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1 //===- PrettyStackTrace.cpp - Pretty Crash Handling -----------------------===//
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2 //
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3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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4 // See https://llvm.org/LICENSE.txt for license information.
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5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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6 //
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7 //===----------------------------------------------------------------------===//
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8 //
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9 // This file defines some helpful functions for dealing with the possibility of
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10 // Unix signals occurring while your program is running.
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11 //
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12 //===----------------------------------------------------------------------===//
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13
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14 #include "llvm/Support/PrettyStackTrace.h"
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15 #include "llvm-c/ErrorHandling.h"
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16 #include "llvm/ADT/SmallString.h"
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17 #include "llvm/Config/config.h"
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18 #include "llvm/Support/Compiler.h"
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19 #include "llvm/Support/SaveAndRestore.h"
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20 #include "llvm/Support/Signals.h"
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21 #include "llvm/Support/Watchdog.h"
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22 #include "llvm/Support/raw_ostream.h"
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23
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24 #include <atomic>
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173
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25 #include <cassert>
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150
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26 #include <cstdarg>
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27 #include <cstdio>
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28 #include <tuple>
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29
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30 #ifdef HAVE_CRASHREPORTERCLIENT_H
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31 #include <CrashReporterClient.h>
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32 #endif
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33
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34 using namespace llvm;
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35
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36 // If backtrace support is not enabled, compile out support for pretty stack
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37 // traces. This has the secondary effect of not requiring thread local storage
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38 // when backtrace support is disabled.
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39 #if ENABLE_BACKTRACES
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40
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41 // We need a thread local pointer to manage the stack of our stack trace
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42 // objects, but we *really* cannot tolerate destructors running and do not want
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43 // to pay any overhead of synchronizing. As a consequence, we use a raw
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44 // thread-local variable.
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45 static LLVM_THREAD_LOCAL PrettyStackTraceEntry *PrettyStackTraceHead = nullptr;
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46
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47 // The use of 'volatile' here is to ensure that any particular thread always
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48 // reloads the value of the counter. The 'std::atomic' allows us to specify that
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49 // this variable is accessed in an unsychronized way (it's not actually
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50 // synchronizing). This does technically mean that the value may not appear to
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51 // be the same across threads running simultaneously on different CPUs, but in
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52 // practice the worst that will happen is that we won't print a stack trace when
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53 // we could have.
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54 //
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55 // This is initialized to 1 because 0 is used as a sentinel for "not enabled on
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56 // the current thread". If the user happens to overflow an 'unsigned' with
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57 // SIGINFO requests, it's possible that some threads will stop responding to it,
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58 // but the program won't crash.
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59 static volatile std::atomic<unsigned> GlobalSigInfoGenerationCounter =
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60 ATOMIC_VAR_INIT(1);
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61 static LLVM_THREAD_LOCAL unsigned ThreadLocalSigInfoGenerationCounter = 0;
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62
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63 namespace llvm {
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64 PrettyStackTraceEntry *ReverseStackTrace(PrettyStackTraceEntry *Head) {
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65 PrettyStackTraceEntry *Prev = nullptr;
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66 while (Head)
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67 std::tie(Prev, Head, Head->NextEntry) =
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68 std::make_tuple(Head, Head->NextEntry, Prev);
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69 return Prev;
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70 }
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71 }
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72
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73 static void PrintStack(raw_ostream &OS) {
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74 // Print out the stack in reverse order. To avoid recursion (which is likely
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75 // to fail if we crashed due to stack overflow), we do an up-front pass to
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76 // reverse the stack, then print it, then reverse it again.
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77 unsigned ID = 0;
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78 SaveAndRestore<PrettyStackTraceEntry *> SavedStack{PrettyStackTraceHead,
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79 nullptr};
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80 PrettyStackTraceEntry *ReversedStack = ReverseStackTrace(SavedStack.get());
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81 for (const PrettyStackTraceEntry *Entry = ReversedStack; Entry;
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82 Entry = Entry->getNextEntry()) {
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83 OS << ID++ << ".\t";
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84 sys::Watchdog W(5);
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85 Entry->print(OS);
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86 }
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87 llvm::ReverseStackTrace(ReversedStack);
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88 }
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89
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90 /// Print the current stack trace to the specified stream.
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91 ///
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92 /// Marked NOINLINE so it can be called from debuggers.
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93 LLVM_ATTRIBUTE_NOINLINE
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94 static void PrintCurStackTrace(raw_ostream &OS) {
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95 // Don't print an empty trace.
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96 if (!PrettyStackTraceHead) return;
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97
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98 // If there are pretty stack frames registered, walk and emit them.
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99 OS << "Stack dump:\n";
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100
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101 PrintStack(OS);
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102 OS.flush();
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103 }
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104
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105 // Integrate with crash reporter libraries.
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106 #if defined (__APPLE__) && defined(HAVE_CRASHREPORTERCLIENT_H)
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107 // If any clients of llvm try to link to libCrashReporterClient.a themselves,
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108 // only one crash info struct will be used.
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109 extern "C" {
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110 CRASH_REPORTER_CLIENT_HIDDEN
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111 struct crashreporter_annotations_t gCRAnnotations
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112 __attribute__((section("__DATA," CRASHREPORTER_ANNOTATIONS_SECTION)))
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113 #if CRASHREPORTER_ANNOTATIONS_VERSION < 5
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114 = { CRASHREPORTER_ANNOTATIONS_VERSION, 0, 0, 0, 0, 0, 0 };
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115 #else
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116 = { CRASHREPORTER_ANNOTATIONS_VERSION, 0, 0, 0, 0, 0, 0, 0 };
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117 #endif
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118 }
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119 #elif defined(__APPLE__) && HAVE_CRASHREPORTER_INFO
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120 extern "C" const char *__crashreporter_info__
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121 __attribute__((visibility("hidden"))) = 0;
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122 asm(".desc ___crashreporter_info__, 0x10");
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123 #endif
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124
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125 static void setCrashLogMessage(const char *msg) LLVM_ATTRIBUTE_UNUSED;
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126 static void setCrashLogMessage(const char *msg) {
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127 #ifdef HAVE_CRASHREPORTERCLIENT_H
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128 (void)CRSetCrashLogMessage(msg);
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129 #elif HAVE_CRASHREPORTER_INFO
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130 __crashreporter_info__ = msg;
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131 #endif
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132 // Don't reorder subsequent operations: whatever comes after might crash and
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133 // we want the system crash handling to see the message we just set.
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134 std::atomic_signal_fence(std::memory_order_seq_cst);
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135 }
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136
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137 #ifdef __APPLE__
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138 using CrashHandlerString = SmallString<2048>;
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139 using CrashHandlerStringStorage =
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140 std::aligned_storage<sizeof(CrashHandlerString),
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141 alignof(CrashHandlerString)>::type;
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142 static CrashHandlerStringStorage crashHandlerStringStorage;
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143 #endif
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144
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173
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145 static const char *BugReportMsg =
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146 "PLEASE submit a bug report to " BUG_REPORT_URL
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147 " and include the crash backtrace.\n";
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148
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150
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149 /// This callback is run if a fatal signal is delivered to the process, it
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150 /// prints the pretty stack trace.
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151 static void CrashHandler(void *) {
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173
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152 errs() << BugReportMsg ;
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153
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150
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154 #ifndef __APPLE__
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155 // On non-apple systems, just emit the crash stack trace to stderr.
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156 PrintCurStackTrace(errs());
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157 #else
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158 // Emit the crash stack trace to a SmallString, put it where the system crash
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159 // handling will find it, and also send it to stderr.
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160 //
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161 // The SmallString is fairly large in the hope that we don't allocate (we're
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162 // handling a fatal signal, something is already pretty wrong, allocation
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163 // might not work). Further, we don't use a magic static in case that's also
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164 // borked. We leak any allocation that does occur because the program is about
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165 // to die anyways. This is technically racy if we were handling two fatal
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166 // signals, however if we're in that situation a race is the least of our
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167 // worries.
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168 auto &crashHandlerString =
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169 *new (&crashHandlerStringStorage) CrashHandlerString;
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170
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171 // If we crash while trying to print the stack trace, we still want the system
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172 // crash handling to have some partial information. That'll work out as long
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173 // as the SmallString doesn't allocate. If it does allocate then the system
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174 // crash handling will see some garbage because the inline buffer now contains
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175 // a pointer.
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176 setCrashLogMessage(crashHandlerString.c_str());
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177
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178 {
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179 raw_svector_ostream Stream(crashHandlerString);
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180 PrintCurStackTrace(Stream);
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181 }
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182
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183 if (!crashHandlerString.empty()) {
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184 setCrashLogMessage(crashHandlerString.c_str());
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185 errs() << crashHandlerString.str();
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186 } else
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187 setCrashLogMessage("No crash information.");
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188 #endif
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189 }
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190
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191 static void printForSigInfoIfNeeded() {
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192 unsigned CurrentSigInfoGeneration =
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193 GlobalSigInfoGenerationCounter.load(std::memory_order_relaxed);
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194 if (ThreadLocalSigInfoGenerationCounter == 0 ||
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195 ThreadLocalSigInfoGenerationCounter == CurrentSigInfoGeneration) {
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196 return;
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197 }
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198
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199 PrintCurStackTrace(errs());
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200 ThreadLocalSigInfoGenerationCounter = CurrentSigInfoGeneration;
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201 }
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202
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203 #endif // ENABLE_BACKTRACES
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204
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173
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205 void llvm::setBugReportMsg(const char *Msg) {
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206 #if ENABLE_BACKTRACES
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207 BugReportMsg = Msg;
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208 #endif
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209 }
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210
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211 PrettyStackTraceEntry::PrettyStackTraceEntry() {
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212 #if ENABLE_BACKTRACES
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213 // Handle SIGINFO first, because we haven't finished constructing yet.
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214 printForSigInfoIfNeeded();
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215 // Link ourselves.
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216 NextEntry = PrettyStackTraceHead;
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217 PrettyStackTraceHead = this;
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218 #endif
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219 }
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220
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221 PrettyStackTraceEntry::~PrettyStackTraceEntry() {
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222 #if ENABLE_BACKTRACES
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223 assert(PrettyStackTraceHead == this &&
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224 "Pretty stack trace entry destruction is out of order");
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225 PrettyStackTraceHead = NextEntry;
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226 // Handle SIGINFO first, because we already started destructing.
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227 printForSigInfoIfNeeded();
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228 #endif
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229 }
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230
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231 void PrettyStackTraceString::print(raw_ostream &OS) const { OS << Str << "\n"; }
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232
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233 PrettyStackTraceFormat::PrettyStackTraceFormat(const char *Format, ...) {
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234 va_list AP;
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235 va_start(AP, Format);
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236 const int SizeOrError = vsnprintf(nullptr, 0, Format, AP);
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237 va_end(AP);
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238 if (SizeOrError < 0) {
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239 return;
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240 }
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241
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242 const int Size = SizeOrError + 1; // '\0'
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243 Str.resize(Size);
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244 va_start(AP, Format);
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245 vsnprintf(Str.data(), Size, Format, AP);
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246 va_end(AP);
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247 }
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248
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249 void PrettyStackTraceFormat::print(raw_ostream &OS) const { OS << Str << "\n"; }
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250
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251 void PrettyStackTraceProgram::print(raw_ostream &OS) const {
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252 OS << "Program arguments: ";
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253 // Print the argument list.
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254 for (unsigned i = 0, e = ArgC; i != e; ++i)
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255 OS << ArgV[i] << ' ';
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256 OS << '\n';
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257 }
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258
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259 #if ENABLE_BACKTRACES
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260 static bool RegisterCrashPrinter() {
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261 sys::AddSignalHandler(CrashHandler, nullptr);
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262 return false;
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263 }
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264 #endif
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265
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266 void llvm::EnablePrettyStackTrace() {
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267 #if ENABLE_BACKTRACES
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268 // The first time this is called, we register the crash printer.
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269 static bool HandlerRegistered = RegisterCrashPrinter();
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270 (void)HandlerRegistered;
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271 #endif
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272 }
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273
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274 void llvm::EnablePrettyStackTraceOnSigInfoForThisThread(bool ShouldEnable) {
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275 #if ENABLE_BACKTRACES
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276 if (!ShouldEnable) {
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277 ThreadLocalSigInfoGenerationCounter = 0;
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278 return;
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279 }
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280
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281 // The first time this is called, we register the SIGINFO handler.
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282 static bool HandlerRegistered = []{
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283 sys::SetInfoSignalFunction([]{
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284 GlobalSigInfoGenerationCounter.fetch_add(1, std::memory_order_relaxed);
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285 });
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286 return false;
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287 }();
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288 (void)HandlerRegistered;
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289
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290 // Next, enable it for the current thread.
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291 ThreadLocalSigInfoGenerationCounter =
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292 GlobalSigInfoGenerationCounter.load(std::memory_order_relaxed);
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293 #endif
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294 }
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295
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296 const void *llvm::SavePrettyStackState() {
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297 #if ENABLE_BACKTRACES
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298 return PrettyStackTraceHead;
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299 #else
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300 return nullptr;
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301 #endif
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302 }
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303
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304 void llvm::RestorePrettyStackState(const void *Top) {
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305 #if ENABLE_BACKTRACES
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306 PrettyStackTraceHead =
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307 static_cast<PrettyStackTraceEntry *>(const_cast<void *>(Top));
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308 #endif
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309 }
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310
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311 void LLVMEnablePrettyStackTrace() {
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312 EnablePrettyStackTrace();
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313 }
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