1/*
2 * Copyright (C) 2013 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 *      http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17#define _GNU_SOURCE 1
18#include <errno.h>
19#include <stdint.h>
20#include <string.h>
21#include <sys/param.h>
22#include <sys/ptrace.h>
23#include <sys/types.h>
24#include <ucontext.h>
25#include <unistd.h>
26
27#include <string>
28
29#include <backtrace/Backtrace.h>
30#include <backtrace/BacktraceMap.h>
31
32#include <cutils/threads.h>
33
34#include "BacktraceCurrent.h"
35#include "BacktraceLog.h"
36#include "ThreadEntry.h"
37#include "thread_utils.h"
38
39bool BacktraceCurrent::ReadWord(uintptr_t ptr, word_t* out_value) {
40  if (!VerifyReadWordArgs(ptr, out_value)) {
41    return false;
42  }
43
44  backtrace_map_t map;
45  FillInMap(ptr, &map);
46  if (BacktraceMap::IsValid(map) && map.flags & PROT_READ) {
47    *out_value = *reinterpret_cast<word_t*>(ptr);
48    return true;
49  } else {
50    BACK_LOGW("pointer %p not in a readable map", reinterpret_cast<void*>(ptr));
51    *out_value = static_cast<word_t>(-1);
52    return false;
53  }
54}
55
56size_t BacktraceCurrent::Read(uintptr_t addr, uint8_t* buffer, size_t bytes) {
57  backtrace_map_t map;
58  FillInMap(addr, &map);
59  if (!BacktraceMap::IsValid(map) || !(map.flags & PROT_READ)) {
60    return 0;
61  }
62  bytes = MIN(map.end - addr, bytes);
63  memcpy(buffer, reinterpret_cast<uint8_t*>(addr), bytes);
64  return bytes;
65}
66
67bool BacktraceCurrent::Unwind(size_t num_ignore_frames, ucontext_t* ucontext) {
68  if (GetMap() == nullptr) {
69    // Without a map object, we can't do anything.
70    return false;
71  }
72
73  if (ucontext) {
74    return UnwindFromContext(num_ignore_frames, ucontext);
75  }
76
77  if (Tid() != gettid()) {
78    return UnwindThread(num_ignore_frames);
79  }
80
81  return UnwindFromContext(num_ignore_frames, nullptr);
82}
83
84bool BacktraceCurrent::DiscardFrame(const backtrace_frame_data_t& frame) {
85  if (BacktraceMap::IsValid(frame.map)) {
86    const std::string library = basename(frame.map.name.c_str());
87    if (library == "libunwind.so" || library == "libbacktrace.so") {
88      return true;
89    }
90  }
91  return false;
92}
93
94static pthread_mutex_t g_sigaction_mutex = PTHREAD_MUTEX_INITIALIZER;
95
96static void SignalHandler(int, siginfo_t*, void* sigcontext) {
97  ThreadEntry* entry = ThreadEntry::Get(getpid(), gettid(), false);
98  if (!entry) {
99    BACK_LOGE("pid %d, tid %d entry not found", getpid(), gettid());
100    return;
101  }
102
103  entry->CopyUcontextFromSigcontext(sigcontext);
104
105  // Indicate the ucontext is now valid.
106  entry->Wake();
107
108  // Pause the thread until the unwind is complete. This avoids having
109  // the thread run ahead causing problems.
110  // The number indicates that we are waiting for the second Wake() call
111  // overall which is made by the thread requesting an unwind.
112  if (entry->Wait(2)) {
113    // Do not remove the entry here because that can result in a deadlock
114    // if the code cannot properly send a signal to the thread under test.
115    entry->Wake();
116  } else {
117    // At this point, it is possible that entry has been freed, so just exit.
118    BACK_LOGE("Timed out waiting for unwind thread to indicate it completed.");
119  }
120}
121
122bool BacktraceCurrent::UnwindThread(size_t num_ignore_frames) {
123  // Prevent multiple threads trying to set the trigger action on different
124  // threads at the same time.
125  pthread_mutex_lock(&g_sigaction_mutex);
126
127  ThreadEntry* entry = ThreadEntry::Get(Pid(), Tid());
128  entry->Lock();
129
130  struct sigaction act, oldact;
131  memset(&act, 0, sizeof(act));
132  act.sa_sigaction = SignalHandler;
133  act.sa_flags = SA_RESTART | SA_SIGINFO | SA_ONSTACK;
134  sigemptyset(&act.sa_mask);
135  if (sigaction(THREAD_SIGNAL, &act, &oldact) != 0) {
136    BACK_LOGE("sigaction failed: %s", strerror(errno));
137    ThreadEntry::Remove(entry);
138    pthread_mutex_unlock(&g_sigaction_mutex);
139    return false;
140  }
141
142  if (tgkill(Pid(), Tid(), THREAD_SIGNAL) != 0) {
143    BACK_LOGE("tgkill %d failed: %s", Tid(), strerror(errno));
144    sigaction(THREAD_SIGNAL, &oldact, nullptr);
145    ThreadEntry::Remove(entry);
146    pthread_mutex_unlock(&g_sigaction_mutex);
147    return false;
148  }
149
150  // Wait for the thread to get the ucontext. The number indicates
151  // that we are waiting for the first Wake() call made by the thread.
152  bool wait_completed = entry->Wait(1);
153
154  // After the thread has received the signal, allow other unwinders to
155  // continue.
156  sigaction(THREAD_SIGNAL, &oldact, nullptr);
157  pthread_mutex_unlock(&g_sigaction_mutex);
158
159  bool unwind_done = false;
160  if (wait_completed) {
161    unwind_done = UnwindFromContext(num_ignore_frames, entry->GetUcontext());
162
163    // Tell the signal handler to exit and release the entry.
164    entry->Wake();
165
166    // Wait for the thread to indicate it is done with the ThreadEntry.
167    if (!entry->Wait(3)) {
168      // Send a warning, but do not mark as a failure to unwind.
169      BACK_LOGW("Timed out waiting for signal handler to indicate it finished.");
170    }
171  } else {
172    BACK_LOGE("Timed out waiting for signal handler to get ucontext data.");
173  }
174
175  ThreadEntry::Remove(entry);
176
177  return unwind_done;
178}
179