cmd/compile, cmd/go, cmd/link: enable -buildmode=shared and related flags on linux/arm64

Change-Id: Ibddbbf6f4a5bd336a8b234d40fad0fcea574cd6e
Reviewed-on: https://go-review.googlesource.com/13994Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/cmd/compile/internal/gc/lex.go

@@ -227,7 +227,8 @@ func Main() {
 	if Thearch.Thechar == '6' {
 		obj.Flagcount("largemodel", "generate code that assumes a large memory model", &flag_largemodel)
 	}
-	if Thearch.Thechar == '5' || Thearch.Thechar == '6' || Thearch.Thechar == '8' || Thearch.Thechar == '9' {
+	switch Thearch.Thechar {
+	case '5', '6', '7', '8', '9':
 		flag.BoolVar(&flag_dynlink, "dynlink", false, "support references to Go symbols defined in other shared libraries")
 	}
 	obj.Flagstr("cpuprofile", "write cpu profile to `file`", &cpuprofile)

src/cmd/go/build.go

@@ -388,7 +388,7 @@ func buildModeInit() {
 			codegenArg = "-fPIC"
 		} else {
 			switch platform {
-			case "linux/386", "linux/amd64", "linux/arm":
+			case "linux/386", "linux/amd64", "linux/arm", "linux/arm64":
 				buildAsmflags = append(buildAsmflags, "-D=shared=1")
 			default:
 				fatalf("-buildmode=shared not supported on %s\n", platform)
@@ -407,7 +407,7 @@ func buildModeInit() {
 			codegenArg = "-fPIC"
 		} else {
 			switch platform {
-			case "linux/386", "linux/amd64", "linux/arm":
+			case "linux/386", "linux/amd64", "linux/arm", "linux/arm64":
 				buildAsmflags = append(buildAsmflags, "-D=shared=1")
 			default:
 				fatalf("-buildmode=shared not supported on %s\n", platform)

src/cmd/link/internal/arm64/obj.go

@@ -104,7 +104,7 @@ func archinit() {
 		break
 	}
 
-	if ld.Buildmode == ld.BuildmodeCShared {
+	if ld.Buildmode == ld.BuildmodeCShared || ld.DynlinkingGo() {
 		ld.Linkmode = ld.LinkExternal
 	}
 

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

@@ -321,7 +321,7 @@ func (mode *BuildMode) Set(s string) error {
 		}
 		*mode = BuildmodeCShared
 	case "shared":
-		if goos != "linux" || (goarch != "386" && goarch != "amd64" && goarch != "arm") {
+		if goos != "linux" || (goarch != "386" && goarch != "amd64" && goarch != "arm" && goarch != "arm64") {
 			return badmode()
 		}
 		*mode = BuildmodeShared