cmd/go: include GOARM and GO386 in computed build ID

Now:
$ GOARCH=arm GOARM=5 go install -x cmd/go
... followed by:
$ GOARCH=arm GOARM= go install -x cmd/go

... actually does work. Previously the second "go install" would reuse
the cached binaries from the GOARM=5 command and not rebuild.
(Or vice versa from GOARM= to GOARM=5)

And do the same for GO386.

Fixes #9737

Change-Id: I9630aab34d06465d5033e6743dfe6592c8247aa0
Reviewed-on: https://go-review.googlesource.com/43855
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/cmd/go/go_test.go

@@ -4138,3 +4138,42 @@ func TestGoTestRaceCoverModeFailures(t *testing.T) {
 	tg.grepStderr(`-covermode must be "atomic", not "set", when -race is enabled`, "-race -covermode=set was allowed")
 	tg.grepBothNot("PASS", "something passed")
 }
+
+// Issue 9737: verify that GOARM and GO386 affect the computed build ID.
+func TestBuildIDContainsArchModeEnv(t *testing.T) {
+	if testing.Short() {
+		t.Skip("skipping in short mode")
+	}
+
+	var tg *testgoData
+	testWith := func(before, after func()) func(*testing.T) {
+		return func(t *testing.T) {
+			tg = testgo(t)
+			defer tg.cleanup()
+			tg.tempFile("src/mycmd/x.go", `package main
+func main() {}`)
+			tg.setenv("GOPATH", tg.path("."))
+
+			tg.cd(tg.path("src/mycmd"))
+			tg.setenv("GOOS", "linux")
+			before()
+			tg.run("install", "mycmd")
+			after()
+			tg.wantStale("mycmd", "build ID mismatch", "should be stale after environment variable change")
+		}
+	}
+
+	t.Run("386", testWith(func() {
+		tg.setenv("GOARCH", "386")
+		tg.setenv("GO386", "387")
+	}, func() {
+		tg.setenv("GO386", "")
+	}))
+
+	t.Run("arm", testWith(func() {
+		tg.setenv("GOARCH", "arm")
+		tg.setenv("GOARM", "5")
+	}, func() {
+		tg.setenv("GOARM", "7")
+	}))
+}

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

@@ -7,10 +7,13 @@
 package cfg
 
 import (
+	"fmt"
 	"go/build"
 	"os"
 	"path/filepath"
 	"runtime"
+
+	"cmd/internal/objabi"
 )
 
 // These are general "build flags" used by build and other commands.
@@ -69,6 +72,10 @@ var (
 	GOROOTbin = filepath.Join(GOROOT, "bin")
 	GOROOTpkg = filepath.Join(GOROOT, "pkg")
 	GOROOTsrc = filepath.Join(GOROOT, "src")
+
+	// Used in envcmd.MkEnv and build ID computations.
+	GOARM = fmt.Sprint(objabi.GOARM)
+	GO386 = objabi.GO386
 )
 
 func findGOROOT() string {

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

@@ -68,9 +68,9 @@ func MkEnv() []cfg.EnvVar {
 
 	switch cfg.Goarch {
 	case "arm":
-		env = append(env, cfg.EnvVar{Name: "GOARM", Value: os.Getenv("GOARM")})
+		env = append(env, cfg.EnvVar{Name: "GOARM", Value: cfg.GOARM})
 	case "386":
-		env = append(env, cfg.EnvVar{Name: "GO386", Value: os.Getenv("GO386")})
+		env = append(env, cfg.EnvVar{Name: "GO386", Value: cfg.GO386})
 	}
 
 	cmd := b.GccCmd(".")

src/cmd/go/internal/load/pkg.go

@@ -1651,6 +1651,14 @@ func computeBuildID(p *Package) {
 			base.Fatalf("go: %s", err)
 		}
 		fmt.Fprintf(h, "zversion %q\n", string(data))
+
+		// Add environment variables that affect code generation.
+		switch cfg.BuildContext.GOARCH {
+		case "arm":
+			fmt.Fprintf(h, "GOARM=%s\n", cfg.GOARM)
+		case "386":
+			fmt.Fprintf(h, "GO386=%s\n", cfg.GO386)
+		}
 	}
 
 	// Include the build IDs of any dependencies in the hash.