cmd/link/internal/ld, cmd/go: -buildmode=c-shared support for darwin/amd64

All of the heavy-lifting was done by minux@, with his external-linking support
for darwin/arm64: golang.org/cl/8781

Change-Id: I7c9fbc19246f418c065c92fb2c13c00026ff0f82
Reviewed-on: https://go-review.googlesource.com/11127
Run-TryBot: Srdjan Petrovic <spetrovic@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

misc/cgo/testcshared/test.bash

@@ -20,7 +20,7 @@ goarch=$(go env GOARCH)
 # Directory where cgo headers and outputs will be installed.
 # The installation directory format varies depending on the platform.
 installdir=pkg/${goos}_${goarch}_testcshared_shared
-if [ "${goos}/${goarch}" == "android/arm" ]; then
+if [ "${goos}/${goarch}" == "android/arm" ] || [ "${goos}/${goarch}" == "darwin/amd64" ]; then
 	installdir=pkg/${goos}_${goarch}_testcshared
 fi
 
@@ -70,15 +70,20 @@ rm -rf pkg
 
 suffix="-installsuffix testcshared"
 
+libext="so"
+if [ "$goos" == "darwin" ]; then
+	libext="dylib"
+fi
+
 # Create the header files.
 GOPATH=$(pwd) go install -buildmode=c-shared $suffix libgo
 
-GOPATH=$(pwd) go build -buildmode=c-shared $suffix -o libgo.so src/libgo/libgo.go
-binpush libgo.so
+GOPATH=$(pwd) go build -buildmode=c-shared $suffix -o libgo.$libext src/libgo/libgo.go
+binpush libgo.$libext
 
 # test0: exported symbols in shared lib are accessible.
 # TODO(iant): using _shared here shouldn't really be necessary.
-$(go env CC) $(go env GOGCCFLAGS) -I ${installdir} -o testp main0.c libgo.so
+$(go env CC) $(go env GOGCCFLAGS) -I ${installdir} -o testp main0.c libgo.$libext
 binpush testp
 
 output=$(run LD_LIBRARY_PATH=. ./testp)
@@ -87,19 +92,23 @@ if [ "$output" != "PASS" ]; then
 	exit 1
 fi
 
-# test1: .so can be dynamically loaded and exported symbols are accessible.
+# test1: shared library can be dynamically loaded and exported symbols are accessible.
 $(go env CC) $(go env GOGCCFLAGS) -o testp main1.c -ldl
 binpush testp
-output=$(run ./testp ./libgo.so)
+output=$(run ./testp ./libgo.$libext)
 if [ "$output" != "PASS" ]; then
 	echo "FAIL test1 got ${output}"
 	exit 1
 fi
 
-# test2: tests libgo2.so which does not export any functions.
-GOPATH=$(pwd) go build -buildmode=c-shared $suffix -o libgo2.so src/libgo2/libgo2.go
-binpush libgo2.so
-$(go env CC) $(go env GOGCCFLAGS) -o testp2 main2.c -Wl,--no-as-needed libgo2.so
+# test2: tests libgo2 which does not export any functions.
+GOPATH=$(pwd) go build -buildmode=c-shared $suffix -o libgo2.$libext src/libgo2/libgo2.go
+binpush libgo2.$libext
+linkflags="-Wl,--no-as-needed"
+if [ "$goos" == "darwin" ]; then
+	linkflags=""
+fi
+$(go env CC) $(go env GOGCCFLAGS) -o testp2 main2.c $linkflags libgo2.$libext
 binpush testp2
 output=$(run LD_LIBRARY_PATH=. ./testp2)
 if [ "$output" != "PASS" ]; then

src/cmd/dist/test.go

@@ -571,7 +571,7 @@ func (t *tester) supportedBuildmode(mode string) bool {
 	case "c-shared":
 		// TODO(hyangah): add linux-386.
 		switch pair {
-		case "linux-amd64", "android-arm":
+		case "linux-amd64", "darwin-amd64", "android-arm":
 			return true
 		}
 		return false

src/cmd/go/build.go

@@ -334,6 +334,7 @@ func buildModeInit() {
 				codegenArg = "-shared"
 			case "linux/arm":
 				buildAsmflags = append(buildAsmflags, "-shared")
+			case "darwin/amd64":
 			case "android/arm":
 			default:
 				fatalf("-buildmode=c-shared not supported on %s\n", platform)

src/cmd/link/internal/ld/lib.go

@@ -926,7 +926,7 @@ func hostlink() {
 	}
 
 	if HEADTYPE == obj.Hdarwin {
-		argv = append(argv, "-Wl,-no_pie,-pagezero_size,4000000,-headerpad,1144")
+		argv = append(argv, "-Wl,-no_pie,-headerpad,1144")
 	}
 	if HEADTYPE == obj.Hopenbsd {
 		argv = append(argv, "-Wl,-nopie")
@@ -944,9 +944,17 @@ func hostlink() {
 	}
 
 	switch Buildmode {
+	case BuildmodeExe:
+		if HEADTYPE == obj.Hdarwin {
+			argv = append(argv, "-Wl,-pagezero_size,4000000")
+		}
 	case BuildmodeCShared:
+		if HEADTYPE == obj.Hdarwin {
+			argv = append(argv, "-dynamiclib")
+		} else {
 			argv = append(argv, "-Wl,-Bsymbolic")
 			argv = append(argv, "-shared")
+		}
 	case BuildmodeShared:
 		// TODO(mwhudson): unless you do this, dynamic relocations fill
 		// out the findfunctab table and for some reason shared libraries

src/cmd/link/internal/ld/macho.go

@@ -356,9 +356,10 @@ func machoshbits(mseg *MachoSeg, sect *Section, segname string) {
 	buf := "__" + strings.Replace(sect.Name[1:], ".", "_", -1)
 
 	var msect *MachoSect
-	if Thearch.Thechar == '7' && sect.Rwx&1 == 0 {
-		// darwin/arm64 forbids absolute relocs in __TEXT, so if
-		// the section is not executable, put it in __DATA segment.
+	if sect.Rwx&1 == 0 && (Thearch.Thechar == '7' || (Thearch.Thechar == '6' && Buildmode == BuildmodeCShared)) {
+		// Darwin external linker on arm64 and on amd64 in c-shared buildmode
+		// complains about absolute relocs in __TEXT, so if the section is not
+		// executable, put it in __DATA segment.
 		msect = newMachoSect(mseg, buf, "__DATA")
 	} else {
 		msect = newMachoSect(mseg, buf, segname)

src/cmd/link/internal/ld/macho_combine_dwarf.go

@@ -22,6 +22,7 @@ var machHeader *macho.FileHeader
 var mappedHeader []byte
 
 const (
+	LC_ID_DYLIB             = 0xd
 	LC_LOAD_DYLINKER        = 0xe
 	LC_PREBOUND_DYLIB       = 0x10
 	LC_LOAD_WEAK_DYLIB      = 0x18
@@ -246,7 +247,7 @@ func machoCombineDwarf(inexe, dsym, outexe string) error {
 			err = machoUpdateLoadCommand(reader, &linkEditDataCmd{}, "DataOff")
 		case LC_ENCRYPTION_INFO, LC_ENCRYPTION_INFO_64:
 			err = machoUpdateLoadCommand(reader, &encryptionInfoCmd{}, "CryptOff")
-		case macho.LoadCmdDylib, macho.LoadCmdThread, macho.LoadCmdUnixThread, LC_PREBOUND_DYLIB, LC_UUID, LC_VERSION_MIN_MACOSX, LC_VERSION_MIN_IPHONEOS, LC_SOURCE_VERSION, LC_MAIN, LC_LOAD_DYLINKER, LC_LOAD_WEAK_DYLIB, LC_REEXPORT_DYLIB, LC_RPATH:
+		case macho.LoadCmdDylib, macho.LoadCmdThread, macho.LoadCmdUnixThread, LC_PREBOUND_DYLIB, LC_UUID, LC_VERSION_MIN_MACOSX, LC_VERSION_MIN_IPHONEOS, LC_SOURCE_VERSION, LC_MAIN, LC_LOAD_DYLINKER, LC_LOAD_WEAK_DYLIB, LC_REEXPORT_DYLIB, LC_RPATH, LC_ID_DYLIB:
 			// Nothing to update
 		default:
 			err = fmt.Errorf("Unknown load command 0x%x (%s)\n", int(cmd.Cmd), cmd.Cmd)