Revert "runtime: use fixed TLS offsets on darwin/amd64 and darwin/386"

This reverts commit 76e92d1c.

Reason for revert: Seems to have broken the darwin/386 builder, the toolchain is barfing on the new inline assembly.

Change-Id: Ic83fa3c85148946529c5fd47d1e1669898031ace
Reviewed-on: https://go-review.googlesource.com/106155Reviewed-by: Keith Randall <khr@golang.org>

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

@@ -113,30 +113,24 @@ func (ctxt *Link) computeTLSOffset() {
 
 		/*
 		 * OS X system constants - offset from 0(GS) to our TLS.
+		 * Explained in src/runtime/cgo/gcc_darwin_*.c.
 		 */
 	case objabi.Hdarwin:
 		switch ctxt.Arch.Family {
 		default:
 			log.Fatalf("unknown thread-local storage offset for darwin/%s", ctxt.Arch.Name)
 
-			/*
-			 * For x86, Apple has reserved a slot in the TLS for Go. See issue 23617.
-			 * That slot is at offset 0x30 on amd64, and 0x18 on 386.
-			 * The slot will hold the G pointer.
-			 * These constants should match those in runtime/sys_darwin_{386,amd64}.s
-			 * and runtime/cgo/gcc_darwin_{386,amd64}.c.
-			 */
-		case sys.I386:
-			ctxt.Tlsoffset = 0x18
-
-		case sys.AMD64:
-			ctxt.Tlsoffset = 0x30
-
 		case sys.ARM:
 			ctxt.Tlsoffset = 0 // dummy value, not needed
 
+		case sys.AMD64:
+			ctxt.Tlsoffset = 0x8a0
+
 		case sys.ARM64:
 			ctxt.Tlsoffset = 0 // dummy value, not needed
+
+		case sys.I386:
+			ctxt.Tlsoffset = 0x468
 		}
 	}
 

src/runtime/cgo/gcc_darwin_386.c

@@ -9,6 +9,89 @@
 #include "libcgo_unix.h"
 
 static void* threadentry(void*);
+static pthread_key_t k1;
+
+#define magic1 (0x23581321U)
+
+static void
+inittls(void)
+{
+	uint32 x;
+	pthread_key_t tofree[128], k;
+	int i, ntofree;
+
+	/*
+	 * Allocate thread-local storage slot for g.
+	 * The key numbers start at 0x100, and we expect to be
+	 * one of the early calls to pthread_key_create, so we
+	 * should be able to get a pretty low number.
+	 *
+	 * In Darwin/386 pthreads, %gs points at the thread
+	 * structure, and each key is an index into the thread-local
+	 * storage array that begins at offset 0x48 within in that structure.
+	 * It may happen that we are not quite the first function to try
+	 * to allocate thread-local storage keys, so instead of depending
+	 * on getting 0x100, we try for 0x108, allocating keys until
+	 * we get the one we want and then freeing the ones we didn't want.
+	 *
+	 * Thus the final offset to use in %gs references is
+	 * 0x48+4*0x108 = 0x468.
+	 *
+	 * The linker and runtime hard-code this constant offset
+	 * from %gs where we expect to find g.
+	 * Known to src/cmd/link/internal/ld/sym.go:/0x468
+	 * and to src/runtime/sys_darwin_386.s:/0x468
+	 *
+	 * This is truly disgusting and a bit fragile, but taking care
+	 * of it here protects the rest of the system from damage.
+	 * The alternative would be to use a global variable that
+	 * held the offset and refer to that variable each time we
+	 * need a %gs variable (g).  That approach would
+	 * require an extra instruction and memory reference in
+	 * every stack growth prolog and would also require
+	 * rewriting the code that 8c generates for extern registers.
+	 *
+	 * Things get more disgusting on OS X 10.7 Lion.
+	 * The 0x48 base mentioned above is the offset of the tsd
+	 * array within the per-thread structure on Leopard and Snow Leopard.
+	 * On Lion, the base moved a little, so while the math above
+	 * still applies, the base is different.  Thus, we cannot
+	 * look for specific key values if we want to build binaries
+	 * that run on both systems.  Instead, forget about the
+	 * specific key values and just allocate and initialize per-thread
+	 * storage until we find a key that writes to the memory location
+	 * we want.  Then keep that key.
+	 */
+	ntofree = 0;
+	for(;;) {
+		if(pthread_key_create(&k, nil) != 0) {
+			fprintf(stderr, "runtime/cgo: pthread_key_create failed\n");
+			abort();
+		}
+		pthread_setspecific(k, (void*)magic1);
+		asm volatile("movl %%gs:0x468, %0" : "=r"(x));
+		pthread_setspecific(k, 0);
+		if(x == magic1) {
+			k1 = k;
+			break;
+		}
+		if(ntofree >= nelem(tofree)) {
+			fprintf(stderr, "runtime/cgo: could not obtain pthread_keys\n");
+			fprintf(stderr, "\ttried");
+			for(i=0; i<ntofree; i++)
+				fprintf(stderr, " %#x", (unsigned)tofree[i]);
+			fprintf(stderr, "\n");
+			abort();
+		}
+		tofree[ntofree++] = k;
+	}
+
+	/*
+	 * We got the key we wanted.  Free the others.
+	 */
+	for(i=0; i<ntofree; i++)
+		pthread_key_delete(tofree[i]);
+}
 
 void
 x_cgo_init(G *g)
@@ -20,6 +103,8 @@ x_cgo_init(G *g)
 	pthread_attr_getstacksize(&attr, &size);
 	g->stacklo = (uintptr)&attr - size + 4096;
 	pthread_attr_destroy(&attr);
+
+	inittls();
 }
 
 
@@ -57,9 +142,10 @@ threadentry(void *v)
 	ts = *(ThreadStart*)v;
 	free(v);
 
-	// Move the g pointer into the slot reserved in thread local storage.
-	// Constant must match the one in cmd/link/internal/ld/sym.go.
-	asm volatile("movq %0, %%gs:0x18" :: "r"(ts.g));
+	if (pthread_setspecific(k1, (void*)ts.g) != 0) {
+		fprintf(stderr, "runtime/cgo: pthread_setspecific failed\n");
+		abort();
+	}
 
 	crosscall_386(ts.fn);
 	return nil;

src/runtime/cgo/gcc_darwin_amd64.c

@@ -9,6 +9,60 @@
 #include "libcgo_unix.h"
 
 static void* threadentry(void*);
+static pthread_key_t k1;
+
+#define magic1 (0x23581321345589ULL)
+
+static void
+inittls(void)
+{
+	uint64 x;
+	pthread_key_t tofree[128], k;
+	int i, ntofree;
+
+	/*
+	 * Same logic, code as darwin_386.c:/inittls, except that words
+	 * are 8 bytes long now, and the thread-local storage starts
+	 * at 0x60 on Leopard / Snow Leopard. So the offset is
+	 * 0x60+8*0x108 = 0x8a0.
+	 *
+	 * The linker and runtime hard-code this constant offset
+	 * from %gs where we expect to find g.
+	 * Known to src/cmd/link/internal/ld/sym.go:/0x8a0
+	 * and to src/runtime/sys_darwin_amd64.s:/0x8a0
+	 *
+	 * As disgusting as on the 386; same justification.
+	 */
+	ntofree = 0;
+	for(;;) {
+		if(pthread_key_create(&k, nil) != 0) {
+			fprintf(stderr, "runtime/cgo: pthread_key_create failed\n");
+			abort();
+		}
+		pthread_setspecific(k, (void*)magic1);
+		asm volatile("movq %%gs:0x8a0, %0" : "=r"(x));
+		pthread_setspecific(k, 0);
+		if(x == magic1) {
+			k1 = k;
+			break;
+		}
+		if(ntofree >= nelem(tofree)) {
+			fprintf(stderr, "runtime/cgo: could not obtain pthread_keys\n");
+			fprintf(stderr, "\ttried");
+			for(i=0; i<ntofree; i++)
+				fprintf(stderr, " %#x", (unsigned)tofree[i]);
+			fprintf(stderr, "\n");
+			abort();
+		}
+		tofree[ntofree++] = k;
+	}
+
+	/*
+	 * We got the key we wanted.  Free the others.
+	 */
+	for(i=0; i<ntofree; i++)
+		pthread_key_delete(tofree[i]);
+}
 
 void
 x_cgo_init(G *g)
@@ -20,6 +74,8 @@ x_cgo_init(G *g)
 	pthread_attr_getstacksize(&attr, &size);
 	g->stacklo = (uintptr)&attr - size + 4096;
 	pthread_attr_destroy(&attr);
+
+	inittls();
 }
 
 
@@ -57,9 +113,10 @@ threadentry(void *v)
 	ts = *(ThreadStart*)v;
 	free(v);
 
-	// Move the g pointer into the slot reserved in thread local storage.
-	// Constant must match the one in cmd/link/internal/ld/sym.go.
-	asm volatile("movq %0, %%gs:0x30" :: "r"(ts.g));
+	if (pthread_setspecific(k1, (void*)ts.g) != 0) {
+		fprintf(stderr, "runtime/cgo: pthread_setspecific failed\n");
+		abort();
+	}
 
 	crosscall_amd64(ts.fn);
 	return nil;

src/runtime/sys_darwin_386.s

@@ -525,14 +525,15 @@ TEXT runtime·setldt(SB),NOSPLIT,$32
 	 * When linking against the system libraries,
 	 * we use its pthread_create and let it set up %gs
 	 * for us.  When we do that, the private storage
-	 * we get is not at 0(GS) but at 0x18(GS).
-	 * The linker rewrites 0(TLS) into 0x18(GS) for us.
+	 * we get is not at 0(GS) but at 0x468(GS).
+	 * 8l rewrites 0(TLS) into 0x468(GS) for us.
 	 * To accommodate that rewrite, we translate the
-	 * address here so that 0x18(GS) maps to 0(address).
+	 * address and limit here so that 0x468(GS) maps to 0(address).
 	 *
-	 * Constant must match the one in cmd/link/internal/ld/sym.go.
+	 * See cgo/gcc_darwin_386.c:/468 for the derivation
+	 * of the constant.
 	 */
-	SUBL	$0x18, BX
+	SUBL	$0x468, BX
 
 	/*
 	 * Must set up as USER_CTHREAD segment because

src/runtime/sys_darwin_amd64.s

@@ -569,10 +569,11 @@ TEXT runtime·mach_semaphore_signal_all(SB),NOSPLIT,$0
 // set tls base to DI
 TEXT runtime·settls(SB),NOSPLIT,$32
 	/*
-	 * Same as in sys_darwin_386.s, but a different constant.
-	 * Constant must match the one in cmd/link/internal/ld/sym.go.
-	 */
-	SUBQ $0x30, DI
+	* Same as in sys_darwin_386.s:/ugliness, different constant.
+	* See cgo/gcc_darwin_amd64.c for the derivation
+	* of the constant.
+	*/
+	SUBQ $0x8a0, DI
 
 	MOVL	$(0x3000000+3), AX	// thread_fast_set_cthread_self - machdep call #3
 	SYSCALL