src/cmd/dist/build.go

// Copyright 2012 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 (
	"bytes"
	"encoding/json"
	"flag"
	"fmt"
	"io/ioutil"
	"log"
	"os"
	"os/exec"
	"path/filepath"
	"regexp"
	"sort"
	"strings"
	"sync"
	"time"
)

// Initialization for any invocation.

// The usual variables.
var (
	goarch           string
	gorootBin        string
	gohostarch       string
	gohostos         string
	goos             string
	goarm            string
	go386            string
	goamd64          string
	gomips           string
	gomips64         string
	goppc64          string
	goroot           string
	goroot_final     string
	goextlinkenabled string
	gogcflags        string // For running built compiler
	goldflags        string
	goexperiment     string
	workdir          string
	tooldir          string
	oldgoos          string
	oldgoarch        string
	exe              string
	defaultcc        map[string]string
	defaultcxx       map[string]string
	defaultpkgconfig string
	defaultldso      string

	rebuildall   bool
	defaultclang bool

	vflag int // verbosity
)

// The known architectures.
var okgoarch = []string{
	"386",
	"amd64",
	"arm",
	"arm64",
	"mips",
	"mipsle",
	"mips64",
	"mips64le",
	"ppc64",
	"ppc64le",
	"riscv64",
	"s390x",
	"sparc64",
	"wasm",
}

// The known operating systems.
var okgoos = []string{
	"darwin",
	"dragonfly",
	"illumos",
	"ios",
	"js",
	"linux",
	"android",
	"solaris",
	"freebsd",
	"nacl", // keep;
	"netbsd",
	"openbsd",
	"plan9",
	"windows",
	"aix",
}

// find reports the first index of p in l[0:n], or else -1.
func find(p string, l []string) int {
	for i, s := range l {
		if p == s {
			return i
		}
	}
	return -1
}

// xinit handles initialization of the various global state, like goroot and goarch.
func xinit() {
	b := os.Getenv("GOROOT")
	if b == "" {
		fatalf("$GOROOT must be set")
	}
	goroot = filepath.Clean(b)
	gorootBin = pathf("%s/bin", goroot)

	b = os.Getenv("GOROOT_FINAL")
	if b == "" {
		b = goroot
	}
	goroot_final = b

	b = os.Getenv("GOOS")
	if b == "" {
		b = gohostos
	}
	goos = b
	if find(goos, okgoos) < 0 {
		fatalf("unknown $GOOS %s", goos)
	}

	b = os.Getenv("GOARM")
	if b == "" {
		b = xgetgoarm()
	}
	goarm = b

	b = os.Getenv("GO386")
	if b == "" {
		b = "sse2"
	}
	go386 = b

	b = os.Getenv("GOAMD64")
	if b == "" {
		b = "v1"
	}
	goamd64 = b

	b = os.Getenv("GOMIPS")
	if b == "" {
		b = "hardfloat"
	}
	gomips = b

	b = os.Getenv("GOMIPS64")
	if b == "" {
		b = "hardfloat"
	}
	gomips64 = b

	b = os.Getenv("GOPPC64")
	if b == "" {
		b = "power8"
	}
	goppc64 = b

	if p := pathf("%s/src/all.bash", goroot); !isfile(p) {
		fatalf("$GOROOT is not set correctly or not exported\n"+
			"\tGOROOT=%s\n"+
			"\t%s does not exist", goroot, p)
	}

	b = os.Getenv("GOHOSTARCH")
	if b != "" {
		gohostarch = b
	}
	if find(gohostarch, okgoarch) < 0 {
		fatalf("unknown $GOHOSTARCH %s", gohostarch)
	}

	b = os.Getenv("GOARCH")
	if b == "" {
		b = gohostarch
	}
	goarch = b
	if find(goarch, okgoarch) < 0 {
		fatalf("unknown $GOARCH %s", goarch)
	}

	b = os.Getenv("GO_EXTLINK_ENABLED")
	if b != "" {
		if b != "0" && b != "1" {
			fatalf("unknown $GO_EXTLINK_ENABLED %s", b)
		}
		goextlinkenabled = b
	}

	goexperiment = os.Getenv("GOEXPERIMENT")
	// TODO(mdempsky): Validate known experiments?

	gogcflags = os.Getenv("BOOT_GO_GCFLAGS")
	goldflags = os.Getenv("BOOT_GO_LDFLAGS")

	cc, cxx := "gcc", "g++"
	if defaultclang {
		cc, cxx = "clang", "clang++"
	}
	defaultcc = compilerEnv("CC", cc)
	defaultcxx = compilerEnv("CXX", cxx)

	b = os.Getenv("PKG_CONFIG")
	if b == "" {
		b = "pkg-config"
	}
	defaultpkgconfig = b

	defaultldso = os.Getenv("GO_LDSO")

	// For tools being invoked but also for os.ExpandEnv.
	os.Setenv("GO386", go386)
	os.Setenv("GOAMD64", goamd64)
	os.Setenv("GOARCH", goarch)
	os.Setenv("GOARM", goarm)
	os.Setenv("GOHOSTARCH", gohostarch)
	os.Setenv("GOHOSTOS", gohostos)
	os.Setenv("GOOS", goos)
	os.Setenv("GOMIPS", gomips)
	os.Setenv("GOMIPS64", gomips64)
	os.Setenv("GOPPC64", goppc64)
	os.Setenv("GOROOT", goroot)
	os.Setenv("GOROOT_FINAL", goroot_final)

	// Use a build cache separate from the default user one.
	// Also one that will be wiped out during startup, so that
	// make.bash really does start from a clean slate.
	os.Setenv("GOCACHE", pathf("%s/pkg/obj/go-build", goroot))

	// Set GOBIN to GOROOT/bin. The meaning of GOBIN has drifted over time
	// (see https://go.dev/issue/3269, https://go.dev/cl/183058,
	// https://go.dev/issue/31576). Since we want binaries installed by 'dist' to
	// always go to GOROOT/bin anyway.
	os.Setenv("GOBIN", gorootBin)

	// Make the environment more predictable.
	os.Setenv("LANG", "C")
	os.Setenv("LANGUAGE", "en_US.UTF8")
	os.Unsetenv("GO111MODULE")
	os.Setenv("GOENV", "off")
	os.Unsetenv("GOFLAGS")
	os.Setenv("GOWORK", "off")

	workdir = xworkdir()
	if err := ioutil.WriteFile(pathf("%s/go.mod", workdir), []byte("module bootstrap"), 0666); err != nil {
		fatalf("cannot write stub go.mod: %s", err)
	}
	xatexit(rmworkdir)

	tooldir = pathf("%s/pkg/tool/%s_%s", goroot, gohostos, gohostarch)
}

// compilerEnv returns a map from "goos/goarch" to the
// compiler setting to use for that platform.
// The entry for key "" covers any goos/goarch not explicitly set in the map.
// For example, compilerEnv("CC", "gcc") returns the C compiler settings
// read from $CC, defaulting to gcc.
//
// The result is a map because additional environment variables
// can be set to change the compiler based on goos/goarch settings.
// The following applies to all envNames but CC is assumed to simplify
// the presentation.
//
// If no environment variables are set, we use def for all goos/goarch.
// $CC, if set, applies to all goos/goarch but is overridden by the following.
// $CC_FOR_TARGET, if set, applies to all goos/goarch except gohostos/gohostarch,
// but is overridden by the following.
// If gohostos=goos and gohostarch=goarch, then $CC_FOR_TARGET applies even for gohostos/gohostarch.
// $CC_FOR_goos_goarch, if set, applies only to goos/goarch.
func compilerEnv(envName, def string) map[string]string {
	m := map[string]string{"": def}

	if env := os.Getenv(envName); env != "" {
		m[""] = env
	}
	if env := os.Getenv(envName + "_FOR_TARGET"); env != "" {
		if gohostos != goos || gohostarch != goarch {
			m[gohostos+"/"+gohostarch] = m[""]
		}
		m[""] = env
	}

	for _, goos := range okgoos {
		for _, goarch := range okgoarch {
			if env := os.Getenv(envName + "_FOR_" + goos + "_" + goarch); env != "" {
				m[goos+"/"+goarch] = env
			}
		}
	}

	return m
}

// compilerEnvLookup returns the compiler settings for goos/goarch in map m.
func compilerEnvLookup(m map[string]string, goos, goarch string) string {
	if cc := m[goos+"/"+goarch]; cc != "" {
		return cc
	}
	return m[""]
}

// rmworkdir deletes the work directory.
func rmworkdir() {
	if vflag > 1 {
		errprintf("rm -rf %s\n", workdir)
	}
	xremoveall(workdir)
}

// Remove trailing spaces.
func chomp(s string) string {
	return strings.TrimRight(s, " \t\r\n")
}

// findgoversion determines the Go version to use in the version string.
func findgoversion() string {
	// The $GOROOT/VERSION file takes priority, for distributions
	// without the source repo.
	path := pathf("%s/VERSION", goroot)
	if isfile(path) {
		b := chomp(readfile(path))
		// Commands such as "dist version > VERSION" will cause
		// the shell to create an empty VERSION file and set dist's
		// stdout to its fd. dist in turn looks at VERSION and uses
		// its content if available, which is empty at this point.
		// Only use the VERSION file if it is non-empty.
		if b != "" {
			// Some builders cross-compile the toolchain on linux-amd64
			// and then copy the toolchain to the target builder (say, linux-arm)
			// for use there. But on non-release (devel) branches, the compiler
			// used on linux-amd64 will be an amd64 binary, and the compiler
			// shipped to linux-arm will be an arm binary, so they will have different
			// content IDs (they are binaries for different architectures) and so the
			// packages compiled by the running-on-amd64 compiler will appear
			// stale relative to the running-on-arm compiler. Avoid this by setting
			// the version string to something that doesn't begin with devel.
			// Then the version string will be used in place of the content ID,
			// and the packages will look up-to-date.
			// TODO(rsc): Really the builders could be writing out a better VERSION file instead,
			// but it is easier to change cmd/dist than to try to make changes to
			// the builder while Brad is away.
			if strings.HasPrefix(b, "devel") {
				if hostType := os.Getenv("META_BUILDLET_HOST_TYPE"); strings.Contains(hostType, "-cross") {
					fmt.Fprintf(os.Stderr, "warning: changing VERSION from %q to %q\n", b, "builder "+hostType)
					b = "builder " + hostType
				}
			}
			return b
		}
	}

	// The $GOROOT/VERSION.cache file is a cache to avoid invoking
	// git every time we run this command. Unlike VERSION, it gets
	// deleted by the clean command.
	path = pathf("%s/VERSION.cache", goroot)
	if isfile(path) {
		return chomp(readfile(path))
	}

	// Show a nicer error message if this isn't a Git repo.
	if !isGitRepo() {
		fatalf("FAILED: not a Git repo; must put a VERSION file in $GOROOT")
	}

	// Otherwise, use Git.
	//
	// Include 1.x base version, hash, and date in the version.
	//
	// Note that we lightly parse internal/goversion/goversion.go to
	// obtain the base version. We can't just import the package,
	// because cmd/dist is built with a bootstrap GOROOT which could
	// be an entirely different version of Go, like 1.4. We assume
	// that the file contains "const Version = <Integer>".
	goversionSource := readfile(pathf("%s/src/internal/goversion/goversion.go", goroot))
	m := regexp.MustCompile(`(?m)^const Version = (\d+)`).FindStringSubmatch(goversionSource)
	if m == nil {
		fatalf("internal/goversion/goversion.go does not contain 'const Version = ...'")
	}
	version := fmt.Sprintf("devel go1.%s-", m[1])
	version += chomp(run(goroot, CheckExit, "git", "log", "-n", "1", "--format=format:%h %cd", "HEAD"))

	// Cache version.
	writefile(version, path, 0)

	return version
}

// isGitRepo reports whether the working directory is inside a Git repository.
func isGitRepo() bool {
	// NB: simply checking the exit code of `git rev-parse --git-dir` would
	// suffice here, but that requires deviating from the infrastructure
	// provided by `run`.
	gitDir := chomp(run(goroot, 0, "git", "rev-parse", "--git-dir"))
	if !filepath.IsAbs(gitDir) {
		gitDir = filepath.Join(goroot, gitDir)
	}
	return isdir(gitDir)
}

/*
 * Initial tree setup.
 */

// The old tools that no longer live in $GOBIN or $GOROOT/bin.
var oldtool = []string{
	"5a", "5c", "5g", "5l",
	"6a", "6c", "6g", "6l",
	"8a", "8c", "8g", "8l",
	"9a", "9c", "9g", "9l",
	"6cov",
	"6nm",
	"6prof",
	"cgo",
	"ebnflint",
	"goapi",
	"gofix",
	"goinstall",
	"gomake",
	"gopack",
	"gopprof",
	"gotest",
	"gotype",
	"govet",
	"goyacc",
	"quietgcc",
}

// Unreleased directories (relative to $GOROOT) that should
// not be in release branches.
var unreleased = []string{
	"src/cmd/newlink",
	"src/cmd/objwriter",
	"src/debug/goobj",
	"src/old",
}

// setup sets up the tree for the initial build.
func setup() {
	// Create bin directory.
	if p := pathf("%s/bin", goroot); !isdir(p) {
		xmkdir(p)
	}

	// Create package directory.
	if p := pathf("%s/pkg", goroot); !isdir(p) {
		xmkdir(p)
	}

	p := pathf("%s/pkg/%s_%s", goroot, gohostos, gohostarch)
	if rebuildall {
		xremoveall(p)
	}
	xmkdirall(p)

	if goos != gohostos || goarch != gohostarch {
		p := pathf("%s/pkg/%s_%s", goroot, goos, goarch)
		if rebuildall {
			xremoveall(p)
		}
		xmkdirall(p)
	}

	// Create object directory.
	// We used to use it for C objects.
	// Now we use it for the build cache, to separate dist's cache
	// from any other cache the user might have.
	p = pathf("%s/pkg/obj/go-build", goroot)
	if rebuildall {
		xremoveall(p)
	}
	xmkdirall(p)
	xatexit(func() { xremoveall(p) })

	// Create tool directory.
	// We keep it in pkg/, just like the object directory above.
	if rebuildall {
		xremoveall(tooldir)
	}
	xmkdirall(tooldir)

	// Remove tool binaries from before the tool/gohostos_gohostarch
	xremoveall(pathf("%s/bin/tool", goroot))

	// Remove old pre-tool binaries.
	for _, old := range oldtool {
		xremove(pathf("%s/bin/%s", goroot, old))
	}

	// For release, make sure excluded things are excluded.
	goversion := findgoversion()
	if strings.HasPrefix(goversion, "release.") || (strings.HasPrefix(goversion, "go") && !strings.Contains(goversion, "beta")) {
		for _, dir := range unreleased {
			if p := pathf("%s/%s", goroot, dir); isdir(p) {
				fatalf("%s should not exist in release build", p)
			}
		}
	}
}

/*
 * Tool building
 */

// 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.
// Note that this table applies only to the build of cmd/go,
// after the main compiler bootstrap.
var deptab = []struct {
	prefix string   // prefix of target
	dep    []string // dependency tweaks for targets with that prefix
}{
	{"cmd/go/internal/cfg", []string{
		"zdefaultcc.go",
		"zosarch.go",
	}},
	{"runtime/internal/sys", []string{
		"zversion.go",
	}},
	{"go/build", []string{
		"zcgo.go",
	}},
}

// depsuffix records the allowed suffixes for source files.
var depsuffix = []string{
	".s",
	".go",
}

// gentab records how to generate some trivial files.
var gentab = []struct {
	nameprefix string
	gen        func(string, string)
}{
	{"zdefaultcc.go", mkzdefaultcc},
	{"zosarch.go", mkzosarch},
	{"zversion.go", mkzversion},
	{"zcgo.go", mkzcgo},

	// not generated anymore, but delete the file if we see it
	{"enam.c", nil},
	{"anames5.c", nil},
	{"anames6.c", nil},
	{"anames8.c", nil},
	{"anames9.c", nil},
}

// installed maps from a dir name (as given to install) to a chan
// closed when the dir's package is installed.
var installed = make(map[string]chan struct{})
var installedMu sync.Mutex

func install(dir string) {
	<-startInstall(dir)
}

func startInstall(dir string) chan struct{} {
	installedMu.Lock()
	ch := installed[dir]
	if ch == nil {
		ch = make(chan struct{})
		installed[dir] = ch
		go runInstall(dir, ch)
	}
	installedMu.Unlock()
	return ch
}

// runInstall installs the library, package, or binary associated with dir,
// which is relative to $GOROOT/src.
func runInstall(pkg string, ch chan struct{}) {
	if pkg == "net" || pkg == "os/user" || pkg == "crypto/x509" {
		fatalf("go_bootstrap cannot depend on cgo package %s", pkg)
	}

	defer close(ch)

	if pkg == "unsafe" {
		return
	}

	if vflag > 0 {
		if goos != gohostos || goarch != gohostarch {
			errprintf("%s (%s/%s)\n", pkg, goos, goarch)
		} else {
			errprintf("%s\n", pkg)
		}
	}

	workdir := pathf("%s/%s", workdir, pkg)
	xmkdirall(workdir)

	var clean []string
	defer func() {
		for _, name := range clean {
			xremove(name)
		}
	}()

	// dir = full path to pkg.
	dir := pathf("%s/src/%s", goroot, pkg)
	name := filepath.Base(dir)

	// ispkg predicts whether the package should be linked as a binary, based
	// on the name. There should be no "main" packages in vendor, since
	// 'go mod vendor' will only copy imported packages there.
	ispkg := !strings.HasPrefix(pkg, "cmd/") || strings.Contains(pkg, "/internal/") || strings.Contains(pkg, "/vendor/")

	// Start final link command line.
	// Note: code below knows that link.p[targ] is the target.
	var (
		link      []string
		targ      int
		ispackcmd bool
	)
	if ispkg {
		// Go library (package).
		ispackcmd = true
		link = []string{"pack", packagefile(pkg)}
		targ = len(link) - 1
		xmkdirall(filepath.Dir(link[targ]))
	} else {
		// Go command.
		elem := name
		if elem == "go" {
			elem = "go_bootstrap"
		}
		link = []string{pathf("%s/link", tooldir)}
		if goos == "android" {
			link = append(link, "-buildmode=pie")
		}
		if goldflags != "" {
			link = append(link, goldflags)
		}
		link = append(link, "-extld="+compilerEnvLookup(defaultcc, goos, goarch))
		link = append(link, "-o", pathf("%s/%s%s", tooldir, elem, exe))
		targ = len(link) - 1
	}
	ttarg := mtime(link[targ])

	// Gather files that are sources for this target.
	// Everything in that directory, and any target-specific
	// additions.
	files := xreaddir(dir)

	// Remove files beginning with . or _,
	// which are likely to be editor temporary files.
	// This is the same heuristic build.ScanDir uses.
	// There do exist real C files beginning with _,
	// so limit that check to just Go files.
	files = filter(files, func(p string) bool {
		return !strings.HasPrefix(p, ".") && (!strings.HasPrefix(p, "_") || !strings.HasSuffix(p, ".go"))
	})

	for _, dt := range deptab {
		if pkg == dt.prefix || strings.HasSuffix(dt.prefix, "/") && strings.HasPrefix(pkg, dt.prefix) {
			for _, p := range dt.dep {
				p = os.ExpandEnv(p)
				files = append(files, p)
			}
		}
	}
	files = uniq(files)

	// Convert to absolute paths.
	for i, p := range files {
		if !filepath.IsAbs(p) {
			files[i] = pathf("%s/%s", dir, p)
		}
	}

	// Is the target up-to-date?
	var gofiles, sfiles, missing []string
	stale := rebuildall
	files = filter(files, func(p string) bool {
		for _, suf := range depsuffix {
			if strings.HasSuffix(p, suf) {
				goto ok
			}
		}
		return false
	ok:
		t := mtime(p)
		if !t.IsZero() && !strings.HasSuffix(p, ".a") && !shouldbuild(p, pkg) {
			return false
		}
		if strings.HasSuffix(p, ".go") {
			gofiles = append(gofiles, p)
		} else if strings.HasSuffix(p, ".s") {
			sfiles = append(sfiles, p)
		}
		if t.After(ttarg) {
			stale = true
		}
		if t.IsZero() {
			missing = append(missing, p)
		}
		return true
	})

	// If there are no files to compile, we're done.
	if len(files) == 0 {
		return
	}

	if !stale {
		return
	}

	// For package runtime, copy some files into the work space.
	if pkg == "runtime" {
		xmkdirall(pathf("%s/pkg/include", goroot))
		// For use by assembly and C files.
		copyfile(pathf("%s/pkg/include/textflag.h", goroot),
			pathf("%s/src/runtime/textflag.h", goroot), 0)
		copyfile(pathf("%s/pkg/include/funcdata.h", goroot),
			pathf("%s/src/runtime/funcdata.h", goroot), 0)
		copyfile(pathf("%s/pkg/include/asm_ppc64x.h", goroot),
			pathf("%s/src/runtime/asm_ppc64x.h", goroot), 0)
		copyfile(pathf("%s/pkg/include/asm_amd64.h", goroot),
			pathf("%s/src/runtime/asm_amd64.h", goroot), 0)
	}

	// Generate any missing files; regenerate existing ones.
	for _, p := range files {
		elem := filepath.Base(p)
		for _, gt := range gentab {
			if gt.gen == nil {
				continue
			}
			if strings.HasPrefix(elem, gt.nameprefix) {
				if vflag > 1 {
					errprintf("generate %s\n", p)
				}
				gt.gen(dir, p)
				// Do not add generated file to clean list.
				// In runtime, we want to be able to
				// build the package with the go tool,
				// and it assumes these generated files already
				// exist (it does not know how to build them).
				// The 'clean' command can remove
				// the generated files.
				goto built
			}
		}
		// Did not rebuild p.
		if find(p, missing) >= 0 {
			fatalf("missing file %s", p)
		}
	built:
	}

	// Resolve imported packages to actual package paths.
	// Make sure they're installed.
	importMap := make(map[string]string)
	for _, p := range gofiles {
		for _, imp := range readimports(p) {
			if imp == "C" {
				fatalf("%s imports C", p)
			}
			importMap[imp] = resolveVendor(imp, dir)
		}
	}
	sortedImports := make([]string, 0, len(importMap))
	for imp := range importMap {
		sortedImports = append(sortedImports, imp)
	}
	sort.Strings(sortedImports)

	for _, dep := range importMap {
		if dep == "C" {
			fatalf("%s imports C", pkg)
		}
		startInstall(dep)
	}
	for _, dep := range importMap {
		install(dep)
	}

	if goos != gohostos || goarch != gohostarch {
		// We've generated the right files; the go command can do the build.
		if vflag > 1 {
			errprintf("skip build for cross-compile %s\n", pkg)
		}
		return
	}

	asmArgs := []string{
		pathf("%s/asm", tooldir),
		"-I", workdir,
		"-I", pathf("%s/pkg/include", goroot),
		"-D", "GOOS_" + goos,
		"-D", "GOARCH_" + goarch,
		"-D", "GOOS_GOARCH_" + goos + "_" + goarch,
		"-p", pkg,
	}
	if goarch == "mips" || goarch == "mipsle" {
		// Define GOMIPS_value from gomips.
		asmArgs = append(asmArgs, "-D", "GOMIPS_"+gomips)
	}
	if goarch == "mips64" || goarch == "mips64le" {
		// Define GOMIPS64_value from gomips64.
		asmArgs = append(asmArgs, "-D", "GOMIPS64_"+gomips64)
	}
	goasmh := pathf("%s/go_asm.h", workdir)
	if IsRuntimePackagePath(pkg) {
		asmArgs = append(asmArgs, "-compiling-runtime")
	}

	// Collect symabis from assembly code.
	var symabis string
	if len(sfiles) > 0 {
		symabis = pathf("%s/symabis", workdir)
		var wg sync.WaitGroup
		asmabis := append(asmArgs[:len(asmArgs):len(asmArgs)], "-gensymabis", "-o", symabis)
		asmabis = append(asmabis, sfiles...)
		if err := ioutil.WriteFile(goasmh, nil, 0666); err != nil {
			fatalf("cannot write empty go_asm.h: %s", err)
		}
		bgrun(&wg, dir, asmabis...)
		bgwait(&wg)
	}

	// Build an importcfg file for the compiler.
	buf := &bytes.Buffer{}
	for _, imp := range sortedImports {
		if imp == "unsafe" {
			continue
		}
		dep := importMap[imp]
		if imp != dep {
			fmt.Fprintf(buf, "importmap %s=%s\n", imp, dep)
		}
		fmt.Fprintf(buf, "packagefile %s=%s\n", dep, packagefile(dep))
	}
	importcfg := pathf("%s/importcfg", workdir)
	if err := ioutil.WriteFile(importcfg, buf.Bytes(), 0666); err != nil {
		fatalf("cannot write importcfg file: %v", err)
	}

	var archive string
	// The next loop will compile individual non-Go files.
	// Hand the Go files to the compiler en masse.
	// For packages containing assembly, this writes go_asm.h, which
	// the assembly files will need.
	pkgName := pkg
	if strings.HasPrefix(pkg, "cmd/") && strings.Count(pkg, "/") == 1 {
		pkgName = "main"
	}
	b := pathf("%s/_go_.a", workdir)
	clean = append(clean, b)
	if !ispackcmd {
		link = append(link, b)
	} else {
		archive = b
	}

	// Compile Go code.
	compile := []string{pathf("%s/compile", tooldir), "-std", "-pack", "-o", b, "-p", pkgName, "-importcfg", importcfg}
	if gogcflags != "" {
		compile = append(compile, strings.Fields(gogcflags)...)
	}
	if pkg == "runtime" {
		compile = append(compile, "-+")
	}
	if len(sfiles) > 0 {
		compile = append(compile, "-asmhdr", goasmh)
	}
	if symabis != "" {
		compile = append(compile, "-symabis", symabis)
	}
	if goos == "android" {
		compile = append(compile, "-shared")
	}

	compile = append(compile, gofiles...)
	var wg sync.WaitGroup
	// We use bgrun and immediately wait for it instead of calling run() synchronously.
	// This executes all jobs through the bgwork channel and allows the process
	// to exit cleanly in case an error occurs.
	bgrun(&wg, dir, compile...)
	bgwait(&wg)

	// Compile the files.
	for _, p := range sfiles {
		// Assembly file for a Go package.
		compile := asmArgs[:len(asmArgs):len(asmArgs)]

		doclean := true
		b := pathf("%s/%s", workdir, filepath.Base(p))

		// Change the last character of the output file (which was c or s).
		b = b[:len(b)-1] + "o"
		compile = append(compile, "-o", b, p)
		bgrun(&wg, dir, compile...)

		link = append(link, b)
		if doclean {
			clean = append(clean, b)
		}
	}
	bgwait(&wg)

	if ispackcmd {
		xremove(link[targ])
		dopack(link[targ], archive, link[targ+1:])
		return
	}

	// Remove target before writing it.
	xremove(link[targ])
	bgrun(&wg, "", link...)
	bgwait(&wg)
}

// packagefile returns the path to a compiled .a file for the given package
// path. Paths may need to be resolved with resolveVendor first.
func packagefile(pkg string) string {
	return pathf("%s/pkg/%s_%s/%s.a", goroot, goos, goarch, pkg)
}

// unixOS is the set of GOOS values matched by the "unix" build tag.
// This is the same list as in go/build/syslist.go.
var unixOS = map[string]bool{
	"aix":       true,
	"android":   true,
	"darwin":    true,
	"dragonfly": true,
	"freebsd":   true,
	"hurd":      true,
	"illumos":   true,
	"ios":       true,
	"linux":     true,
	"netbsd":    true,
	"openbsd":   true,
	"solaris":   true,
}

// matchtag reports whether the tag matches this build.
func matchtag(tag string) bool {
	switch tag {
	case "gc", "cmd_go_bootstrap", "go1.1":
		return true
	case "linux":
		return goos == "linux" || goos == "android"
	case "solaris":
		return goos == "solaris" || goos == "illumos"
	case "darwin":
		return goos == "darwin" || goos == "ios"
	case goos, goarch:
		return true
	case "unix":
		return unixOS[goos]
	default:
		return false
	}
}

// shouldbuild reports whether we should build this file.
// It applies the same rules that are used with context tags
// in package go/build, except it's less picky about the order
// of GOOS and GOARCH.
// We also allow the special tag cmd_go_bootstrap.
// See ../go/bootstrap.go and package go/build.
func shouldbuild(file, pkg string) bool {
	// Check file name for GOOS or GOARCH.
	name := filepath.Base(file)
	excluded := func(list []string, ok string) bool {
		for _, x := range list {
			if x == ok || (ok == "android" && x == "linux") || (ok == "illumos" && x == "solaris") || (ok == "ios" && x == "darwin") {
				continue
			}
			i := strings.Index(name, x)
			if i <= 0 || name[i-1] != '_' {
				continue
			}
			i += len(x)
			if i == len(name) || name[i] == '.' || name[i] == '_' {
				return true
			}
		}
		return false
	}
	if excluded(okgoos, goos) || excluded(okgoarch, goarch) {
		return false
	}

	// Omit test files.
	if strings.Contains(name, "_test") {
		return false
	}

	// Check file contents for //go:build lines.
	for _, p := range strings.Split(readfile(file), "\n") {
		p = strings.TrimSpace(p)
		if p == "" {
			continue
		}
		code := p
		i := strings.Index(code, "//")
		if i > 0 {
			code = strings.TrimSpace(code[:i])
		}
		if code == "package documentation" {
			return false
		}
		if code == "package main" && pkg != "cmd/go" && pkg != "cmd/cgo" {
			return false
		}
		if !strings.HasPrefix(p, "//") {
			break
		}
		if strings.HasPrefix(p, "//go:build ") {
			matched, err := matchexpr(p[len("//go:build "):])
			if err != nil {
				errprintf("%s: %v", file, err)
			}
			return matched
		}
	}

	return true
}

// copy copies the file src to dst, via memory (so only good for small files).
func copyfile(dst, src string, flag int) {
	if vflag > 1 {
		errprintf("cp %s %s\n", src, dst)
	}
	writefile(readfile(src), dst, flag)
}

// dopack copies the package src to dst,
// appending the files listed in extra.
// The archive format is the traditional Unix ar format.
func dopack(dst, src string, extra []string) {
	bdst := bytes.NewBufferString(readfile(src))
	for _, file := range extra {
		b := readfile(file)
		// find last path element for archive member name
		i := strings.LastIndex(file, "/") + 1
		j := strings.LastIndex(file, `\`) + 1
		if i < j {
			i = j
		}
		fmt.Fprintf(bdst, "%-16.16s%-12d%-6d%-6d%-8o%-10d`\n", file[i:], 0, 0, 0, 0644, len(b))
		bdst.WriteString(b)
		if len(b)&1 != 0 {
			bdst.WriteByte(0)
		}
	}
	writefile(bdst.String(), dst, 0)
}

var runtimegen = []string{
	"zaexperiment.h",
	"zversion.go",
}

// cleanlist is a list of packages with generated files and commands.
var cleanlist = []string{
	"runtime/internal/sys",
	"cmd/cgo",
	"cmd/go/internal/cfg",
	"go/build",
}

func clean() {
	for _, name := range cleanlist {
		path := pathf("%s/src/%s", goroot, name)
		// Remove generated files.
		for _, elem := range xreaddir(path) {
			for _, gt := range gentab {
				if strings.HasPrefix(elem, gt.nameprefix) {
					xremove(pathf("%s/%s", path, elem))
				}
			}
		}
		// Remove generated binary named for directory.
		if strings.HasPrefix(name, "cmd/") {
			xremove(pathf("%s/%s", path, name[4:]))
		}
	}

	// remove runtimegen files.
	path := pathf("%s/src/runtime", goroot)
	for _, elem := range runtimegen {
		xremove(pathf("%s/%s", path, elem))
	}

	if rebuildall {
		// Remove object tree.
		xremoveall(pathf("%s/pkg/obj/%s_%s", goroot, gohostos, gohostarch))

		// Remove installed packages and tools.
		xremoveall(pathf("%s/pkg/%s_%s", goroot, gohostos, gohostarch))
		xremoveall(pathf("%s/pkg/%s_%s", goroot, goos, goarch))
		xremoveall(pathf("%s/pkg/%s_%s_race", goroot, gohostos, gohostarch))
		xremoveall(pathf("%s/pkg/%s_%s_race", goroot, goos, goarch))
		xremoveall(tooldir)

		// Remove cached version info.
		xremove(pathf("%s/VERSION.cache", goroot))
	}
}

/*
 * command implementations
 */

// The env command prints the default environment.
func cmdenv() {
	path := flag.Bool("p", false, "emit updated PATH")
	plan9 := flag.Bool("9", gohostos == "plan9", "emit plan 9 syntax")
	windows := flag.Bool("w", gohostos == "windows", "emit windows syntax")
	xflagparse(0)

	format := "%s=\"%s\"\n"
	switch {
	case *plan9:
		format = "%s='%s'\n"
	case *windows:
		format = "set %s=%s\r\n"
	}

	xprintf(format, "GO111MODULE", "")
	xprintf(format, "GOARCH", goarch)
	xprintf(format, "GOBIN", gorootBin)
	xprintf(format, "GOCACHE", os.Getenv("GOCACHE"))
	xprintf(format, "GODEBUG", os.Getenv("GODEBUG"))
	xprintf(format, "GOENV", "off")
	xprintf(format, "GOFLAGS", "")
	xprintf(format, "GOHOSTARCH", gohostarch)
	xprintf(format, "GOHOSTOS", gohostos)
	xprintf(format, "GOOS", goos)
	xprintf(format, "GOPROXY", os.Getenv("GOPROXY"))
	xprintf(format, "GOROOT", goroot)
	xprintf(format, "GOTMPDIR", os.Getenv("GOTMPDIR"))
	xprintf(format, "GOTOOLDIR", tooldir)
	if goarch == "arm" {
		xprintf(format, "GOARM", goarm)
	}
	if goarch == "386" {
		xprintf(format, "GO386", go386)
	}
	if goarch == "amd64" {
		xprintf(format, "GOAMD64", goamd64)
	}
	if goarch == "mips" || goarch == "mipsle" {
		xprintf(format, "GOMIPS", gomips)
	}
	if goarch == "mips64" || goarch == "mips64le" {
		xprintf(format, "GOMIPS64", gomips64)
	}
	if goarch == "ppc64" || goarch == "ppc64le" {
		xprintf(format, "GOPPC64", goppc64)
	}
	xprintf(format, "GOWORK", "off")

	if *path {
		sep := ":"
		if gohostos == "windows" {
			sep = ";"
		}
		xprintf(format, "PATH", fmt.Sprintf("%s%s%s", gorootBin, sep, os.Getenv("PATH")))
	}
}

var (
	timeLogEnabled = os.Getenv("GOBUILDTIMELOGFILE") != ""
	timeLogMu      sync.Mutex
	timeLogFile    *os.File
	timeLogStart   time.Time
)

func timelog(op, name string) {
	if !timeLogEnabled {
		return
	}
	timeLogMu.Lock()
	defer timeLogMu.Unlock()
	if timeLogFile == nil {
		f, err := os.OpenFile(os.Getenv("GOBUILDTIMELOGFILE"), os.O_RDWR|os.O_APPEND, 0666)
		if err != nil {
			log.Fatal(err)
		}
		buf := make([]byte, 100)
		n, _ := f.Read(buf)
		s := string(buf[:n])
		if i := strings.Index(s, "\n"); i >= 0 {
			s = s[:i]
		}
		i := strings.Index(s, " start")
		if i < 0 {
			log.Fatalf("time log %s does not begin with start line", os.Getenv("GOBUILDTIMELOGFILE"))
		}
		t, err := time.Parse(time.UnixDate, s[:i])
		if err != nil {
			log.Fatalf("cannot parse time log line %q: %v", s, err)
		}
		timeLogStart = t
		timeLogFile = f
	}
	t := time.Now()
	fmt.Fprintf(timeLogFile, "%s %+.1fs %s %s\n", t.Format(time.UnixDate), t.Sub(timeLogStart).Seconds(), op, name)
}

var toolchain = []string{"cmd/asm", "cmd/cgo", "cmd/compile", "cmd/link"}

// The bootstrap command runs a build from scratch,
// stopping at having installed the go_bootstrap command.
//
// WARNING: This command runs after cmd/dist is built with Go 1.4.
// It rebuilds and installs cmd/dist with the new toolchain, so other
// commands (like "go tool dist test" in run.bash) can rely on bug fixes
// made since Go 1.4, but this function cannot. In particular, the uses
// of os/exec in this function cannot assume that
//
//	cmd.Env = append(os.Environ(), "X=Y")
//
// sets $X to Y in the command's environment. That guarantee was
// added after Go 1.4, and in fact in Go 1.4 it was typically the opposite:
// if $X was already present in os.Environ(), most systems preferred
// that setting, not the new one.
func cmdbootstrap() {
	timelog("start", "dist bootstrap")
	defer timelog("end", "dist bootstrap")

	var noBanner, noClean bool
	var debug bool
	flag.BoolVar(&rebuildall, "a", rebuildall, "rebuild all")
	flag.BoolVar(&debug, "d", debug, "enable debugging of bootstrap process")
	flag.BoolVar(&noBanner, "no-banner", noBanner, "do not print banner")
	flag.BoolVar(&noClean, "no-clean", noClean, "print deprecation warning")

	xflagparse(0)

	if noClean {
		xprintf("warning: --no-clean is deprecated and has no effect; use 'go install std cmd' instead\n")
	}

	// Set GOPATH to an internal directory. We shouldn't actually
	// need to store files here, since the toolchain won't
	// depend on modules outside of vendor directories, but if
	// GOPATH points somewhere else (e.g., to GOROOT), the
	// go tool may complain.
	os.Setenv("GOPATH", pathf("%s/pkg/obj/gopath", goroot))

	// Disable GOEXPERIMENT when building toolchain1 and
	// go_bootstrap. We don't need any experiments for the
	// bootstrap toolchain, and this lets us avoid duplicating the
	// GOEXPERIMENT-related build logic from cmd/go here. If the
	// bootstrap toolchain is < Go 1.17, it will ignore this
	// anyway since GOEXPERIMENT is baked in; otherwise it will
	// pick it up from the environment we set here. Once we're
	// using toolchain1 with dist as the build system, we need to
	// override this to keep the experiments assumed by the
	// toolchain and by dist consistent. Once go_bootstrap takes
	// over the build process, we'll set this back to the original
	// GOEXPERIMENT.
	os.Setenv("GOEXPERIMENT", "none")

	if debug {
		// cmd/buildid is used in debug mode.
		toolchain = append(toolchain, "cmd/buildid")
	}

	if isdir(pathf("%s/src/pkg", goroot)) {
		fatalf("\n\n"+
			"The Go package sources have moved to $GOROOT/src.\n"+
			"*** %s still exists. ***\n"+
			"It probably contains stale files that may confuse the build.\n"+
			"Please (check what's there and) remove it and try again.\n"+
			"See https://golang.org/s/go14nopkg\n",
			pathf("%s/src/pkg", goroot))
	}

	if rebuildall {
		clean()
	}

	setup()

	timelog("build", "toolchain1")
	checkCC()
	bootstrapBuildTools()

	// Remember old content of $GOROOT/bin for comparison below.
	oldBinFiles, _ := filepath.Glob(pathf("%s/bin/*", goroot))

	// For the main bootstrap, building for host os/arch.
	oldgoos = goos
	oldgoarch = goarch
	goos = gohostos
	goarch = gohostarch
	os.Setenv("GOHOSTARCH", gohostarch)
	os.Setenv("GOHOSTOS", gohostos)
	os.Setenv("GOARCH", goarch)
	os.Setenv("GOOS", goos)

	timelog("build", "go_bootstrap")
	xprintf("Building Go bootstrap cmd/go (go_bootstrap) using Go toolchain1.\n")
	install("runtime") // dependency not visible in sources; also sets up textflag.h
	install("cmd/go")
	if vflag > 0 {
		xprintf("\n")
	}

	gogcflags = os.Getenv("GO_GCFLAGS") // we were using $BOOT_GO_GCFLAGS until now
	goldflags = os.Getenv("GO_LDFLAGS") // we were using $BOOT_GO_LDFLAGS until now
	goBootstrap := pathf("%s/go_bootstrap", tooldir)
	cmdGo := pathf("%s/go", gorootBin)
	if debug {
		run("", ShowOutput|CheckExit, pathf("%s/compile", tooldir), "-V=full")
		copyfile(pathf("%s/compile1", tooldir), pathf("%s/compile", tooldir), writeExec)
	}

	// To recap, so far we have built the new toolchain
	// (cmd/asm, cmd/cgo, cmd/compile, cmd/link)
	// using Go 1.4's toolchain and go command.
	// Then we built the new go command (as go_bootstrap)
	// using the new toolchain and our own build logic (above).
	//
	//	toolchain1 = mk(new toolchain, go1.4 toolchain, go1.4 cmd/go)
	//	go_bootstrap = mk(new cmd/go, toolchain1, cmd/dist)
	//
	// The toolchain1 we built earlier is built from the new sources,
	// but because it was built using cmd/go it has no build IDs.
	// The eventually installed toolchain needs build IDs, so we need
	// to do another round:
	//
	//	toolchain2 = mk(new toolchain, toolchain1, go_bootstrap)
	//
	timelog("build", "toolchain2")
	if vflag > 0 {
		xprintf("\n")
	}
	xprintf("Building Go toolchain2 using go_bootstrap and Go toolchain1.\n")
	os.Setenv("CC", compilerEnvLookup(defaultcc, goos, goarch))
	// Now that cmd/go is in charge of the build process, enable GOEXPERIMENT.
	os.Setenv("GOEXPERIMENT", goexperiment)
	goInstall(goBootstrap, append([]string{"-i"}, toolchain...)...)
	if debug {
		run("", ShowOutput|CheckExit, pathf("%s/compile", tooldir), "-V=full")
		run("", ShowOutput|CheckExit, pathf("%s/buildid", tooldir), pathf("%s/pkg/%s_%s/runtime/internal/sys.a", goroot, goos, goarch))
		copyfile(pathf("%s/compile2", tooldir), pathf("%s/compile", tooldir), writeExec)
	}

	// Toolchain2 should be semantically equivalent to toolchain1,
	// but it was built using the new compilers instead of the Go 1.4 compilers,
	// so it should at the least run faster. Also, toolchain1 had no build IDs
	// in the binaries, while toolchain2 does. In non-release builds, the
	// toolchain's build IDs feed into constructing the build IDs of built targets,
	// so in non-release builds, everything now looks out-of-date due to
	// toolchain2 having build IDs - that is, due to the go command seeing
	// that there are new compilers. In release builds, the toolchain's reported
	// version is used in place of the build ID, and the go command does not
	// see that change from toolchain1 to toolchain2, so in release builds,
	// nothing looks out of date.
	// To keep the behavior the same in both non-release and release builds,
	// we force-install everything here.
	//
	//	toolchain3 = mk(new toolchain, toolchain2, go_bootstrap)
	//
	timelog("build", "toolchain3")
	if vflag > 0 {
		xprintf("\n")
	}
	xprintf("Building Go toolchain3 using go_bootstrap and Go toolchain2.\n")
	goInstall(goBootstrap, append([]string{"-a", "-i"}, toolchain...)...)
	if debug {
		run("", ShowOutput|CheckExit, pathf("%s/compile", tooldir), "-V=full")
		run("", ShowOutput|CheckExit, pathf("%s/buildid", tooldir), pathf("%s/pkg/%s_%s/runtime/internal/sys.a", goroot, goos, goarch))
		copyfile(pathf("%s/compile3", tooldir), pathf("%s/compile", tooldir), writeExec)
	}
	checkNotStale(goBootstrap, append(toolchain, "runtime/internal/sys")...)

	if goos == oldgoos && goarch == oldgoarch {
		// Common case - not setting up for cross-compilation.
		timelog("build", "toolchain")
		if vflag > 0 {
			xprintf("\n")
		}
		xprintf("Building packages and commands for %s/%s.\n", goos, goarch)
	} else {
		// GOOS/GOARCH does not match GOHOSTOS/GOHOSTARCH.
		// Finish GOHOSTOS/GOHOSTARCH installation and then
		// run GOOS/GOARCH installation.
		timelog("build", "host toolchain")
		if vflag > 0 {
			xprintf("\n")
		}
		xprintf("Building packages and commands for host, %s/%s.\n", goos, goarch)
		goInstall(goBootstrap, "std", "cmd")
		checkNotStale(goBootstrap, "std", "cmd")
		checkNotStale(cmdGo, "std", "cmd")

		timelog("build", "target toolchain")
		if vflag > 0 {
			xprintf("\n")
		}
		goos = oldgoos
		goarch = oldgoarch
		os.Setenv("GOOS", goos)
		os.Setenv("GOARCH", goarch)
		os.Setenv("CC", compilerEnvLookup(defaultcc, goos, goarch))
		xprintf("Building packages and commands for target, %s/%s.\n", goos, goarch)
	}
	targets := []string{"std", "cmd"}
	if goos == "js" && goarch == "wasm" {
		// Skip the cmd tools for js/wasm. They're not usable.
		targets = targets[:1]
	}
	goInstall(goBootstrap, targets...)
	checkNotStale(goBootstrap, targets...)
	checkNotStale(cmdGo, targets...)
	if debug {
		run("", ShowOutput|CheckExit, pathf("%s/compile", tooldir), "-V=full")
		run("", ShowOutput|CheckExit, pathf("%s/buildid", tooldir), pathf("%s/pkg/%s_%s/runtime/internal/sys.a", goroot, goos, goarch))
		checkNotStale(goBootstrap, append(toolchain, "runtime/internal/sys")...)
		copyfile(pathf("%s/compile4", tooldir), pathf("%s/compile", tooldir), writeExec)
	}

	// Check that there are no new files in $GOROOT/bin other than
	// go and gofmt and $GOOS_$GOARCH (target bin when cross-compiling).
	binFiles, _ := filepath.Glob(pathf("%s/bin/*", goroot))
	ok := map[string]bool{}
	for _, f := range oldBinFiles {
		ok[f] = true
	}
	for _, f := range binFiles {
		elem := strings.TrimSuffix(filepath.Base(f), ".exe")
		if !ok[f] && elem != "go" && elem != "gofmt" && elem != goos+"_"+goarch {
			fatalf("unexpected new file in $GOROOT/bin: %s", elem)
		}
	}

	// Remove go_bootstrap now that we're done.
	xremove(pathf("%s/go_bootstrap", tooldir))

	if goos == "android" {
		// Make sure the exec wrapper will sync a fresh $GOROOT to the device.
		xremove(pathf("%s/go_android_exec-adb-sync-status", os.TempDir()))
	}

	if wrapperPath := wrapperPathFor(goos, goarch); wrapperPath != "" {
		oldcc := os.Getenv("CC")
		os.Setenv("GOOS", gohostos)
		os.Setenv("GOARCH", gohostarch)
		os.Setenv("CC", compilerEnvLookup(defaultcc, gohostos, gohostarch))
		goCmd(cmdGo, "build", "-o", pathf("%s/go_%s_%s_exec%s", gorootBin, goos, goarch, exe), wrapperPath)
		// Restore environment.
		// TODO(elias.naur): support environment variables in goCmd?
		os.Setenv("GOOS", goos)
		os.Setenv("GOARCH", goarch)
		os.Setenv("CC", oldcc)
	}

	// Print trailing banner unless instructed otherwise.
	if !noBanner {
		banner()
	}
}

func wrapperPathFor(goos, goarch string) string {
	switch {
	case goos == "android":
		if gohostos != "android" {
			return pathf("%s/misc/android/go_android_exec.go", goroot)
		}
	case goos == "ios":
		if gohostos != "ios" {
			return pathf("%s/misc/ios/go_ios_exec.go", goroot)
		}
	}
	return ""
}

func goInstall(goBinary string, args ...string) {
	goCmd(goBinary, "install", args...)
}

func appendCompilerFlags(args []string) []string {
	if gogcflags != "" {
		args = append(args, "-gcflags=all="+gogcflags)
	}
	if goldflags != "" {
		args = append(args, "-ldflags=all="+goldflags)
	}
	return args
}

func goCmd(goBinary string, cmd string, args ...string) {
	goCmd := []string{goBinary, cmd}
	goCmd = appendCompilerFlags(goCmd)
	if vflag > 0 {
		goCmd = append(goCmd, "-v")
	}

	// Force only one process at a time on vx32 emulation.
	if gohostos == "plan9" && os.Getenv("sysname") == "vx32" {
		goCmd = append(goCmd, "-p=1")
	}

	run(workdir, ShowOutput|CheckExit, append(goCmd, args...)...)
}

func checkNotStale(goBinary string, targets ...string) {
	goCmd := []string{goBinary, "list"}
	goCmd = appendCompilerFlags(goCmd)
	goCmd = append(goCmd, "-f={{if .Stale}}\tSTALE {{.ImportPath}}: {{.StaleReason}}{{end}}")

	out := run(workdir, CheckExit, append(goCmd, targets...)...)
	if strings.Contains(out, "\tSTALE ") {
		os.Setenv("GODEBUG", "gocachehash=1")
		for _, target := range []string{"runtime/internal/sys", "cmd/dist", "cmd/link"} {
			if strings.Contains(out, "STALE "+target) {
				run(workdir, ShowOutput|CheckExit, goBinary, "list", "-f={{.ImportPath}} {{.Stale}}", target)
				break
			}
		}
		fatalf("unexpected stale targets reported by %s list -gcflags=\"%s\" -ldflags=\"%s\" for %v (consider rerunning with GOMAXPROCS=1 GODEBUG=gocachehash=1):\n%s", goBinary, gogcflags, goldflags, targets, out)
	}
}

// Cannot use go/build directly because cmd/dist for a new release
// builds against an old release's go/build, which may be out of sync.
// To reduce duplication, we generate the list for go/build from this.
//
// We list all supported platforms in this list, so that this is the
// single point of truth for supported platforms. This list is used
// by 'go tool dist list'.
var cgoEnabled = map[string]bool{
	"aix/ppc64":       true,
	"darwin/amd64":    true,
	"darwin/arm64":    true,
	"dragonfly/amd64": true,
	"freebsd/386":     true,
	"freebsd/amd64":   true,
	"freebsd/arm":     true,
	"freebsd/arm64":   true,
	"illumos/amd64":   true,
	"linux/386":       true,
	"linux/amd64":     true,
	"linux/arm":       true,
	"linux/arm64":     true,
	"linux/ppc64":     false,
	"linux/ppc64le":   true,
	"linux/mips":      true,
	"linux/mipsle":    true,
	"linux/mips64":    true,
	"linux/mips64le":  true,
	"linux/riscv64":   true,
	"linux/s390x":     true,
	"linux/sparc64":   true,
	"android/386":     true,
	"android/amd64":   true,
	"android/arm":     true,
	"android/arm64":   true,
	"ios/arm64":       true,
	"ios/amd64":       true,
	"js/wasm":         false,
	"netbsd/386":      true,
	"netbsd/amd64":    true,
	"netbsd/arm":      true,
	"netbsd/arm64":    true,
	"openbsd/386":     true,
	"openbsd/amd64":   true,
	"openbsd/arm":     true,
	"openbsd/arm64":   true,
	"openbsd/mips64":  true,
	"plan9/386":       false,
	"plan9/amd64":     false,
	"plan9/arm":       false,
	"solaris/amd64":   true,
	"windows/386":     true,
	"windows/amd64":   true,
	"windows/arm":     false,
	"windows/arm64":   true,
}

// List of platforms which are supported but not complete yet. These get
// filtered out of cgoEnabled for 'dist list'. See golang.org/issue/28944
var incomplete = map[string]bool{
	"linux/sparc64": true,
}

// List of platforms which are first class ports. See golang.org/issue/38874.
var firstClass = map[string]bool{
	"darwin/amd64":  true,
	"darwin/arm64":  true,
	"linux/386":     true,
	"linux/amd64":   true,
	"linux/arm":     true,
	"linux/arm64":   true,
	"windows/386":   true,
	"windows/amd64": true,
}

func needCC() bool {
	switch os.Getenv("CGO_ENABLED") {
	case "1":
		return true
	case "0":
		return false
	}
	return cgoEnabled[gohostos+"/"+gohostarch]
}

func checkCC() {
	if !needCC() {
		return
	}
	if output, err := exec.Command(defaultcc[""], "--help").CombinedOutput(); err != nil {
		outputHdr := ""
		if len(output) > 0 {
			outputHdr = "\nCommand output:\n\n"
		}
		fatalf("cannot invoke C compiler %q: %v\n\n"+
			"Go needs a system C compiler for use with cgo.\n"+
			"To set a C compiler, set CC=the-compiler.\n"+
			"To disable cgo, set CGO_ENABLED=0.\n%s%s", defaultcc[""], err, outputHdr, output)
	}
}

func defaulttarg() string {
	// xgetwd might return a path with symlinks fully resolved, and if
	// there happens to be symlinks in goroot, then the hasprefix test
	// will never succeed. Instead, we use xrealwd to get a canonical
	// goroot/src before the comparison to avoid this problem.
	pwd := xgetwd()
	src := pathf("%s/src/", goroot)
	real_src := xrealwd(src)
	if !strings.HasPrefix(pwd, real_src) {
		fatalf("current directory %s is not under %s", pwd, real_src)
	}
	pwd = pwd[len(real_src):]
	// guard against xrealwd returning the directory without the trailing /
	pwd = strings.TrimPrefix(pwd, "/")

	return pwd
}

// Install installs the list of packages named on the command line.
func cmdinstall() {
	xflagparse(-1)

	if flag.NArg() == 0 {
		install(defaulttarg())
	}

	for _, arg := range flag.Args() {
		install(arg)
	}
}

// Clean deletes temporary objects.
func cmdclean() {
	xflagparse(0)
	clean()
}

// Banner prints the 'now you've installed Go' banner.
func cmdbanner() {
	xflagparse(0)
	banner()
}

func banner() {
	if vflag > 0 {
		xprintf("\n")
	}
	xprintf("---\n")
	xprintf("Installed Go for %s/%s in %s\n", goos, goarch, goroot)
	xprintf("Installed commands in %s\n", gorootBin)

	if !xsamefile(goroot_final, goroot) {
		// If the files are to be moved, don't check that gobin
		// is on PATH; assume they know what they are doing.
	} else if gohostos == "plan9" {
		// Check that GOROOT/bin is bound before /bin.
		pid := strings.Replace(readfile("#c/pid"), " ", "", -1)
		ns := fmt.Sprintf("/proc/%s/ns", pid)
		if !strings.Contains(readfile(ns), fmt.Sprintf("bind -b %s /bin", gorootBin)) {
			xprintf("*** You need to bind %s before /bin.\n", gorootBin)
		}
	} else {
		// Check that GOROOT/bin appears in $PATH.
		pathsep := ":"
		if gohostos == "windows" {
			pathsep = ";"
		}
		if !strings.Contains(pathsep+os.Getenv("PATH")+pathsep, pathsep+gorootBin+pathsep) {
			xprintf("*** You need to add %s to your PATH.\n", gorootBin)
		}
	}

	if !xsamefile(goroot_final, goroot) {
		xprintf("\n"+
			"The binaries expect %s to be copied or moved to %s\n",
			goroot, goroot_final)
	}
}

// Version prints the Go version.
func cmdversion() {
	xflagparse(0)
	xprintf("%s\n", findgoversion())
}

// cmdlist lists all supported platforms.
func cmdlist() {
	jsonFlag := flag.Bool("json", false, "produce JSON output")
	xflagparse(0)

	var plats []string
	for p := range cgoEnabled {
		if incomplete[p] {
			continue
		}
		plats = append(plats, p)
	}
	sort.Strings(plats)

	if !*jsonFlag {
		for _, p := range plats {
			xprintf("%s\n", p)
		}
		return
	}

	type jsonResult struct {
		GOOS         string
		GOARCH       string
		CgoSupported bool
		FirstClass   bool
	}
	var results []jsonResult
	for _, p := range plats {
		fields := strings.Split(p, "/")
		results = append(results, jsonResult{
			GOOS:         fields[0],
			GOARCH:       fields[1],
			CgoSupported: cgoEnabled[p],
			FirstClass:   firstClass[p]})
	}
	out, err := json.MarshalIndent(results, "", "\t")
	if err != nil {
		fatalf("json marshal error: %v", err)
	}
	if _, err := os.Stdout.Write(out); err != nil {
		fatalf("write failed: %v", err)
	}
}

// IsRuntimePackagePath examines 'pkgpath' and returns TRUE if it
// belongs to the collection of "runtime-related" packages, including
// "runtime" itself, "reflect", "syscall", and the
// "runtime/internal/*" packages.
//
// Keep in sync with cmd/internal/objabi/path.go:IsRuntimePackagePath.
func IsRuntimePackagePath(pkgpath string) bool {
	rval := false
	switch pkgpath {
	case "runtime":
		rval = true
	case "reflect":
		rval = true
	case "syscall":
		rval = true
	case "internal/bytealg":
		rval = true
	default:
		rval = strings.HasPrefix(pkgpath, "runtime/internal")
	}
	return rval
}