cmd/dist, cmd/link, cmd/go: make c-shared work on windows

Thanks to Christopher Nelson for spearheading the effort.

Fixes #11058

Change-Id: Icafabac8dc697626ff1bd943cc577b0b1cc6b349
Reviewed-on: https://go-review.googlesource.com/69091
Run-TryBot: Alex Brainman <alex.brainman@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/cmd/dist/test.go

@@ -817,7 +817,8 @@ func (t *tester) supportedBuildmode(mode string) bool {
 		switch pair {
 		case "linux-386", "linux-amd64", "linux-arm", "linux-arm64", "linux-ppc64le",
 			"darwin-amd64", "darwin-386",
-			"android-arm", "android-arm64", "android-386":
+			"android-arm", "android-arm64", "android-386",
+			"windows-amd64", "windows-386":
 			return true
 		}
 		return false

src/cmd/go/internal/work/build.go

@@ -301,6 +301,9 @@ func BuildModeInit() {
 				"android/amd64", "android/arm", "android/arm64", "android/386":
 				codegenArg = "-shared"
 			case "darwin/amd64", "darwin/386":
+			case "windows/amd64", "windows/386":
+				// Do not add usual .exe suffix to the .dll file.
+				cfg.ExeSuffix = ""
 			default:
 				base.Fatalf("-buildmode=c-shared not supported on %s\n", platform)
 			}
@@ -997,12 +1000,14 @@ func (b *Builder) action1(mode BuildMode, depMode BuildMode, p *load.Package, lo
 			name := "a.out"
 			if p.Internal.ExeName != "" {
 				name = p.Internal.ExeName
-			} else if cfg.Goos == "darwin" && cfg.BuildBuildmode == "c-shared" && p.Internal.Target != "" {
+			} else if (cfg.Goos == "darwin" || cfg.Goos == "windows") && cfg.BuildBuildmode == "c-shared" && p.Internal.Target != "" {
 				// On OS X, the linker output name gets recorded in the
 				// shared library's LC_ID_DYLIB load command.
 				// The code invoking the linker knows to pass only the final
 				// path element. Arrange that the path element matches what
 				// we'll install it as; otherwise the library is only loadable as "a.out".
+				// On Windows, DLL file name is recorded in PE file
+				// export section, so do like on OS X.
 				_, name = filepath.Split(p.Internal.Target)
 			}
 			a.Target = a.Objdir + filepath.Join("exe", name) + cfg.ExeSuffix
@@ -2641,8 +2646,10 @@ func (gcToolchain) ld(b *Builder, root *Action, out, importcfg string, allaction
 	// (and making the resulting shared library useless),
 	// run the link in the output directory so that -o can name
 	// just the final path element.
+	// On Windows, DLL file name is recorded in PE file
+	// export section, so do like on OS X.
 	dir := "."
-	if cfg.Goos == "darwin" && cfg.BuildBuildmode == "c-shared" {
+	if (cfg.Goos == "darwin" || cfg.Goos == "windows") && cfg.BuildBuildmode == "c-shared" {
 		dir, out = filepath.Split(out)
 	}
 

src/cmd/internal/obj/x86/asm6.go

@@ -2290,7 +2290,7 @@ func prefixof(ctxt *obj.Link, p *obj.Prog, a *obj.Addr) int {
 		return 0x26
 
 	case REG_TLS:
-		if ctxt.Flag_shared {
+		if ctxt.Flag_shared && ctxt.Headtype != objabi.Hwindows {
 			// When building for inclusion into a shared library, an instruction of the form
 			//     MOV 0(CX)(TLS*1), AX
 			// becomes

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

@@ -592,7 +592,7 @@ func (ctxt *Link) loadlib() {
 	}
 
 	if ctxt.Arch == sys.Arch386 {
-		if (ctxt.BuildMode == BuildModeCArchive && Iself) || ctxt.BuildMode == BuildModeCShared || ctxt.BuildMode == BuildModePIE || ctxt.DynlinkingGo() {
+		if (ctxt.BuildMode == BuildModeCArchive && Iself) || (ctxt.BuildMode == BuildModeCShared && Headtype != objabi.Hwindows) || ctxt.BuildMode == BuildModePIE || ctxt.DynlinkingGo() {
 			got := ctxt.Syms.Lookup("_GLOBAL_OFFSET_TABLE_", 0)
 			got.Type = sym.SDYNIMPORT
 			got.Attr |= sym.AttrReachable
@@ -1126,9 +1126,12 @@ func (ctxt *Link) hostlink() {
 			if ctxt.UseRelro() {
 				argv = append(argv, "-Wl,-z,relro")
 			}
+			argv = append(argv, "-shared")
+			if Headtype != objabi.Hwindows {
 				// Pass -z nodelete to mark the shared library as
 				// non-closeable: a dlclose will do nothing.
-			argv = append(argv, "-shared", "-Wl,-z,nodelete")
+				argv = append(argv, "-Wl,-z,nodelete")
+			}
 		}
 	case BuildModeShared:
 		if ctxt.UseRelro() {