runtime: use default system stack size, not 64 kB, on non-cgo macOS

At least one libc call we make
(res_search, which calls _mdns_query and then mdns_item_call)
pushes a 64 kB stack frame onto the stack.
Then it faults on the guard page.

Use the default system stack size, under the assumption
that the C code being called is compatible with that stack size.

For #31705.

Change-Id: I1b0bfc2e54043c49f0709255988ef920ce30ee82
Reviewed-on: https://go-review.googlesource.com/c/go/+/180779
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/runtime/os_darwin.go

@@ -145,14 +145,14 @@ func newosproc(mp *m) {
 		exit(1)
 	}
 
-	// Set the stack size we want to use.  64KB for now.
-	// TODO: just use OS default size?
-	const stackSize = 1 << 16
-	if pthread_attr_setstacksize(&attr, stackSize) != 0 {
+	// Find out OS stack size for our own stack guard.
+	var stacksize uintptr
+	if pthread_attr_getstacksize(&attr, &stacksize) != 0 {
 		write(2, unsafe.Pointer(&failthreadcreate[0]), int32(len(failthreadcreate)))
 		exit(1)
 	}
-	//mSysStatInc(&memstats.stacks_sys, stackSize) //TODO: do this?
+	mp.g0.stack.hi = stacksize // for mstart
+	//mSysStatInc(&memstats.stacks_sys, stacksize) //TODO: do this?
 
 	// Tell the pthread library we won't join with this thread.
 	if pthread_attr_setdetachstate(&attr, _PTHREAD_CREATE_DETACHED) != 0 {
@@ -191,11 +191,16 @@ func newosproc0(stacksize uintptr, fn uintptr) {
 		exit(1)
 	}
 
-	// Set the stack we want to use.
-	if pthread_attr_setstacksize(&attr, stacksize) != 0 {
+	// The caller passes in a suggested stack size,
+	// from when we allocated the stack and thread ourselves,
+	// without libpthread. Now that we're using libpthread,
+	// we use the OS default stack size instead of the suggestion.
+	// Find out that stack size for our own stack guard.
+	if pthread_attr_getstacksize(&attr, &stacksize) != 0 {
 		write(2, unsafe.Pointer(&failthreadcreate[0]), int32(len(failthreadcreate)))
 		exit(1)
 	}
+	g0.stack.hi = stacksize // for mstart
 	mSysStatInc(&memstats.stacks_sys, stacksize)
 
 	// Tell the pthread library we won't join with this thread.

src/runtime/sys_darwin.go

@@ -128,10 +128,10 @@ func pthread_attr_init_trampoline()
 
 //go:nosplit
 //go:cgo_unsafe_args
-func pthread_attr_setstacksize(attr *pthreadattr, size uintptr) int32 {
-	return libcCall(unsafe.Pointer(funcPC(pthread_attr_setstacksize_trampoline)), unsafe.Pointer(&attr))
+func pthread_attr_getstacksize(attr *pthreadattr, size *uintptr) int32 {
+	return libcCall(unsafe.Pointer(funcPC(pthread_attr_getstacksize_trampoline)), unsafe.Pointer(&attr))
 }
-func pthread_attr_setstacksize_trampoline()
+func pthread_attr_getstacksize_trampoline()
 
 //go:nosplit
 //go:cgo_unsafe_args
@@ -396,7 +396,7 @@ func closeonexec(fd int32) {
 // in a system library, with the libc_ prefix missing.
 
 //go:cgo_import_dynamic libc_pthread_attr_init pthread_attr_init "/usr/lib/libSystem.B.dylib"
-//go:cgo_import_dynamic libc_pthread_attr_setstacksize pthread_attr_setstacksize "/usr/lib/libSystem.B.dylib"
+//go:cgo_import_dynamic libc_pthread_attr_getstacksize pthread_attr_getstacksize "/usr/lib/libSystem.B.dylib"
 //go:cgo_import_dynamic libc_pthread_attr_setdetachstate pthread_attr_setdetachstate "/usr/lib/libSystem.B.dylib"
 //go:cgo_import_dynamic libc_pthread_create pthread_create "/usr/lib/libSystem.B.dylib"
 //go:cgo_import_dynamic libc_exit exit "/usr/lib/libSystem.B.dylib"

src/runtime/sys_darwin_386.s

@@ -474,7 +474,7 @@ TEXT runtime·pthread_attr_init_trampoline(SB),NOSPLIT,$0
 	POPL	BP
 	RET
 
-TEXT runtime·pthread_attr_setstacksize_trampoline(SB),NOSPLIT,$0
+TEXT runtime·pthread_attr_getstacksize_trampoline(SB),NOSPLIT,$0
 	PUSHL	BP
 	MOVL	SP, BP
 	SUBL	$8, SP
@@ -483,7 +483,7 @@ TEXT runtime·pthread_attr_setstacksize_trampoline(SB),NOSPLIT,$0
 	MOVL	AX, 0(SP)
 	MOVL	4(CX), AX	// arg 2 size
 	MOVL	AX, 4(SP)
-	CALL	libc_pthread_attr_setstacksize(SB)
+	CALL	libc_pthread_attr_getstacksize(SB)
 	MOVL	BP, SP
 	POPL	BP
 	RET

src/runtime/sys_darwin_amd64.s

@@ -443,12 +443,12 @@ TEXT runtime·pthread_attr_init_trampoline(SB),NOSPLIT,$0
 	POPQ	BP
 	RET
 
-TEXT runtime·pthread_attr_setstacksize_trampoline(SB),NOSPLIT,$0
+TEXT runtime·pthread_attr_getstacksize_trampoline(SB),NOSPLIT,$0
 	PUSHQ	BP
 	MOVQ	SP, BP
 	MOVQ	8(DI), SI	// arg 2 size
 	MOVQ	0(DI), DI	// arg 1 attr
-	CALL	libc_pthread_attr_setstacksize(SB)
+	CALL	libc_pthread_attr_getstacksize(SB)
 	POPQ	BP
 	RET
 

src/runtime/sys_darwin_arm.s

@@ -323,7 +323,7 @@ TEXT runtime·pthread_attr_init_trampoline(SB),NOSPLIT,$0
 	BL	libc_exit(SB)
 	RET
 
-TEXT runtime·pthread_attr_setstacksize_trampoline(SB),NOSPLIT,$0
+TEXT runtime·pthread_attr_getstacksize_trampoline(SB),NOSPLIT,$0
 	MOVW	$46, R0
 	BL	libc_exit(SB)
 	RET

src/runtime/sys_darwin_arm64.s

@@ -382,10 +382,10 @@ TEXT runtime·pthread_attr_init_trampoline(SB),NOSPLIT,$0
 	BL	libc_pthread_attr_init(SB)
 	RET
 
-TEXT runtime·pthread_attr_setstacksize_trampoline(SB),NOSPLIT,$0
+TEXT runtime·pthread_attr_getstacksize_trampoline(SB),NOSPLIT,$0
 	MOVD	8(R0), R1	// arg 2 size
 	MOVD	0(R0), R0	// arg 1 attr
-	BL	libc_pthread_attr_setstacksize(SB)
+	BL	libc_pthread_attr_getstacksize(SB)
 	RET
 
 TEXT runtime·pthread_attr_setdetachstate_trampoline(SB),NOSPLIT,$0