// 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.

//

// The dist tool enables this by build flag when testing.

//go:build 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"

#include "libcgo_unix.h"

void xx_cgo_panicmem(void);

uintptr_t x_cgo_panicmem = (uintptr_t)xx_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_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.

#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) {

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)(uintptr_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;

sigset_t ign, oset;

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();

}

// Block all signals to the exception handler thread

sigfillset(&ign);

pthread_sigmask(SIG_SETMASK, &ign, &oset);

// 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 = _cgo_try_pthread_create(&thr, &attr, mach_exception_handler, (void*)port_set);

pthread_sigmask(SIG_SETMASK, &oset, nil);

if (ret) {

fprintf(stderr, "runtime/cgo: pthread_create failed: %d\n", ret);

abort();

}

pthread_attr_destroy(&attr);

}