debugger.cpp revision 20dc3f8fa4b192d902d58f496ae15ff33faa78ac 
1/*
2 * Copyright (C) 2008 The Android Open Source Project
3 * All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 *  * Redistributions of source code must retain the above copyright
9 *    notice, this list of conditions and the following disclaimer.
10 *  * Redistributions in binary form must reproduce the above copyright
11 *    notice, this list of conditions and the following disclaimer in
12 *    the documentation and/or other materials provided with the
13 *    distribution.
14 *
15 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
16 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
17 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
18 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
19 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
20 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
21 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
22 * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
23 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
24 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
25 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
26 * SUCH DAMAGE.
27 */
28
29#include "linker.h"
30
31#include <errno.h>
32#include <inttypes.h>
33#include <signal.h>
34#include <stdio.h>
35#include <stdlib.h>
36#include <sys/mman.h>
37#include <sys/prctl.h>
38#include <sys/socket.h>
39#include <sys/un.h>
40#include <unistd.h>
41
42extern "C" int tgkill(int tgid, int tid, int sig);
43
44#if __LP64__
45#define DEBUGGER_SOCKET_NAME "android:debuggerd64"
46#else
47#define DEBUGGER_SOCKET_NAME "android:debuggerd"
48#endif
49
50enum debugger_action_t {
51  // dump a crash
52  DEBUGGER_ACTION_CRASH,
53  // dump a tombstone file
54  DEBUGGER_ACTION_DUMP_TOMBSTONE,
55  // dump a backtrace only back to the socket
56  DEBUGGER_ACTION_DUMP_BACKTRACE,
57};
58
59/* message sent over the socket */
60struct debugger_msg_t {
61  // version 1 included:
62  debugger_action_t action;
63  pid_t tid;
64
65  // version 2 added:
66  uintptr_t abort_msg_address;
67
68  // version 3 added:
69  int32_t original_si_code;
70};
71
72// see man(2) prctl, specifically the section about PR_GET_NAME
73#define MAX_TASK_NAME_LEN (16)
74
75static int socket_abstract_client(const char* name, int type) {
76  sockaddr_un addr;
77
78  // Test with length +1 for the *initial* '\0'.
79  size_t namelen = strlen(name);
80  if ((namelen + 1) > sizeof(addr.sun_path)) {
81    errno = EINVAL;
82    return -1;
83  }
84
85  // This is used for abstract socket namespace, we need
86  // an initial '\0' at the start of the Unix socket path.
87  //
88  // Note: The path in this case is *not* supposed to be
89  // '\0'-terminated. ("man 7 unix" for the gory details.)
90  memset(&addr, 0, sizeof(addr));
91  addr.sun_family = AF_LOCAL;
92  addr.sun_path[0] = 0;
93  memcpy(addr.sun_path + 1, name, namelen);
94
95  socklen_t alen = namelen + offsetof(sockaddr_un, sun_path) + 1;
96
97  int s = socket(AF_LOCAL, type, 0);
98  if (s == -1) {
99    return -1;
100  }
101
102  int rc = TEMP_FAILURE_RETRY(connect(s, reinterpret_cast<sockaddr*>(&addr), alen));
103  if (rc == -1) {
104    close(s);
105    return -1;
106  }
107
108  return s;
109}
110
111/*
112 * Writes a summary of the signal to the log file.  We do this so that, if
113 * for some reason we're not able to contact debuggerd, there is still some
114 * indication of the failure in the log.
115 *
116 * We could be here as a result of native heap corruption, or while a
117 * mutex is being held, so we don't want to use any libc functions that
118 * could allocate memory or hold a lock.
119 */
120static void log_signal_summary(int signum, const siginfo_t* info) {
121  const char* signal_name = "???";
122  bool has_address = false;
123  switch (signum) {
124    case SIGABRT:
125      signal_name = "SIGABRT";
126      break;
127    case SIGBUS:
128      signal_name = "SIGBUS";
129      has_address = true;
130      break;
131    case SIGFPE:
132      signal_name = "SIGFPE";
133      has_address = true;
134      break;
135    case SIGILL:
136      signal_name = "SIGILL";
137      has_address = true;
138      break;
139    case SIGPIPE:
140      signal_name = "SIGPIPE";
141      break;
142    case SIGSEGV:
143      signal_name = "SIGSEGV";
144      has_address = true;
145      break;
146#if defined(SIGSTKFLT)
147    case SIGSTKFLT:
148      signal_name = "SIGSTKFLT";
149      break;
150#endif
151    case SIGTRAP:
152      signal_name = "SIGTRAP";
153      break;
154  }
155
156  char thread_name[MAX_TASK_NAME_LEN + 1]; // one more for termination
157  if (prctl(PR_GET_NAME, (unsigned long)thread_name, 0, 0, 0) != 0) {
158    strcpy(thread_name, "<name unknown>");
159  } else {
160    // short names are null terminated by prctl, but the man page
161    // implies that 16 byte names are not.
162    thread_name[MAX_TASK_NAME_LEN] = 0;
163  }
164
165  // "info" will be NULL if the siginfo_t information was not available.
166  // Many signals don't have an address or a code.
167  char code_desc[32]; // ", code -6"
168  char addr_desc[32]; // ", fault addr 0x1234"
169  addr_desc[0] = code_desc[0] = 0;
170  if (info != NULL) {
171    // For a rethrown signal, this si_code will be right and the one debuggerd shows will
172    // always be SI_TKILL.
173    __libc_format_buffer(code_desc, sizeof(code_desc), ", code %d", info->si_code);
174    if (has_address) {
175      __libc_format_buffer(addr_desc, sizeof(addr_desc), ", fault addr %p", info->si_addr);
176    }
177  }
178  __libc_format_log(ANDROID_LOG_FATAL, "libc",
179                    "Fatal signal %d (%s)%s%s in tid %d (%s)",
180                    signum, signal_name, code_desc, addr_desc, gettid(), thread_name);
181}
182
183/*
184 * Returns true if the handler for signal "signum" has SA_SIGINFO set.
185 */
186static bool have_siginfo(int signum) {
187  struct sigaction old_action, new_action;
188
189  memset(&new_action, 0, sizeof(new_action));
190  new_action.sa_handler = SIG_DFL;
191  new_action.sa_flags = SA_RESTART;
192  sigemptyset(&new_action.sa_mask);
193
194  if (sigaction(signum, &new_action, &old_action) < 0) {
195    __libc_format_log(ANDROID_LOG_WARN, "libc", "Failed testing for SA_SIGINFO: %s",
196                      strerror(errno));
197    return false;
198  }
199  bool result = (old_action.sa_flags & SA_SIGINFO) != 0;
200
201  if (sigaction(signum, &old_action, NULL) == -1) {
202    __libc_format_log(ANDROID_LOG_WARN, "libc", "Restore failed in test for SA_SIGINFO: %s",
203                      strerror(errno));
204  }
205  return result;
206}
207
208static void send_debuggerd_packet(siginfo_t* info) {
209  if (prctl(PR_GET_DUMPABLE, 0, 0, 0, 0) == 0) {
210    // process has disabled core dumps and PTRACE_ATTACH, and does not want to be dumped.
211    // Honor that intention by not connecting to debuggerd and asking it
212    // to dump our internal state.
213    __libc_format_log(ANDROID_LOG_INFO, "libc",
214                      "Suppressing debuggerd output because prctl(PR_GET_DUMPABLE)==0");
215    return;
216  }
217
218  int s = socket_abstract_client(DEBUGGER_SOCKET_NAME, SOCK_STREAM);
219  if (s == -1) {
220    __libc_format_log(ANDROID_LOG_FATAL, "libc", "Unable to open connection to debuggerd: %s",
221                      strerror(errno));
222    return;
223  }
224
225  // debuggerd knows our pid from the credentials on the
226  // local socket but we need to tell it the tid of the crashing thread.
227  // debuggerd will be paranoid and verify that we sent a tid
228  // that's actually in our process.
229  debugger_msg_t msg;
230  msg.action = DEBUGGER_ACTION_CRASH;
231  msg.tid = gettid();
232  msg.abort_msg_address = reinterpret_cast<uintptr_t>(g_abort_message);
233  msg.original_si_code = (info != NULL) ? info->si_code : 0;
234  int ret = TEMP_FAILURE_RETRY(write(s, &msg, sizeof(msg)));
235  if (ret == sizeof(msg)) {
236    char debuggerd_ack;
237    ret = TEMP_FAILURE_RETRY(read(s, &debuggerd_ack, 1));
238    int saved_errno = errno;
239    notify_gdb_of_libraries();
240    errno = saved_errno;
241  } else {
242    // read or write failed -- broken connection?
243    __libc_format_log(ANDROID_LOG_FATAL, "libc", "Failed while talking to debuggerd: %s",
244                      strerror(errno));
245  }
246
247  close(s);
248}
249
250/*
251 * Catches fatal signals so we can ask debuggerd to ptrace us before
252 * we crash.
253 */
254static void debuggerd_signal_handler(int signal_number, siginfo_t* info, void*) {
255  // It's possible somebody cleared the SA_SIGINFO flag, which would mean
256  // our "info" arg holds an undefined value.
257  if (!have_siginfo(signal_number)) {
258    info = NULL;
259  }
260
261  log_signal_summary(signal_number, info);
262
263  send_debuggerd_packet(info);
264
265  // Remove our net so we fault for real when we return.
266  signal(signal_number, SIG_DFL);
267
268  // These signals are not re-thrown when we resume.  This means that
269  // crashing due to (say) SIGPIPE doesn't work the way you'd expect it
270  // to.  We work around this by throwing them manually.  We don't want
271  // to do this for *all* signals because it'll screw up the si_addr for
272  // faults like SIGSEGV. It does screw up the si_code, which is why we
273  // passed that to debuggerd above.
274  switch (signal_number) {
275    case SIGABRT:
276    case SIGFPE:
277    case SIGPIPE:
278#if defined(SIGSTKFLT)
279    case SIGSTKFLT:
280#endif
281    case SIGTRAP:
282      tgkill(getpid(), gettid(), signal_number);
283      break;
284    default:    // SIGILL, SIGBUS, SIGSEGV
285      break;
286  }
287}
288
289__LIBC_HIDDEN__ void debuggerd_init() {
290  struct sigaction action;
291  memset(&action, 0, sizeof(action));
292  sigemptyset(&action.sa_mask);
293  action.sa_sigaction = debuggerd_signal_handler;
294  action.sa_flags = SA_RESTART | SA_SIGINFO;
295
296  // Use the alternate signal stack if available so we can catch stack overflows.
297  action.sa_flags |= SA_ONSTACK;
298
299  sigaction(SIGABRT, &action, NULL);
300  sigaction(SIGBUS, &action, NULL);
301  sigaction(SIGFPE, &action, NULL);
302  sigaction(SIGILL, &action, NULL);
303  sigaction(SIGPIPE, &action, NULL);
304  sigaction(SIGSEGV, &action, NULL);
305#if defined(SIGSTKFLT)
306  sigaction(SIGSTKFLT, &action, NULL);
307#endif
308  sigaction(SIGTRAP, &action, NULL);
309}
310