runtime: use sigaltstack on macOS/ARM64

Currently we don't use sigaltstack on darwin/arm64, as is not
supported on iOS. However, it is supported on macOS. Use it.
(iOS remains unchanged.)

Change-Id: Icc154c5e2edf2dbdc8ca68741ad9157fc15a72ee
Reviewed-on: https://go-review.googlesource.com/c/go/+/256917
Trust: Cherry Zhang <cherryyz@google.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

misc/cgo/test/sigaltstack.go

@@ -62,7 +62,7 @@ import (
 
 func testSigaltstack(t *testing.T) {
 	switch {
-	case runtime.GOOS == "solaris", runtime.GOOS == "illumos", (runtime.GOOS == "darwin" || runtime.GOOS == "ios") && runtime.GOARCH == "arm64":
+	case runtime.GOOS == "solaris", runtime.GOOS == "illumos", runtime.GOOS == "ios" && runtime.GOARCH == "arm64":
 		t.Skipf("switching signal stack not implemented on %s/%s", runtime.GOOS, runtime.GOARCH)
 	}
 

src/cmd/internal/obj/arm64/obj7.go

@@ -589,7 +589,7 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
 				q1.To.Reg = REGSP
 				q1.Spadj = c.autosize
 
-				if c.ctxt.Headtype == objabi.Hdarwin {
+				if objabi.GOOS == "ios" {
 					// iOS does not support SA_ONSTACK. We will run the signal handler
 					// on the G stack. If we write below SP, it may be clobbered by
 					// the signal handler. So we save LR after decrementing SP.

src/runtime/mkpreempt.go

@@ -340,12 +340,9 @@ func genARM64() {
 	p("MOVD R29, -8(RSP)") // save frame pointer (only used on Linux)
 	p("SUB $8, RSP, R29")  // set up new frame pointer
 	p("#endif")
-	// On darwin, save the LR again after decrementing SP. We run the
+	// On iOS, save the LR again after decrementing SP. We run the
-	// signal handler on the G stack (as it doesn't support SA_ONSTACK),
+	// signal handler on the G stack (as it doesn't support sigaltstack),
 	// so any writes below SP may be clobbered.
-	p("#ifdef GOOS_darwin")
-	p("MOVD R30, (RSP)")
-	p("#endif")
 	p("#ifdef GOOS_ios")
 	p("MOVD R30, (RSP)")
 	p("#endif")

src/runtime/os_darwin.go

@@ -289,9 +289,9 @@ func mpreinit(mp *m) {
 // Called to initialize a new m (including the bootstrap m).
 // Called on the new thread, cannot allocate memory.
 func minit() {
-	// The alternate signal stack is buggy on arm64.
+	// iOS does not support alternate signal stack.
 	// The signal handler handles it directly.
-	if GOARCH != "arm64" {
+	if !(GOOS == "ios" && GOARCH == "arm64") {
 		minitSignalStack()
 	}
 	minitSignalMask()
@@ -301,9 +301,9 @@ func minit() {
 // Called from dropm to undo the effect of an minit.
 //go:nosplit
 func unminit() {
-	// The alternate signal stack is buggy on arm64.
+	// iOS does not support alternate signal stack.
 	// See minit.
-	if GOARCH != "arm64" {
+	if !(GOOS == "ios" && GOARCH == "arm64") {
 		unminitSignals()
 	}
 }

src/runtime/preempt_arm64.s

@@ -10,9 +10,6 @@ TEXT ·asyncPreempt(SB),NOSPLIT|NOFRAME,$0-0
 	MOVD R29, -8(RSP)
 	SUB $8, RSP, R29
 	#endif
-	#ifdef GOOS_darwin
-	MOVD R30, (RSP)
-	#endif
 	#ifdef GOOS_ios
 	MOVD R30, (RSP)
 	#endif

src/runtime/stack.go

@@ -66,7 +66,7 @@ const (
 	// to each stack below the usual guard area for OS-specific
 	// purposes like signal handling. Used on Windows, Plan 9,
 	// and iOS because they do not use a separate stack.
-	_StackSystem = sys.GoosWindows*512*sys.PtrSize + sys.GoosPlan9*512 + (sys.GoosDarwin+sys.GoosIos)*sys.GoarchArm64*1024
+	_StackSystem = sys.GoosWindows*512*sys.PtrSize + sys.GoosPlan9*512 + sys.GoosIos*sys.GoarchArm64*1024
 
 	// The minimum size of stack used by Go code
 	_StackMin = 2048

src/runtime/sys_darwin_arm64.s

@@ -202,6 +202,7 @@ TEXT runtime·sigtramp(SB),NOSPLIT,$192
 	BEQ	2(PC)
 	BL	runtime·load_g(SB)
 
+#ifdef GOOS_ios
 	MOVD	RSP, R6
 	CMP	$0, g
 	BEQ	nog
@@ -226,16 +227,21 @@ nog:
 	// Switch to gsignal stack.
 	MOVD	R6, RSP
 
-	// Call sigtrampgo.
+	// Save arguments.
 	MOVW	R0, (8*1)(RSP)
 	MOVD	R1, (8*2)(RSP)
 	MOVD	R2, (8*3)(RSP)
+#endif
+
+	// Call sigtrampgo.
 	MOVD	$runtime·sigtrampgo(SB), R11
 	BL	(R11)
 
+#ifdef GOOS_ios
 	// Switch to old stack.
 	MOVD	(8*4)(RSP), R5
 	MOVD	R5, RSP
+#endif
 
 	// Restore callee-save registers.
 	MOVD	(8*4)(RSP), R19
@@ -329,12 +335,20 @@ TEXT runtime·fcntl_trampoline(SB),NOSPLIT,$0
 	ADD	$16, RSP
 	RET
 
-// sigaltstack on iOS is not supported and will always
-// run the signal handler on the main stack, so our sigtramp has
-// to do the stack switch ourselves.
 TEXT runtime·sigaltstack_trampoline(SB),NOSPLIT,$0
+#ifdef GOOS_ios
+	// sigaltstack on iOS is not supported and will always
+	// run the signal handler on the main stack, so our sigtramp has
+	// to do the stack switch ourselves.
 	MOVW	$43, R0
 	BL	libc_exit(SB)
+#else
+	MOVD	8(R0), R1		// arg 2 old
+	MOVD	0(R0), R0		// arg 1 new
+	CALL	libc_sigaltstack(SB)
+	CBZ	R0, 2(PC)
+	BL	notok<>(SB)
+#endif
 	RET
 
 // Thread related functions