action.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  // Action graph creation (planning).
     6  
     7  package work
     8  
     9  import (
    10  	"bufio"
    11  	"bytes"
    12  	"cmd/internal/cov/covcmd"
    13  	"container/heap"
    14  	"context"
    15  	"debug/elf"
    16  	"encoding/json"
    17  	"fmt"
    18  	"internal/platform"
    19  	"os"
    20  	"path/filepath"
    21  	"strings"
    22  	"sync"
    23  	"time"
    24  
    25  	"cmd/go/internal/base"
    26  	"cmd/go/internal/cache"
    27  	"cmd/go/internal/cfg"
    28  	"cmd/go/internal/load"
    29  	"cmd/go/internal/str"
    30  	"cmd/go/internal/trace"
    31  	"cmd/internal/buildid"
    32  	"cmd/internal/robustio"
    33  )
    34  
    35  // A Builder holds global state about a build.
    36  // It does not hold per-package state, because we
    37  // build packages in parallel, and the builder is shared.
    38  type Builder struct {
    39  	WorkDir            string                    // the temporary work directory (ends in filepath.Separator)
    40  	actionCache        map[cacheKey]*Action      // a cache of already-constructed actions
    41  	flagCache          map[[2]string]bool        // a cache of supported compiler flags
    42  	gccCompilerIDCache map[string]cache.ActionID // cache for gccCompilerID
    43  
    44  	IsCmdList           bool // running as part of go list; set p.Stale and additional fields below
    45  	NeedError           bool // list needs p.Error
    46  	NeedExport          bool // list needs p.Export
    47  	NeedCompiledGoFiles bool // list needs p.CompiledGoFiles
    48  	AllowErrors         bool // errors don't immediately exit the program
    49  
    50  	objdirSeq int // counter for NewObjdir
    51  	pkgSeq    int
    52  
    53  	backgroundSh *Shell // Shell that per-Action Shells are derived from
    54  
    55  	exec      sync.Mutex
    56  	readySema chan bool
    57  	ready     actionQueue
    58  
    59  	id           sync.Mutex
    60  	toolIDCache  map[string]string // tool name -> tool ID
    61  	buildIDCache map[string]string // file name -> build ID
    62  }
    63  
    64  // NOTE: Much of Action would not need to be exported if not for test.
    65  // Maybe test functionality should move into this package too?
    66  
    67  // An Actor runs an action.
    68  type Actor interface {
    69  	Act(*Builder, context.Context, *Action) error
    70  }
    71  
    72  // An ActorFunc is an Actor that calls the function.
    73  type ActorFunc func(*Builder, context.Context, *Action) error
    74  
    75  func (f ActorFunc) Act(b *Builder, ctx context.Context, a *Action) error {
    76  	return f(b, ctx, a)
    77  }
    78  
    79  // An Action represents a single action in the action graph.
    80  type Action struct {
    81  	Mode       string        // description of action operation
    82  	Package    *load.Package // the package this action works on
    83  	Deps       []*Action     // actions that must happen before this one
    84  	Actor      Actor         // the action itself (nil = no-op)
    85  	IgnoreFail bool          // whether to run f even if dependencies fail
    86  	TestOutput *bytes.Buffer // test output buffer
    87  	Args       []string      // additional args for runProgram
    88  
    89  	triggers []*Action // inverse of deps
    90  
    91  	buggyInstall bool // is this a buggy install (see -linkshared)?
    92  
    93  	TryCache func(*Builder, *Action) bool // callback for cache bypass
    94  
    95  	CacheExecutable bool // Whether to cache executables produced by link steps
    96  
    97  	// Generated files, directories.
    98  	Objdir   string         // directory for intermediate objects
    99  	Target   string         // goal of the action: the created package or executable
   100  	built    string         // the actual created package or executable
   101  	actionID cache.ActionID // cache ID of action input
   102  	buildID  string         // build ID of action output
   103  
   104  	VetxOnly  bool       // Mode=="vet": only being called to supply info about dependencies
   105  	needVet   bool       // Mode=="build": need to fill in vet config
   106  	needBuild bool       // Mode=="build": need to do actual build (can be false if needVet is true)
   107  	vetCfg    *vetConfig // vet config
   108  	output    []byte     // output redirect buffer (nil means use b.Print)
   109  
   110  	sh *Shell // lazily created per-Action shell; see Builder.Shell
   111  
   112  	// Execution state.
   113  	pending      int               // number of deps yet to complete
   114  	priority     int               // relative execution priority
   115  	Failed       *Action           // set to root cause if the action failed
   116  	json         *actionJSON       // action graph information
   117  	nonGoOverlay map[string]string // map from non-.go source files to copied files in objdir. Nil if no overlay is used.
   118  	traceSpan    *trace.Span
   119  }
   120  
   121  // BuildActionID returns the action ID section of a's build ID.
   122  func (a *Action) BuildActionID() string { return actionID(a.buildID) }
   123  
   124  // BuildContentID returns the content ID section of a's build ID.
   125  func (a *Action) BuildContentID() string { return contentID(a.buildID) }
   126  
   127  // BuildID returns a's build ID.
   128  func (a *Action) BuildID() string { return a.buildID }
   129  
   130  // BuiltTarget returns the actual file that was built. This differs
   131  // from Target when the result was cached.
   132  func (a *Action) BuiltTarget() string { return a.built }
   133  
   134  // An actionQueue is a priority queue of actions.
   135  type actionQueue []*Action
   136  
   137  // Implement heap.Interface
   138  func (q *actionQueue) Len() int           { return len(*q) }
   139  func (q *actionQueue) Swap(i, j int)      { (*q)[i], (*q)[j] = (*q)[j], (*q)[i] }
   140  func (q *actionQueue) Less(i, j int) bool { return (*q)[i].priority < (*q)[j].priority }
   141  func (q *actionQueue) Push(x any)         { *q = append(*q, x.(*Action)) }
   142  func (q *actionQueue) Pop() any {
   143  	n := len(*q) - 1
   144  	x := (*q)[n]
   145  	*q = (*q)[:n]
   146  	return x
   147  }
   148  
   149  func (q *actionQueue) push(a *Action) {
   150  	if a.json != nil {
   151  		a.json.TimeReady = time.Now()
   152  	}
   153  	heap.Push(q, a)
   154  }
   155  
   156  func (q *actionQueue) pop() *Action {
   157  	return heap.Pop(q).(*Action)
   158  }
   159  
   160  type actionJSON struct {
   161  	ID         int
   162  	Mode       string
   163  	Package    string
   164  	Deps       []int     `json:",omitempty"`
   165  	IgnoreFail bool      `json:",omitempty"`
   166  	Args       []string  `json:",omitempty"`
   167  	Link       bool      `json:",omitempty"`
   168  	Objdir     string    `json:",omitempty"`
   169  	Target     string    `json:",omitempty"`
   170  	Priority   int       `json:",omitempty"`
   171  	Failed     bool      `json:",omitempty"`
   172  	Built      string    `json:",omitempty"`
   173  	VetxOnly   bool      `json:",omitempty"`
   174  	NeedVet    bool      `json:",omitempty"`
   175  	NeedBuild  bool      `json:",omitempty"`
   176  	ActionID   string    `json:",omitempty"`
   177  	BuildID    string    `json:",omitempty"`
   178  	TimeReady  time.Time `json:",omitempty"`
   179  	TimeStart  time.Time `json:",omitempty"`
   180  	TimeDone   time.Time `json:",omitempty"`
   181  
   182  	Cmd     []string      // `json:",omitempty"`
   183  	CmdReal time.Duration `json:",omitempty"`
   184  	CmdUser time.Duration `json:",omitempty"`
   185  	CmdSys  time.Duration `json:",omitempty"`
   186  }
   187  
   188  // cacheKey is the key for the action cache.
   189  type cacheKey struct {
   190  	mode string
   191  	p    *load.Package
   192  }
   193  
   194  func actionGraphJSON(a *Action) string {
   195  	var workq []*Action
   196  	var inWorkq = make(map[*Action]int)
   197  
   198  	add := func(a *Action) {
   199  		if _, ok := inWorkq[a]; ok {
   200  			return
   201  		}
   202  		inWorkq[a] = len(workq)
   203  		workq = append(workq, a)
   204  	}
   205  	add(a)
   206  
   207  	for i := 0; i < len(workq); i++ {
   208  		for _, dep := range workq[i].Deps {
   209  			add(dep)
   210  		}
   211  	}
   212  
   213  	list := make([]*actionJSON, 0, len(workq))
   214  	for id, a := range workq {
   215  		if a.json == nil {
   216  			a.json = &actionJSON{
   217  				Mode:       a.Mode,
   218  				ID:         id,
   219  				IgnoreFail: a.IgnoreFail,
   220  				Args:       a.Args,
   221  				Objdir:     a.Objdir,
   222  				Target:     a.Target,
   223  				Failed:     a.Failed != nil,
   224  				Priority:   a.priority,
   225  				Built:      a.built,
   226  				VetxOnly:   a.VetxOnly,
   227  				NeedBuild:  a.needBuild,
   228  				NeedVet:    a.needVet,
   229  			}
   230  			if a.Package != nil {
   231  				// TODO(rsc): Make this a unique key for a.Package somehow.
   232  				a.json.Package = a.Package.ImportPath
   233  			}
   234  			for _, a1 := range a.Deps {
   235  				a.json.Deps = append(a.json.Deps, inWorkq[a1])
   236  			}
   237  		}
   238  		list = append(list, a.json)
   239  	}
   240  
   241  	js, err := json.MarshalIndent(list, "", "\t")
   242  	if err != nil {
   243  		fmt.Fprintf(os.Stderr, "go: writing debug action graph: %v\n", err)
   244  		return ""
   245  	}
   246  	return string(js)
   247  }
   248  
   249  // BuildMode specifies the build mode:
   250  // are we just building things or also installing the results?
   251  type BuildMode int
   252  
   253  const (
   254  	ModeBuild BuildMode = iota
   255  	ModeInstall
   256  	ModeBuggyInstall
   257  
   258  	ModeVetOnly = 1 << 8
   259  )
   260  
   261  // NewBuilder returns a new Builder ready for use.
   262  //
   263  // If workDir is the empty string, NewBuilder creates a WorkDir if needed
   264  // and arranges for it to be removed in case of an unclean exit.
   265  // The caller must Close the builder explicitly to clean up the WorkDir
   266  // before a clean exit.
   267  func NewBuilder(workDir string) *Builder {
   268  	b := new(Builder)
   269  
   270  	b.actionCache = make(map[cacheKey]*Action)
   271  	b.toolIDCache = make(map[string]string)
   272  	b.buildIDCache = make(map[string]string)
   273  
   274  	printWorkDir := false
   275  	if workDir != "" {
   276  		b.WorkDir = workDir
   277  	} else if cfg.BuildN {
   278  		b.WorkDir = "$WORK"
   279  	} else {
   280  		if !buildInitStarted {
   281  			panic("internal error: NewBuilder called before BuildInit")
   282  		}
   283  		tmp, err := os.MkdirTemp(cfg.Getenv("GOTMPDIR"), "go-build")
   284  		if err != nil {
   285  			base.Fatalf("go: creating work dir: %v", err)
   286  		}
   287  		if !filepath.IsAbs(tmp) {
   288  			abs, err := filepath.Abs(tmp)
   289  			if err != nil {
   290  				os.RemoveAll(tmp)
   291  				base.Fatalf("go: creating work dir: %v", err)
   292  			}
   293  			tmp = abs
   294  		}
   295  		b.WorkDir = tmp
   296  		builderWorkDirs.Store(b, b.WorkDir)
   297  		printWorkDir = cfg.BuildX || cfg.BuildWork
   298  	}
   299  
   300  	b.backgroundSh = NewShell(b.WorkDir, nil)
   301  
   302  	if printWorkDir {
   303  		b.BackgroundShell().Printf("WORK=%s\n", b.WorkDir)
   304  	}
   305  
   306  	if err := CheckGOOSARCHPair(cfg.Goos, cfg.Goarch); err != nil {
   307  		fmt.Fprintf(os.Stderr, "go: %v\n", err)
   308  		base.SetExitStatus(2)
   309  		base.Exit()
   310  	}
   311  
   312  	for _, tag := range cfg.BuildContext.BuildTags {
   313  		if strings.Contains(tag, ",") {
   314  			fmt.Fprintf(os.Stderr, "go: -tags space-separated list contains comma\n")
   315  			base.SetExitStatus(2)
   316  			base.Exit()
   317  		}
   318  	}
   319  
   320  	return b
   321  }
   322  
   323  var builderWorkDirs sync.Map // *Builder → WorkDir
   324  
   325  func (b *Builder) Close() error {
   326  	wd, ok := builderWorkDirs.Load(b)
   327  	if !ok {
   328  		return nil
   329  	}
   330  	defer builderWorkDirs.Delete(b)
   331  
   332  	if b.WorkDir != wd.(string) {
   333  		base.Errorf("go: internal error: Builder WorkDir unexpectedly changed from %s to %s", wd, b.WorkDir)
   334  	}
   335  
   336  	if !cfg.BuildWork {
   337  		if err := robustio.RemoveAll(b.WorkDir); err != nil {
   338  			return err
   339  		}
   340  	}
   341  	b.WorkDir = ""
   342  	return nil
   343  }
   344  
   345  func closeBuilders() {
   346  	leakedBuilders := 0
   347  	builderWorkDirs.Range(func(bi, _ any) bool {
   348  		leakedBuilders++
   349  		if err := bi.(*Builder).Close(); err != nil {
   350  			base.Error(err)
   351  		}
   352  		return true
   353  	})
   354  
   355  	if leakedBuilders > 0 && base.GetExitStatus() == 0 {
   356  		fmt.Fprintf(os.Stderr, "go: internal error: Builder leaked on successful exit\n")
   357  		base.SetExitStatus(1)
   358  	}
   359  }
   360  
   361  func CheckGOOSARCHPair(goos, goarch string) error {
   362  	if !platform.BuildModeSupported(cfg.BuildContext.Compiler, "default", goos, goarch) {
   363  		return fmt.Errorf("unsupported GOOS/GOARCH pair %s/%s", goos, goarch)
   364  	}
   365  	return nil
   366  }
   367  
   368  // NewObjdir returns the name of a fresh object directory under b.WorkDir.
   369  // It is up to the caller to call b.Mkdir on the result at an appropriate time.
   370  // The result ends in a slash, so that file names in that directory
   371  // can be constructed with direct string addition.
   372  //
   373  // NewObjdir must be called only from a single goroutine at a time,
   374  // so it is safe to call during action graph construction, but it must not
   375  // be called during action graph execution.
   376  func (b *Builder) NewObjdir() string {
   377  	b.objdirSeq++
   378  	return str.WithFilePathSeparator(filepath.Join(b.WorkDir, fmt.Sprintf("b%03d", b.objdirSeq)))
   379  }
   380  
   381  // readpkglist returns the list of packages that were built into the shared library
   382  // at shlibpath. For the native toolchain this list is stored, newline separated, in
   383  // an ELF note with name "Go\x00\x00" and type 1. For GCCGO it is extracted from the
   384  // .go_export section.
   385  func readpkglist(shlibpath string) (pkgs []*load.Package) {
   386  	var stk load.ImportStack
   387  	if cfg.BuildToolchainName == "gccgo" {
   388  		f, err := elf.Open(shlibpath)
   389  		if err != nil {
   390  			base.Fatal(fmt.Errorf("failed to open shared library: %v", err))
   391  		}
   392  		defer f.Close()
   393  		sect := f.Section(".go_export")
   394  		if sect == nil {
   395  			base.Fatal(fmt.Errorf("%s: missing .go_export section", shlibpath))
   396  		}
   397  		data, err := sect.Data()
   398  		if err != nil {
   399  			base.Fatal(fmt.Errorf("%s: failed to read .go_export section: %v", shlibpath, err))
   400  		}
   401  		pkgpath := []byte("pkgpath ")
   402  		for _, line := range bytes.Split(data, []byte{'\n'}) {
   403  			if path, found := bytes.CutPrefix(line, pkgpath); found {
   404  				path = bytes.TrimSuffix(path, []byte{';'})
   405  				pkgs = append(pkgs, load.LoadPackageWithFlags(string(path), base.Cwd(), &stk, nil, 0))
   406  			}
   407  		}
   408  	} else {
   409  		pkglistbytes, err := buildid.ReadELFNote(shlibpath, "Go\x00\x00", 1)
   410  		if err != nil {
   411  			base.Fatalf("readELFNote failed: %v", err)
   412  		}
   413  		scanner := bufio.NewScanner(bytes.NewBuffer(pkglistbytes))
   414  		for scanner.Scan() {
   415  			t := scanner.Text()
   416  			pkgs = append(pkgs, load.LoadPackageWithFlags(t, base.Cwd(), &stk, nil, 0))
   417  		}
   418  	}
   419  	return
   420  }
   421  
   422  // cacheAction looks up {mode, p} in the cache and returns the resulting action.
   423  // If the cache has no such action, f() is recorded and returned.
   424  // TODO(rsc): Change the second key from *load.Package to interface{},
   425  // to make the caching in linkShared less awkward?
   426  func (b *Builder) cacheAction(mode string, p *load.Package, f func() *Action) *Action {
   427  	a := b.actionCache[cacheKey{mode, p}]
   428  	if a == nil {
   429  		a = f()
   430  		b.actionCache[cacheKey{mode, p}] = a
   431  	}
   432  	return a
   433  }
   434  
   435  // AutoAction returns the "right" action for go build or go install of p.
   436  func (b *Builder) AutoAction(mode, depMode BuildMode, p *load.Package) *Action {
   437  	if p.Name == "main" {
   438  		return b.LinkAction(mode, depMode, p)
   439  	}
   440  	return b.CompileAction(mode, depMode, p)
   441  }
   442  
   443  // buildActor implements the Actor interface for package build
   444  // actions. For most package builds this simply means invoking th
   445  // *Builder.build method; in the case of "go test -cover" for
   446  // a package with no test files, we stores some additional state
   447  // information in the build actor to help with reporting.
   448  type buildActor struct {
   449  	// name of static meta-data file fragment emitted by the cover
   450  	// tool as part of the package build action, for selected
   451  	// "go test -cover" runs.
   452  	covMetaFileName string
   453  }
   454  
   455  // newBuildActor returns a new buildActor object, setting up the
   456  // covMetaFileName field if 'genCoverMeta' flag is set.
   457  func newBuildActor(p *load.Package, genCoverMeta bool) *buildActor {
   458  	ba := &buildActor{}
   459  	if genCoverMeta {
   460  		ba.covMetaFileName = covcmd.MetaFileForPackage(p.ImportPath)
   461  	}
   462  	return ba
   463  }
   464  
   465  func (ba *buildActor) Act(b *Builder, ctx context.Context, a *Action) error {
   466  	return b.build(ctx, a)
   467  }
   468  
   469  // pgoActionID computes the action ID for a preprocess PGO action.
   470  func (b *Builder) pgoActionID(input string) cache.ActionID {
   471  	h := cache.NewHash("preprocess PGO profile " + input)
   472  
   473  	fmt.Fprintf(h, "preprocess PGO profile\n")
   474  	fmt.Fprintf(h, "preprofile %s\n", b.toolID("preprofile"))
   475  	fmt.Fprintf(h, "input %q\n", b.fileHash(input))
   476  
   477  	return h.Sum()
   478  }
   479  
   480  // pgoActor implements the Actor interface for preprocessing PGO profiles.
   481  type pgoActor struct {
   482  	// input is the path to the original pprof profile.
   483  	input string
   484  }
   485  
   486  func (p *pgoActor) Act(b *Builder, ctx context.Context, a *Action) error {
   487  	if b.useCache(a, b.pgoActionID(p.input), a.Target, !b.IsCmdList) || b.IsCmdList {
   488  		return nil
   489  	}
   490  	defer b.flushOutput(a)
   491  
   492  	sh := b.Shell(a)
   493  
   494  	if err := sh.Mkdir(a.Objdir); err != nil {
   495  		return err
   496  	}
   497  
   498  	if err := sh.run(".", p.input, nil, cfg.BuildToolexec, base.Tool("preprofile"), "-o", a.Target, "-i", p.input); err != nil {
   499  		return err
   500  	}
   501  
   502  	// N.B. Builder.build looks for the out in a.built, regardless of
   503  	// whether this came from cache.
   504  	a.built = a.Target
   505  
   506  	if !cfg.BuildN {
   507  		// Cache the output.
   508  		//
   509  		// N.B. We don't use updateBuildID here, as preprocessed PGO profiles
   510  		// do not contain a build ID. updateBuildID is typically responsible
   511  		// for adding to the cache, thus we must do so ourselves instead.
   512  
   513  		r, err := os.Open(a.Target)
   514  		if err != nil {
   515  			return fmt.Errorf("error opening target for caching: %w", err)
   516  		}
   517  
   518  		c := cache.Default()
   519  		outputID, _, err := c.Put(a.actionID, r)
   520  		r.Close()
   521  		if err != nil {
   522  			return fmt.Errorf("error adding target to cache: %w", err)
   523  		}
   524  		if cfg.BuildX {
   525  			sh.ShowCmd("", "%s # internal", joinUnambiguously(str.StringList("cp", a.Target, c.OutputFile(outputID))))
   526  		}
   527  	}
   528  
   529  	return nil
   530  }
   531  
   532  // CompileAction returns the action for compiling and possibly installing
   533  // (according to mode) the given package. The resulting action is only
   534  // for building packages (archives), never for linking executables.
   535  // depMode is the action (build or install) to use when building dependencies.
   536  // To turn package main into an executable, call b.Link instead.
   537  func (b *Builder) CompileAction(mode, depMode BuildMode, p *load.Package) *Action {
   538  	vetOnly := mode&ModeVetOnly != 0
   539  	mode &^= ModeVetOnly
   540  
   541  	if mode != ModeBuild && p.Target == "" {
   542  		// No permanent target.
   543  		mode = ModeBuild
   544  	}
   545  	if mode != ModeBuild && p.Name == "main" {
   546  		// We never install the .a file for a main package.
   547  		mode = ModeBuild
   548  	}
   549  
   550  	// Construct package build action.
   551  	a := b.cacheAction("build", p, func() *Action {
   552  		a := &Action{
   553  			Mode:    "build",
   554  			Package: p,
   555  			Actor:   newBuildActor(p, p.Internal.Cover.GenMeta),
   556  			Objdir:  b.NewObjdir(),
   557  		}
   558  
   559  		if p.Error == nil || !p.Error.IsImportCycle {
   560  			for _, p1 := range p.Internal.Imports {
   561  				a.Deps = append(a.Deps, b.CompileAction(depMode, depMode, p1))
   562  			}
   563  		}
   564  
   565  		if p.Internal.PGOProfile != "" {
   566  			pgoAction := b.cacheAction("preprocess PGO profile "+p.Internal.PGOProfile, nil, func() *Action {
   567  				a := &Action{
   568  					Mode:   "preprocess PGO profile",
   569  					Actor:  &pgoActor{input: p.Internal.PGOProfile},
   570  					Objdir: b.NewObjdir(),
   571  				}
   572  				a.Target = filepath.Join(a.Objdir, "pgo.preprofile")
   573  
   574  				return a
   575  			})
   576  			a.Deps = append(a.Deps, pgoAction)
   577  		}
   578  
   579  		if p.Standard {
   580  			switch p.ImportPath {
   581  			case "builtin", "unsafe":
   582  				// Fake packages - nothing to build.
   583  				a.Mode = "built-in package"
   584  				a.Actor = nil
   585  				return a
   586  			}
   587  
   588  			// gccgo standard library is "fake" too.
   589  			if cfg.BuildToolchainName == "gccgo" {
   590  				// the target name is needed for cgo.
   591  				a.Mode = "gccgo stdlib"
   592  				a.Target = p.Target
   593  				a.Actor = nil
   594  				return a
   595  			}
   596  		}
   597  
   598  		return a
   599  	})
   600  
   601  	// Find the build action; the cache entry may have been replaced
   602  	// by the install action during (*Builder).installAction.
   603  	buildAction := a
   604  	switch buildAction.Mode {
   605  	case "build", "built-in package", "gccgo stdlib":
   606  		// ok
   607  	case "build-install":
   608  		buildAction = a.Deps[0]
   609  	default:
   610  		panic("lost build action: " + buildAction.Mode)
   611  	}
   612  	buildAction.needBuild = buildAction.needBuild || !vetOnly
   613  
   614  	// Construct install action.
   615  	if mode == ModeInstall || mode == ModeBuggyInstall {
   616  		a = b.installAction(a, mode)
   617  	}
   618  
   619  	return a
   620  }
   621  
   622  // VetAction returns the action for running go vet on package p.
   623  // It depends on the action for compiling p.
   624  // If the caller may be causing p to be installed, it is up to the caller
   625  // to make sure that the install depends on (runs after) vet.
   626  func (b *Builder) VetAction(mode, depMode BuildMode, p *load.Package) *Action {
   627  	a := b.vetAction(mode, depMode, p)
   628  	a.VetxOnly = false
   629  	return a
   630  }
   631  
   632  func (b *Builder) vetAction(mode, depMode BuildMode, p *load.Package) *Action {
   633  	// Construct vet action.
   634  	a := b.cacheAction("vet", p, func() *Action {
   635  		a1 := b.CompileAction(mode|ModeVetOnly, depMode, p)
   636  
   637  		// vet expects to be able to import "fmt".
   638  		var stk load.ImportStack
   639  		stk.Push(load.NewImportInfo("vet", nil))
   640  		p1, err := load.LoadImportWithFlags("fmt", p.Dir, p, &stk, nil, 0)
   641  		if err != nil {
   642  			base.Fatalf("unexpected error loading fmt package from package %s: %v", p.ImportPath, err)
   643  		}
   644  		stk.Pop()
   645  		aFmt := b.CompileAction(ModeBuild, depMode, p1)
   646  
   647  		var deps []*Action
   648  		if a1.buggyInstall {
   649  			// (*Builder).vet expects deps[0] to be the package
   650  			// and deps[1] to be "fmt". If we see buggyInstall
   651  			// here then a1 is an install of a shared library,
   652  			// and the real package is a1.Deps[0].
   653  			deps = []*Action{a1.Deps[0], aFmt, a1}
   654  		} else {
   655  			deps = []*Action{a1, aFmt}
   656  		}
   657  		for _, p1 := range p.Internal.Imports {
   658  			deps = append(deps, b.vetAction(mode, depMode, p1))
   659  		}
   660  
   661  		a := &Action{
   662  			Mode:       "vet",
   663  			Package:    p,
   664  			Deps:       deps,
   665  			Objdir:     a1.Objdir,
   666  			VetxOnly:   true,
   667  			IgnoreFail: true, // it's OK if vet of dependencies "fails" (reports problems)
   668  		}
   669  		if a1.Actor == nil {
   670  			// Built-in packages like unsafe.
   671  			return a
   672  		}
   673  		deps[0].needVet = true
   674  		a.Actor = ActorFunc((*Builder).vet)
   675  		return a
   676  	})
   677  	return a
   678  }
   679  
   680  // LinkAction returns the action for linking p into an executable
   681  // and possibly installing the result (according to mode).
   682  // depMode is the action (build or install) to use when compiling dependencies.
   683  func (b *Builder) LinkAction(mode, depMode BuildMode, p *load.Package) *Action {
   684  	// Construct link action.
   685  	a := b.cacheAction("link", p, func() *Action {
   686  		a := &Action{
   687  			Mode:    "link",
   688  			Package: p,
   689  		}
   690  
   691  		a1 := b.CompileAction(ModeBuild, depMode, p)
   692  		a.Actor = ActorFunc((*Builder).link)
   693  		a.Deps = []*Action{a1}
   694  		a.Objdir = a1.Objdir
   695  
   696  		// An executable file. (This is the name of a temporary file.)
   697  		// Because we run the temporary file in 'go run' and 'go test',
   698  		// the name will show up in ps listings. If the caller has specified
   699  		// a name, use that instead of a.out. The binary is generated
   700  		// in an otherwise empty subdirectory named exe to avoid
   701  		// naming conflicts. The only possible conflict is if we were
   702  		// to create a top-level package named exe.
   703  		name := "a.out"
   704  		if p.Internal.ExeName != "" {
   705  			name = p.Internal.ExeName
   706  		} else if (cfg.Goos == "darwin" || cfg.Goos == "windows") && cfg.BuildBuildmode == "c-shared" && p.Target != "" {
   707  			// On OS X, the linker output name gets recorded in the
   708  			// shared library's LC_ID_DYLIB load command.
   709  			// The code invoking the linker knows to pass only the final
   710  			// path element. Arrange that the path element matches what
   711  			// we'll install it as; otherwise the library is only loadable as "a.out".
   712  			// On Windows, DLL file name is recorded in PE file
   713  			// export section, so do like on OS X.
   714  			_, name = filepath.Split(p.Target)
   715  		}
   716  		a.Target = a.Objdir + filepath.Join("exe", name) + cfg.ExeSuffix
   717  		a.built = a.Target
   718  		b.addTransitiveLinkDeps(a, a1, "")
   719  
   720  		// Sequence the build of the main package (a1) strictly after the build
   721  		// of all other dependencies that go into the link. It is likely to be after
   722  		// them anyway, but just make sure. This is required by the build ID-based
   723  		// shortcut in (*Builder).useCache(a1), which will call b.linkActionID(a).
   724  		// In order for that linkActionID call to compute the right action ID, all the
   725  		// dependencies of a (except a1) must have completed building and have
   726  		// recorded their build IDs.
   727  		a1.Deps = append(a1.Deps, &Action{Mode: "nop", Deps: a.Deps[1:]})
   728  		return a
   729  	})
   730  
   731  	if mode == ModeInstall || mode == ModeBuggyInstall {
   732  		a = b.installAction(a, mode)
   733  	}
   734  
   735  	return a
   736  }
   737  
   738  // installAction returns the action for installing the result of a1.
   739  func (b *Builder) installAction(a1 *Action, mode BuildMode) *Action {
   740  	// Because we overwrite the build action with the install action below,
   741  	// a1 may already be an install action fetched from the "build" cache key,
   742  	// and the caller just doesn't realize.
   743  	if strings.HasSuffix(a1.Mode, "-install") {
   744  		if a1.buggyInstall && mode == ModeInstall {
   745  			//  Congratulations! The buggy install is now a proper install.
   746  			a1.buggyInstall = false
   747  		}
   748  		return a1
   749  	}
   750  
   751  	// If there's no actual action to build a1,
   752  	// there's nothing to install either.
   753  	// This happens if a1 corresponds to reusing an already-built object.
   754  	if a1.Actor == nil {
   755  		return a1
   756  	}
   757  
   758  	p := a1.Package
   759  	return b.cacheAction(a1.Mode+"-install", p, func() *Action {
   760  		// The install deletes the temporary build result,
   761  		// so we need all other actions, both past and future,
   762  		// that attempt to depend on the build to depend instead
   763  		// on the install.
   764  
   765  		// Make a private copy of a1 (the build action),
   766  		// no longer accessible to any other rules.
   767  		buildAction := new(Action)
   768  		*buildAction = *a1
   769  
   770  		// Overwrite a1 with the install action.
   771  		// This takes care of updating past actions that
   772  		// point at a1 for the build action; now they will
   773  		// point at a1 and get the install action.
   774  		// We also leave a1 in the action cache as the result
   775  		// for "build", so that actions not yet created that
   776  		// try to depend on the build will instead depend
   777  		// on the install.
   778  		*a1 = Action{
   779  			Mode:    buildAction.Mode + "-install",
   780  			Actor:   ActorFunc(BuildInstallFunc),
   781  			Package: p,
   782  			Objdir:  buildAction.Objdir,
   783  			Deps:    []*Action{buildAction},
   784  			Target:  p.Target,
   785  			built:   p.Target,
   786  
   787  			buggyInstall: mode == ModeBuggyInstall,
   788  		}
   789  
   790  		b.addInstallHeaderAction(a1)
   791  		return a1
   792  	})
   793  }
   794  
   795  // addTransitiveLinkDeps adds to the link action a all packages
   796  // that are transitive dependencies of a1.Deps.
   797  // That is, if a is a link of package main, a1 is the compile of package main
   798  // and a1.Deps is the actions for building packages directly imported by
   799  // package main (what the compiler needs). The linker needs all packages
   800  // transitively imported by the whole program; addTransitiveLinkDeps
   801  // makes sure those are present in a.Deps.
   802  // If shlib is non-empty, then a corresponds to the build and installation of shlib,
   803  // so any rebuild of shlib should not be added as a dependency.
   804  func (b *Builder) addTransitiveLinkDeps(a, a1 *Action, shlib string) {
   805  	// Expand Deps to include all built packages, for the linker.
   806  	// Use breadth-first search to find rebuilt-for-test packages
   807  	// before the standard ones.
   808  	// TODO(rsc): Eliminate the standard ones from the action graph,
   809  	// which will require doing a little bit more rebuilding.
   810  	workq := []*Action{a1}
   811  	haveDep := map[string]bool{}
   812  	if a1.Package != nil {
   813  		haveDep[a1.Package.ImportPath] = true
   814  	}
   815  	for i := 0; i < len(workq); i++ {
   816  		a1 := workq[i]
   817  		for _, a2 := range a1.Deps {
   818  			// TODO(rsc): Find a better discriminator than the Mode strings, once the dust settles.
   819  			if a2.Package == nil || (a2.Mode != "build-install" && a2.Mode != "build") || haveDep[a2.Package.ImportPath] {
   820  				continue
   821  			}
   822  			haveDep[a2.Package.ImportPath] = true
   823  			a.Deps = append(a.Deps, a2)
   824  			if a2.Mode == "build-install" {
   825  				a2 = a2.Deps[0] // walk children of "build" action
   826  			}
   827  			workq = append(workq, a2)
   828  		}
   829  	}
   830  
   831  	// If this is go build -linkshared, then the link depends on the shared libraries
   832  	// in addition to the packages themselves. (The compile steps do not.)
   833  	if cfg.BuildLinkshared {
   834  		haveShlib := map[string]bool{shlib: true}
   835  		for _, a1 := range a.Deps {
   836  			p1 := a1.Package
   837  			if p1 == nil || p1.Shlib == "" || haveShlib[filepath.Base(p1.Shlib)] {
   838  				continue
   839  			}
   840  			haveShlib[filepath.Base(p1.Shlib)] = true
   841  			// TODO(rsc): The use of ModeInstall here is suspect, but if we only do ModeBuild,
   842  			// we'll end up building an overall library or executable that depends at runtime
   843  			// on other libraries that are out-of-date, which is clearly not good either.
   844  			// We call it ModeBuggyInstall to make clear that this is not right.
   845  			a.Deps = append(a.Deps, b.linkSharedAction(ModeBuggyInstall, ModeBuggyInstall, p1.Shlib, nil))
   846  		}
   847  	}
   848  }
   849  
   850  // addInstallHeaderAction adds an install header action to a, if needed.
   851  // The action a should be an install action as generated by either
   852  // b.CompileAction or b.LinkAction with mode=ModeInstall,
   853  // and so a.Deps[0] is the corresponding build action.
   854  func (b *Builder) addInstallHeaderAction(a *Action) {
   855  	// Install header for cgo in c-archive and c-shared modes.
   856  	p := a.Package
   857  	if p.UsesCgo() && (cfg.BuildBuildmode == "c-archive" || cfg.BuildBuildmode == "c-shared") {
   858  		hdrTarget := a.Target[:len(a.Target)-len(filepath.Ext(a.Target))] + ".h"
   859  		if cfg.BuildContext.Compiler == "gccgo" && cfg.BuildO == "" {
   860  			// For the header file, remove the "lib"
   861  			// added by go/build, so we generate pkg.h
   862  			// rather than libpkg.h.
   863  			dir, file := filepath.Split(hdrTarget)
   864  			file = strings.TrimPrefix(file, "lib")
   865  			hdrTarget = filepath.Join(dir, file)
   866  		}
   867  		ah := &Action{
   868  			Mode:    "install header",
   869  			Package: a.Package,
   870  			Deps:    []*Action{a.Deps[0]},
   871  			Actor:   ActorFunc((*Builder).installHeader),
   872  			Objdir:  a.Deps[0].Objdir,
   873  			Target:  hdrTarget,
   874  		}
   875  		a.Deps = append(a.Deps, ah)
   876  	}
   877  }
   878  
   879  // buildmodeShared takes the "go build" action a1 into the building of a shared library of a1.Deps.
   880  // That is, the input a1 represents "go build pkgs" and the result represents "go build -buildmode=shared pkgs".
   881  func (b *Builder) buildmodeShared(mode, depMode BuildMode, args []string, pkgs []*load.Package, a1 *Action) *Action {
   882  	name, err := libname(args, pkgs)
   883  	if err != nil {
   884  		base.Fatalf("%v", err)
   885  	}
   886  	return b.linkSharedAction(mode, depMode, name, a1)
   887  }
   888  
   889  // linkSharedAction takes a grouping action a1 corresponding to a list of built packages
   890  // and returns an action that links them together into a shared library with the name shlib.
   891  // If a1 is nil, shlib should be an absolute path to an existing shared library,
   892  // and then linkSharedAction reads that library to find out the package list.
   893  func (b *Builder) linkSharedAction(mode, depMode BuildMode, shlib string, a1 *Action) *Action {
   894  	fullShlib := shlib
   895  	shlib = filepath.Base(shlib)
   896  	a := b.cacheAction("build-shlib "+shlib, nil, func() *Action {
   897  		if a1 == nil {
   898  			// TODO(rsc): Need to find some other place to store config,
   899  			// not in pkg directory. See golang.org/issue/22196.
   900  			pkgs := readpkglist(fullShlib)
   901  			a1 = &Action{
   902  				Mode: "shlib packages",
   903  			}
   904  			for _, p := range pkgs {
   905  				a1.Deps = append(a1.Deps, b.CompileAction(mode, depMode, p))
   906  			}
   907  		}
   908  
   909  		// Fake package to hold ldflags.
   910  		// As usual shared libraries are a kludgy, abstraction-violating special case:
   911  		// we let them use the flags specified for the command-line arguments.
   912  		p := &load.Package{}
   913  		p.Internal.CmdlinePkg = true
   914  		p.Internal.Ldflags = load.BuildLdflags.For(p)
   915  		p.Internal.Gccgoflags = load.BuildGccgoflags.For(p)
   916  
   917  		// Add implicit dependencies to pkgs list.
   918  		// Currently buildmode=shared forces external linking mode, and
   919  		// external linking mode forces an import of runtime/cgo (and
   920  		// math on arm). So if it was not passed on the command line and
   921  		// it is not present in another shared library, add it here.
   922  		// TODO(rsc): Maybe this should only happen if "runtime" is in the original package set.
   923  		// TODO(rsc): This should probably be changed to use load.LinkerDeps(p).
   924  		// TODO(rsc): We don't add standard library imports for gccgo
   925  		// because they are all always linked in anyhow.
   926  		// Maybe load.LinkerDeps should be used and updated.
   927  		a := &Action{
   928  			Mode:    "go build -buildmode=shared",
   929  			Package: p,
   930  			Objdir:  b.NewObjdir(),
   931  			Actor:   ActorFunc((*Builder).linkShared),
   932  			Deps:    []*Action{a1},
   933  		}
   934  		a.Target = filepath.Join(a.Objdir, shlib)
   935  		if cfg.BuildToolchainName != "gccgo" {
   936  			add := func(a1 *Action, pkg string, force bool) {
   937  				for _, a2 := range a1.Deps {
   938  					if a2.Package != nil && a2.Package.ImportPath == pkg {
   939  						return
   940  					}
   941  				}
   942  				var stk load.ImportStack
   943  				p := load.LoadPackageWithFlags(pkg, base.Cwd(), &stk, nil, 0)
   944  				if p.Error != nil {
   945  					base.Fatalf("load %s: %v", pkg, p.Error)
   946  				}
   947  				// Assume that if pkg (runtime/cgo or math)
   948  				// is already accounted for in a different shared library,
   949  				// then that shared library also contains runtime,
   950  				// so that anything we do will depend on that library,
   951  				// so we don't need to include pkg in our shared library.
   952  				if force || p.Shlib == "" || filepath.Base(p.Shlib) == pkg {
   953  					a1.Deps = append(a1.Deps, b.CompileAction(depMode, depMode, p))
   954  				}
   955  			}
   956  			add(a1, "runtime/cgo", false)
   957  			if cfg.Goarch == "arm" {
   958  				add(a1, "math", false)
   959  			}
   960  
   961  			// The linker step still needs all the usual linker deps.
   962  			// (For example, the linker always opens runtime.a.)
   963  			ldDeps, err := load.LinkerDeps(nil)
   964  			if err != nil {
   965  				base.Error(err)
   966  			}
   967  			for _, dep := range ldDeps {
   968  				add(a, dep, true)
   969  			}
   970  		}
   971  		b.addTransitiveLinkDeps(a, a1, shlib)
   972  		return a
   973  	})
   974  
   975  	// Install result.
   976  	if (mode == ModeInstall || mode == ModeBuggyInstall) && a.Actor != nil {
   977  		buildAction := a
   978  
   979  		a = b.cacheAction("install-shlib "+shlib, nil, func() *Action {
   980  			// Determine the eventual install target.
   981  			// The install target is root/pkg/shlib, where root is the source root
   982  			// in which all the packages lie.
   983  			// TODO(rsc): Perhaps this cross-root check should apply to the full
   984  			// transitive package dependency list, not just the ones named
   985  			// on the command line?
   986  			pkgDir := a1.Deps[0].Package.Internal.Build.PkgTargetRoot
   987  			for _, a2 := range a1.Deps {
   988  				if dir := a2.Package.Internal.Build.PkgTargetRoot; dir != pkgDir {
   989  					base.Fatalf("installing shared library: cannot use packages %s and %s from different roots %s and %s",
   990  						a1.Deps[0].Package.ImportPath,
   991  						a2.Package.ImportPath,
   992  						pkgDir,
   993  						dir)
   994  				}
   995  			}
   996  			// TODO(rsc): Find out and explain here why gccgo is different.
   997  			if cfg.BuildToolchainName == "gccgo" {
   998  				pkgDir = filepath.Join(pkgDir, "shlibs")
   999  			}
  1000  			target := filepath.Join(pkgDir, shlib)
  1001  
  1002  			a := &Action{
  1003  				Mode:   "go install -buildmode=shared",
  1004  				Objdir: buildAction.Objdir,
  1005  				Actor:  ActorFunc(BuildInstallFunc),
  1006  				Deps:   []*Action{buildAction},
  1007  				Target: target,
  1008  			}
  1009  			for _, a2 := range buildAction.Deps[0].Deps {
  1010  				p := a2.Package
  1011  				pkgTargetRoot := p.Internal.Build.PkgTargetRoot
  1012  				if pkgTargetRoot == "" {
  1013  					continue
  1014  				}
  1015  				a.Deps = append(a.Deps, &Action{
  1016  					Mode:    "shlibname",
  1017  					Package: p,
  1018  					Actor:   ActorFunc((*Builder).installShlibname),
  1019  					Target:  filepath.Join(pkgTargetRoot, p.ImportPath+".shlibname"),
  1020  					Deps:    []*Action{a.Deps[0]},
  1021  				})
  1022  			}
  1023  			return a
  1024  		})
  1025  	}
  1026  
  1027  	return a
  1028  }
  1029
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