2 * Copyright 2014 Facebook, Inc.
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
8 * http://www.apache.org/licenses/LICENSE-2.0
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.
17 // This is heavily inspired by the signal handler from google-glog
19 #include <folly/experimental/symbolizer/SignalHandler.h>
21 #include <sys/types.h>
30 #include <glog/logging.h>
32 #include <folly/Conv.h>
33 #include <folly/FileUtil.h>
34 #include <folly/Portability.h>
35 #include <folly/ScopeGuard.h>
36 #include <folly/experimental/symbolizer/Symbolizer.h>
38 namespace folly { namespace symbolizer {
43 * Fatal signal handler registry.
45 class FatalSignalCallbackRegistry {
47 FatalSignalCallbackRegistry();
49 void add(SignalCallback func);
54 std::atomic<bool> installed_;
56 std::vector<SignalCallback> handlers_;
59 FatalSignalCallbackRegistry::FatalSignalCallbackRegistry()
63 void FatalSignalCallbackRegistry::add(SignalCallback func) {
64 std::lock_guard<std::mutex> lock(mutex_);
66 << "FatalSignalCallbackRegistry::add may not be used "
67 "after installing the signal handlers.";
68 handlers_.push_back(func);
71 void FatalSignalCallbackRegistry::markInstalled() {
72 std::lock_guard<std::mutex> lock(mutex_);
73 CHECK(!installed_.exchange(true))
74 << "FatalSignalCallbackRegistry::markInstalled must be called "
78 void FatalSignalCallbackRegistry::run() {
83 for (auto& fn : handlers_) {
88 // Leak it so we don't have to worry about destruction order
89 FatalSignalCallbackRegistry* gFatalSignalCallbackRegistry =
90 new FatalSignalCallbackRegistry;
95 struct sigaction oldAction;
97 { SIGSEGV, "SIGSEGV" },
100 { SIGABRT, "SIGABRT" },
101 { SIGBUS, "SIGBUS" },
102 { SIGTERM, "SIGTERM" },
106 void callPreviousSignalHandler(int signum) {
107 // Restore disposition to old disposition, then kill ourselves with the same
108 // signal. The signal will be blocked until we return from our handler,
109 // then it will invoke the default handler and abort.
110 for (auto p = kFatalSignals; p->name; ++p) {
111 if (p->number == signum) {
112 sigaction(signum, &p->oldAction, nullptr);
118 // Not one of the signals we know about. Oh well. Reset to default.
120 memset(&sa, 0, sizeof(sa));
121 sa.sa_handler = SIG_DFL;
122 sigaction(signum, &sa, nullptr);
126 constexpr size_t kDefaultCapacity = 500;
128 // Note: not thread-safe, but that's okay, as we only let one thread
129 // in our signal handler at a time.
131 // Leak it so we don't have to worry about destruction order
132 auto gSignalSafeElfCache = new SignalSafeElfCache(kDefaultCapacity);
134 // Buffered writer (using a fixed-size buffer). We try to write only once
135 // to prevent interleaving with messages written from other threads.
137 // Leak it so we don't have to worry about destruction order.
138 auto gPrinter = new FDSymbolizePrinter(STDERR_FILENO,
139 SymbolizePrinter::COLOR_IF_TTY,
140 size_t(64) << 10); // 64KiB
142 // Flush gPrinter, also fsync, in case we're about to crash again...
145 fsyncNoInt(STDERR_FILENO);
148 void printDec(uint64_t val) {
150 uint32_t n = uint64ToBufferUnsafe(val, buf);
151 gPrinter->print(StringPiece(buf, n));
154 const char kHexChars[] = "0123456789abcdef";
155 void printHex(uint64_t val) {
156 // TODO(tudorb): Add this to folly/Conv.h
157 char buf[2 + 2 * sizeof(uint64_t)]; // "0x" prefix, 2 digits for each byte
159 char* end = buf + sizeof(buf);
162 *--p = kHexChars[val & 0x0f];
168 gPrinter->print(StringPiece(p, end));
171 void print(StringPiece sp) {
175 void dumpTimeInfo() {
176 SCOPE_EXIT { flush(); };
177 time_t now = time(nullptr);
178 print("*** Aborted at ");
180 print(" (Unix time, try 'date -d @");
185 void dumpSignalInfo(int signum, siginfo_t* siginfo) {
186 SCOPE_EXIT { flush(); };
187 // Get the signal name, if possible.
188 const char* name = nullptr;
189 for (auto p = kFatalSignals; p->name; ++p) {
190 if (p->number == signum) {
196 print("*** Signal ");
205 printHex(reinterpret_cast<uint64_t>(siginfo->si_addr));
206 print(") received by PID ");
209 printHex((uint64_t)pthread_self());
210 print("), stack trace: ***\n");
213 FOLLY_NOINLINE void dumpStackTrace(bool symbolize);
215 void dumpStackTrace(bool symbolize) {
216 SCOPE_EXIT { flush(); };
217 // Get and symbolize stack trace
218 constexpr size_t kMaxStackTraceDepth = 100;
219 FrameArray<kMaxStackTraceDepth> addresses;
221 // Skip the getStackTrace frame
222 if (!getStackTraceSafe(addresses)) {
223 print("(error retrieving stack trace)\n");
224 } else if (symbolize) {
225 Symbolizer symbolizer(gSignalSafeElfCache);
226 symbolizer.symbolize(addresses);
228 // Skip the top 2 frames:
230 // dumpStackTrace (here)
232 // Leaving signalHandler on the stack for clarity, I think.
233 gPrinter->println(addresses, 2);
235 print("(safe mode, symbolizer not available)\n");
236 AddressFormatter formatter;
237 for (size_t i = 0; i < addresses.frameCount; ++i) {
238 print(formatter.format(addresses.addresses[i]));
244 // On Linux, pthread_t is a pointer, so 0 is an invalid value, which we
245 // take to indicate "no thread in the signal handler".
247 // POSIX defines PTHREAD_NULL for this purpose, but that's not available.
248 constexpr pthread_t kInvalidThreadId = 0;
250 std::atomic<pthread_t> gSignalThread(kInvalidThreadId);
251 std::atomic<bool> gInRecursiveSignalHandler(false);
254 void innerSignalHandler(int signum, siginfo_t* info, void* uctx) {
255 // First, let's only let one thread in here at a time.
256 pthread_t myId = pthread_self();
258 pthread_t prevSignalThread = kInvalidThreadId;
259 while (!gSignalThread.compare_exchange_strong(prevSignalThread, myId)) {
260 if (pthread_equal(prevSignalThread, myId)) {
261 // First time here. Try to dump the stack trace without symbolization.
262 // If we still fail, well, we're mightily screwed, so we do nothing the
264 if (!gInRecursiveSignalHandler.exchange(true)) {
265 print("Entered fatal signal handler recursively. We're in trouble.\n");
266 dumpStackTrace(false); // no symbolization
271 // Wait a while, try again.
274 ts.tv_nsec = 100L * 1000 * 1000; // 100ms
275 nanosleep(&ts, nullptr);
277 prevSignalThread = kInvalidThreadId;
281 dumpSignalInfo(signum, info);
282 dumpStackTrace(true); // with symbolization
284 // Run user callbacks
285 gFatalSignalCallbackRegistry->run();
288 void signalHandler(int signum, siginfo_t* info, void* uctx) {
289 SCOPE_EXIT { flush(); };
290 innerSignalHandler(signum, info, uctx);
292 gSignalThread = kInvalidThreadId;
293 // Kill ourselves with the previous handler.
294 callPreviousSignalHandler(signum);
299 void addFatalSignalCallback(SignalCallback cb) {
300 gFatalSignalCallbackRegistry->add(cb);
303 void installFatalSignalCallbacks() {
304 gFatalSignalCallbackRegistry->markInstalled();
309 std::atomic<bool> gAlreadyInstalled;
313 void installFatalSignalHandler() {
314 if (gAlreadyInstalled.exchange(true)) {
320 memset(&sa, 0, sizeof(sa));
321 sigemptyset(&sa.sa_mask);
322 sa.sa_flags |= SA_SIGINFO;
323 sa.sa_sigaction = &signalHandler;
325 for (auto p = kFatalSignals; p->name; ++p) {
326 CHECK_ERR(sigaction(p->number, &sa, &p->oldAction));