internal/buildcfg: move build configuration out of cmd/internal/objabi

The go/build package needs access to this configuration,
so move it into a new package available to the standard library.

Change-Id: I868a94148b52350c76116451f4ad9191246adcff
Reviewed-on: https://go-review.googlesource.com/c/go/+/310731
Trust: Russ Cox <rsc@golang.org>
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Austin Clements <austin@google.com>
Reviewed-by: Jay Conrod <jayconrod@google.com>

14 files changed, 40 insertions, 284 deletions

diff --git a/src/cmd/internal/dwarf/dwarf.go b/src/cmd/internal/dwarf/dwarf.go
index c48e1723c8..ec441c2bcb 100644
--- a/src/cmd/internal/dwarf/dwarf.go
+++ b/src/cmd/internal/dwarf/dwarf.go
@@ -9,13 +9,15 @@ package dwarf
 
 import (
 	"bytes"
-	"cmd/internal/objabi"
 	"errors"
 	"fmt"
+	"internal/buildcfg"
 	exec "internal/execabs"
 	"sort"
 	"strconv"
 	"strings"
+
+	"cmd/internal/objabi"
 )
 
 // InfoPrefix is the prefix for all the symbols containing DWARF info entries.
@@ -381,7 +383,7 @@ func expandPseudoForm(form uint8) uint8 {
 		return form
 	}
 	expandedForm := DW_FORM_udata
-	if objabi.GOOS == "darwin" || objabi.GOOS == "ios" {
+	if buildcfg.GOOS == "darwin" || buildcfg.GOOS == "ios" {
 		expandedForm = DW_FORM_data4
 	}
 	return uint8(expandedForm)
diff --git a/src/cmd/internal/goobj/objfile_test.go b/src/cmd/internal/goobj/objfile_test.go
index ad80ede0f3..ed942aa934 100644
--- a/src/cmd/internal/goobj/objfile_test.go
+++ b/src/cmd/internal/goobj/objfile_test.go
@@ -10,6 +10,7 @@ import (
 	"cmd/internal/bio"
 	"cmd/internal/objabi"
 	"fmt"
+	"internal/buildcfg"
 	"internal/testenv"
 	"io/ioutil"
 	"os"
@@ -91,8 +92,8 @@ func main() {
 `
 
 func TestIssue41621LargeNumberOfRelocations(t *testing.T) {
-	if testing.Short() || (objabi.GOARCH != "amd64") {
-		t.Skipf("Skipping large number of relocations test in short mode or on %s", objabi.GOARCH)
+	if testing.Short() || (buildcfg.GOARCH != "amd64") {
+		t.Skipf("Skipping large number of relocations test in short mode or on %s", buildcfg.GOARCH)
 	}
 	testenv.MustHaveGoBuild(t)
 
diff --git a/src/cmd/internal/obj/arm/asm5.go b/src/cmd/internal/obj/arm/asm5.go
index ebb98b4859..ccf5f9e7f8 100644
--- a/src/cmd/internal/obj/arm/asm5.go
+++ b/src/cmd/internal/obj/arm/asm5.go
@@ -34,6 +34,7 @@ import (
 	"cmd/internal/obj"
 	"cmd/internal/objabi"
 	"fmt"
+	"internal/buildcfg"
 	"log"
 	"math"
 	"sort"
@@ -976,7 +977,7 @@ func (c *ctxt5) aclass(a *obj.Addr) int {
 			if immrot(^uint32(c.instoffset)) != 0 {
 				return C_NCON
 			}
-			if uint32(c.instoffset) <= 0xffff && objabi.GOARM == 7 {
+			if uint32(c.instoffset) <= 0xffff && buildcfg.GOARM == 7 {
 				return C_SCON
 			}
 			if x, y := immrot2a(uint32(c.instoffset)); x != 0 && y != 0 {
@@ -3044,7 +3045,7 @@ func (c *ctxt5) omvl(p *obj.Prog, a *obj.Addr, dr int) uint32 {
 
 func (c *ctxt5) chipzero5(e float64) int {
 	// We use GOARM=7 to gate the use of VFPv3 vmov (imm) instructions.
-	if objabi.GOARM < 7 || math.Float64bits(e) != 0 {
+	if buildcfg.GOARM < 7 || math.Float64bits(e) != 0 {
 		return -1
 	}
 	return 0
@@ -3052,7 +3053,7 @@ func (c *ctxt5) chipzero5(e float64) int {
 
 func (c *ctxt5) chipfloat5(e float64) int {
 	// We use GOARM=7 to gate the use of VFPv3 vmov (imm) instructions.
-	if objabi.GOARM < 7 {
+	if buildcfg.GOARM < 7 {
 		return -1
 	}
 
diff --git a/src/cmd/internal/obj/arm/obj5.go b/src/cmd/internal/obj/arm/obj5.go
index edb384806b..1454d8a7c9 100644
--- a/src/cmd/internal/obj/arm/obj5.go
+++ b/src/cmd/internal/obj/arm/obj5.go
@@ -34,6 +34,7 @@ import (
 	"cmd/internal/obj"
 	"cmd/internal/objabi"
 	"cmd/internal/sys"
+	"internal/buildcfg"
 	"log"
 )
 
@@ -64,7 +65,7 @@ func progedit(ctxt *obj.Link, p *obj.Prog, newprog obj.ProgAlloc) {
 				ctxt.Diag("%v: TLS MRC instruction must write to R0 as it might get translated into a BL instruction", p.Line())
 			}
 
-			if objabi.GOARM < 7 {
+			if buildcfg.GOARM < 7 {
 				// Replace it with BL runtime.read_tls_fallback(SB) for ARM CPUs that lack the tls extension.
 				if progedit_tlsfallback == nil {
 					progedit_tlsfallback = ctxt.Lookup("runtime.read_tls_fallback")
diff --git a/src/cmd/internal/obj/arm64/obj7.go b/src/cmd/internal/obj/arm64/obj7.go
index 514991e340..e41fb3bb75 100644
--- a/src/cmd/internal/obj/arm64/obj7.go
+++ b/src/cmd/internal/obj/arm64/obj7.go
@@ -35,6 +35,7 @@ import (
 	"cmd/internal/objabi"
 	"cmd/internal/src"
 	"cmd/internal/sys"
+	"internal/buildcfg"
 	"log"
 	"math"
 )
@@ -576,7 +577,7 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
 				q1.To.Reg = REGSP
 				q1.Spadj = c.autosize
 
-				if objabi.GOOS == "ios" {
+				if buildcfg.GOOS == "ios" {
 					// iOS does not support SA_ONSTACK. We will run the signal handler
 					// on the G stack. If we write below SP, it may be clobbered by
 					// the signal handler. So we save LR after decrementing SP.
diff --git a/src/cmd/internal/obj/sym.go b/src/cmd/internal/obj/sym.go
index 98c7364e2a..9e8b4dd790 100644
--- a/src/cmd/internal/obj/sym.go
+++ b/src/cmd/internal/obj/sym.go
@@ -35,6 +35,7 @@ import (
 	"cmd/internal/goobj"
 	"cmd/internal/objabi"
 	"fmt"
+	"internal/buildcfg"
 	"log"
 	"math"
 	"sort"
@@ -49,8 +50,8 @@ func Linknew(arch *LinkArch) *Link {
 	ctxt.Arch = arch
 	ctxt.Pathname = objabi.WorkingDir()
 
-	if err := ctxt.Headtype.Set(objabi.GOOS); err != nil {
-		log.Fatalf("unknown goos %s", objabi.GOOS)
+	if err := ctxt.Headtype.Set(buildcfg.GOOS); err != nil {
+		log.Fatalf("unknown goos %s", buildcfg.GOOS)
 	}
 
 	ctxt.Flag_optimize = true
diff --git a/src/cmd/internal/obj/util.go b/src/cmd/internal/obj/util.go
index 1c34b4e833..e8441a6969 100644
--- a/src/cmd/internal/obj/util.go
+++ b/src/cmd/internal/obj/util.go
@@ -8,6 +8,7 @@ import (
 	"bytes"
 	"cmd/internal/objabi"
 	"fmt"
+	"internal/buildcfg"
 	"io"
 	"strings"
 )
@@ -83,7 +84,7 @@ func CConv(s uint8) string {
 	}
 	for i := range opSuffixSpace {
 		sset := &opSuffixSpace[i]
-		if sset.arch == objabi.GOARCH {
+		if sset.arch == buildcfg.GOARCH {
 			return sset.cconv(s)
 		}
 	}
@@ -330,7 +331,7 @@ func writeDconv(w io.Writer, p *Prog, a *Addr, abiDetail bool) {
 	case TYPE_SHIFT:
 		v := int(a.Offset)
 		ops := "<<>>->@>"
-		switch objabi.GOARCH {
+		switch buildcfg.GOARCH {
 		case "arm":
 			op := ops[((v>>5)&3)<<1:]
 			if v&(1<<4) != 0 {
@@ -346,7 +347,7 @@ func writeDconv(w io.Writer, p *Prog, a *Addr, abiDetail bool) {
 			r := (v >> 16) & 31
 			fmt.Fprintf(w, "%s%c%c%d", Rconv(r+RBaseARM64), op[0], op[1], (v>>10)&63)
 		default:
-			panic("TYPE_SHIFT is not supported on " + objabi.GOARCH)
+			panic("TYPE_SHIFT is not supported on " + buildcfg.GOARCH)
 		}
 
 	case TYPE_REGREG:
diff --git a/src/cmd/internal/obj/x86/asm6.go b/src/cmd/internal/obj/x86/asm6.go
index 52ac567a36..17fa76727e 100644
--- a/src/cmd/internal/obj/x86/asm6.go
+++ b/src/cmd/internal/obj/x86/asm6.go
@@ -36,6 +36,7 @@ import (
 	"cmd/internal/sys"
 	"encoding/binary"
 	"fmt"
+	"internal/buildcfg"
 	"log"
 	"strings"
 )
@@ -2460,7 +2461,7 @@ func instinit(ctxt *obj.Link) {
 	}
 }
 
-var isAndroid = objabi.GOOS == "android"
+var isAndroid = buildcfg.GOOS == "android"
 
 func prefixof(ctxt *obj.Link, a *obj.Addr) int {
 	if a.Reg < REG_CS && a.Index < REG_CS { // fast path
diff --git a/src/cmd/internal/obj/x86/obj6.go b/src/cmd/internal/obj/x86/obj6.go
index 06736d43bd..e2732d53e3 100644
--- a/src/cmd/internal/obj/x86/obj6.go
+++ b/src/cmd/internal/obj/x86/obj6.go
@@ -35,6 +35,7 @@ import (
 	"cmd/internal/objabi"
 	"cmd/internal/src"
 	"cmd/internal/sys"
+	"internal/buildcfg"
 	"log"
 	"math"
 	"path"
@@ -646,13 +647,13 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
 
 	var regg int16
 	if !p.From.Sym.NoSplit() || p.From.Sym.Wrapper() {
-		if ctxt.Arch.Family == sys.AMD64 && objabi.Experiment.RegabiG && cursym.ABI() == obj.ABIInternal {
+		if ctxt.Arch.Family == sys.AMD64 && buildcfg.Experiment.RegabiG && cursym.ABI() == obj.ABIInternal {
 			regg = REGG // use the g register directly in ABIInternal
 		} else {
 			p = obj.Appendp(p, newprog)
 			regg = REG_CX
 			if ctxt.Arch.Family == sys.AMD64 {
-				// Using this register means that stacksplit works w/ //go:registerparams even when !objabi.Experiment.RegabiG
+				// Using this register means that stacksplit works w/ //go:registerparams even when !buildcfg.Experiment.RegabiG
 				regg = REGG // == REG_R14
 			}
 			p = load_g(ctxt, p, newprog, regg) // load g into regg
diff --git a/src/cmd/internal/objabi/exp.go b/src/cmd/internal/objabi/exp.go
deleted file mode 100644
index 3371c6c8f8..0000000000
--- a/src/cmd/internal/objabi/exp.go
+++ /dev/null
@@ -1,151 +0,0 @@
-// 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 objabi
-
-import (
-	"fmt"
-	"os"
-	"reflect"
-	"strings"
-
-	"internal/goexperiment"
-)
-
-// Experiment contains the toolchain experiments enabled for the
-// current build.
-//
-// (This is not necessarily the set of experiments the compiler itself
-// was built with.)
-var Experiment goexperiment.Flags = parseExperiments()
-
-// experimentBaseline specifies the experiment flags that are enabled by
-// default in the current toolchain. This is, in effect, the "control"
-// configuration and any variation from this is an experiment.
-var experimentBaseline goexperiment.Flags
-
-// FramePointerEnabled enables the use of platform conventions for
-// saving frame pointers.
-//
-// This used to be an experiment, but now it's always enabled on
-// platforms that support it.
-//
-// Note: must agree with runtime.framepointer_enabled.
-var FramePointerEnabled = GOARCH == "amd64" || GOARCH == "arm64"
-
-func parseExperiments() goexperiment.Flags {
-	// Start with the statically enabled set of experiments.
-	flags := experimentBaseline
-
-	// Pick up any changes to the baseline configuration from the
-	// GOEXPERIMENT environment. This can be set at make.bash time
-	// and overridden at build time.
-	env := envOr("GOEXPERIMENT", defaultGOEXPERIMENT)
-
-	if env != "" {
-		// Create a map of known experiment names.
-		names := make(map[string]reflect.Value)
-		rv := reflect.ValueOf(&flags).Elem()
-		rt := rv.Type()
-		for i := 0; i < rt.NumField(); i++ {
-			field := rv.Field(i)
-			names[strings.ToLower(rt.Field(i).Name)] = field
-		}
-
-		// Parse names.
-		for _, f := range strings.Split(env, ",") {
-			if f == "" {
-				continue
-			}
-			if f == "none" {
-				// GOEXPERIMENT=none disables all experiment flags.
-				// This is used by cmd/dist, which doesn't know how
-				// to build with any experiment flags.
-				flags = goexperiment.Flags{}
-				continue
-			}
-			val := true
-			if strings.HasPrefix(f, "no") {
-				f, val = f[2:], false
-			}
-			field, ok := names[f]
-			if !ok {
-				fmt.Printf("unknown experiment %s\n", f)
-				os.Exit(2)
-			}
-			field.SetBool(val)
-		}
-	}
-
-	// regabi is only supported on amd64.
-	if GOARCH != "amd64" {
-		flags.Regabi = false
-		flags.RegabiWrappers = false
-		flags.RegabiG = false
-		flags.RegabiReflect = false
-		flags.RegabiDefer = false
-		flags.RegabiArgs = false
-	}
-	// Setting regabi sets working sub-experiments.
-	if flags.Regabi {
-		flags.RegabiWrappers = true
-		flags.RegabiG = true
-		flags.RegabiReflect = true
-		flags.RegabiDefer = true
-		// Not ready yet:
-		//flags.RegabiArgs = true
-	}
-	// Check regabi dependencies.
-	if flags.RegabiG && !flags.RegabiWrappers {
-		panic("GOEXPERIMENT regabig requires regabiwrappers")
-	}
-	if flags.RegabiArgs && !(flags.RegabiWrappers && flags.RegabiG && flags.RegabiReflect && flags.RegabiDefer) {
-		panic("GOEXPERIMENT regabiargs requires regabiwrappers,regabig,regabireflect,regabidefer")
-	}
-	return flags
-}
-
-// expList returns the list of lower-cased experiment names for
-// experiments that differ from base. base may be nil to indicate no
-// experiments. If all is true, then include all experiment flags,
-// regardless of base.
-func expList(exp, base *goexperiment.Flags, all bool) []string {
-	var list []string
-	rv := reflect.ValueOf(exp).Elem()
-	var rBase reflect.Value
-	if base != nil {
-		rBase = reflect.ValueOf(base).Elem()
-	}
-	rt := rv.Type()
-	for i := 0; i < rt.NumField(); i++ {
-		name := strings.ToLower(rt.Field(i).Name)
-		val := rv.Field(i).Bool()
-		baseVal := false
-		if base != nil {
-			baseVal = rBase.Field(i).Bool()
-		}
-		if all || val != baseVal {
-			if val {
-				list = append(list, name)
-			} else {
-				list = append(list, "no"+name)
-			}
-		}
-	}
-	return list
-}
-
-// GOEXPERIMENT is a comma-separated list of enabled or disabled
-// experiments that differ from the baseline experiment configuration.
-// GOEXPERIMENT is exactly what a user would set on the command line
-// to get the set of enabled experiments.
-func GOEXPERIMENT() string {
-	return strings.Join(expList(&Experiment, &experimentBaseline, false), ",")
-}
-
-// EnabledExperiments returns a list of enabled experiments, as
-// lower-cased experiment names.
-func EnabledExperiments() []string {
-	return expList(&Experiment, nil, false)
-}
diff --git a/src/cmd/internal/objabi/flag.go b/src/cmd/internal/objabi/flag.go
index 9fcab4cc85..e41fc570b0 100644
--- a/src/cmd/internal/objabi/flag.go
+++ b/src/cmd/internal/objabi/flag.go
@@ -8,6 +8,7 @@ import (
 	"bytes"
 	"flag"
 	"fmt"
+	"internal/buildcfg"
 	"io"
 	"io/ioutil"
 	"log"
@@ -96,11 +97,11 @@ func (versionFlag) Set(s string) error {
 	if s == "goexperiment" {
 		// test/run.go uses this to discover the full set of
 		// experiment tags. Report everything.
-		p = " X:" + strings.Join(expList(&Experiment, nil, true), ",")
+		p = " X:" + strings.Join(buildcfg.AllExperiments(), ",")
 	} else {
 		// If the enabled experiments differ from the defaults,
 		// include that difference.
-		if goexperiment := GOEXPERIMENT(); goexperiment != "" {
+		if goexperiment := buildcfg.GOEXPERIMENT(); goexperiment != "" {
 			p = " X:" + goexperiment
 		}
 	}
@@ -111,12 +112,12 @@ func (versionFlag) Set(s string) error {
 	// build ID of the binary, so that if the compiler is changed and
 	// rebuilt, we notice and rebuild all packages.
 	if s == "full" {
-		if strings.HasPrefix(Version, "devel") {
+		if strings.HasPrefix(buildcfg.Version, "devel") {
 			p += " buildID=" + buildID
 		}
 	}
 
-	fmt.Printf("%s version %s%s\n", name, Version, p)
+	fmt.Printf("%s version %s%s\n", name, buildcfg.Version, p)
 	os.Exit(0)
 	return nil
 }
diff --git a/src/cmd/internal/objabi/line.go b/src/cmd/internal/objabi/line.go
index 0733b65138..0b1e0bb181 100644
--- a/src/cmd/internal/objabi/line.go
+++ b/src/cmd/internal/objabi/line.go
@@ -5,6 +5,7 @@
 package objabi
 
 import (
+	"internal/buildcfg"
 	"os"
 	"path/filepath"
 	"strings"
@@ -38,8 +39,8 @@ func AbsFile(dir, file, rewrites string) string {
 	}
 
 	abs, rewritten := ApplyRewrites(abs, rewrites)
-	if !rewritten && hasPathPrefix(abs, GOROOT) {
-		abs = "$GOROOT" + abs[len(GOROOT):]
+	if !rewritten && hasPathPrefix(abs, buildcfg.GOROOT) {
+		abs = "$GOROOT" + abs[len(buildcfg.GOROOT):]
 	}
 
 	if abs == "" {
diff --git a/src/cmd/internal/objabi/stack.go b/src/cmd/internal/objabi/stack.go
index 1f531176cc..0c82a7c6dd 100644
--- a/src/cmd/internal/objabi/stack.go
+++ b/src/cmd/internal/objabi/stack.go
@@ -4,6 +4,8 @@
 
 package objabi
 
+import "internal/buildcfg"
+
 // For the linkers. Must match Go definitions.
 
 const (
@@ -22,7 +24,7 @@ var StackLimit = StackGuard - StackSystem - StackSmall
 // builds that have larger stack frames or for specific targets.
 func stackGuardMultiplier() int {
 	// On AIX, a larger stack is needed for syscalls.
-	if GOOS == "aix" {
+	if buildcfg.GOOS == "aix" {
 		return 2
 	}
 	return stackGuardMultiplierDefault
diff --git a/src/cmd/internal/objabi/util.go b/src/cmd/internal/objabi/util.go
index 5a7a74cfde..63640950d9 100644
--- a/src/cmd/internal/objabi/util.go
+++ b/src/cmd/internal/objabi/util.go
@@ -6,32 +6,9 @@ package objabi
 
 import (
 	"fmt"
-	"log"
-	"os"
 	"strings"
-)
-
-func envOr(key, value string) string {
-	if x := os.Getenv(key); x != "" {
-		return x
-	}
-	return value
-}
 
-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
+	"internal/buildcfg"
 )
 
 const (
@@ -39,94 +16,10 @@ const (
 	MachoRelocOffset = 2048 // reserve enough space for ELF relocations
 )
 
-func goarm() int {
-	def := defaultGOARM
-	if GOOS == "android" && GOARCH == "arm" {
-		// Android arm devices always support GOARM=7.
-		def = "7"
-	}
-	switch v := envOr("GOARM", def); v {
-	case "5":
-		return 5
-	case "6":
-		return 6
-	case "7":
-		return 7
-	}
-	// Fail here, rather than validate at multiple call sites.
-	log.Fatalf("Invalid GOARM value. Must be 5, 6, or 7.")
-	panic("unreachable")
-}
-
-func gomips() string {
-	switch v := envOr("GOMIPS", defaultGOMIPS); v {
-	case "hardfloat", "softfloat":
-		return v
-	}
-	log.Fatalf("Invalid GOMIPS value. Must be hardfloat or softfloat.")
-	panic("unreachable")
-}
-
-func gomips64() string {
-	switch v := envOr("GOMIPS64", defaultGOMIPS64); v {
-	case "hardfloat", "softfloat":
-		return v
-	}
-	log.Fatalf("Invalid GOMIPS64 value. Must be hardfloat or softfloat.")
-	panic("unreachable")
-}
-
-func goppc64() int {
-	switch v := envOr("GOPPC64", defaultGOPPC64); v {
-	case "power8":
-		return 8
-	case "power9":
-		return 9
-	}
-	log.Fatalf("Invalid GOPPC64 value. Must be power8 or power9.")
-	panic("unreachable")
-}
-
-type gowasmFeatures struct {
-	SignExt bool
-	SatConv bool
-}
-
-func (f gowasmFeatures) String() string {
-	var flags []string
-	if f.SatConv {
-		flags = append(flags, "satconv")
-	}
-	if f.SignExt {
-		flags = append(flags, "signext")
-	}
-	return strings.Join(flags, ",")
-}
-
-func gowasm() (f gowasmFeatures) {
-	for _, opt := range strings.Split(envOr("GOWASM", ""), ",") {
-		switch opt {
-		case "satconv":
-			f.SatConv = true
-		case "signext":
-			f.SignExt = true
-		case "":
-			// ignore
-		default:
-			log.Fatalf("Invalid GOWASM value. No such feature: " + opt)
-		}
-	}
-	return
-}
-
-func Getgoextlinkenabled() string {
-	return envOr("GO_EXTLINK_ENABLED", defaultGO_EXTLINK_ENABLED)
-}
-
 // HeaderString returns the toolchain configuration string written in
 // Go object headers. This string ensures we don't attempt to import
 // or link object files that are incompatible with each other. This
 // string always starts with "go object ".
 func HeaderString() string {
-	return fmt.Sprintf("go object %s %s %s X:%s\n", GOOS, GOARCH, Version, strings.Join(EnabledExperiments(), ","))
+	return fmt.Sprintf("go object %s %s %s X:%s\n", buildcfg.GOOS, buildcfg.GOARCH, buildcfg.Version, strings.Join(buildcfg.EnabledExperiments(), ","))
 }