cmd/dist: leave cgo enabled if external linking is required

Certain ios and android configurations do not yet support internal
linking.

On ios, attempting to build without cgo causes tests to fail on
essentially every run (golang#57961).

On android, it produces a lot of warning spam from the linker,
obscuring real problems.

Since external linking makes the result of `go install` depend on the
installed C toolchain either way, the reproducibility benefit of
disabling cgo seems minimal on these platforms anyway.

Fixes golang#57961.
For golang#24904.
Updates golang#57007.

Change-Id: Ied2454804e958dd670467db3d5e9ab50a40bb899
Reviewed-on: https://go-review.googlesource.com/c/go/+/463739
Reviewed-by: Russ Cox <[email protected]>
Run-TryBot: Bryan Mills <[email protected]>
Auto-Submit: Bryan Mills <[email protected]>
Reviewed-by: Cherry Mui <[email protected]>
TryBot-Bypass: Bryan Mills <[email protected]>

src/cmd/dist/build.go

@@ -55,6 +55,7 @@ var (
 
 	rebuildall bool
 	noOpt      bool
+	isRelease  bool
 
 	vflag int // verbosity
 )
@@ -257,6 +258,9 @@ func xinit() {
 	xatexit(rmworkdir)
 
 	tooldir = pathf("%s/pkg/tool/%s_%s", goroot, gohostos, gohostarch)
+
+	goversion := findgoversion()
+	isRelease = strings.HasPrefix(goversion, "release.") || strings.HasPrefix(goversion, "go")
 }
 
 // compilerEnv returns a map from "goos/goarch" to the
@@ -302,7 +306,7 @@ func compilerEnv(envName, def string) map[string]string {
 
 // clangos lists the operating systems where we prefer clang to gcc.
 var clangos = []string{
-	"darwin",  // macOS 10.9 and later require clang
+	"darwin", "ios", // macOS 10.9 and later require clang
 	"freebsd", // FreeBSD 10 and later do not ship gcc
 	"openbsd", // OpenBSD ships with GCC 4.2, which is now quite old.
 }
@@ -519,8 +523,6 @@ func setup() {
 	}
 
 	// Special release-specific setup.
-	goversion := findgoversion()
-	isRelease := strings.HasPrefix(goversion, "release.") || (strings.HasPrefix(goversion, "go") && !strings.Contains(goversion, "beta"))
 	if isRelease {
 		// Make sure release-excluded things are excluded.
 		for _, dir := range unreleased {
@@ -529,20 +531,29 @@ func setup() {
 			}
 		}
 	}
-	if isRelease || os.Getenv("GO_BUILDER_NAME") != "" {
-		// Add -trimpath for reproducible builds of releases.
-		// Include builders so that -trimpath is well-tested ahead of releases.
-		// Do not include local development, so that people working in the
-		// main branch for day-to-day work on the Go toolchain itself can
-		// still have full paths for stack traces for compiler crashes and the like.
-		// toolenv = append(toolenv, "GOFLAGS=-trimpath")
-	}
 }
 
 /*
  * Tool building
  */
 
+// mustLinkExternal is a copy of internal/platform.MustLinkExternal,
+// duplicated here to avoid version skew in the MustLinkExternal function
+// during bootstrapping.
+func mustLinkExternal(goos, goarch string) bool {
+	switch goos {
+	case "android":
+		if goarch != "arm64" {
+			return true
+		}
+	case "ios":
+		if goarch == "arm64" {
+			return true
+		}
+	}
+	return false
+}
+
 // deptab lists changes to the default dependencies for a given prefix.
 // deps ending in /* read the whole directory; deps beginning with -
 // exclude files with that prefix.
@@ -1266,14 +1277,33 @@ func timelog(op, name string) {
 	fmt.Fprintf(timeLogFile, "%s %+.1fs %s %s\n", t.Format(time.UnixDate), t.Sub(timeLogStart).Seconds(), op, name)
 }
 
-// toolenv is the environment to use when building cmd.
-// We disable cgo to get static binaries for cmd/go and cmd/pprof,
-// so that they work on systems without the same dynamic libraries
-// as the original build system.
-// In release branches, we add -trimpath for reproducible builds.
-// In the main branch we leave it off, so that compiler crashes and
-// the like have full path names for easier navigation to source files.
-var toolenv = []string{"CGO_ENABLED=0"}
+// toolenv returns the environment to use when building commands in cmd.
+//
+// This is a function instead of a variable because the exact toolenv depends
+// on the GOOS and GOARCH, and (at least for now) those are modified in place
+// to switch between the host and target configurations when cross-compiling.
+func toolenv() []string {
+	var env []string
+	if !mustLinkExternal(goos, goarch) {
+		// Unless the platform requires external linking,
+		// we disable cgo to get static binaries for cmd/go and cmd/pprof,
+		// so that they work on systems without the same dynamic libraries
+		// as the original build system.
+		env = append(env, "CGO_ENABLED=0")
+	}
+	if isRelease || os.Getenv("GO_BUILDER_NAME") != "" {
+		// Add -trimpath for reproducible builds of releases.
+		// Include builders so that -trimpath is well-tested ahead of releases.
+		// Do not include local development, so that people working in the
+		// main branch for day-to-day work on the Go toolchain itself can
+		// still have full paths for stack traces for compiler crashes and the like.
+		//
+		// TODO(bcmills): This was added but commented out in CL 454836.
+		// Uncomment or delete it.
+		// env = append(env, "GOFLAGS=-trimpath")
+	}
+	return env
+}
 
 var toolchain = []string{"cmd/asm", "cmd/cgo", "cmd/compile", "cmd/link"}
 
@@ -1414,7 +1444,7 @@ func cmdbootstrap() {
 	os.Setenv("CC", compilerEnvLookup("CC", defaultcc, goos, goarch))
 	// Now that cmd/go is in charge of the build process, enable GOEXPERIMENT.
 	os.Setenv("GOEXPERIMENT", goexperiment)
-	goInstall(toolenv, goBootstrap, toolchain...)
+	goInstall(toolenv(), goBootstrap, toolchain...)
 	if debug {
 		run("", ShowOutput|CheckExit, pathf("%s/compile", tooldir), "-V=full")
 		copyfile(pathf("%s/compile2", tooldir), pathf("%s/compile", tooldir), writeExec)
@@ -1441,7 +1471,7 @@ func cmdbootstrap() {
 		xprintf("\n")
 	}
 	xprintf("Building Go toolchain3 using go_bootstrap and Go toolchain2.\n")
-	goInstall(toolenv, goBootstrap, append([]string{"-a"}, toolchain...)...)
+	goInstall(toolenv(), goBootstrap, append([]string{"-a"}, toolchain...)...)
 	if debug {
 		run("", ShowOutput|CheckExit, pathf("%s/compile", tooldir), "-V=full")
 		copyfile(pathf("%s/compile3", tooldir), pathf("%s/compile", tooldir), writeExec)
@@ -1470,9 +1500,9 @@ func cmdbootstrap() {
 			xprintf("\n")
 		}
 		xprintf("Building commands for host, %s/%s.\n", goos, goarch)
-		goInstall(toolenv, goBootstrap, "cmd")
-		checkNotStale(toolenv, goBootstrap, "cmd")
-		checkNotStale(toolenv, gorootBinGo, "cmd")
+		goInstall(toolenv(), goBootstrap, "cmd")
+		checkNotStale(toolenv(), goBootstrap, "cmd")
+		checkNotStale(toolenv(), gorootBinGo, "cmd")
 
 		timelog("build", "target toolchain")
 		if vflag > 0 {
@@ -1486,15 +1516,15 @@ func cmdbootstrap() {
 		xprintf("Building packages and commands for target, %s/%s.\n", goos, goarch)
 	}
 	goInstall(nil, goBootstrap, "std")
-	goInstall(toolenv, goBootstrap, "cmd")
-	checkNotStale(toolenv, goBootstrap, append(toolchain, "runtime/internal/sys")...)
+	goInstall(toolenv(), goBootstrap, "cmd")
+	checkNotStale(toolenv(), goBootstrap, append(toolchain, "runtime/internal/sys")...)
 	checkNotStale(nil, goBootstrap, "std")
-	checkNotStale(toolenv, goBootstrap, "cmd")
+	checkNotStale(toolenv(), goBootstrap, "cmd")
 	checkNotStale(nil, gorootBinGo, "std")
-	checkNotStale(toolenv, gorootBinGo, "cmd")
+	checkNotStale(toolenv(), gorootBinGo, "cmd")
 	if debug {
 		run("", ShowOutput|CheckExit, pathf("%s/compile", tooldir), "-V=full")
-		checkNotStale(toolenv, goBootstrap, append(toolchain, "runtime/internal/sys")...)
+		checkNotStale(toolenv(), goBootstrap, append(toolchain, "runtime/internal/sys")...)
 		copyfile(pathf("%s/compile4", tooldir), pathf("%s/compile", tooldir), writeExec)
 	}
 

src/cmd/dist/build_test.go

@@ -0,0 +1,24 @@
+// Copyright 2023 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 (
+	"internal/platform"
+	"testing"
+)
+
+// TestMustLinkExternal verifies that the mustLinkExternal helper
+// function matches internal/platform.MustLinkExternal.
+func TestMustLinkExternal(t *testing.T) {
+	for _, goos := range okgoos {
+		for _, goarch := range okgoarch {
+			got := mustLinkExternal(goos, goarch)
+			want := platform.MustLinkExternal(goos, goarch)
+			if got != want {
+				t.Errorf("mustLinkExternal(%q, %q) = %v; want %v", goos, goarch, got, want)
+			}
+		}
+	}
+}

src/cmd/dist/test.go

@@ -149,7 +149,7 @@ func (t *tester) run() {
 	if t.rebuild {
 		t.out("Building packages and commands.")
 		// Force rebuild the whole toolchain.
-		goInstall(toolenv, gorootBinGo, append([]string{"-a"}, toolchain...)...)
+		goInstall(toolenv(), gorootBinGo, append([]string{"-a"}, toolchain...)...)
 	}
 
 	if !t.listMode {
@@ -166,9 +166,9 @@ func (t *tester) run() {
 			// and virtualization we usually start with a clean GOCACHE, so we would
 			// end up rebuilding large parts of the standard library that aren't
 			// otherwise relevant to the actual set of packages under test.
-			goInstall(toolenv, gorootBinGo, toolchain...)
-			goInstall(toolenv, gorootBinGo, toolchain...)
-			goInstall(toolenv, gorootBinGo, "cmd")
+			goInstall(toolenv(), gorootBinGo, toolchain...)
+			goInstall(toolenv(), gorootBinGo, toolchain...)
+			goInstall(toolenv(), gorootBinGo, "cmd")
 		}
 	}