PrettyStackTrace.cpp revision 360784
1//===- PrettyStackTrace.cpp - Pretty Crash Handling -----------------------===// 2// 3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 4// See https://llvm.org/LICENSE.txt for license information. 5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 6// 7//===----------------------------------------------------------------------===// 8// 9// This file defines some helpful functions for dealing with the possibility of 10// Unix signals occurring while your program is running. 11// 12//===----------------------------------------------------------------------===// 13 14#include "llvm/Support/PrettyStackTrace.h" 15#include "llvm-c/ErrorHandling.h" 16#include "llvm/ADT/SmallString.h" 17#include "llvm/Config/config.h" 18#include "llvm/Support/Compiler.h" 19#include "llvm/Support/SaveAndRestore.h" 20#include "llvm/Support/Signals.h" 21#include "llvm/Support/Watchdog.h" 22#include "llvm/Support/raw_ostream.h" 23 24#include <atomic> 25#include <cstdarg> 26#include <cstdio> 27#include <tuple> 28 29#ifdef HAVE_CRASHREPORTERCLIENT_H 30#include <CrashReporterClient.h> 31#endif 32 33using namespace llvm; 34 35// If backtrace support is not enabled, compile out support for pretty stack 36// traces. This has the secondary effect of not requiring thread local storage 37// when backtrace support is disabled. 38#if ENABLE_BACKTRACES 39 40// We need a thread local pointer to manage the stack of our stack trace 41// objects, but we *really* cannot tolerate destructors running and do not want 42// to pay any overhead of synchronizing. As a consequence, we use a raw 43// thread-local variable. 44static LLVM_THREAD_LOCAL PrettyStackTraceEntry *PrettyStackTraceHead = nullptr; 45 46// The use of 'volatile' here is to ensure that any particular thread always 47// reloads the value of the counter. The 'std::atomic' allows us to specify that 48// this variable is accessed in an unsychronized way (it's not actually 49// synchronizing). This does technically mean that the value may not appear to 50// be the same across threads running simultaneously on different CPUs, but in 51// practice the worst that will happen is that we won't print a stack trace when 52// we could have. 53// 54// This is initialized to 1 because 0 is used as a sentinel for "not enabled on 55// the current thread". If the user happens to overflow an 'unsigned' with 56// SIGINFO requests, it's possible that some threads will stop responding to it, 57// but the program won't crash. 58static volatile std::atomic<unsigned> GlobalSigInfoGenerationCounter = 59 ATOMIC_VAR_INIT(1); 60static LLVM_THREAD_LOCAL unsigned ThreadLocalSigInfoGenerationCounter = 0; 61 62namespace llvm { 63PrettyStackTraceEntry *ReverseStackTrace(PrettyStackTraceEntry *Head) { 64 PrettyStackTraceEntry *Prev = nullptr; 65 while (Head) 66 std::tie(Prev, Head, Head->NextEntry) = 67 std::make_tuple(Head, Head->NextEntry, Prev); 68 return Prev; 69} 70} 71 72static void PrintStack(raw_ostream &OS) { 73 // Print out the stack in reverse order. To avoid recursion (which is likely 74 // to fail if we crashed due to stack overflow), we do an up-front pass to 75 // reverse the stack, then print it, then reverse it again. 76 unsigned ID = 0; 77 SaveAndRestore<PrettyStackTraceEntry *> SavedStack{PrettyStackTraceHead, 78 nullptr}; 79 PrettyStackTraceEntry *ReversedStack = ReverseStackTrace(SavedStack.get()); 80 for (const PrettyStackTraceEntry *Entry = ReversedStack; Entry; 81 Entry = Entry->getNextEntry()) { 82 OS << ID++ << ".\t"; 83 sys::Watchdog W(5); 84 Entry->print(OS); 85 } 86 llvm::ReverseStackTrace(ReversedStack); 87} 88 89/// Print the current stack trace to the specified stream. 90/// 91/// Marked NOINLINE so it can be called from debuggers. 92LLVM_ATTRIBUTE_NOINLINE 93static void PrintCurStackTrace(raw_ostream &OS) { 94 // Don't print an empty trace. 95 if (!PrettyStackTraceHead) return; 96 97 // If there are pretty stack frames registered, walk and emit them. 98 OS << "Stack dump:\n"; 99 100 PrintStack(OS); 101 OS.flush(); 102} 103 104// Integrate with crash reporter libraries. 105#if defined (__APPLE__) && defined(HAVE_CRASHREPORTERCLIENT_H) 106// If any clients of llvm try to link to libCrashReporterClient.a themselves, 107// only one crash info struct will be used. 108extern "C" { 109CRASH_REPORTER_CLIENT_HIDDEN 110struct crashreporter_annotations_t gCRAnnotations 111 __attribute__((section("__DATA," CRASHREPORTER_ANNOTATIONS_SECTION))) 112#if CRASHREPORTER_ANNOTATIONS_VERSION < 5 113 = { CRASHREPORTER_ANNOTATIONS_VERSION, 0, 0, 0, 0, 0, 0 }; 114#else 115 = { CRASHREPORTER_ANNOTATIONS_VERSION, 0, 0, 0, 0, 0, 0, 0 }; 116#endif 117} 118#elif defined(__APPLE__) && HAVE_CRASHREPORTER_INFO 119extern "C" const char *__crashreporter_info__ 120 __attribute__((visibility("hidden"))) = 0; 121asm(".desc ___crashreporter_info__, 0x10"); 122#endif 123 124static void setCrashLogMessage(const char *msg) LLVM_ATTRIBUTE_UNUSED; 125static void setCrashLogMessage(const char *msg) { 126#ifdef HAVE_CRASHREPORTERCLIENT_H 127 (void)CRSetCrashLogMessage(msg); 128#elif HAVE_CRASHREPORTER_INFO 129 __crashreporter_info__ = msg; 130#endif 131 // Don't reorder subsequent operations: whatever comes after might crash and 132 // we want the system crash handling to see the message we just set. 133 std::atomic_signal_fence(std::memory_order_seq_cst); 134} 135 136#ifdef __APPLE__ 137using CrashHandlerString = SmallString<2048>; 138using CrashHandlerStringStorage = 139 std::aligned_storage<sizeof(CrashHandlerString), 140 alignof(CrashHandlerString)>::type; 141static CrashHandlerStringStorage crashHandlerStringStorage; 142#endif 143 144/// This callback is run if a fatal signal is delivered to the process, it 145/// prints the pretty stack trace. 146static void CrashHandler(void *) { 147#ifndef __APPLE__ 148 // On non-apple systems, just emit the crash stack trace to stderr. 149 PrintCurStackTrace(errs()); 150#else 151 // Emit the crash stack trace to a SmallString, put it where the system crash 152 // handling will find it, and also send it to stderr. 153 // 154 // The SmallString is fairly large in the hope that we don't allocate (we're 155 // handling a fatal signal, something is already pretty wrong, allocation 156 // might not work). Further, we don't use a magic static in case that's also 157 // borked. We leak any allocation that does occur because the program is about 158 // to die anyways. This is technically racy if we were handling two fatal 159 // signals, however if we're in that situation a race is the least of our 160 // worries. 161 auto &crashHandlerString = 162 *new (&crashHandlerStringStorage) CrashHandlerString; 163 164 // If we crash while trying to print the stack trace, we still want the system 165 // crash handling to have some partial information. That'll work out as long 166 // as the SmallString doesn't allocate. If it does allocate then the system 167 // crash handling will see some garbage because the inline buffer now contains 168 // a pointer. 169 setCrashLogMessage(crashHandlerString.c_str()); 170 171 { 172 raw_svector_ostream Stream(crashHandlerString); 173 PrintCurStackTrace(Stream); 174 } 175 176 if (!crashHandlerString.empty()) { 177 setCrashLogMessage(crashHandlerString.c_str()); 178 errs() << crashHandlerString.str(); 179 } else 180 setCrashLogMessage("No crash information."); 181#endif 182} 183 184static void printForSigInfoIfNeeded() { 185 unsigned CurrentSigInfoGeneration = 186 GlobalSigInfoGenerationCounter.load(std::memory_order_relaxed); 187 if (ThreadLocalSigInfoGenerationCounter == 0 || 188 ThreadLocalSigInfoGenerationCounter == CurrentSigInfoGeneration) { 189 return; 190 } 191 192 PrintCurStackTrace(errs()); 193 ThreadLocalSigInfoGenerationCounter = CurrentSigInfoGeneration; 194} 195 196#endif // ENABLE_BACKTRACES 197 198PrettyStackTraceEntry::PrettyStackTraceEntry() { 199#if ENABLE_BACKTRACES 200 // Handle SIGINFO first, because we haven't finished constructing yet. 201 printForSigInfoIfNeeded(); 202 // Link ourselves. 203 NextEntry = PrettyStackTraceHead; 204 PrettyStackTraceHead = this; 205#endif 206} 207 208PrettyStackTraceEntry::~PrettyStackTraceEntry() { 209#if ENABLE_BACKTRACES 210 assert(PrettyStackTraceHead == this && 211 "Pretty stack trace entry destruction is out of order"); 212 PrettyStackTraceHead = NextEntry; 213 // Handle SIGINFO first, because we already started destructing. 214 printForSigInfoIfNeeded(); 215#endif 216} 217 218void PrettyStackTraceString::print(raw_ostream &OS) const { OS << Str << "\n"; } 219 220PrettyStackTraceFormat::PrettyStackTraceFormat(const char *Format, ...) { 221 va_list AP; 222 va_start(AP, Format); 223 const int SizeOrError = vsnprintf(nullptr, 0, Format, AP); 224 va_end(AP); 225 if (SizeOrError < 0) { 226 return; 227 } 228 229 const int Size = SizeOrError + 1; // '\0' 230 Str.resize(Size); 231 va_start(AP, Format); 232 vsnprintf(Str.data(), Size, Format, AP); 233 va_end(AP); 234} 235 236void PrettyStackTraceFormat::print(raw_ostream &OS) const { OS << Str << "\n"; } 237 238void PrettyStackTraceProgram::print(raw_ostream &OS) const { 239 OS << "Program arguments: "; 240 // Print the argument list. 241 for (unsigned i = 0, e = ArgC; i != e; ++i) 242 OS << ArgV[i] << ' '; 243 OS << '\n'; 244} 245 246#if ENABLE_BACKTRACES 247static bool RegisterCrashPrinter() { 248 sys::AddSignalHandler(CrashHandler, nullptr); 249 return false; 250} 251#endif 252 253void llvm::EnablePrettyStackTrace() { 254#if ENABLE_BACKTRACES 255 // The first time this is called, we register the crash printer. 256 static bool HandlerRegistered = RegisterCrashPrinter(); 257 (void)HandlerRegistered; 258#endif 259} 260 261void llvm::EnablePrettyStackTraceOnSigInfoForThisThread(bool ShouldEnable) { 262#if ENABLE_BACKTRACES 263 if (!ShouldEnable) { 264 ThreadLocalSigInfoGenerationCounter = 0; 265 return; 266 } 267 268 // The first time this is called, we register the SIGINFO handler. 269 static bool HandlerRegistered = []{ 270 sys::SetInfoSignalFunction([]{ 271 GlobalSigInfoGenerationCounter.fetch_add(1, std::memory_order_relaxed); 272 }); 273 return false; 274 }(); 275 (void)HandlerRegistered; 276 277 // Next, enable it for the current thread. 278 ThreadLocalSigInfoGenerationCounter = 279 GlobalSigInfoGenerationCounter.load(std::memory_order_relaxed); 280#endif 281} 282 283const void *llvm::SavePrettyStackState() { 284#if ENABLE_BACKTRACES 285 return PrettyStackTraceHead; 286#else 287 return nullptr; 288#endif 289} 290 291void llvm::RestorePrettyStackState(const void *Top) { 292#if ENABLE_BACKTRACES 293 PrettyStackTraceHead = 294 static_cast<PrettyStackTraceEntry *>(const_cast<void *>(Top)); 295#endif 296} 297 298void LLVMEnablePrettyStackTrace() { 299 EnablePrettyStackTrace(); 300} 301