runtime/cgo: EXC_BAD_ACCESS handler for arm64

Change-Id: Ia9ff9c0d381fad43fc5d3e5972dd6e66503733a5
Reviewed-on: https://go-review.googlesource.com/8815Reviewed-by: Minux Ma <minux@golang.org>

src/runtime/cgo/gcc_signal_darwin_armx.c

@@ -20,9 +20,9 @@
 //
 //	go test -tags lldb -installsuffix lldb
 
-// +build darwin,arm,!lldb
-
-// TODO(crawshaw): darwin,arm64,!lldb
+// +build !lldb
+// +build darwin
+// +build arm arm64
 
 #include <limits.h>
 #include <pthread.h>
@@ -77,9 +77,31 @@ catch_exception_raise(
 
 	// Bounce call to sigpanic through asm that makes it look like
 	// we call sigpanic directly from the faulting code.
+#ifdef __arm64__
+	thread_state.ts_64.__x[1] = thread_state.ts_64.__lr;
+	thread_state.ts_64.__x[2] = thread_state.ts_64.__pc;
+	thread_state.ts_64.__pc = x_cgo_panicmem;
+#else
 	thread_state.ts_32.__r[1] = thread_state.ts_32.__lr;
 	thread_state.ts_32.__r[2] = thread_state.ts_32.__pc;
 	thread_state.ts_32.__pc = x_cgo_panicmem;
+#endif
+
+	if (0) {
+		// Useful debugging logic when panicmem is broken.
+		//
+		// Sends the first SIGSEGV and lets lldb catch the
+		// second one, avoiding a loop that locks up iOS
+		// devices requiring a hard reboot.
+		fprintf(stderr, "runtime/cgo: caught exc_bad_access\n");
+		fprintf(stderr, "__lr = %llx\n", thread_state.ts_64.__lr);
+		fprintf(stderr, "__pc = %llx\n", thread_state.ts_64.__pc);
+		static int pass1 = 0;
+		if (pass1) {
+			return KERN_FAILURE;
+		}
+		pass1 = 1;
+	}
 
 	ret = thread_set_state(thread, ARM_UNIFIED_THREAD_STATE, (thread_state_t)&thread_state, state_count);
 	if (ret) {
@@ -174,9 +196,10 @@ darwin_arm_init_mach_exception_handler()
 	}
 
 	// Start a thread to handle exceptions.
+	uintptr_t port_set = (uintptr_t)mach_exception_handler_port_set;
 	pthread_attr_init(&attr);
 	pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);
-	ret = pthread_create(&thr, &attr, mach_exception_handler, (void*)mach_exception_handler_port_set);
+	ret = pthread_create(&thr, &attr, mach_exception_handler, (void*)port_set);
 	if (ret) {
 		fprintf(stderr, "runtime/cgo: pthread_create failed: %d\n", ret);
 		abort();

src/runtime/cgo/signal_darwin_arm64.s

+// Copyright 2015 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+#include "textflag.h"
+
+// panicmem is the entrypoint for SIGSEGV as intercepted via a
+// mach thread port as EXC_BAD_ACCESS. As the segfault may have happened
+// in C code, we first need to load_g then call panicmem.
+//
+//	R1 - LR at moment of fault
+//	R2 - PC at moment of fault
+TEXT ·panicmem(SB),NOSPLIT,$-8
+	// If in external C code, we need to load the g register.
+	BL  runtime·load_g(SB)
+	CMP $0, g
+	BNE ongothread
+
+	// On a foreign thread.
+	// TODO(crawshaw): call badsignal
+	MOVW $139, R1
+	MOVW R1, (RSP)
+	B    runtime·exit(SB)
+
+ongothread:
+	// Trigger a SIGSEGV panic.
+	//
+	// The goal is to arrange the stack so it looks like the runtime
+	// function sigpanic was called from the PC that faulted. It has
+	// to be sigpanic, as the stack unwinding code in traceback.go
+	// looks explicitly for it.
+	//
+	// To do this we call into runtime·setsigsegv, which sets the
+	// appropriate state inside the g object. We give it the faulting
+	// PC on the stack, then put it in the LR before calling sigpanic.
+	STP.W (R1, R2), -16(RSP)
+	BL runtime·setsigsegv(SB)
+	LDP.P 16(RSP), (R1, R2)
+
+	MOVD R1, 8(RSP)
+	MOVD R2, R30 // link register
+	B runtime·sigpanic(SB)