cmd/go, cmd/cgo: support older versions of gccgo that lack cgo.Incomplete

Test whether gccgo/GoLLVM supports cgo.Incomplete. If it doesn't, use a
local definition rather than importing it.

Roll back 426496, which skipped a gccgo test, as it now works.

For #46731
Fixes #54761

Change-Id: I8bb2ad84c317094495405e178bf5c9694f82af56
Reviewed-on: https://go-review.googlesource.com/c/go/+/446260
Reviewed-by: Bryan Mills <bcmills@google.com>
Run-TryBot: Ian Lance Taylor <iant@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Run-TryBot: Bryan Mills <bcmills@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

src/cmd/cgo/doc.go

@@ -498,6 +498,9 @@ The following options are available when running cgo directly:
 		The -fgo-prefix option to be used with gccgo.
 	-gccgopkgpath path
 		The -fgo-pkgpath option to be used with gccgo.
+	-gccgo_define_cgoincomplete
+		Define cgo.Incomplete locally rather than importing it from
+		the "runtime/cgo" package. Used for old gccgo versions.
 	-godefs
 		Write out input file in Go syntax replacing C package
 		names with real values. Used to generate files in the

src/cmd/cgo/gcc.go

@@ -47,6 +47,8 @@ var nameToC = map[string]string{
 	"complexdouble": "double _Complex",
 }
 
+var incomplete = "_cgopackage.Incomplete"
+
 // cname returns the C name to use for C.s.
 // The expansions are listed in nameToC and also
 // struct_foo becomes "struct foo", and similarly for
@@ -2565,7 +2567,7 @@ func (c *typeConv) loadType(dtype dwarf.Type, pos token.Pos, parent string) *Typ
 			// get writebarrier-ed or adjusted during a stack copy. This should handle
 			// all the cases badPointerTypedef used to handle, but hopefully will
 			// continue to work going forward without any more need for cgo changes.
-			tt.Go = c.Ident("_cgopackage.Incomplete")
+			tt.Go = c.Ident(incomplete)
 			typedef[name.Name] = &tt
 			break
 		}
@@ -2592,7 +2594,7 @@ func (c *typeConv) loadType(dtype dwarf.Type, pos token.Pos, parent string) *Typ
 			}
 			tt.Go = g
 			if c.incompleteStructs[tag] {
-				tt.Go = c.Ident("_cgopackage.Incomplete")
+				tt.Go = c.Ident(incomplete)
 			}
 			typedef[name.Name] = &tt
 		}
@@ -2640,7 +2642,7 @@ func (c *typeConv) loadType(dtype dwarf.Type, pos token.Pos, parent string) *Typ
 		if c.badVoidPointerTypedef(dt) {
 			// Treat this typedef as a pointer to a _cgopackage.Incomplete.
 			s := *sub
-			s.Go = c.Ident("*_cgopackage.Incomplete")
+			s.Go = c.Ident("*" + incomplete)
 			sub = &s
 			// Make sure we update any previously computed type.
 			if oldType := typedef[name.Name]; oldType != nil {
@@ -2656,7 +2658,7 @@ func (c *typeConv) loadType(dtype dwarf.Type, pos token.Pos, parent string) *Typ
 					// Make sure we update any previously computed type.
 					name := "_Ctype_struct_" + strct.StructName
 					if oldType := typedef[name]; oldType != nil {
-						oldType.Go = c.Ident("_cgopackage.Incomplete")
+						oldType.Go = c.Ident(incomplete)
 					}
 				}
 			}
@@ -3196,7 +3198,7 @@ func (c *typeConv) anonymousStructTypedef(dt *dwarf.TypedefType) bool {
 // non-pointers in this type.
 // TODO: Currently our best solution is to find these manually and list them as
 // they come up. A better solution is desired.
-// Note: DEPRECATED. There is now a better solution. Search for _cgopackage.Incomplete in this file.
+// Note: DEPRECATED. There is now a better solution. Search for incomplete in this file.
 func (c *typeConv) badPointerTypedef(dt *dwarf.TypedefType) bool {
 	if c.badCFType(dt) {
 		return true

src/cmd/cgo/main.go

@@ -242,6 +242,7 @@ var gccgo = flag.Bool("gccgo", false, "generate files for use with gccgo")
 var gccgoprefix = flag.String("gccgoprefix", "", "-fgo-prefix option used with gccgo")
 var gccgopkgpath = flag.String("gccgopkgpath", "", "-fgo-pkgpath option used with gccgo")
 var gccgoMangler func(string) string
+var gccgoDefineCgoIncomplete = flag.Bool("gccgo_define_cgoincomplete", false, "define cgo.Incomplete for older gccgo/GoLLVM")
 var importRuntimeCgo = flag.Bool("import_runtime_cgo", true, "import runtime/cgo in generated code")
 var importSyscall = flag.Bool("import_syscall", true, "import syscall in generated code")
 var trimpath = flag.String("trimpath", "", "applies supplied rewrites or trims prefixes to recorded source file paths")
@@ -253,6 +254,14 @@ func main() {
 	objabi.AddVersionFlag() // -V
 	objabi.Flagparse(usage)
 
+	if *gccgoDefineCgoIncomplete {
+		if !*gccgo {
+			fmt.Fprintf(os.Stderr, "cgo: -gccgo_define_cgoincomplete without -gccgo\n")
+			os.Exit(2)
+		}
+		incomplete = "_cgopackage_Incomplete"
+	}
+
 	if *dynobj != "" {
 		// cgo -dynimport is essentially a separate helper command
 		// built into the cgo binary. It scans a gcc-produced executable

src/cmd/cgo/out.go

@@ -85,8 +85,13 @@ func (p *Package) writeDefs() {
 		fmt.Fprintf(fgo2, "import \"syscall\"\n\n")
 	}
 	if *importRuntimeCgo {
-		fmt.Fprintf(fgo2, "import _cgopackage \"runtime/cgo\"\n\n")
-		fmt.Fprintf(fgo2, "type _ _cgopackage.Incomplete\n") // prevent import-not-used error
+		if !*gccgoDefineCgoIncomplete {
+			fmt.Fprintf(fgo2, "import _cgopackage \"runtime/cgo\"\n\n")
+			fmt.Fprintf(fgo2, "type _ _cgopackage.Incomplete\n") // prevent import-not-used error
+		} else {
+			fmt.Fprintf(fgo2, "//go:notinheap\n")
+			fmt.Fprintf(fgo2, "type _cgopackage_Incomplete struct{ _ struct{ _ struct{} } }\n")
+		}
 	}
 	if *importSyscall {
 		fmt.Fprintf(fgo2, "var _ syscall.Errno\n")

src/cmd/go/internal/work/exec.go

@@ -2953,6 +2953,9 @@ func (b *Builder) cgo(a *Action, cgoExe, objdir string, pcCFLAGS, pcLDFLAGS, cgo
 		if pkgpath := gccgoPkgpath(p); pkgpath != "" {
 			cgoflags = append(cgoflags, "-gccgopkgpath="+pkgpath)
 		}
+		if !BuildToolchain.(gccgoToolchain).supportsCgoIncomplete(b) {
+			cgoflags = append(cgoflags, "-gccgo_define_cgoincomplete")
+		}
 	}
 
 	switch cfg.BuildBuildmode {

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

@@ -617,3 +617,63 @@ func (tools gccgoToolchain) gccgoCleanPkgpath(b *Builder, p *load.Package) strin
 
 	return gccgoToSymbolFunc(gccgoPkgpath(p))
 }
+
+var (
+	gccgoSupportsCgoIncompleteOnce sync.Once
+	gccgoSupportsCgoIncomplete     bool
+)
+
+const gccgoSupportsCgoIncompleteCode = `
+package p
+
+import "runtime/cgo"
+
+type I cgo.Incomplete
+`
+
+// supportsCgoIncomplete reports whether the gccgo/GoLLVM compiler
+// being used supports cgo.Incomplete, which was added in GCC 13.
+func (tools gccgoToolchain) supportsCgoIncomplete(b *Builder) bool {
+	gccgoSupportsCgoIncompleteOnce.Do(func() {
+		fail := func(err error) {
+			fmt.Fprintf(os.Stderr, "cmd/go: %v\n", err)
+			base.SetExitStatus(2)
+			base.Exit()
+		}
+
+		tmpdir := b.WorkDir
+		if cfg.BuildN {
+			tmpdir = os.TempDir()
+		}
+		f, err := os.CreateTemp(tmpdir, "*_gccgo_cgoincomplete.go")
+		if err != nil {
+			fail(err)
+		}
+		fn := f.Name()
+		f.Close()
+		defer os.Remove(fn)
+
+		if err := os.WriteFile(fn, []byte(gccgoSupportsCgoIncompleteCode), 0644); err != nil {
+			fail(err)
+		}
+
+		on := strings.TrimSuffix(fn, ".go") + ".o"
+		if cfg.BuildN || cfg.BuildX {
+			b.Showcmd(tmpdir, "%s -c -o %s %s || true", tools.compiler(), on, fn)
+			// Since this function affects later builds,
+			// and only generates temporary files,
+			// we run the command even with -n.
+		}
+		cmd := exec.Command(tools.compiler(), "-c", "-o", on, fn)
+		cmd.Dir = tmpdir
+		var buf strings.Builder
+		cmd.Stdout = &buf
+		cmd.Stderr = &buf
+		err = cmd.Run()
+		if out := buf.String(); len(out) > 0 {
+			b.showOutput(nil, tmpdir, b.fmtcmd(tmpdir, "%s -c -o %s %s", tools.compiler(), on, fn), buf.String())
+		}
+		gccgoSupportsCgoIncomplete = err == nil
+	})
+	return gccgoSupportsCgoIncomplete
+}

src/cmd/go/testdata/script/build_overlay.txt

@@ -83,11 +83,6 @@ go build -compiler=gccgo -overlay overlay.json -o print_trimpath_gccgo$GOEXE -tr
 exec ./print_trimpath_gccgo$GOEXE
 stdout ^\.[/\\]printpath[/\\]main.go
 
-go build -compiler=gccgo -overlay overlay.json -o main_call_asm_gccgo$GOEXE ./call_asm
-exec ./main_call_asm_gccgo$GOEXE
-! stdout .
-
-skip 'broken as of CL 421879: see https://go.dev/issue/54761'
 
 go build -compiler=gccgo  -overlay overlay.json -o main_cgo_replace_gccgo$GOEXE ./cgo_hello_replace
 exec ./main_cgo_replace_gccgo$GOEXE
@@ -101,6 +96,10 @@ go build -compiler=gccgo  -overlay overlay.json -o main_cgo_angle_gccgo$GOEXE ./
 exec ./main_cgo_angle_gccgo$GOEXE
 stdout '^hello cgo\r?\n'
 
+go build -compiler=gccgo -overlay overlay.json -o main_call_asm_gccgo$GOEXE ./call_asm
+exec ./main_call_asm_gccgo$GOEXE
+! stdout .
+
 
 -- m/go.mod --
 // TODO(matloob): how do overlays work with go.mod (especially if mod=readonly)