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/Config/config.h"
17#include "llvm/Support/Compiler.h"
18#include "llvm/Support/SaveAndRestore.h"
19#include "llvm/Support/Signals.h"
20#include "llvm/Support/Watchdog.h"
21#include "llvm/Support/raw_ostream.h"
22
23#ifdef __APPLE__
24#include "llvm/ADT/SmallString.h"
25#endif
26
27#include <atomic>
28#include <cassert>
29#include <cstdarg>
30#include <cstdio>
31#include <cstring>
32#include <tuple>
33
34#ifdef HAVE_CRASHREPORTERCLIENT_H
35#include <CrashReporterClient.h>
36#endif
37
38using namespace llvm;
39
40static const char *BugReportMsg =
41 "PLEASE submit a bug report to " BUG_REPORT_URL
42 " and include the crash backtrace.\n";
43
44// If backtrace support is not enabled, compile out support for pretty stack
45// traces. This has the secondary effect of not requiring thread local storage
46// when backtrace support is disabled.
47#if ENABLE_BACKTRACES
48
49// We need a thread local pointer to manage the stack of our stack trace
50// objects, but we *really* cannot tolerate destructors running and do not want
51// to pay any overhead of synchronizing. As a consequence, we use a raw
52// thread-local variable.
53static LLVM_THREAD_LOCAL PrettyStackTraceEntry *PrettyStackTraceHead = nullptr;
54
55// The use of 'volatile' here is to ensure that any particular thread always
56// reloads the value of the counter. The 'std::atomic' allows us to specify that
57// this variable is accessed in an unsychronized way (it's not actually
58// synchronizing). This does technically mean that the value may not appear to
59// be the same across threads running simultaneously on different CPUs, but in
60// practice the worst that will happen is that we won't print a stack trace when
61// we could have.
62//
63// This is initialized to 1 because 0 is used as a sentinel for "not enabled on
64// the current thread". If the user happens to overflow an 'unsigned' with
65// SIGINFO requests, it's possible that some threads will stop responding to it,
66// but the program won't crash.
67static volatile std::atomic<unsigned> GlobalSigInfoGenerationCounter = 1;
68static LLVM_THREAD_LOCAL unsigned ThreadLocalSigInfoGenerationCounter = 0;
69
70namespace llvm {
71PrettyStackTraceEntry *ReverseStackTrace(PrettyStackTraceEntry *Head) {
72 PrettyStackTraceEntry *Prev = nullptr;
73 while (Head)
74 std::tie(args&: Prev, args&: Head, args&: Head->NextEntry) =
75 std::make_tuple(args&: Head, args&: Head->NextEntry, args&: Prev);
76 return Prev;
77}
78} // namespace llvm
79
80static void PrintStack(raw_ostream &OS) {
81 // Print out the stack in reverse order. To avoid recursion (which is likely
82 // to fail if we crashed due to stack overflow), we do an up-front pass to
83 // reverse the stack, then print it, then reverse it again.
84 unsigned ID = 0;
85 SaveAndRestore<PrettyStackTraceEntry *> SavedStack{PrettyStackTraceHead,
86 nullptr};
87 PrettyStackTraceEntry *ReversedStack = ReverseStackTrace(Head: SavedStack.get());
88 for (const PrettyStackTraceEntry *Entry = ReversedStack; Entry;
89 Entry = Entry->getNextEntry()) {
90 OS << ID++ << ".\t";
91 sys::Watchdog W(5);
92 Entry->print(OS);
93 }
94 llvm::ReverseStackTrace(Head: ReversedStack);
95}
96
97/// Print the current stack trace to the specified stream.
98///
99/// Marked NOINLINE so it can be called from debuggers.
100LLVM_ATTRIBUTE_NOINLINE
101static void PrintCurStackTrace(raw_ostream &OS) {
102 // Don't print an empty trace.
103 if (!PrettyStackTraceHead) return;
104
105 // If there are pretty stack frames registered, walk and emit them.
106 OS << "Stack dump:\n";
107
108 PrintStack(OS);
109 OS.flush();
110}
111
112// Integrate with crash reporter libraries.
113#if defined (__APPLE__) && defined(HAVE_CRASHREPORTERCLIENT_H)
114// If any clients of llvm try to link to libCrashReporterClient.a themselves,
115// only one crash info struct will be used.
116extern "C" {
117CRASH_REPORTER_CLIENT_HIDDEN
118struct crashreporter_annotations_t gCRAnnotations
119 __attribute__((section("__DATA," CRASHREPORTER_ANNOTATIONS_SECTION)))
120#if CRASHREPORTER_ANNOTATIONS_VERSION < 5
121 = { CRASHREPORTER_ANNOTATIONS_VERSION, 0, 0, 0, 0, 0, 0 };
122#else
123 = { CRASHREPORTER_ANNOTATIONS_VERSION, 0, 0, 0, 0, 0, 0, 0 };
124#endif
125}
126#elif defined(__APPLE__) && HAVE_CRASHREPORTER_INFO
127extern "C" const char *__crashreporter_info__
128 __attribute__((visibility("hidden"))) = 0;
129asm(".desc ___crashreporter_info__, 0x10");
130#endif
131
132static void setCrashLogMessage(const char *msg) LLVM_ATTRIBUTE_UNUSED;
133static void setCrashLogMessage(const char *msg) {
134#ifdef HAVE_CRASHREPORTERCLIENT_H
135 (void)CRSetCrashLogMessage(msg);
136#elif HAVE_CRASHREPORTER_INFO
137 __crashreporter_info__ = msg;
138#endif
139 // Don't reorder subsequent operations: whatever comes after might crash and
140 // we want the system crash handling to see the message we just set.
141 std::atomic_signal_fence(m: std::memory_order_seq_cst);
142}
143
144#ifdef __APPLE__
145using CrashHandlerString = SmallString<2048>;
146using CrashHandlerStringStorage = std::byte[sizeof(CrashHandlerString)];
147alignas(CrashHandlerString) static CrashHandlerStringStorage
148 crashHandlerStringStorage;
149#endif
150
151/// This callback is run if a fatal signal is delivered to the process, it
152/// prints the pretty stack trace.
153static void CrashHandler(void *) {
154 errs() << BugReportMsg ;
155
156#ifndef __APPLE__
157 // On non-apple systems, just emit the crash stack trace to stderr.
158 PrintCurStackTrace(OS&: errs());
159#else
160 // Emit the crash stack trace to a SmallString, put it where the system crash
161 // handling will find it, and also send it to stderr.
162 //
163 // The SmallString is fairly large in the hope that we don't allocate (we're
164 // handling a fatal signal, something is already pretty wrong, allocation
165 // might not work). Further, we don't use a magic static in case that's also
166 // borked. We leak any allocation that does occur because the program is about
167 // to die anyways. This is technically racy if we were handling two fatal
168 // signals, however if we're in that situation a race is the least of our
169 // worries.
170 auto &crashHandlerString =
171 *new (&crashHandlerStringStorage) CrashHandlerString;
172
173 // If we crash while trying to print the stack trace, we still want the system
174 // crash handling to have some partial information. That'll work out as long
175 // as the SmallString doesn't allocate. If it does allocate then the system
176 // crash handling will see some garbage because the inline buffer now contains
177 // a pointer.
178 setCrashLogMessage(crashHandlerString.c_str());
179
180 {
181 raw_svector_ostream Stream(crashHandlerString);
182 PrintCurStackTrace(Stream);
183 }
184
185 if (!crashHandlerString.empty()) {
186 setCrashLogMessage(crashHandlerString.c_str());
187 errs() << crashHandlerString.str();
188 } else {
189 setCrashLogMessage("No crash information.");
190 }
191#endif
192}
193
194static void printForSigInfoIfNeeded() {
195 unsigned CurrentSigInfoGeneration =
196 GlobalSigInfoGenerationCounter.load(m: std::memory_order_relaxed);
197 if (ThreadLocalSigInfoGenerationCounter == 0 ||
198 ThreadLocalSigInfoGenerationCounter == CurrentSigInfoGeneration) {
199 return;
200 }
201
202 PrintCurStackTrace(OS&: errs());
203 ThreadLocalSigInfoGenerationCounter = CurrentSigInfoGeneration;
204}
205
206#endif // ENABLE_BACKTRACES
207
208void llvm::setBugReportMsg(const char *Msg) {
209 BugReportMsg = Msg;
210}
211
212const char *llvm::getBugReportMsg() {
213 return BugReportMsg;
214}
215
216PrettyStackTraceEntry::PrettyStackTraceEntry() {
217#if ENABLE_BACKTRACES
218 // Handle SIGINFO first, because we haven't finished constructing yet.
219 printForSigInfoIfNeeded();
220 // Link ourselves.
221 NextEntry = PrettyStackTraceHead;
222 PrettyStackTraceHead = this;
223#endif
224}
225
226PrettyStackTraceEntry::~PrettyStackTraceEntry() {
227#if ENABLE_BACKTRACES
228 assert(PrettyStackTraceHead == this &&
229 "Pretty stack trace entry destruction is out of order");
230 PrettyStackTraceHead = NextEntry;
231 // Handle SIGINFO first, because we already started destructing.
232 printForSigInfoIfNeeded();
233#endif
234}
235
236void PrettyStackTraceString::print(raw_ostream &OS) const { OS << Str << "\n"; }
237
238PrettyStackTraceFormat::PrettyStackTraceFormat(const char *Format, ...) {
239 va_list AP;
240 va_start(AP, Format);
241 const int SizeOrError = vsnprintf(s: nullptr, maxlen: 0, format: Format, arg: AP);
242 va_end(AP);
243 if (SizeOrError < 0) {
244 return;
245 }
246
247 const int Size = SizeOrError + 1; // '\0'
248 Str.resize(N: Size);
249 va_start(AP, Format);
250 vsnprintf(s: Str.data(), maxlen: Size, format: Format, arg: AP);
251 va_end(AP);
252}
253
254void PrettyStackTraceFormat::print(raw_ostream &OS) const { OS << Str << "\n"; }
255
256void PrettyStackTraceProgram::print(raw_ostream &OS) const {
257 OS << "Program arguments: ";
258 // Print the argument list.
259 for (int I = 0; I < ArgC; ++I) {
260 const bool HaveSpace = ::strchr(s: ArgV[I], c: ' ');
261 if (I)
262 OS << ' ';
263 if (HaveSpace)
264 OS << '"';
265 OS.write_escaped(Str: ArgV[I]);
266 if (HaveSpace)
267 OS << '"';
268 }
269 OS << '\n';
270}
271
272#if ENABLE_BACKTRACES
273static bool RegisterCrashPrinter() {
274 sys::AddSignalHandler(FnPtr: CrashHandler, Cookie: nullptr);
275 return false;
276}
277#endif
278
279void llvm::EnablePrettyStackTrace() {
280#if ENABLE_BACKTRACES
281 // The first time this is called, we register the crash printer.
282 static bool HandlerRegistered = RegisterCrashPrinter();
283 (void)HandlerRegistered;
284#endif
285}
286
287void llvm::EnablePrettyStackTraceOnSigInfoForThisThread(bool ShouldEnable) {
288#if ENABLE_BACKTRACES
289 if (!ShouldEnable) {
290 ThreadLocalSigInfoGenerationCounter = 0;
291 return;
292 }
293
294 // The first time this is called, we register the SIGINFO handler.
295 static bool HandlerRegistered = []{
296 sys::SetInfoSignalFunction([]{
297 GlobalSigInfoGenerationCounter.fetch_add(i: 1, m: std::memory_order_relaxed);
298 });
299 return false;
300 }();
301 (void)HandlerRegistered;
302
303 // Next, enable it for the current thread.
304 ThreadLocalSigInfoGenerationCounter =
305 GlobalSigInfoGenerationCounter.load(m: std::memory_order_relaxed);
306#endif
307}
308
309const void *llvm::SavePrettyStackState() {
310#if ENABLE_BACKTRACES
311 return PrettyStackTraceHead;
312#else
313 return nullptr;
314#endif
315}
316
317void llvm::RestorePrettyStackState(const void *Top) {
318#if ENABLE_BACKTRACES
319 PrettyStackTraceHead =
320 static_cast<PrettyStackTraceEntry *>(const_cast<void *>(Top));
321#endif
322}
323
324void LLVMEnablePrettyStackTrace() {
325 EnablePrettyStackTrace();
326}
327