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
ReadWord(uintptr_t ptr,word_t * out_value)39 bool 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
Read(uintptr_t addr,uint8_t * buffer,size_t bytes)56 size_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
Unwind(size_t num_ignore_frames,ucontext_t * ucontext)67 bool 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
DiscardFrame(const backtrace_frame_data_t & frame)84 bool 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
94 static pthread_mutex_t g_sigaction_mutex = PTHREAD_MUTEX_INITIALIZER;
95
SignalHandler(int,siginfo_t *,void * sigcontext)96 static 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
UnwindThread(size_t num_ignore_frames)122 bool 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