--- /dev/null
+// 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.
+
+// Emulation of the Unix signal SIGSEGV.
+//
+// On iOS, Go tests and apps under development are run by lldb.
+// The debugger uses a task-level exception handler to intercept signals.
+// Despite having a 'handle' mechanism like gdb, lldb will not allow a
+// SIGSEGV to pass to the running program. For Go, this means we cannot
+// generate a panic, which cannot be recovered, and so tests fail.
+//
+// We work around this by registering a thread-level mach exception handler
+// and intercepting EXC_BAD_ACCESS. The kernel offers thread handlers a
+// chance to resolve exceptions before the task handler, so we can generate
+// the panic and avoid lldb's SIGSEGV handler.
+//
+// If you want to debug a segfault under lldb, compile the standard library
+// with the build tag lldb:
+//
+// go test -tags lldb -installsuffix lldb
+
+// +build darwin,arm,!lldb
+
+// TODO(crawshaw): darwin,arm64,!lldb
+
+#include <limits.h>
+#include <pthread.h>
+#include <stdio.h>
+#include <signal.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+#include <mach/arm/thread_status.h>
+#include <mach/exception_types.h>
+#include <mach/mach.h>
+#include <mach/mach_init.h>
+#include <mach/mach_port.h>
+#include <mach/thread_act.h>
+#include <mach/thread_status.h>
+
+#include "libcgo.h"
+
+uintptr_t x_cgo_panicmem;
+
+static pthread_mutex_t mach_exception_handler_port_set_mu;
+static mach_port_t mach_exception_handler_port_set = MACH_PORT_NULL;
+
+kern_return_t
+catch_exception_raise(
+ mach_port_t exception_port,
+ mach_port_t thread,
+ mach_port_t task,
+ exception_type_t exception,
+ exception_data_t code_vector,
+ mach_msg_type_number_t code_count)
+{
+ kern_return_t ret;
+ arm_unified_thread_state_t thread_state;
+ mach_msg_type_number_t state_count = ARM_UNIFIED_THREAD_STATE_COUNT;
+
+ // Returning KERN_SUCCESS intercepts the exception.
+ //
+ // Returning KERN_FAILURE lets the exception fall through to the
+ // next handler, which is the standard signal emulation code
+ // registered on the task port.
+
+ if (exception != EXC_BAD_ACCESS) {
+ return KERN_FAILURE;
+ }
+
+ ret = thread_get_state(thread, ARM_UNIFIED_THREAD_STATE, (thread_state_t)&thread_state, &state_count);
+ if (ret) {
+ fprintf(stderr, "runtime/cgo: thread_get_state failed: %d\n", ret);
+ abort();
+ }
+
+ // Bounce call to sigpanic through asm that makes it look like
+ // we call sigpanic directly from the faulting code.
+ 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;
+
+ ret = thread_set_state(thread, ARM_UNIFIED_THREAD_STATE, (thread_state_t)&thread_state, state_count);
+ if (ret) {
+ fprintf(stderr, "runtime/cgo: thread_set_state failed: %d\n", ret);
+ abort();
+ }
+
+ return KERN_SUCCESS;
+}
+
+void
+darwin_arm_init_thread_exception_port()
+{
+ // Called by each new OS thread to bind its EXC_BAD_ACCESS exception
+ // to mach_exception_handler_port_set.
+ int ret;
+ mach_port_t port = MACH_PORT_NULL;
+
+ ret = mach_port_allocate(mach_task_self(), MACH_PORT_RIGHT_RECEIVE, &port);
+ if (ret) {
+ fprintf(stderr, "runtime/cgo: mach_port_allocate failed: %d\n", ret);
+ abort();
+ }
+ ret = mach_port_insert_right(
+ mach_task_self(),
+ port,
+ port,
+ MACH_MSG_TYPE_MAKE_SEND);
+ if (ret) {
+ fprintf(stderr, "runtime/cgo: mach_port_insert_right failed: %d\n", ret);
+ abort();
+ }
+
+ ret = thread_set_exception_ports(
+ mach_thread_self(),
+ EXC_MASK_BAD_ACCESS,
+ port,
+ EXCEPTION_DEFAULT,
+ THREAD_STATE_NONE);
+ if (ret) {
+ fprintf(stderr, "runtime/cgo: thread_set_exception_ports failed: %d\n", ret);
+ abort();
+ }
+
+ ret = pthread_mutex_lock(&mach_exception_handler_port_set_mu);
+ if (ret) {
+ fprintf(stderr, "runtime/cgo: pthread_mutex_lock failed: %d\n", ret);
+ abort();
+ }
+ ret = mach_port_move_member(
+ mach_task_self(),
+ port,
+ mach_exception_handler_port_set);
+ if (ret) {
+ fprintf(stderr, "runtime/cgo: mach_port_move_member failed: %d\n", ret);
+ abort();
+ }
+ ret = pthread_mutex_unlock(&mach_exception_handler_port_set_mu);
+ if (ret) {
+ fprintf(stderr, "runtime/cgo: pthread_mutex_unlock failed: %d\n", ret);
+ abort();
+ }
+}
+
+static void*
+mach_exception_handler(void *port)
+{
+ // Calls catch_exception_raise.
+ extern boolean_t exc_server();
+ mach_msg_server(exc_server, 2048, (mach_port_t)port, 0);
+ abort(); // never returns
+}
+
+void
+darwin_arm_init_mach_exception_handler()
+{
+ pthread_mutex_init(&mach_exception_handler_port_set_mu, NULL);
+
+ // Called once per process to initialize a mach port server, listening
+ // for EXC_BAD_ACCESS thread exceptions.
+ int ret;
+ pthread_t thr = NULL;
+ pthread_attr_t attr;
+
+ ret = mach_port_allocate(
+ mach_task_self(),
+ MACH_PORT_RIGHT_PORT_SET,
+ &mach_exception_handler_port_set);
+ if (ret) {
+ fprintf(stderr, "runtime/cgo: mach_port_allocate failed for port_set: %d\n", ret);
+ abort();
+ }
+
+ // Start a thread to handle exceptions.
+ 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);
+ if (ret) {
+ fprintf(stderr, "runtime/cgo: pthread_create failed: %d\n", ret);
+ abort();
+ }
+ pthread_attr_destroy(&attr);
+}
--- /dev/null
+// 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,$-4
+ // 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. We call badsignal, which will, if all
+ // goes according to plan, not return.
+ SUB $4, R13
+ MOVW $11, R1
+ MOVW $11, R2
+ MOVM.DB.W [R1,R2], (R13)
+ // TODO: badsignal should not return, but it does. Issue #10139.
+ //BL runtime·badsignal(SB)
+ MOVW $139, R1
+ MOVW R1, 4(R13)
+ 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.
+ MOVM.DB.W [R1,R2], (R13)
+ BL runtime·setsigsegv(SB)
+ MOVM.IA.W (R13), [R1,R2]
+
+ SUB $4, R13
+ MOVW R1, 0(R13)
+ MOVW R2, R14
+ B runtime·sigpanic(SB)