Text file
src/runtime/cgo/gcc_signal_ios_arm64.c
1// Copyright 2015 The Go Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style
3// license that can be found in the LICENSE file.
4
5// Emulation of the Unix signal SIGSEGV.
6//
7// On iOS, Go tests and apps under development are run by lldb.
8// The debugger uses a task-level exception handler to intercept signals.
9// Despite having a 'handle' mechanism like gdb, lldb will not allow a
10// SIGSEGV to pass to the running program. For Go, this means we cannot
11// generate a panic, which cannot be recovered, and so tests fail.
12//
13// We work around this by registering a thread-level mach exception handler
14// and intercepting EXC_BAD_ACCESS. The kernel offers thread handlers a
15// chance to resolve exceptions before the task handler, so we can generate
16// the panic and avoid lldb's SIGSEGV handler.
17//
18// The dist tool enables this by build flag when testing.
19
20//go:build lldb
21
22#include <limits.h>
23#include <pthread.h>
24#include <stdio.h>
25#include <signal.h>
26#include <stdlib.h>
27#include <unistd.h>
28
29#include <mach/arm/thread_status.h>
30#include <mach/exception_types.h>
31#include <mach/mach.h>
32#include <mach/mach_init.h>
33#include <mach/mach_port.h>
34#include <mach/thread_act.h>
35#include <mach/thread_status.h>
36
37#include "libcgo.h"
38#include "libcgo_unix.h"
39
40void xx_cgo_panicmem(void);
41uintptr_t x_cgo_panicmem = (uintptr_t)xx_cgo_panicmem;
42
43static pthread_mutex_t mach_exception_handler_port_set_mu;
44static mach_port_t mach_exception_handler_port_set = MACH_PORT_NULL;
45
46kern_return_t
47catch_exception_raise(
48 mach_port_t exception_port,
49 mach_port_t thread,
50 mach_port_t task,
51 exception_type_t exception,
52 exception_data_t code_vector,
53 mach_msg_type_number_t code_count)
54{
55 kern_return_t ret;
56 arm_unified_thread_state_t thread_state;
57 mach_msg_type_number_t state_count = ARM_UNIFIED_THREAD_STATE_COUNT;
58
59 // Returning KERN_SUCCESS intercepts the exception.
60 //
61 // Returning KERN_FAILURE lets the exception fall through to the
62 // next handler, which is the standard signal emulation code
63 // registered on the task port.
64
65 if (exception != EXC_BAD_ACCESS) {
66 return KERN_FAILURE;
67 }
68
69 ret = thread_get_state(thread, ARM_UNIFIED_THREAD_STATE, (thread_state_t)&thread_state, &state_count);
70 if (ret) {
71 fprintf(stderr, "runtime/cgo: thread_get_state failed: %d\n", ret);
72 abort();
73 }
74
75 // Bounce call to sigpanic through asm that makes it look like
76 // we call sigpanic directly from the faulting code.
77#ifdef __arm64__
78 thread_state.ts_64.__x[1] = thread_state.ts_64.__lr;
79 thread_state.ts_64.__x[2] = thread_state.ts_64.__pc;
80 thread_state.ts_64.__pc = x_cgo_panicmem;
81#else
82 thread_state.ts_32.__r[1] = thread_state.ts_32.__lr;
83 thread_state.ts_32.__r[2] = thread_state.ts_32.__pc;
84 thread_state.ts_32.__pc = x_cgo_panicmem;
85#endif
86
87 if (0) {
88 // Useful debugging logic when panicmem is broken.
89 //
90 // Sends the first SIGSEGV and lets lldb catch the
91 // second one, avoiding a loop that locks up iOS
92 // devices requiring a hard reboot.
93 fprintf(stderr, "runtime/cgo: caught exc_bad_access\n");
94 fprintf(stderr, "__lr = %llx\n", thread_state.ts_64.__lr);
95 fprintf(stderr, "__pc = %llx\n", thread_state.ts_64.__pc);
96 static int pass1 = 0;
97 if (pass1) {
98 return KERN_FAILURE;
99 }
100 pass1 = 1;
101 }
102
103 ret = thread_set_state(thread, ARM_UNIFIED_THREAD_STATE, (thread_state_t)&thread_state, state_count);
104 if (ret) {
105 fprintf(stderr, "runtime/cgo: thread_set_state failed: %d\n", ret);
106 abort();
107 }
108
109 return KERN_SUCCESS;
110}
111
112void
113darwin_arm_init_thread_exception_port()
114{
115 // Called by each new OS thread to bind its EXC_BAD_ACCESS exception
116 // to mach_exception_handler_port_set.
117 int ret;
118 mach_port_t port = MACH_PORT_NULL;
119
120 ret = mach_port_allocate(mach_task_self(), MACH_PORT_RIGHT_RECEIVE, &port);
121 if (ret) {
122 fprintf(stderr, "runtime/cgo: mach_port_allocate failed: %d\n", ret);
123 abort();
124 }
125 ret = mach_port_insert_right(
126 mach_task_self(),
127 port,
128 port,
129 MACH_MSG_TYPE_MAKE_SEND);
130 if (ret) {
131 fprintf(stderr, "runtime/cgo: mach_port_insert_right failed: %d\n", ret);
132 abort();
133 }
134
135 ret = thread_set_exception_ports(
136 mach_thread_self(),
137 EXC_MASK_BAD_ACCESS,
138 port,
139 EXCEPTION_DEFAULT,
140 THREAD_STATE_NONE);
141 if (ret) {
142 fprintf(stderr, "runtime/cgo: thread_set_exception_ports failed: %d\n", ret);
143 abort();
144 }
145
146 ret = pthread_mutex_lock(&mach_exception_handler_port_set_mu);
147 if (ret) {
148 fprintf(stderr, "runtime/cgo: pthread_mutex_lock failed: %d\n", ret);
149 abort();
150 }
151 ret = mach_port_move_member(
152 mach_task_self(),
153 port,
154 mach_exception_handler_port_set);
155 if (ret) {
156 fprintf(stderr, "runtime/cgo: mach_port_move_member failed: %d\n", ret);
157 abort();
158 }
159 ret = pthread_mutex_unlock(&mach_exception_handler_port_set_mu);
160 if (ret) {
161 fprintf(stderr, "runtime/cgo: pthread_mutex_unlock failed: %d\n", ret);
162 abort();
163 }
164}
165
166static void*
167mach_exception_handler(void *port)
168{
169 // Calls catch_exception_raise.
170 extern boolean_t exc_server();
171 mach_msg_server(exc_server, 2048, (mach_port_t)port, 0);
172 abort(); // never returns
173}
174
175void
176darwin_arm_init_mach_exception_handler()
177{
178 pthread_mutex_init(&mach_exception_handler_port_set_mu, NULL);
179
180 // Called once per process to initialize a mach port server, listening
181 // for EXC_BAD_ACCESS thread exceptions.
182 int ret;
183 pthread_t thr = NULL;
184 pthread_attr_t attr;
185 sigset_t ign, oset;
186
187 ret = mach_port_allocate(
188 mach_task_self(),
189 MACH_PORT_RIGHT_PORT_SET,
190 &mach_exception_handler_port_set);
191 if (ret) {
192 fprintf(stderr, "runtime/cgo: mach_port_allocate failed for port_set: %d\n", ret);
193 abort();
194 }
195
196 // Block all signals to the exception handler thread
197 sigfillset(&ign);
198 pthread_sigmask(SIG_SETMASK, &ign, &oset);
199
200 // Start a thread to handle exceptions.
201 uintptr_t port_set = (uintptr_t)mach_exception_handler_port_set;
202 pthread_attr_init(&attr);
203 pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);
204 ret = _cgo_try_pthread_create(&thr, &attr, mach_exception_handler, (void*)port_set);
205
206 pthread_sigmask(SIG_SETMASK, &oset, nil);
207
208 if (ret) {
209 fprintf(stderr, "runtime/cgo: pthread_create failed: %d\n", ret);
210 abort();
211 }
212 pthread_attr_destroy(&attr);
213}
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