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