cmd/go, cmd/dist: introduce GOMIPS environment variable

GOMIPS is a GOARCH=mips{,le} specific option, for a choice between
hard-float and soft-float. Valid values are 'hardfloat' (default) and
'softfloat'. It is passed to the assembler as
'GOMIPS_{hardfloat,softfloat}'.

Note: GOMIPS will later also be used for a choice of MIPS instruction
set (mips32/mips32r2).

Updates #18162

Change-Id: I35417db8625695f09d6ccc3042431dd2eaa756a6
Reviewed-on: https://go-review.googlesource.com/37954
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>

doc/asm.html

@@ -876,6 +876,12 @@ Addressing modes:
 
 </ul>
 
+<p>
+The value of <code>GOMIPS</code> environment variable (<code>hardfloat</code> or
+<code>softfloat</code>) is made available to assembly code by predefining either
+<code>GOMIPS_hardfloat</code> or <code>GOMIPS_softfloat</code>.
+</p>
+
 <h3 id="unsupported_opcodes">Unsupported opcodes</h3>
 
 <p>

src/cmd/dist/build.go

@@ -30,6 +30,7 @@ var (
 	goos             string
 	goarm            string
 	go386            string
+	gomips           string
 	goroot           string
 	goroot_final     string
 	goextlinkenabled string
@@ -138,6 +139,12 @@ func xinit() {
 	}
 	go386 = b
 
+	b = os.Getenv("GOMIPS")
+	if b == "" {
+		b = "hardfloat"
+	}
+	gomips = b
+
 	if p := pathf("%s/src/all.bash", goroot); !isfile(p) {
 		fatalf("$GOROOT is not set correctly or not exported\n"+
 			"\tGOROOT=%s\n"+
@@ -194,6 +201,7 @@ func xinit() {
 	os.Setenv("GOHOSTARCH", gohostarch)
 	os.Setenv("GOHOSTOS", gohostos)
 	os.Setenv("GOOS", goos)
+	os.Setenv("GOMIPS", gomips)
 	os.Setenv("GOROOT", goroot)
 	os.Setenv("GOROOT_FINAL", goroot_final)
 
@@ -804,6 +812,11 @@ func runInstall(dir string, ch chan struct{}) {
 			"-D", "GOOS_GOARCH_" + goos + "_" + goarch,
 		}
 
+		if goarch == "mips" || goarch == "mipsle" {
+			// Define GOMIPS_value from gomips.
+			compile = append(compile, "-D", "GOMIPS_"+gomips)
+		}
+
 		doclean := true
 		b := pathf("%s/%s", workdir, filepath.Base(p))
 
@@ -1042,6 +1055,9 @@ func cmdenv() {
 	if goarch == "386" {
 		xprintf(format, "GO386", go386)
 	}
+	if goarch == "mips" || goarch == "mipsle" {
+		xprintf(format, "GOMIPS", gomips)
+	}
 
 	if *path {
 		sep := ":"

src/cmd/dist/buildruntime.go

@@ -46,6 +46,7 @@ func mkzversion(dir, file string) {
 //	const defaultGOROOT = <goroot>
 //	const defaultGO386 = <go386>
 //	const defaultGOARM = <goarm>
+//	const defaultGOMIPS = <gomips>
 //	const defaultGOOS = runtime.GOOS
 //	const defaultGOARCH = runtime.GOARCH
 //	const defaultGO_EXTLINK_ENABLED = <goextlinkenabled>
@@ -73,6 +74,7 @@ func mkzbootstrap(file string) {
 	fmt.Fprintf(&buf, "const defaultGOROOT = `%s`\n", goroot_final)
 	fmt.Fprintf(&buf, "const defaultGO386 = `%s`\n", go386)
 	fmt.Fprintf(&buf, "const defaultGOARM = `%s`\n", goarm)
+	fmt.Fprintf(&buf, "const defaultGOMIPS = `%s`\n", gomips)
 	fmt.Fprintf(&buf, "const defaultGOOS = runtime.GOOS\n")
 	fmt.Fprintf(&buf, "const defaultGOARCH = runtime.GOARCH\n")
 	fmt.Fprintf(&buf, "const defaultGO_EXTLINK_ENABLED = `%s`\n", goextlinkenabled)

src/cmd/go/alldocs.go

@@ -1199,6 +1199,9 @@
 // 	GO386
 // 		For GOARCH=386, the floating point instruction set.
 // 		Valid values are 387, sse2.
+//	GOMIPS
+//		For GOARCH=mips{,le}, whether to use floating point instructions.
+//		Valid values are hardfloat (default), softfloat.
 //
 // Special-purpose environment variables:
 //

src/cmd/go/internal/cfg/cfg.go

@@ -85,6 +85,7 @@ var (
 	// Used in envcmd.MkEnv and build ID computations.
 	GOARM  = fmt.Sprint(objabi.GOARM)
 	GO386  = objabi.GO386
+	GOMIPS = objabi.GOMIPS
 )
 
 // Update build context to use our computed GOROOT.

src/cmd/go/internal/envcmd/env.go

@@ -76,6 +76,8 @@ func MkEnv() []cfg.EnvVar {
 		env = append(env, cfg.EnvVar{Name: "GOARM", Value: cfg.GOARM})
 	case "386":
 		env = append(env, cfg.EnvVar{Name: "GO386", Value: cfg.GO386})
+	case "mips", "mipsle":
+		env = append(env, cfg.EnvVar{Name: "GOMIPS", Value: cfg.GOMIPS})
 	}
 
 	cc := cfg.DefaultCC(cfg.Goos, cfg.Goarch)

src/cmd/go/internal/help/helpdoc.go

@@ -511,6 +511,9 @@ Architecture-specific environment variables:
 	GO386
 		For GOARCH=386, the floating point instruction set.
 		Valid values are 387, sse2.
+	GOMIPS
+		For GOARCH=mips{,le}, whether to use floating point instructions.
+		Valid values are hardfloat (default), softfloat.
 
 Special-purpose environment variables:
 

src/cmd/go/internal/work/gc.go

@@ -221,6 +221,12 @@ func (gcToolchain) asm(b *Builder, a *Action, sfiles []string) ([]string, error)
 			}
 		}
 	}
+
+	if cfg.Goarch == "mips" || cfg.Goarch == "mipsle" {
+		// Define GOMIPS_value from cfg.GOMIPS.
+		args = append(args, "-D", "GOMIPS_"+cfg.GOMIPS)
+	}
+
 	var ofiles []string
 	for _, sfile := range sfiles {
 		ofile := a.Objdir + sfile[:len(sfile)-len(".s")] + ".o"

src/cmd/internal/objabi/util.go

@@ -24,6 +24,7 @@ var (
 	GOOS    = envOr("GOOS", defaultGOOS)
 	GO386   = envOr("GO386", defaultGO386)
 	GOARM   = goarm()
+	GOMIPS  = gomips()
 	Version = version
 )
 
@@ -41,6 +42,15 @@ func goarm() int {
 	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 Getgoextlinkenabled() string {
 	return envOr("GO_EXTLINK_ENABLED", defaultGO_EXTLINK_ENABLED)
 }