gc.go

     1  // Copyright 2011 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package work
     6  
     7  import (
     8  	"bufio"
     9  	"bytes"
    10  	"fmt"
    11  	"internal/buildcfg"
    12  	"internal/platform"
    13  	"io"
    14  	"log"
    15  	"os"
    16  	"path/filepath"
    17  	"runtime"
    18  	"strings"
    19  
    20  	"cmd/go/internal/base"
    21  	"cmd/go/internal/cfg"
    22  	"cmd/go/internal/fips140"
    23  	"cmd/go/internal/fsys"
    24  	"cmd/go/internal/gover"
    25  	"cmd/go/internal/load"
    26  	"cmd/go/internal/str"
    27  	"cmd/internal/quoted"
    28  	"crypto/sha1"
    29  )
    30  
    31  // Tests can override this by setting $TESTGO_TOOLCHAIN_VERSION.
    32  var ToolchainVersion = runtime.Version()
    33  
    34  // The Go toolchain.
    35  
    36  type gcToolchain struct{}
    37  
    38  func (gcToolchain) compiler() string {
    39  	return base.Tool("compile")
    40  }
    41  
    42  func (gcToolchain) linker() string {
    43  	return base.Tool("link")
    44  }
    45  
    46  func pkgPath(a *Action) string {
    47  	p := a.Package
    48  	ppath := p.ImportPath
    49  	if cfg.BuildBuildmode == "plugin" {
    50  		ppath = pluginPath(a)
    51  	} else if p.Name == "main" && !p.Internal.ForceLibrary {
    52  		ppath = "main"
    53  	}
    54  	return ppath
    55  }
    56  
    57  func (gcToolchain) gc(b *Builder, a *Action, archive string, importcfg, embedcfg []byte, symabis string, asmhdr bool, pgoProfile string, gofiles []string) (ofile string, output []byte, err error) {
    58  	p := a.Package
    59  	sh := b.Shell(a)
    60  	objdir := a.Objdir
    61  	if archive != "" {
    62  		ofile = archive
    63  	} else {
    64  		out := "_go_.o"
    65  		ofile = objdir + out
    66  	}
    67  
    68  	pkgpath := pkgPath(a)
    69  	defaultGcFlags := []string{"-p", pkgpath}
    70  	vers := gover.Local()
    71  	if p.Module != nil {
    72  		v := p.Module.GoVersion
    73  		if v == "" {
    74  			v = gover.DefaultGoModVersion
    75  		}
    76  		// TODO(samthanawalla): Investigate when allowedVersion is not true.
    77  		if allowedVersion(v) {
    78  			vers = v
    79  		}
    80  	}
    81  	defaultGcFlags = append(defaultGcFlags, "-lang=go"+gover.Lang(vers))
    82  	if p.Standard {
    83  		defaultGcFlags = append(defaultGcFlags, "-std")
    84  	}
    85  
    86  	// If we're giving the compiler the entire package (no C etc files), tell it that,
    87  	// so that it can give good error messages about forward declarations.
    88  	// Exceptions: a few standard packages have forward declarations for
    89  	// pieces supplied behind-the-scenes by package runtime.
    90  	extFiles := len(p.CgoFiles) + len(p.CFiles) + len(p.CXXFiles) + len(p.MFiles) + len(p.FFiles) + len(p.SFiles) + len(p.SysoFiles) + len(p.SwigFiles) + len(p.SwigCXXFiles)
    91  	if p.Standard {
    92  		switch p.ImportPath {
    93  		case "bytes", "internal/poll", "net", "os":
    94  			fallthrough
    95  		case "runtime/metrics", "runtime/pprof", "runtime/trace":
    96  			fallthrough
    97  		case "sync", "syscall", "time":
    98  			extFiles++
    99  		}
   100  	}
   101  	if extFiles == 0 {
   102  		defaultGcFlags = append(defaultGcFlags, "-complete")
   103  	}
   104  	if cfg.BuildContext.InstallSuffix != "" {
   105  		defaultGcFlags = append(defaultGcFlags, "-installsuffix", cfg.BuildContext.InstallSuffix)
   106  	}
   107  	if a.buildID != "" {
   108  		defaultGcFlags = append(defaultGcFlags, "-buildid", a.buildID)
   109  	}
   110  	if p.Internal.OmitDebug || cfg.Goos == "plan9" || cfg.Goarch == "wasm" {
   111  		defaultGcFlags = append(defaultGcFlags, "-dwarf=false")
   112  	}
   113  	if strings.HasPrefix(ToolchainVersion, "go1") && !strings.Contains(os.Args[0], "go_bootstrap") {
   114  		defaultGcFlags = append(defaultGcFlags, "-goversion", ToolchainVersion)
   115  	}
   116  	if p.Internal.Cover.Cfg != "" {
   117  		defaultGcFlags = append(defaultGcFlags, "-coveragecfg="+p.Internal.Cover.Cfg)
   118  	}
   119  	if pgoProfile != "" {
   120  		defaultGcFlags = append(defaultGcFlags, "-pgoprofile="+pgoProfile)
   121  	}
   122  	if symabis != "" {
   123  		defaultGcFlags = append(defaultGcFlags, "-symabis", symabis)
   124  	}
   125  
   126  	gcflags := str.StringList(forcedGcflags, p.Internal.Gcflags)
   127  	if p.Internal.FuzzInstrument {
   128  		gcflags = append(gcflags, fuzzInstrumentFlags()...)
   129  	}
   130  	// Add -c=N to use concurrent backend compilation, if possible.
   131  	if c := gcBackendConcurrency(gcflags); c > 1 {
   132  		defaultGcFlags = append(defaultGcFlags, fmt.Sprintf("-c=%d", c))
   133  	}
   134  
   135  	args := []any{cfg.BuildToolexec, base.Tool("compile"), "-o", ofile, "-trimpath", a.trimpath(), defaultGcFlags, gcflags}
   136  	if p.Internal.LocalPrefix == "" {
   137  		args = append(args, "-nolocalimports")
   138  	} else {
   139  		args = append(args, "-D", p.Internal.LocalPrefix)
   140  	}
   141  	if importcfg != nil {
   142  		if err := sh.writeFile(objdir+"importcfg", importcfg); err != nil {
   143  			return "", nil, err
   144  		}
   145  		args = append(args, "-importcfg", objdir+"importcfg")
   146  	}
   147  	if embedcfg != nil {
   148  		if err := sh.writeFile(objdir+"embedcfg", embedcfg); err != nil {
   149  			return "", nil, err
   150  		}
   151  		args = append(args, "-embedcfg", objdir+"embedcfg")
   152  	}
   153  	if ofile == archive {
   154  		args = append(args, "-pack")
   155  	}
   156  	if asmhdr {
   157  		args = append(args, "-asmhdr", objdir+"go_asm.h")
   158  	}
   159  
   160  	for _, f := range gofiles {
   161  		f := mkAbs(p.Dir, f)
   162  
   163  		// Handle overlays. Convert path names using fsys.Actual
   164  		// so these paths can be handed directly to tools.
   165  		// Deleted files won't show up in when scanning directories earlier,
   166  		// so Actual will never return "" (meaning a deleted file) here.
   167  		// TODO(#39958): Handle cases where the package directory
   168  		// doesn't exist on disk (this can happen when all the package's
   169  		// files are in an overlay): the code expects the package directory
   170  		// to exist and runs some tools in that directory.
   171  		// TODO(#39958): Process the overlays when the
   172  		// gofiles, cgofiles, cfiles, sfiles, and cxxfiles variables are
   173  		// created in (*Builder).build. Doing that requires rewriting the
   174  		// code that uses those values to expect absolute paths.
   175  		args = append(args, fsys.Actual(f))
   176  	}
   177  
   178  	output, err = sh.runOut(base.Cwd(), nil, args...)
   179  	return ofile, output, err
   180  }
   181  
   182  // gcBackendConcurrency returns the backend compiler concurrency level for a package compilation.
   183  func gcBackendConcurrency(gcflags []string) int {
   184  	// First, check whether we can use -c at all for this compilation.
   185  	canDashC := concurrentGCBackendCompilationEnabledByDefault
   186  
   187  	switch e := os.Getenv("GO19CONCURRENTCOMPILATION"); e {
   188  	case "0":
   189  		canDashC = false
   190  	case "1":
   191  		canDashC = true
   192  	case "":
   193  		// Not set. Use default.
   194  	default:
   195  		log.Fatalf("GO19CONCURRENTCOMPILATION must be 0, 1, or unset, got %q", e)
   196  	}
   197  
   198  	// TODO: Test and delete these conditions.
   199  	if cfg.ExperimentErr != nil || cfg.Experiment.FieldTrack || cfg.Experiment.PreemptibleLoops {
   200  		canDashC = false
   201  	}
   202  
   203  	if !canDashC {
   204  		return 1
   205  	}
   206  
   207  	// Decide how many concurrent backend compilations to allow.
   208  	//
   209  	// If we allow too many, in theory we might end up with p concurrent processes,
   210  	// each with c concurrent backend compiles, all fighting over the same resources.
   211  	// However, in practice, that seems not to happen too much.
   212  	// Most build graphs are surprisingly serial, so p==1 for much of the build.
   213  	// Furthermore, concurrent backend compilation is only enabled for a part
   214  	// of the overall compiler execution, so c==1 for much of the build.
   215  	// So don't worry too much about that interaction for now.
   216  	//
   217  	// However, in practice, setting c above 4 tends not to help very much.
   218  	// See the analysis in CL 41192.
   219  	//
   220  	// TODO(josharian): attempt to detect whether this particular compilation
   221  	// is likely to be a bottleneck, e.g. when:
   222  	//   - it has no successor packages to compile (usually package main)
   223  	//   - all paths through the build graph pass through it
   224  	//   - critical path scheduling says it is high priority
   225  	// and in such a case, set c to runtime.GOMAXPROCS(0).
   226  	// By default this is the same as runtime.NumCPU.
   227  	// We do this now when p==1.
   228  	// To limit parallelism, set GOMAXPROCS below numCPU; this may be useful
   229  	// on a low-memory builder, or if a deterministic build order is required.
   230  	c := runtime.GOMAXPROCS(0)
   231  	if cfg.BuildP == 1 {
   232  		// No process parallelism, do not cap compiler parallelism.
   233  		return c
   234  	}
   235  	// Some process parallelism. Set c to min(4, maxprocs).
   236  	if c > 4 {
   237  		c = 4
   238  	}
   239  	return c
   240  }
   241  
   242  // trimpath returns the -trimpath argument to use
   243  // when compiling the action.
   244  func (a *Action) trimpath() string {
   245  	// Keep in sync with Builder.ccompile
   246  	// The trimmed paths are a little different, but we need to trim in the
   247  	// same situations.
   248  
   249  	// Strip the object directory entirely.
   250  	objdir := strings.TrimSuffix(a.Objdir, string(filepath.Separator))
   251  	rewrite := ""
   252  
   253  	rewriteDir := a.Package.Dir
   254  	if cfg.BuildTrimpath {
   255  		importPath := a.Package.Internal.OrigImportPath
   256  		if m := a.Package.Module; m != nil && m.Version != "" {
   257  			rewriteDir = m.Path + "@" + m.Version + strings.TrimPrefix(importPath, m.Path)
   258  		} else {
   259  			rewriteDir = importPath
   260  		}
   261  		rewrite += a.Package.Dir + "=>" + rewriteDir + ";"
   262  	}
   263  
   264  	// Add rewrites for overlays. The 'from' and 'to' paths in overlays don't need to have
   265  	// same basename, so go from the overlay contents file path (passed to the compiler)
   266  	// to the path the disk path would be rewritten to.
   267  
   268  	cgoFiles := make(map[string]bool)
   269  	for _, f := range a.Package.CgoFiles {
   270  		cgoFiles[f] = true
   271  	}
   272  
   273  	// TODO(matloob): Higher up in the stack, when the logic for deciding when to make copies
   274  	// of c/c++/m/f/hfiles is consolidated, use the same logic that Build uses to determine
   275  	// whether to create the copies in objdir to decide whether to rewrite objdir to the
   276  	// package directory here.
   277  	var overlayNonGoRewrites string // rewrites for non-go files
   278  	hasCgoOverlay := false
   279  	if fsys.OverlayFile != "" {
   280  		for _, filename := range a.Package.AllFiles() {
   281  			path := filename
   282  			if !filepath.IsAbs(path) {
   283  				path = filepath.Join(a.Package.Dir, path)
   284  			}
   285  			base := filepath.Base(path)
   286  			isGo := strings.HasSuffix(filename, ".go") || strings.HasSuffix(filename, ".s")
   287  			isCgo := cgoFiles[filename] || !isGo
   288  			if fsys.Replaced(path) {
   289  				if isCgo {
   290  					hasCgoOverlay = true
   291  				} else {
   292  					rewrite += fsys.Actual(path) + "=>" + filepath.Join(rewriteDir, base) + ";"
   293  				}
   294  			} else if isCgo {
   295  				// Generate rewrites for non-Go files copied to files in objdir.
   296  				if filepath.Dir(path) == a.Package.Dir {
   297  					// This is a file copied to objdir.
   298  					overlayNonGoRewrites += filepath.Join(objdir, base) + "=>" + filepath.Join(rewriteDir, base) + ";"
   299  				}
   300  			} else {
   301  				// Non-overlay Go files are covered by the a.Package.Dir rewrite rule above.
   302  			}
   303  		}
   304  	}
   305  	if hasCgoOverlay {
   306  		rewrite += overlayNonGoRewrites
   307  	}
   308  	rewrite += objdir + "=>"
   309  
   310  	return rewrite
   311  }
   312  
   313  func asmArgs(a *Action, p *load.Package) []any {
   314  	// Add -I pkg/GOOS_GOARCH so #include "textflag.h" works in .s files.
   315  	inc := filepath.Join(cfg.GOROOT, "pkg", "include")
   316  	pkgpath := pkgPath(a)
   317  	args := []any{cfg.BuildToolexec, base.Tool("asm"), "-p", pkgpath, "-trimpath", a.trimpath(), "-I", a.Objdir, "-I", inc, "-D", "GOOS_" + cfg.Goos, "-D", "GOARCH_" + cfg.Goarch, forcedAsmflags, p.Internal.Asmflags}
   318  	if p.ImportPath == "runtime" && cfg.Goarch == "386" {
   319  		for _, arg := range forcedAsmflags {
   320  			if arg == "-dynlink" {
   321  				args = append(args, "-D=GOBUILDMODE_shared=1")
   322  			}
   323  		}
   324  	}
   325  
   326  	if cfg.Goarch == "386" {
   327  		// Define GO386_value from cfg.GO386.
   328  		args = append(args, "-D", "GO386_"+cfg.GO386)
   329  	}
   330  
   331  	if cfg.Goarch == "amd64" {
   332  		// Define GOAMD64_value from cfg.GOAMD64.
   333  		args = append(args, "-D", "GOAMD64_"+cfg.GOAMD64)
   334  	}
   335  
   336  	if cfg.Goarch == "mips" || cfg.Goarch == "mipsle" {
   337  		// Define GOMIPS_value from cfg.GOMIPS.
   338  		args = append(args, "-D", "GOMIPS_"+cfg.GOMIPS)
   339  	}
   340  
   341  	if cfg.Goarch == "mips64" || cfg.Goarch == "mips64le" {
   342  		// Define GOMIPS64_value from cfg.GOMIPS64.
   343  		args = append(args, "-D", "GOMIPS64_"+cfg.GOMIPS64)
   344  	}
   345  
   346  	if cfg.Goarch == "ppc64" || cfg.Goarch == "ppc64le" {
   347  		// Define GOPPC64_power8..N from cfg.PPC64.
   348  		// We treat each powerpc version as a superset of functionality.
   349  		switch cfg.GOPPC64 {
   350  		case "power10":
   351  			args = append(args, "-D", "GOPPC64_power10")
   352  			fallthrough
   353  		case "power9":
   354  			args = append(args, "-D", "GOPPC64_power9")
   355  			fallthrough
   356  		default: // This should always be power8.
   357  			args = append(args, "-D", "GOPPC64_power8")
   358  		}
   359  	}
   360  
   361  	if cfg.Goarch == "riscv64" {
   362  		// Define GORISCV64_value from cfg.GORISCV64.
   363  		args = append(args, "-D", "GORISCV64_"+cfg.GORISCV64)
   364  	}
   365  
   366  	if cfg.Goarch == "arm" {
   367  		// Define GOARM_value from cfg.GOARM, which can be either a version
   368  		// like "6", or a version and a FP mode, like "7,hardfloat".
   369  		switch {
   370  		case strings.Contains(cfg.GOARM, "7"):
   371  			args = append(args, "-D", "GOARM_7")
   372  			fallthrough
   373  		case strings.Contains(cfg.GOARM, "6"):
   374  			args = append(args, "-D", "GOARM_6")
   375  			fallthrough
   376  		default:
   377  			args = append(args, "-D", "GOARM_5")
   378  		}
   379  	}
   380  
   381  	if cfg.Goarch == "arm64" {
   382  		g, err := buildcfg.ParseGoarm64(cfg.GOARM64)
   383  		if err == nil && g.LSE {
   384  			args = append(args, "-D", "GOARM64_LSE")
   385  		}
   386  	}
   387  
   388  	return args
   389  }
   390  
   391  func (gcToolchain) asm(b *Builder, a *Action, sfiles []string) ([]string, error) {
   392  	p := a.Package
   393  	args := asmArgs(a, p)
   394  
   395  	var ofiles []string
   396  	for _, sfile := range sfiles {
   397  		ofile := a.Objdir + sfile[:len(sfile)-len(".s")] + ".o"
   398  		ofiles = append(ofiles, ofile)
   399  		args1 := append(args, "-o", ofile, fsys.Actual(mkAbs(p.Dir, sfile)))
   400  		if err := b.Shell(a).run(p.Dir, p.ImportPath, nil, args1...); err != nil {
   401  			return nil, err
   402  		}
   403  	}
   404  	return ofiles, nil
   405  }
   406  
   407  func (gcToolchain) symabis(b *Builder, a *Action, sfiles []string) (string, error) {
   408  	sh := b.Shell(a)
   409  
   410  	mkSymabis := func(p *load.Package, sfiles []string, path string) error {
   411  		args := asmArgs(a, p)
   412  		args = append(args, "-gensymabis", "-o", path)
   413  		for _, sfile := range sfiles {
   414  			if p.ImportPath == "runtime/cgo" && strings.HasPrefix(sfile, "gcc_") {
   415  				continue
   416  			}
   417  			args = append(args, fsys.Actual(mkAbs(p.Dir, sfile)))
   418  		}
   419  
   420  		// Supply an empty go_asm.h as if the compiler had been run.
   421  		// -gensymabis parsing is lax enough that we don't need the
   422  		// actual definitions that would appear in go_asm.h.
   423  		if err := sh.writeFile(a.Objdir+"go_asm.h", nil); err != nil {
   424  			return err
   425  		}
   426  
   427  		return sh.run(p.Dir, p.ImportPath, nil, args...)
   428  	}
   429  
   430  	var symabis string // Only set if we actually create the file
   431  	p := a.Package
   432  	if len(sfiles) != 0 {
   433  		symabis = a.Objdir + "symabis"
   434  		if err := mkSymabis(p, sfiles, symabis); err != nil {
   435  			return "", err
   436  		}
   437  	}
   438  
   439  	return symabis, nil
   440  }
   441  
   442  // toolVerify checks that the command line args writes the same output file
   443  // if run using newTool instead.
   444  // Unused now but kept around for future use.
   445  func toolVerify(a *Action, b *Builder, p *load.Package, newTool string, ofile string, args []any) error {
   446  	newArgs := make([]any, len(args))
   447  	copy(newArgs, args)
   448  	newArgs[1] = base.Tool(newTool)
   449  	newArgs[3] = ofile + ".new" // x.6 becomes x.6.new
   450  	if err := b.Shell(a).run(p.Dir, p.ImportPath, nil, newArgs...); err != nil {
   451  		return err
   452  	}
   453  	data1, err := os.ReadFile(ofile)
   454  	if err != nil {
   455  		return err
   456  	}
   457  	data2, err := os.ReadFile(ofile + ".new")
   458  	if err != nil {
   459  		return err
   460  	}
   461  	if !bytes.Equal(data1, data2) {
   462  		return fmt.Errorf("%s and %s produced different output files:\n%s\n%s", filepath.Base(args[1].(string)), newTool, strings.Join(str.StringList(args...), " "), strings.Join(str.StringList(newArgs...), " "))
   463  	}
   464  	os.Remove(ofile + ".new")
   465  	return nil
   466  }
   467  
   468  func (gcToolchain) pack(b *Builder, a *Action, afile string, ofiles []string) error {
   469  	absOfiles := make([]string, 0, len(ofiles))
   470  	for _, f := range ofiles {
   471  		absOfiles = append(absOfiles, mkAbs(a.Objdir, f))
   472  	}
   473  	absAfile := mkAbs(a.Objdir, afile)
   474  
   475  	// The archive file should have been created by the compiler.
   476  	// Since it used to not work that way, verify.
   477  	if !cfg.BuildN {
   478  		if _, err := os.Stat(absAfile); err != nil {
   479  			base.Fatalf("os.Stat of archive file failed: %v", err)
   480  		}
   481  	}
   482  
   483  	p := a.Package
   484  	sh := b.Shell(a)
   485  	if cfg.BuildN || cfg.BuildX {
   486  		cmdline := str.StringList(base.Tool("pack"), "r", absAfile, absOfiles)
   487  		sh.ShowCmd(p.Dir, "%s # internal", joinUnambiguously(cmdline))
   488  	}
   489  	if cfg.BuildN {
   490  		return nil
   491  	}
   492  	if err := packInternal(absAfile, absOfiles); err != nil {
   493  		return sh.reportCmd("", "", nil, err)
   494  	}
   495  	return nil
   496  }
   497  
   498  func packInternal(afile string, ofiles []string) error {
   499  	dst, err := os.OpenFile(afile, os.O_WRONLY|os.O_APPEND, 0)
   500  	if err != nil {
   501  		return err
   502  	}
   503  	defer dst.Close() // only for error returns or panics
   504  	w := bufio.NewWriter(dst)
   505  
   506  	for _, ofile := range ofiles {
   507  		src, err := os.Open(ofile)
   508  		if err != nil {
   509  			return err
   510  		}
   511  		fi, err := src.Stat()
   512  		if err != nil {
   513  			src.Close()
   514  			return err
   515  		}
   516  		// Note: Not using %-16.16s format because we care
   517  		// about bytes, not runes.
   518  		name := fi.Name()
   519  		if len(name) > 16 {
   520  			name = name[:16]
   521  		} else {
   522  			name += strings.Repeat(" ", 16-len(name))
   523  		}
   524  		size := fi.Size()
   525  		fmt.Fprintf(w, "%s%-12d%-6d%-6d%-8o%-10d`\n",
   526  			name, 0, 0, 0, 0644, size)
   527  		n, err := io.Copy(w, src)
   528  		src.Close()
   529  		if err == nil && n < size {
   530  			err = io.ErrUnexpectedEOF
   531  		} else if err == nil && n > size {
   532  			err = fmt.Errorf("file larger than size reported by stat")
   533  		}
   534  		if err != nil {
   535  			return fmt.Errorf("copying %s to %s: %v", ofile, afile, err)
   536  		}
   537  		if size&1 != 0 {
   538  			w.WriteByte(0)
   539  		}
   540  	}
   541  
   542  	if err := w.Flush(); err != nil {
   543  		return err
   544  	}
   545  	return dst.Close()
   546  }
   547  
   548  // setextld sets the appropriate linker flags for the specified compiler.
   549  func setextld(ldflags []string, compiler []string) ([]string, error) {
   550  	for _, f := range ldflags {
   551  		if f == "-extld" || strings.HasPrefix(f, "-extld=") {
   552  			// don't override -extld if supplied
   553  			return ldflags, nil
   554  		}
   555  	}
   556  	joined, err := quoted.Join(compiler)
   557  	if err != nil {
   558  		return nil, err
   559  	}
   560  	return append(ldflags, "-extld="+joined), nil
   561  }
   562  
   563  // pluginPath computes the package path for a plugin main package.
   564  //
   565  // This is typically the import path of the main package p, unless the
   566  // plugin is being built directly from source files. In that case we
   567  // combine the package build ID with the contents of the main package
   568  // source files. This allows us to identify two different plugins
   569  // built from two source files with the same name.
   570  func pluginPath(a *Action) string {
   571  	p := a.Package
   572  	if p.ImportPath != "command-line-arguments" {
   573  		return p.ImportPath
   574  	}
   575  	h := sha1.New()
   576  	buildID := a.buildID
   577  	if a.Mode == "link" {
   578  		// For linking, use the main package's build ID instead of
   579  		// the binary's build ID, so it is the same hash used in
   580  		// compiling and linking.
   581  		// When compiling, we use actionID/actionID (instead of
   582  		// actionID/contentID) as a temporary build ID to compute
   583  		// the hash. Do the same here. (See buildid.go:useCache)
   584  		// The build ID matters because it affects the overall hash
   585  		// in the plugin's pseudo-import path returned below.
   586  		// We need to use the same import path when compiling and linking.
   587  		id := strings.Split(buildID, buildIDSeparator)
   588  		buildID = id[1] + buildIDSeparator + id[1]
   589  	}
   590  	fmt.Fprintf(h, "build ID: %s\n", buildID)
   591  	for _, file := range str.StringList(p.GoFiles, p.CgoFiles, p.SFiles) {
   592  		data, err := os.ReadFile(filepath.Join(p.Dir, file))
   593  		if err != nil {
   594  			base.Fatalf("go: %s", err)
   595  		}
   596  		h.Write(data)
   597  	}
   598  	return fmt.Sprintf("plugin/unnamed-%x", h.Sum(nil))
   599  }
   600  
   601  func (gcToolchain) ld(b *Builder, root *Action, targetPath, importcfg, mainpkg string) error {
   602  	cxx := len(root.Package.CXXFiles) > 0 || len(root.Package.SwigCXXFiles) > 0
   603  	for _, a := range root.Deps {
   604  		if a.Package != nil && (len(a.Package.CXXFiles) > 0 || len(a.Package.SwigCXXFiles) > 0) {
   605  			cxx = true
   606  		}
   607  	}
   608  	var ldflags []string
   609  	if cfg.BuildContext.InstallSuffix != "" {
   610  		ldflags = append(ldflags, "-installsuffix", cfg.BuildContext.InstallSuffix)
   611  	}
   612  	if root.Package.Internal.OmitDebug {
   613  		ldflags = append(ldflags, "-s", "-w")
   614  	}
   615  	if cfg.BuildBuildmode == "plugin" {
   616  		ldflags = append(ldflags, "-pluginpath", pluginPath(root))
   617  	}
   618  	if fips140.Enabled() {
   619  		ldflags = append(ldflags, "-fipso", filepath.Join(root.Objdir, "fips.o"))
   620  	}
   621  
   622  	// Store BuildID inside toolchain binaries as a unique identifier of the
   623  	// tool being run, for use by content-based staleness determination.
   624  	if root.Package.Goroot && strings.HasPrefix(root.Package.ImportPath, "cmd/") {
   625  		// External linking will include our build id in the external
   626  		// linker's build id, which will cause our build id to not
   627  		// match the next time the tool is built.
   628  		// Rely on the external build id instead.
   629  		if !platform.MustLinkExternal(cfg.Goos, cfg.Goarch, false) {
   630  			ldflags = append(ldflags, "-X=cmd/internal/objabi.buildID="+root.buildID)
   631  		}
   632  	}
   633  
   634  	// Store default GODEBUG in binaries.
   635  	if root.Package.DefaultGODEBUG != "" {
   636  		ldflags = append(ldflags, "-X=runtime.godebugDefault="+root.Package.DefaultGODEBUG)
   637  	}
   638  
   639  	// If the user has not specified the -extld option, then specify the
   640  	// appropriate linker. In case of C++ code, use the compiler named
   641  	// by the CXX environment variable or defaultCXX if CXX is not set.
   642  	// Else, use the CC environment variable and defaultCC as fallback.
   643  	var compiler []string
   644  	if cxx {
   645  		compiler = envList("CXX", cfg.DefaultCXX(cfg.Goos, cfg.Goarch))
   646  	} else {
   647  		compiler = envList("CC", cfg.DefaultCC(cfg.Goos, cfg.Goarch))
   648  	}
   649  	ldflags = append(ldflags, "-buildmode="+ldBuildmode)
   650  	if root.buildID != "" {
   651  		ldflags = append(ldflags, "-buildid="+root.buildID)
   652  	}
   653  	ldflags = append(ldflags, forcedLdflags...)
   654  	ldflags = append(ldflags, root.Package.Internal.Ldflags...)
   655  	ldflags, err := setextld(ldflags, compiler)
   656  	if err != nil {
   657  		return err
   658  	}
   659  
   660  	// On OS X when using external linking to build a shared library,
   661  	// the argument passed here to -o ends up recorded in the final
   662  	// shared library in the LC_ID_DYLIB load command.
   663  	// To avoid putting the temporary output directory name there
   664  	// (and making the resulting shared library useless),
   665  	// run the link in the output directory so that -o can name
   666  	// just the final path element.
   667  	// On Windows, DLL file name is recorded in PE file
   668  	// export section, so do like on OS X.
   669  	// On Linux, for a shared object, at least with the Gold linker,
   670  	// the output file path is recorded in the .gnu.version_d section.
   671  	dir := "."
   672  	if cfg.BuildBuildmode == "c-shared" || cfg.BuildBuildmode == "plugin" {
   673  		dir, targetPath = filepath.Split(targetPath)
   674  	}
   675  
   676  	env := []string{}
   677  	// When -trimpath is used, GOROOT is cleared
   678  	if cfg.BuildTrimpath {
   679  		env = append(env, "GOROOT=")
   680  	} else {
   681  		env = append(env, "GOROOT="+cfg.GOROOT)
   682  	}
   683  	return b.Shell(root).run(dir, root.Package.ImportPath, env, cfg.BuildToolexec, base.Tool("link"), "-o", targetPath, "-importcfg", importcfg, ldflags, mainpkg)
   684  }
   685  
   686  func (gcToolchain) ldShared(b *Builder, root *Action, toplevelactions []*Action, targetPath, importcfg string, allactions []*Action) error {
   687  	ldflags := []string{"-installsuffix", cfg.BuildContext.InstallSuffix}
   688  	ldflags = append(ldflags, "-buildmode=shared")
   689  	ldflags = append(ldflags, forcedLdflags...)
   690  	ldflags = append(ldflags, root.Package.Internal.Ldflags...)
   691  	cxx := false
   692  	for _, a := range allactions {
   693  		if a.Package != nil && (len(a.Package.CXXFiles) > 0 || len(a.Package.SwigCXXFiles) > 0) {
   694  			cxx = true
   695  		}
   696  	}
   697  	// If the user has not specified the -extld option, then specify the
   698  	// appropriate linker. In case of C++ code, use the compiler named
   699  	// by the CXX environment variable or defaultCXX if CXX is not set.
   700  	// Else, use the CC environment variable and defaultCC as fallback.
   701  	var compiler []string
   702  	if cxx {
   703  		compiler = envList("CXX", cfg.DefaultCXX(cfg.Goos, cfg.Goarch))
   704  	} else {
   705  		compiler = envList("CC", cfg.DefaultCC(cfg.Goos, cfg.Goarch))
   706  	}
   707  	ldflags, err := setextld(ldflags, compiler)
   708  	if err != nil {
   709  		return err
   710  	}
   711  	for _, d := range toplevelactions {
   712  		if !strings.HasSuffix(d.Target, ".a") { // omit unsafe etc and actions for other shared libraries
   713  			continue
   714  		}
   715  		ldflags = append(ldflags, d.Package.ImportPath+"="+d.Target)
   716  	}
   717  
   718  	// On OS X when using external linking to build a shared library,
   719  	// the argument passed here to -o ends up recorded in the final
   720  	// shared library in the LC_ID_DYLIB load command.
   721  	// To avoid putting the temporary output directory name there
   722  	// (and making the resulting shared library useless),
   723  	// run the link in the output directory so that -o can name
   724  	// just the final path element.
   725  	// On Windows, DLL file name is recorded in PE file
   726  	// export section, so do like on OS X.
   727  	// On Linux, for a shared object, at least with the Gold linker,
   728  	// the output file path is recorded in the .gnu.version_d section.
   729  	dir, targetPath := filepath.Split(targetPath)
   730  
   731  	return b.Shell(root).run(dir, targetPath, nil, cfg.BuildToolexec, base.Tool("link"), "-o", targetPath, "-importcfg", importcfg, ldflags)
   732  }
   733  
   734  func (gcToolchain) cc(b *Builder, a *Action, ofile, cfile string) error {
   735  	return fmt.Errorf("%s: C source files not supported without cgo", mkAbs(a.Package.Dir, cfile))
   736  }
   737
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