main.go
+++ b/src/cmd/link/internal/ld/main.go
@@ -119,6 +119,8 @@ func Main(arch *sys.Arch, theArch Arch) {
 	addstrdata1(ctxt, "runtime.defaultGOROOT="+final)
 	addstrdata1(ctxt, "cmd/internal/objabi.defaultGOROOT="+final)
 
+	addstrdata1(ctxt, "runtime/internal/sys.GOEXPERIMENT="+objabi.GOEXPERIMENT)
+
 	// TODO(matloob): define these above and then check flag values here
 	if ctxt.Arch.Family == sys.AMD64 && objabi.GOOS == "plan9" {
 		flag.BoolVar(&flag8, "8", false, "use 64-bit addresses in symbol table")
diff --git a/src/internal/cfg/cfg.go b/src/internal/cfg/cfg.go
index 553021374d..815994b679 100644
--- a/src/internal/cfg/cfg.go
+++ b/src/internal/cfg/cfg.go
@@ -39,6 +39,7 @@ const KnownEnv = `
 	GOCACHE
 	GOENV
 	GOEXE
+	GOEXPERIMENT
 	GOFLAGS
 	GOGCCFLAGS
 	GOHOSTARCH
diff --git a/src/runtime/heapdump.go b/src/runtime/heapdump.go
index 1b8c19b476..e0913162a4 100644
--- a/src/runtime/heapdump.go
+++ b/src/runtime/heapdump.go
@@ -532,7 +532,7 @@ func dumpparams() {
 	dumpint(uint64(arenaStart))
 	dumpint(uint64(arenaEnd))
 	dumpstr(sys.GOARCH)
-	dumpstr(sys.Goexperiment)
+	dumpstr(sys.GOEXPERIMENT)
 	dumpint(uint64(ncpu))
 }
 
diff --git a/src/runtime/internal/sys/arch.go b/src/runtime/internal/sys/arch.go
index 3c99a2f7da..f00c55913f 100644
--- a/src/runtime/internal/sys/arch.go
+++ b/src/runtime/internal/sys/arch.go
@@ -52,3 +52,5 @@ const MinFrameSize = _MinFrameSize
 // StackAlign is the required alignment of the SP register.
 // The stack must be at least word aligned, but some architectures require more.
 const StackAlign = _StackAlign
+
+var GOEXPERIMENT string // set by cmd/link
diff --git a/src/runtime/proc.go b/src/runtime/proc.go
index 5f372bb063..8db3b767d1 100644
--- a/src/runtime/proc.go
+++ b/src/runtime/proc.go
@@ -6027,7 +6027,7 @@ func setMaxThreads(in int) (out int) {
 }
 
 func haveexperiment(name string) bool {
-	x := sys.Goexperiment
+	x := sys.GOEXPERIMENT
 	for x != "" {
 		xname := ""
 		i := bytealg.IndexByteString(x, ',')