cmd/go: make gccgo -buildmode=shared and -linkshared work again

After CL 69831, addTransitiveLinkDeps ensures that all dependencies of
a link appear in Deps. We no longer need to traverse through all
actions to find them. And the old scheme of looking through all the
actions and assuming we would see shared library actions before
libraries they depend on no longer works.

Now that we have complete deps, change to a simpler scheme in which we
find the shared libraries in the deps, and then use that to sort the
deps into archives and shared libraries.

Fixes #22224

Change-Id: I14fcc773ac59b6f5c2965cc04d4ed962442cc89e
Reviewed-on: https://go-review.googlesource.com/87497
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>

misc/cgo/testshared/shared_test.go

@@ -351,10 +351,10 @@ func readNotes(f *elf.File) ([]*note, error) {
 
 func dynStrings(t *testing.T, path string, flag elf.DynTag) []string {
 	f, err := elf.Open(path)
-	defer f.Close()
 	if err != nil {
 		t.Fatalf("elf.Open(%q) failed: %v", path, err)
 	}
+	defer f.Close()
 	dynstrings, err := f.DynString(flag)
 	if err != nil {
 		t.Fatalf("DynString(%s) failed on %s: %v", flag, path, err)
@@ -598,7 +598,6 @@ func TestThreeGopathShlibs(t *testing.T) {
 // If gccgo is not available or not new enough call t.Skip. Otherwise,
 // return a build.Context that is set up for gccgo.
 func prepGccgo(t *testing.T) build.Context {
-	t.Skip("golang.org/issue/22472")
 	gccgoName := os.Getenv("GCCGO")
 	if gccgoName == "" {
 		gccgoName = "gccgo"
@@ -648,8 +647,6 @@ func TestGoPathShlibGccgo(t *testing.T) {
 // library with gccgo, another GOPATH package that depends on the first and an
 // executable that links the second library.
 func TestTwoGopathShlibsGccgo(t *testing.T) {
-	t.Skip("golang.org/issue/22224")
-
 	gccgoContext := prepGccgo(t)
 
 	libgoRE := regexp.MustCompile("libgo.so.[0-9]+")

src/cmd/go/internal/work/action.go

@@ -647,11 +647,9 @@ func (b *Builder) linkSharedAction(mode, depMode BuildMode, shlib string, a1 *Ac
 		// it is not present in another shared library, add it here.
 		// TODO(rsc): Maybe this should only happen if "runtime" is in the original package set.
 		// TODO(rsc): This should probably be changed to use load.LinkerDeps(p).
-		// TODO(rsc): Find out and explain here why gccgo is excluded.
-		// If the answer is that gccgo is different in implicit linker deps, maybe
-		// load.LinkerDeps should be used and updated.
-		// Link packages into a shared library.
-
+		// TODO(rsc): We don't add standard library imports for gccgo
+		// because they are all always linked in anyhow.
+		// Maybe load.LinkerDeps should be used and updated.
 		a := &Action{
 			Mode:    "go build -buildmode=shared",
 			Package: p,

src/cmd/go/internal/work/gccgo.go

@@ -192,7 +192,6 @@ func (gccgoToolchain) pack(b *Builder, a *Action, afile string, ofiles []string)
 func (tools gccgoToolchain) link(b *Builder, root *Action, out, importcfg string, allactions []*Action, buildmode, desc string) error {
 	// gccgo needs explicit linking with all package dependencies,
 	// and all LDFLAGS from cgo dependencies.
-	apackagePathsSeen := make(map[string]bool)
 	afiles := []string{}
 	shlibs := []string{}
 	ldflags := b.gccArchArgs()
@@ -261,56 +260,57 @@ func (tools gccgoToolchain) link(b *Builder, root *Action, out, importcfg string
 		return newArchive, nil
 	}
 
-	actionsSeen := make(map[*Action]bool)
-	// Make a pre-order depth-first traversal of the action graph, taking note of
-	// whether a shared library action has been seen on the way to an action (the
-	// construction of the graph means that if any path to a node passes through
-	// a shared library action, they all do).
-	var walk func(a *Action, seenShlib bool)
-	var err error
-	walk = func(a *Action, seenShlib bool) {
-		if actionsSeen[a] {
-			return
-		}
-		actionsSeen[a] = true
-		if a.Package != nil && !seenShlib {
-			if a.Package.Standard {
-				return
+	// If using -linkshared, find the shared library deps.
+	haveShlib := make(map[string]bool)
+	targetBase := filepath.Base(root.Target)
+	if cfg.BuildLinkshared {
+		for _, a := range root.Deps {
+			p := a.Package
+			if p == nil || p.Shlib == "" {
+				continue
 			}
-			// We record the target of the first time we see a .a file
-			// for a package to make sure that we prefer the 'install'
-			// rather than the 'build' location (which may not exist any
-			// more). We still need to traverse the dependencies of the
-			// build action though so saying
-			// if apackagePathsSeen[a.Package.ImportPath] { return }
-			// doesn't work.
-			if !apackagePathsSeen[a.Package.ImportPath] {
-				apackagePathsSeen[a.Package.ImportPath] = true
-				target := a.built
-				if len(a.Package.CgoFiles) > 0 || a.Package.UsesSwig() {
-					target, err = readAndRemoveCgoFlags(target)
-					if err != nil {
-						return
-					}
-				}
-				afiles = append(afiles, target)
-			}
-		}
-		if strings.HasSuffix(a.Target, ".so") {
-			shlibs = append(shlibs, a.Target)
-			seenShlib = true
-		}
-		for _, a1 := range a.Deps {
-			walk(a1, seenShlib)
-			if err != nil {
-				return
+
+			// The .a we are linking into this .so
+			// will have its Shlib set to this .so.
+			// Don't start thinking we want to link
+			// this .so into itself.
+			base := filepath.Base(p.Shlib)
+			if base != targetBase {
+				haveShlib[base] = true
 			}
 		}
 	}
-	for _, a1 := range root.Deps {
-		walk(a1, false)
-		if err != nil {
-			return err
+
+	// Arrange the deps into afiles and shlibs.
+	addedShlib := make(map[string]bool)
+	for _, a := range root.Deps {
+		p := a.Package
+		if p != nil && p.Shlib != "" && haveShlib[filepath.Base(p.Shlib)] {
+			// This is a package linked into a shared
+			// library that we will put into shlibs.
+			continue
+		}
+
+		if haveShlib[filepath.Base(a.Target)] {
+			// This is a shared library we want to link againt.
+			if !addedShlib[a.Target] {
+				shlibs = append(shlibs, a.Target)
+				addedShlib[a.Target] = true
+			}
+			continue
+		}
+
+		if p != nil {
+			target := a.built
+			if p.UsesCgo() || p.UsesSwig() {
+				var err error
+				target, err = readAndRemoveCgoFlags(target)
+				if err != nil {
+					continue
+				}
+			}
+
+			afiles = append(afiles, target)
 		}
 	}
 
@@ -457,9 +457,7 @@ func (tools gccgoToolchain) ld(b *Builder, root *Action, out, importcfg, mainpkg
 }
 
 func (tools gccgoToolchain) ldShared(b *Builder, root *Action, toplevelactions []*Action, out, importcfg string, allactions []*Action) error {
-	fakeRoot := *root
-	fakeRoot.Deps = toplevelactions
-	return tools.link(b, &fakeRoot, out, importcfg, allactions, "shared", out)
+	return tools.link(b, root, out, importcfg, allactions, "shared", out)
 }
 
 func (tools gccgoToolchain) cc(b *Builder, a *Action, ofile, cfile string) error {