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"
	"io/fs"
	"log"
	"os"
	"os/exec"
	"path/filepath"
	"regexp"
	"sort"
	"strings"
	"sync"
	"time"
)

// Initialization for any invocation.

// The usual variables.
var (
	goarch           string
	gorootBin        string
	gorootBinGo      string
	gohostarch       string
	gohostos         string
	goos             string
	goarm            string
	go386            string
	goamd64          string
	gomips           string
	gomips64         string
	goppc64          string
	goriscv64        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
	oldgocache       string
	exe              string
	defaultcc        map[string]string
	defaultcxx       map[string]string
	defaultpkgconfig string
	defaultldso      string

	rebuildall bool
	noOpt      bool
	isRelease  bool

	vflag int // verbosity
)

// The known architectures.
var okgoarch = []string{
	"386",
	"amd64",
	"arm",
	"arm64",
	"loong64",
	"mips",
	"mipsle",
	"mips64",
	"mips64le",
	"ppc64",
	"ppc64le",
	"riscv64",
	"s390x",
	"sparc64",
	"wasm",
}

// The known operating systems.
var okgoos = []string{
	"darwin",
	"dragonfly",
	"illumos",
	"ios",
	"js",
	"wasip1",
	"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)

	// Don't run just 'go' because the build infrastructure
	// runs cmd/dist inside go/bin often, and on Windows
	// it will be found in the current directory and refuse to exec.
	// All exec calls rewrite "go" into gorootBinGo.
	gorootBinGo = pathf("%s/bin/go", 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

	b = os.Getenv("GORISCV64")
	if b == "" {
		b = "rva20u64"
	}
	goriscv64 = 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")

	defaultcc = compilerEnv("CC", "")
	defaultcxx = compilerEnv("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("GORISCV64", goriscv64)
	os.Setenv("GOROOT", goroot)
	os.Setenv("GOROOT_FINAL", goroot_final)

	// 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 := os.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)

	goversion := findgoversion()
	isRelease = strings.HasPrefix(goversion, "release.") || strings.HasPrefix(goversion, "go")
}

// 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
}

// clangos lists the operating systems where we prefer clang to gcc.
var clangos = []string{
	"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.
}

// compilerEnvLookup returns the compiler settings for goos/goarch in map m.
// kind is "CC" or "CXX".
func compilerEnvLookup(kind string, m map[string]string, goos, goarch string) string {
	if !needCC() {
		return ""
	}
	if cc := m[goos+"/"+goarch]; cc != "" {
		return cc
	}
	if cc := m[""]; cc != "" {
		return cc
	}
	for _, os := range clangos {
		if goos == os {
			if kind == "CXX" {
				return "clang++"
			}
			return "clang"
		}
	}
	if kind == "CXX" {
		return "g++"
	}
	return "gcc"
}

// 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.
// It also parses any other metadata found in the version file.
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))

		// Starting in Go 1.21 the VERSION file starts with the
		// version on a line by itself but then can contain other
		// metadata about the release, one item per line.
		if i := strings.Index(b, "\n"); i >= 0 {
			rest := b[i+1:]
			b = chomp(b[:i])
			for _, line := range strings.Split(rest, "\n") {
				f := strings.Fields(line)
				if len(f) == 0 {
					continue
				}
				switch f[0] {
				default:
					fatalf("VERSION: unexpected line: %s", line)
				case "time":
					if len(f) != 2 {
						fatalf("VERSION: unexpected time line: %s", line)
					}
					_, err := time.Parse(time.RFC3339, f[1])
					if err != nil {
						fatalf("VERSION: bad time: %s", err)
					}
				}
			}
		}

		// 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 != "" {
			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. 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)
	}

	goosGoarch := pathf("%s/pkg/%s_%s", goroot, gohostos, gohostarch)
	if rebuildall {
		xremoveall(goosGoarch)
	}
	xmkdirall(goosGoarch)
	xatexit(func() {
		if files := xreaddir(goosGoarch); len(files) == 0 {
			xremove(goosGoarch)
		}
	})

	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, and for the location
	// to build the bootstrap versions of the standard library.
	obj := pathf("%s/pkg/obj", goroot)
	if !isdir(obj) {
		xmkdir(obj)
	}
	xatexit(func() { xremove(obj) })

	// Create build cache directory.
	objGobuild := pathf("%s/pkg/obj/go-build", goroot)
	if rebuildall {
		xremoveall(objGobuild)
	}
	xmkdirall(objGobuild)
	xatexit(func() { xremoveall(objGobuild) })

	// Create directory for bootstrap versions of standard library .a files.
	objGoBootstrap := pathf("%s/pkg/obj/go-bootstrap", goroot)
	if rebuildall {
		xremoveall(objGoBootstrap)
	}
	xmkdirall(objGoBootstrap)
	xatexit(func() { xremoveall(objGoBootstrap) })

	// 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))
	}

	// Special release-specific setup.
	if isRelease {
		// Make sure release-excluded things are excluded.
		for _, dir := range unreleased {
			if p := pathf("%s/%s", goroot, dir); isdir(p) {
				fatalf("%s should not exist in release build", p)
			}
		}
	}
}

/*
 * 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, cgoEnabled bool) bool {
	if cgoEnabled {
		switch goarch {
		case "loong64", "mips", "mipsle", "mips64", "mips64le":
			// Internally linking cgo is incomplete on some architectures.
			// https://golang.org/issue/14449
			return true
		case "arm64":
			if goos == "windows" {
				// windows/arm64 internal linking is not implemented.
				return true
			}
		case "ppc64":
			// Big Endian PPC64 cgo internal linking is not implemented for aix or linux.
			if goos == "aix" || goos == "linux" {
				return true
			}
		}

		switch goos {
		case "android":
			return true
		case "dragonfly":
			// It seems that on Dragonfly thread local storage is
			// set up by the dynamic linker, so internal cgo linking
			// doesn't work. Test case is "go test runtime/cgo".
			return true
		}
	}

	switch goos {
	case "android":
		if goarch != "arm64" {
			return true
		}
	case "ios":
		if goarch == "arm64" {
			return true
		}
	}
	return false
}

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

// gentab records how to generate some trivial files.
// Files listed here should also be listed in ../distpack/pack.go's srcArch.Remove list.
var gentab = []struct {
	pkg  string // Relative to $GOROOT/src
	file string
	gen  func(dir, file string)
}{
	{"go/build", "zcgo.go", mkzcgo},
	{"cmd/go/internal/cfg", "zdefaultcc.go", mkzdefaultcc},
	{"runtime/internal/sys", "zversion.go", mkzversion},
	{"time/tzdata", "zzipdata.go", mktzdata},
}

// 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 pkg,
// 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("CC", defaultcc, goos, goarch))
		link = append(link, "-L="+pathf("%s/pkg/obj/go-bootstrap/%s_%s", goroot, 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"))
	})

	// Add generated files for this package.
	for _, gt := range gentab {
		if gt.pkg == pkg {
			files = append(files, gt.file)
		}
	}
	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 []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
		}
		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 _, gt := range gentab {
		if gt.pkg != pkg {
			continue
		}
		p := pathf("%s/%s", dir, gt.file)
		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.
	}

	// 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)
	}
	if goarch == "ppc64" || goarch == "ppc64le" {
		// We treat each powerpc version as a superset of functionality.
		switch goppc64 {
		case "power10":
			asmArgs = append(asmArgs, "-D", "GOPPC64_power10")
			fallthrough
		case "power9":
			asmArgs = append(asmArgs, "-D", "GOPPC64_power9")
			fallthrough
		default: // This should always be power8.
			asmArgs = append(asmArgs, "-D", "GOPPC64_power8")
		}
	}
	if goarch == "riscv64" {
		// Define GORISCV64_value from goriscv64
		asmArgs = append(asmArgs, "-D", "GORISCV64_"+goriscv64)
	}
	goasmh := pathf("%s/go_asm.h", workdir)

	// 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 := os.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 := os.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 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/obj/go-bootstrap/%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 and
// cmd/go/internal/imports/build.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
}

// copyfile 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)
}

func clean() {
	generated := []byte(generatedHeader)

	// Remove generated source files.
	filepath.WalkDir(pathf("%s/src", goroot), func(path string, d fs.DirEntry, err error) error {
		switch {
		case err != nil:
			// ignore
		case d.IsDir() && (d.Name() == "vendor" || d.Name() == "testdata"):
			return filepath.SkipDir
		case d.IsDir() && d.Name() != "dist":
			// Remove generated binary named for directory, but not dist out from under us.
			exe := filepath.Join(path, d.Name())
			if info, err := os.Stat(exe); err == nil && !info.IsDir() {
				xremove(exe)
			}
			xremove(exe + ".exe")
		case !d.IsDir() && strings.HasPrefix(d.Name(), "z"):
			// Remove generated file, identified by marker string.
			head := make([]byte, 512)
			if f, err := os.Open(path); err == nil {
				io.ReadFull(f, head)
				f.Close()
			}
			if bytes.HasPrefix(head, generated) {
				xremove(path)
			}
		}
		return nil
	})

	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))

		// Remove distribution packages.
		xremoveall(pathf("%s/pkg/distpack", 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" // Include ; to separate variables when 'dist env' output is used with eval.
	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, "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)
	}
	if goarch == "riscv64" {
		xprintf(format, "GORISCV64", goriscv64)
	}
	xprintf(format, "GOWORK", "off")

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

		// Also include $DIST_UNMODIFIED_PATH with the original $PATH
		// for the internal needs of "dist banner", along with export
		// so that it reaches the dist process. See its comment below.
		var exportFormat string
		if !*windows && !*plan9 {
			exportFormat = "export " + format
		} else {
			exportFormat = format
		}
		xprintf(exportFormat, "DIST_UNMODIFIED_PATH", 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)
}

// 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, false) {
		// 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.
		env = append(env, "GOFLAGS=-trimpath -ldflags=-w -gcflags=cmd/...=-dwarf=false")
	}
	return env
}

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 the Go bootstrap toolchain.
// 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 the Go bootstrap version, but this function cannot.
func cmdbootstrap() {
	timelog("start", "dist bootstrap")
	defer timelog("end", "dist bootstrap")

	var debug, distpack, force, noBanner, noClean bool
	flag.BoolVar(&rebuildall, "a", rebuildall, "rebuild all")
	flag.BoolVar(&debug, "d", debug, "enable debugging of bootstrap process")
	flag.BoolVar(&distpack, "distpack", distpack, "write distribution files to pkg/distpack")
	flag.BoolVar(&force, "force", force, "build even if the port is marked as broken")
	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")
	}

	// Don't build broken ports by default.
	if broken[goos+"/"+goarch] && !force {
		fatalf("build stopped because the port %s/%s is marked as broken\n\n"+
			"Use the -force flag to build anyway.\n", goos, goarch)
	}

	// 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))

	// 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.
	oldgocache = os.Getenv("GOCACHE")
	os.Setenv("GOCACHE", pathf("%s/pkg/obj/go-build", 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, err := filepath.Glob(pathf("%s/bin/*", goroot))
	if err != nil {
		fatalf("glob: %v", err)
	}

	// 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("time/tzdata") // no dependency in sources; creates generated file
	install("cmd/go")
	if vflag > 0 {
		xprintf("\n")
	}

	gogcflags = os.Getenv("GO_GCFLAGS") // we were using $BOOT_GO_GCFLAGS until now
	setNoOpt()
	goldflags = os.Getenv("GO_LDFLAGS") // we were using $BOOT_GO_LDFLAGS until now
	goBootstrap := pathf("%s/go_bootstrap", tooldir)
	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 the Go bootstrap 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, go1.17 toolchain, go1.17 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("CC", defaultcc, goos, goarch))
	// Now that cmd/go is in charge of the build process, enable GOEXPERIMENT.
	os.Setenv("GOEXPERIMENT", goexperiment)
	// No need to enable PGO for toolchain2.
	goInstall(toolenv(), goBootstrap, append([]string{"-pgo=off"}, toolchain...)...)
	if debug {
		run("", ShowOutput|CheckExit, pathf("%s/compile", tooldir), "-V=full")
		copyfile(pathf("%s/compile2", tooldir), pathf("%s/compile", tooldir), writeExec)
	}

	// Toolchain2 should be semantically equivalent to toolchain1,
	// but it was built using the newly built compiler instead of the Go bootstrap compiler,
	// 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(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)
	}

	// Now that toolchain3 has been built from scratch, its compiler and linker
	// should have accurate build IDs suitable for caching.
	// Now prime the build cache with the rest of the standard library for
	// testing, and so that the user can run 'go install std cmd' to quickly
	// iterate on local changes without waiting for a full rebuild.
	if _, err := os.Stat(pathf("%s/VERSION", goroot)); err == nil {
		// If we have a VERSION file, then we use the Go version
		// instead of build IDs as a cache key, and there is no guarantee
		// that code hasn't changed since the last time we ran a build
		// with this exact VERSION file (especially if someone is working
		// on a release branch). We must not fall back to the shared build cache
		// in this case. Leave $GOCACHE alone.
	} else {
		os.Setenv("GOCACHE", oldgocache)
	}

	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 commands for host, %s/%s.\n", goos, goarch)
		goInstall(toolenv(), goBootstrap, "cmd")
		checkNotStale(toolenv(), goBootstrap, "cmd")
		checkNotStale(toolenv(), gorootBinGo, "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("CC", defaultcc, goos, goarch))
		xprintf("Building packages and commands for target, %s/%s.\n", goos, goarch)
	}
	goInstall(nil, goBootstrap, "std")
	goInstall(toolenv(), goBootstrap, "cmd")
	checkNotStale(toolenv(), goBootstrap, toolchain...)
	checkNotStale(nil, goBootstrap, "std")
	checkNotStale(toolenv(), goBootstrap, "cmd")
	checkNotStale(nil, gorootBinGo, "std")
	checkNotStale(toolenv(), gorootBinGo, "cmd")
	if debug {
		run("", ShowOutput|CheckExit, pathf("%s/compile", tooldir), "-V=full")
		checkNotStale(toolenv(), goBootstrap, toolchain...)
		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, err := filepath.Glob(pathf("%s/bin/*", goroot))
	if err != nil {
		fatalf("glob: %v", err)
	}

	ok := map[string]bool{}
	for _, f := range oldBinFiles {
		ok[f] = true
	}
	for _, f := range binFiles {
		if gohostos == "darwin" && filepath.Base(f) == ".DS_Store" {
			continue // unfortunate but not unexpected
		}
		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"+exe, 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("CC", defaultcc, gohostos, gohostarch))
		goCmd(nil, gorootBinGo, "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)
	}

	if distpack {
		xprintf("Packaging archives for %s/%s.\n", goos, goarch)
		run("", ShowOutput|CheckExit, pathf("%s/distpack", tooldir))
	}

	// 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/go_android_exec/main.go", goroot)
		}
	case goos == "ios":
		if gohostos != "ios" {
			return pathf("%s/misc/ios/go_ios_exec.go", goroot)
		}
	}
	return ""
}

func goInstall(env []string, goBinary string, args ...string) {
	goCmd(env, 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(env []string, goBinary string, cmd string, args ...string) {
	goCmd := []string{goBinary, cmd}
	if noOpt {
		goCmd = append(goCmd, "-tags=noopt")
	}
	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")
	}

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

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

	out := runEnv(workdir, CheckExit, env, 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,
	"freebsd/riscv64": true,
	"illumos/amd64":   true,
	"linux/386":       true,
	"linux/amd64":     true,
	"linux/arm":       true,
	"linux/arm64":     true,
	"linux/loong64":   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,
	"wasip1/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,
	"openbsd/ppc64":   false,
	"openbsd/riscv64": false,
	"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 that are marked as broken ports.
// These require -force flag to build, and also
// get filtered out of cgoEnabled for 'dist list'.
// See go.dev/issue/56679.
var broken = map[string]bool{
	"linux/sparc64":   true, // An incomplete port. See CL 132155.
	"openbsd/mips64":  true, // Broken: go.dev/issue/58110.
	"openbsd/riscv64": true, // An incomplete port: go.dev/issue/55999.
}

// List of platforms which are first class ports. See go.dev/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,
}

// We only need CC if cgo is forced on, or if the platform requires external linking.
// Otherwise the go command will automatically disable it.
func needCC() bool {
	return os.Getenv("CGO_ENABLED") == "1" || mustLinkExternal(gohostos, gohostarch, false)
}

func checkCC() {
	if !needCC() {
		return
	}
	cc1 := defaultcc[""]
	if cc1 == "" {
		cc1 = "gcc"
		for _, os := range clangos {
			if gohostos == os {
				cc1 = "clang"
				break
			}
		}
	}
	cc, err := quotedSplit(cc1)
	if err != nil {
		fatalf("split CC: %v", err)
	}
	var ccHelp = append(cc, "--help")

	if output, err := exec.Command(ccHelp[0], ccHelp[1:]...).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", cc, 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 = ";"
		}
		path := os.Getenv("PATH")
		if p, ok := os.LookupEnv("DIST_UNMODIFIED_PATH"); ok {
			// Scripts that modify $PATH and then run dist should also provide
			// dist with an unmodified copy of $PATH via $DIST_UNMODIFIED_PATH.
			// Use it here when determining if the user still needs to update
			// their $PATH. See go.dev/issue/42563.
			path = p
		}
		if !strings.Contains(pathsep+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")
	brokenFlag := flag.Bool("broken", false, "include broken ports")
	xflagparse(0)

	var plats []string
	for p := range cgoEnabled {
		if broken[p] && !*brokenFlag {
			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
		Broken       bool `json:",omitempty"`
	}
	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],
			Broken:       broken[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)
	}
}

func setNoOpt() {
	for _, gcflag := range strings.Split(gogcflags, " ") {
		if gcflag == "-N" || gcflag == "-l" {
			noOpt = true
			break
		}
	}
}