xref: /freebsd/contrib/llvm-project/llvm/lib/Support/PrettyStackTrace.cpp (revision 2f513db72b034fd5ef7f080b11be5c711c15186a)
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 
33 using 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.
44 static 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.
58 static volatile std::atomic<unsigned> GlobalSigInfoGenerationCounter =
59     ATOMIC_VAR_INIT(1);
60 static LLVM_THREAD_LOCAL unsigned ThreadLocalSigInfoGenerationCounter = 0;
61 
62 namespace llvm {
63 PrettyStackTraceEntry *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 
72 static 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.
92 LLVM_ATTRIBUTE_NOINLINE
93 static 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.
108 extern "C" {
109 CRASH_REPORTER_CLIENT_HIDDEN
110 struct 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
119 extern "C" const char *__crashreporter_info__
120     __attribute__((visibility("hidden"))) = 0;
121 asm(".desc ___crashreporter_info__, 0x10");
122 #endif
123 
124 /// CrashHandler - This callback is run if a fatal signal is delivered to the
125 /// process, it prints the pretty stack trace.
126 static void CrashHandler(void *) {
127 #ifndef __APPLE__
128   // On non-apple systems, just emit the crash stack trace to stderr.
129   PrintCurStackTrace(errs());
130 #else
131   // Otherwise, emit to a smallvector of chars, send *that* to stderr, but also
132   // put it into __crashreporter_info__.
133   SmallString<2048> TmpStr;
134   {
135     raw_svector_ostream Stream(TmpStr);
136     PrintCurStackTrace(Stream);
137   }
138 
139   if (!TmpStr.empty()) {
140 #ifdef HAVE_CRASHREPORTERCLIENT_H
141     // Cast to void to avoid warning.
142     (void)CRSetCrashLogMessage(TmpStr.c_str());
143 #elif HAVE_CRASHREPORTER_INFO
144     __crashreporter_info__ = strdup(TmpStr.c_str());
145 #endif
146     errs() << TmpStr.str();
147   }
148 
149 #endif
150 }
151 
152 static void printForSigInfoIfNeeded() {
153   unsigned CurrentSigInfoGeneration =
154       GlobalSigInfoGenerationCounter.load(std::memory_order_relaxed);
155   if (ThreadLocalSigInfoGenerationCounter == 0 ||
156       ThreadLocalSigInfoGenerationCounter == CurrentSigInfoGeneration) {
157     return;
158   }
159 
160   PrintCurStackTrace(errs());
161   ThreadLocalSigInfoGenerationCounter = CurrentSigInfoGeneration;
162 }
163 
164 #endif // ENABLE_BACKTRACES
165 
166 PrettyStackTraceEntry::PrettyStackTraceEntry() {
167 #if ENABLE_BACKTRACES
168   // Handle SIGINFO first, because we haven't finished constructing yet.
169   printForSigInfoIfNeeded();
170   // Link ourselves.
171   NextEntry = PrettyStackTraceHead;
172   PrettyStackTraceHead = this;
173 #endif
174 }
175 
176 PrettyStackTraceEntry::~PrettyStackTraceEntry() {
177 #if ENABLE_BACKTRACES
178   assert(PrettyStackTraceHead == this &&
179          "Pretty stack trace entry destruction is out of order");
180   PrettyStackTraceHead = NextEntry;
181   // Handle SIGINFO first, because we already started destructing.
182   printForSigInfoIfNeeded();
183 #endif
184 }
185 
186 void PrettyStackTraceString::print(raw_ostream &OS) const { OS << Str << "\n"; }
187 
188 PrettyStackTraceFormat::PrettyStackTraceFormat(const char *Format, ...) {
189   va_list AP;
190   va_start(AP, Format);
191   const int SizeOrError = vsnprintf(nullptr, 0, Format, AP);
192   va_end(AP);
193   if (SizeOrError < 0) {
194     return;
195   }
196 
197   const int Size = SizeOrError + 1; // '\0'
198   Str.resize(Size);
199   va_start(AP, Format);
200   vsnprintf(Str.data(), Size, Format, AP);
201   va_end(AP);
202 }
203 
204 void PrettyStackTraceFormat::print(raw_ostream &OS) const { OS << Str << "\n"; }
205 
206 void PrettyStackTraceProgram::print(raw_ostream &OS) const {
207   OS << "Program arguments: ";
208   // Print the argument list.
209   for (unsigned i = 0, e = ArgC; i != e; ++i)
210     OS << ArgV[i] << ' ';
211   OS << '\n';
212 }
213 
214 #if ENABLE_BACKTRACES
215 static bool RegisterCrashPrinter() {
216   sys::AddSignalHandler(CrashHandler, nullptr);
217   return false;
218 }
219 #endif
220 
221 void llvm::EnablePrettyStackTrace() {
222 #if ENABLE_BACKTRACES
223   // The first time this is called, we register the crash printer.
224   static bool HandlerRegistered = RegisterCrashPrinter();
225   (void)HandlerRegistered;
226 #endif
227 }
228 
229 void llvm::EnablePrettyStackTraceOnSigInfoForThisThread(bool ShouldEnable) {
230 #if ENABLE_BACKTRACES
231   if (!ShouldEnable) {
232     ThreadLocalSigInfoGenerationCounter = 0;
233     return;
234   }
235 
236   // The first time this is called, we register the SIGINFO handler.
237   static bool HandlerRegistered = []{
238     sys::SetInfoSignalFunction([]{
239       GlobalSigInfoGenerationCounter.fetch_add(1, std::memory_order_relaxed);
240     });
241     return false;
242   }();
243   (void)HandlerRegistered;
244 
245   // Next, enable it for the current thread.
246   ThreadLocalSigInfoGenerationCounter =
247       GlobalSigInfoGenerationCounter.load(std::memory_order_relaxed);
248 #endif
249 }
250 
251 const void *llvm::SavePrettyStackState() {
252 #if ENABLE_BACKTRACES
253   return PrettyStackTraceHead;
254 #else
255   return nullptr;
256 #endif
257 }
258 
259 void llvm::RestorePrettyStackState(const void *Top) {
260 #if ENABLE_BACKTRACES
261   PrettyStackTraceHead =
262       static_cast<PrettyStackTraceEntry *>(const_cast<void *>(Top));
263 #endif
264 }
265 
266 void LLVMEnablePrettyStackTrace() {
267   EnablePrettyStackTrace();
268 }
269