build: on OS X 10.8 and later, use clang instead of gcc

Fixes #5822.
Will no doubt cause other problems, but Apple has forced our hand.

R=golang-dev, bradfitz, khr
CC=golang-dev
https://golang.org/cl/12350044

src/cmd/cgo/gcc.go

@@ -646,19 +646,20 @@ func (p *Package) rewriteRef(f *File) {
 	}
 }
 
-// gccName returns the name of the compiler to run.  Use $CC if set in
-// the environment, otherwise just "gcc".
-
-func (p *Package) gccName() string {
+// gccBaseCmd returns the start of the compiler command line.
+// It uses $CC if set, or else $GCC, or else the compiler recorded
+// during the initial build as defaultCC.
+// defaultCC is defined in zdefaultcc.go, written by cmd/dist.
+func (p *Package) gccBaseCmd() []string {
 	// Use $CC if set, since that's what the build uses.
-	if ret := os.Getenv("CC"); ret != "" {
+	if ret := strings.Fields(os.Getenv("CC")); len(ret) > 0 {
 		return ret
 	}
-	// Fall back to $GCC if set, since that's what we used to use.
-	if ret := os.Getenv("GCC"); ret != "" {
+	// Try $GCC if set, since that's what we used to use.
+	if ret := strings.Fields(os.Getenv("GCC")); len(ret) > 0 {
 		return ret
 	}
-	return "gcc"
+	return strings.Fields(defaultCC)
 }
 
 // gccMachine returns the gcc -m flag to use, either "-m32", "-m64" or "-marm".
@@ -681,17 +682,16 @@ func gccTmp() string {
 // gccCmd returns the gcc command line to use for compiling
 // the input.
 func (p *Package) gccCmd() []string {
-	c := []string{
-		p.gccName(),
+	c := append(p.gccBaseCmd(),
 		"-Wall",                             // many warnings
 		"-Werror",                           // warnings are errors
-		"-o" + gccTmp(),                     // write object to tmp
+		"-o"+gccTmp(),                       // write object to tmp
 		"-gdwarf-2",                         // generate DWARF v2 debugging symbols
 		"-fno-eliminate-unused-debug-types", // gets rid of e.g. untyped enum otherwise
 		"-c",  // do not link
 		"-xc", // input language is C
-	}
-	if strings.Contains(p.gccName(), "clang") {
+	)
+	if strings.Contains(c[0], "clang") {
 		c = append(c,
 			"-ferror-limit=0",
 			// Apple clang version 1.7 (tags/Apple/clang-77) (based on LLVM 2.9svn)
@@ -800,7 +800,7 @@ func (p *Package) gccDebug(stdin []byte) (*dwarf.Data, binary.ByteOrder, []byte)
 // #defines that gcc encountered while processing the input
 // and its included files.
 func (p *Package) gccDefines(stdin []byte) string {
-	base := []string{p.gccName(), "-E", "-dM", "-xc"}
+	base := append(p.gccBaseCmd(), "-E", "-dM", "-xc")
 	base = append(base, p.gccMachine()...)
 	stdout, _ := runGcc(stdin, append(append(base, p.GccOptions...), "-"))
 	return stdout

src/cmd/cgo/out.go

@@ -498,7 +498,7 @@ func (p *Package) writeOutputFunc(fgcc *os.File, n *Name) {
 	// Use __gcc_struct__ to work around http://gcc.gnu.org/PR52991 on x86,
 	// and http://golang.org/issue/5603.
 	extraAttr := ""
-	if !strings.Contains(p.gccName(), "clang") && (goarch == "amd64" || goarch == "386") {
+	if !strings.Contains(p.gccBaseCmd()[0], "clang") && (goarch == "amd64" || goarch == "386") {
 		extraAttr = ", __gcc_struct__"
 	}
 	fmt.Fprintf(fgcc, "\t%s __attribute__((__packed__%v)) *a = v;\n", ctype, extraAttr)

src/cmd/dist/a.h

@@ -74,10 +74,12 @@ extern char *goroot;
 extern char *goroot_final;
 extern char *goextlinkenabled;
 extern char *goversion;
+extern char *defaultcc;
 extern char *workdir;
 extern char *tooldir;
 extern char *slash;
 extern bool rebuildall;
+extern bool defaultclang;
 
 int	find(char*, char**, int);
 void	init(void);
@@ -100,6 +102,9 @@ void	mkzgoos(char*, char*);
 void	mkzruntimedefs(char*, char*);
 void	mkzversion(char*, char*);
 
+// buildgo.c
+void	mkzdefaultcc(char*, char*);
+
 // goc2c.c
 void	goc2c(char*, char*);
 

src/cmd/dist/build.c

@@ -26,8 +26,9 @@ char *tooldir;
 char *gochar;
 char *goversion;
 char *slash;	// / for unix, \ for windows
-
-bool	rebuildall = 0;
+char *defaultcc;
+bool	rebuildall;
+bool defaultclang;
 
 static bool shouldbuild(char*, char*);
 static void copy(char*, char*, int);
@@ -146,6 +147,20 @@ init(void)
 		if(!streq(goextlinkenabled, "0") && !streq(goextlinkenabled, "1"))
 			fatal("unknown $GO_EXTLINK_ENABLED %s", goextlinkenabled);
 	}
+	
+	xgetenv(&b, "CC");
+	if(b.len == 0) {
+		// Use clang on OS X, because gcc is deprecated there.
+		// Xcode for OS X 10.9 Mavericks will ship a fake "gcc" binary that
+		// actually runs clang. We prepare different command
+		// lines for the two binaries, so it matters what we call it.
+		// See golang.org/issue/5822.
+		if(defaultclang)
+			bprintf(&b, "clang");
+		else
+			bprintf(&b, "gcc");
+	}
+	defaultcc = btake(&b);
 
 	xsetenv("GOROOT", goroot);
 	xsetenv("GOARCH", goarch);
@@ -525,6 +540,9 @@ static struct {
 		"../ld/*",
 		"enam.c",
 	}},
+	{"cmd/go", {
+		"zdefaultcc.go",
+	}},
 	{"cmd/", {
 		"$GOROOT/pkg/obj/$GOOS_$GOARCH/libmach.a",
 		"$GOROOT/pkg/obj/$GOOS_$GOARCH/libbio.a",
@@ -557,6 +575,7 @@ static struct {
 	{"opnames.h", gcopnames},
 	{"enam.c", mkenam},
 	{"zasm_", mkzasm},
+	{"zdefaultcc.go", mkzdefaultcc},
 	{"zsys_", mkzsys},
 	{"zgoarch_", mkzgoarch},
 	{"zgoos_", mkzgoos},
@@ -616,10 +635,7 @@ install(char *dir)
 
 	// set up gcc command line on first run.
 	if(gccargs.len == 0) {
-		xgetenv(&b, "CC");
-		if(b.len == 0)
-			bprintf(&b, "gcc");
-		clang = contains(bstr(&b), "clang");
+		bprintf(&b, "%s", defaultcc);
 		splitfields(&gccargs, bstr(&b));
 		for(i=0; i<nelem(proto_gccargs); i++)
 			vadd(&gccargs, proto_gccargs[i]);
@@ -1443,6 +1459,7 @@ cmdenv(int argc, char **argv)
 	if(argc > 0)
 		usage();
 
+	xprintf(format, "CC", defaultcc);
 	xprintf(format, "GOROOT", goroot);
 	xprintf(format, "GOBIN", gobin);
 	xprintf(format, "GOARCH", goarch);

src/cmd/dist/unix.c

@@ -651,6 +651,7 @@ int
 main(int argc, char **argv)
 {
 	Buf b;
+	int osx;
 	struct utsname u;
 
 	setvbuf(stdout, nil, _IOLBF, 0);
@@ -700,17 +701,23 @@ main(int argc, char **argv)
 	if(strcmp(gohostarch, "arm") == 0)
 		maxnbg = 1;
 
-	// The OS X 10.6 linker does not support external
-	// linking mode; see
-	// https://code.google.com/p/go/issues/detail?id=5130 .
-	// The mapping from the uname release field to the OS X
-	// version number is complicated, but basically 10 or under is
-	// OS X 10.6 or earlier.
+	// The OS X 10.6 linker does not support external linking mode.
+	// See golang.org/issue/5130.
+	//
+	// OS X 10.6 does not work with clang either, but OS X 10.9 requires it.
+	// It seems to work with OS X 10.8, so we default to clang for 10.8 and later.
+	// See golang.org/issue/5822.
+	//
+	// Roughly, OS X 10.N shows up as uname release (N+4),
+	// so OS X 10.6 is uname version 10 and OS X 10.8 is uname version 12.
 	if(strcmp(gohostos, "darwin") == 0) {
 		if(uname(&u) < 0)
 			fatal("uname: %s", strerror(errno));
-		if(u.release[1] == '.' || hasprefix(u.release, "10"))
+		osx = atoi(u.release) - 4;
+		if(osx <= 6)
 			goextlinkenabled = "0";
+		if(osx >= 8)
+			defaultclang = 1;
 	}
 
 	init();

src/cmd/go/build.go

@@ -1772,8 +1772,9 @@ func (b *builder) gccld(p *Package, out string, flags []string, obj []string) er
 }
 
 // gccCmd returns a gcc command line prefix
+// defaultCC is defined in zdefaultcc.go, written by cmd/dist.
 func (b *builder) gccCmd(objdir string) []string {
-	return b.ccompilerCmd("CC", "gcc", objdir)
+	return b.ccompilerCmd("CC", defaultCC, objdir)
 }
 
 // gxxCmd returns a g++ command line prefix
@@ -1789,7 +1790,7 @@ func (b *builder) ccompilerCmd(envvar, defcmd, objdir string) []string {
 
 	compiler := strings.Fields(os.Getenv(envvar))
 	if len(compiler) == 0 {
-		compiler = append(compiler, defcmd)
+		compiler = strings.Fields(defcmd)
 	}
 	a := []string{compiler[0], "-I", objdir, "-g", "-O2"}
 	a = append(a, compiler[1:]...)

src/run.bash

@@ -124,7 +124,10 @@ freebsd-386 | freebsd-amd64 | linux-386 | linux-amd64 | netbsd-386 | netbsd-amd6
 esac
 ) || exit $?
 
-[ "$CGO_ENABLED" != 1 ] ||
+# This tests cgo -godefs. That mode is not supported,
+# so it's okay if it doesn't work on some systems.
+# In particular, it works badly with clang on OS X.
+[ "$CGO_ENABLED" != 1 ] || [ "$GOOS" == darwin ] ||
 (xcd ../misc/cgo/testcdefs
 ./test.bash || exit 1
 ) || exit $?