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"
	"sort"
	"strings"
	"sync"
	"time"
)

// Initialization for any invocation.

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

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

	b = os.Getenv("GOBIN")
	if b == "" {
		b = pathf("%s/bin", goroot)
	}
	gobin = 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("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
	}

	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)

	defaultcflags = os.Getenv("CFLAGS")
	defaultldflags = os.Getenv("LDFLAGS")

	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("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))

	// Make the environment more predictable.
	os.Setenv("LANG", "C")
	os.Setenv("LANGUAGE", "en_US.UTF8")

	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")
}

func branchtag(branch string) (tag string, precise bool) {
	log := run(goroot, CheckExit, "git", "log", "--decorate=full", "--format=format:%d", "master.."+branch)
	tag = branch
	for row, line := range strings.Split(log, "\n") {
		// Each line is either blank, or looks like
		//	  (tag: refs/tags/go1.4rc2, refs/remotes/origin/release-branch.go1.4, refs/heads/release-branch.go1.4)
		// We need to find an element starting with refs/tags/.
		const s = " refs/tags/"
		i := strings.Index(line, s)
		if i < 0 {
			continue
		}
		// Trim off known prefix.
		line = line[i+len(s):]
		// The tag name ends at a comma or paren.
		j := strings.IndexAny(line, ",)")
		if j < 0 {
			continue // malformed line; ignore it
		}
		tag = line[:j]
		if row == 0 {
			precise = true // tag denotes HEAD
		}
		break
	}
	return
}

// 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.
	// What is the current branch?
	branch := chomp(run(goroot, CheckExit, "git", "rev-parse", "--abbrev-ref", "HEAD"))

	// What are the tags along the current branch?
	tag := "devel"
	precise := false

	// If we're on a release branch, use the closest matching tag
	// that is on the release branch (and not on the master branch).
	if strings.HasPrefix(branch, "release-branch.") {
		tag, precise = branchtag(branch)
	}

	if !precise {
		// Tag does not point at HEAD; add hash and date to version.
		tag += chomp(run(goroot, CheckExit, "git", "log", "-n", "1", "--format=format: +%h %cd", "HEAD"))
	}

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

	return tag
}

// 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))
	}

	// If $GOBIN is set and has a Go compiler, it must be cleaned.
	for _, char := range "56789" {
		if isfile(pathf("%s/%c%s", gobin, char, "g")) {
			for _, old := range oldtool {
				xremove(pathf("%s/%s", gobin, old))
			}
			break
		}
	}

	// 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)
	}

	// 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) {
			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 {
		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")
		if os.Getenv("GOEXPERIMENT") == "regabi" {
			// In order to make it easier to port runtime assembly
			// to the register ABI, we introduce a macro
			// indicating the experiment is enabled.
			//
			// Note: a similar change also appears in
			// cmd/go/internal/work/gc.go.
			//
			// TODO(austin): Remove this once we commit to the
			// register ABI (#40724).
			asmArgs = append(asmArgs, "-D=GOEXPERIMENT_REGABI=1")
		}
	}

	// 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)
}

// matchfield reports whether the field (x,y,z) matches this build.
// all the elements in the field must be satisfied.
func matchfield(f string) bool {
	for _, tag := range strings.Split(f, ",") {
		if !matchtag(tag) {
			return false
		}
	}
	return true
}

// matchtag reports whether the tag (x or !x) matches this build.
func matchtag(tag string) bool {
	if tag == "" {
		return false
	}
	if tag[0] == '!' {
		if len(tag) == 1 || tag[1] == '!' {
			return false
		}
		return !matchtag(tag[1:])
	}
	if os.Getenv("GOEXPERIMENT") == "regabi" && tag == "goexperiment.regabi" {
		// TODO: maybe we can handle GOEXPERIMENT more generally.
		// Or remove once we commit to regabi (#40724).
		return true
	}
	return tag == "gc" || tag == goos || tag == goarch || tag == "cmd_go_bootstrap" || tag == "go1.1" ||
		(goos == "android" && tag == "linux") ||
		(goos == "illumos" && tag == "solaris") ||
		(goos == "ios" && tag == "darwin")
}

// 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.