1 //===- Signals.cpp - Signal Handling support --------------------*- C++ -*-===//
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/Signals.h"
15 
16 #include "DebugOptions.h"
17 
18 #include "llvm/ADT/StringRef.h"
19 #include "llvm/Config/llvm-config.h"
20 #include "llvm/Support/CommandLine.h"
21 #include "llvm/Support/ErrorOr.h"
22 #include "llvm/Support/FileSystem.h"
23 #include "llvm/Support/FileUtilities.h"
24 #include "llvm/Support/Format.h"
25 #include "llvm/Support/FormatVariadic.h"
26 #include "llvm/Support/ManagedStatic.h"
27 #include "llvm/Support/MemoryBuffer.h"
28 #include "llvm/Support/Path.h"
29 #include "llvm/Support/Program.h"
30 #include "llvm/Support/StringSaver.h"
31 #include "llvm/Support/raw_ostream.h"
32 #include <array>
33 #include <vector>
34 
35 //===----------------------------------------------------------------------===//
36 //=== WARNING: Implementation here must contain only TRULY operating system
37 //===          independent code.
38 //===----------------------------------------------------------------------===//
39 
40 using namespace llvm;
41 
42 // Use explicit storage to avoid accessing cl::opt in a signal handler.
43 static bool DisableSymbolicationFlag = false;
44 static ManagedStatic<std::string> CrashDiagnosticsDirectory;
45 namespace {
46 struct CreateDisableSymbolication {
call__anon578ba39d0111::CreateDisableSymbolication47   static void *call() {
48     return new cl::opt<bool, true>(
49         "disable-symbolication",
50         cl::desc("Disable symbolizing crash backtraces."),
51         cl::location(DisableSymbolicationFlag), cl::Hidden);
52   }
53 };
54 struct CreateCrashDiagnosticsDir {
call__anon578ba39d0111::CreateCrashDiagnosticsDir55   static void *call() {
56     return new cl::opt<std::string, true>(
57         "crash-diagnostics-dir", cl::value_desc("directory"),
58         cl::desc("Directory for crash diagnostic files."),
59         cl::location(*CrashDiagnosticsDirectory), cl::Hidden);
60   }
61 };
62 } // namespace
initSignalsOptions()63 void llvm::initSignalsOptions() {
64   static ManagedStatic<cl::opt<bool, true>, CreateDisableSymbolication>
65       DisableSymbolication;
66   static ManagedStatic<cl::opt<std::string, true>, CreateCrashDiagnosticsDir>
67       CrashDiagnosticsDir;
68   *DisableSymbolication;
69   *CrashDiagnosticsDir;
70 }
71 
72 constexpr char DisableSymbolizationEnv[] = "LLVM_DISABLE_SYMBOLIZATION";
73 constexpr char LLVMSymbolizerPathEnv[] = "LLVM_SYMBOLIZER_PATH";
74 
75 // Callbacks to run in signal handler must be lock-free because a signal handler
76 // could be running as we add new callbacks. We don't add unbounded numbers of
77 // callbacks, an array is therefore sufficient.
78 struct CallbackAndCookie {
79   sys::SignalHandlerCallback Callback;
80   void *Cookie;
81   enum class Status { Empty, Initializing, Initialized, Executing };
82   std::atomic<Status> Flag;
83 };
84 
85 static constexpr size_t MaxSignalHandlerCallbacks = 8;
86 
87 // A global array of CallbackAndCookie may not compile with
88 // -Werror=global-constructors in c++20 and above
89 static std::array<CallbackAndCookie, MaxSignalHandlerCallbacks> &
CallBacksToRun()90 CallBacksToRun() {
91   static std::array<CallbackAndCookie, MaxSignalHandlerCallbacks> callbacks;
92   return callbacks;
93 }
94 
95 // Signal-safe.
RunSignalHandlers()96 void sys::RunSignalHandlers() {
97   for (CallbackAndCookie &RunMe : CallBacksToRun()) {
98     auto Expected = CallbackAndCookie::Status::Initialized;
99     auto Desired = CallbackAndCookie::Status::Executing;
100     if (!RunMe.Flag.compare_exchange_strong(Expected, Desired))
101       continue;
102     (*RunMe.Callback)(RunMe.Cookie);
103     RunMe.Callback = nullptr;
104     RunMe.Cookie = nullptr;
105     RunMe.Flag.store(CallbackAndCookie::Status::Empty);
106   }
107 }
108 
109 // Signal-safe.
insertSignalHandler(sys::SignalHandlerCallback FnPtr,void * Cookie)110 static void insertSignalHandler(sys::SignalHandlerCallback FnPtr,
111                                 void *Cookie) {
112   for (CallbackAndCookie &SetMe : CallBacksToRun()) {
113     auto Expected = CallbackAndCookie::Status::Empty;
114     auto Desired = CallbackAndCookie::Status::Initializing;
115     if (!SetMe.Flag.compare_exchange_strong(Expected, Desired))
116       continue;
117     SetMe.Callback = FnPtr;
118     SetMe.Cookie = Cookie;
119     SetMe.Flag.store(CallbackAndCookie::Status::Initialized);
120     return;
121   }
122   report_fatal_error("too many signal callbacks already registered");
123 }
124 
125 static bool findModulesAndOffsets(void **StackTrace, int Depth,
126                                   const char **Modules, intptr_t *Offsets,
127                                   const char *MainExecutableName,
128                                   StringSaver &StrPool);
129 
130 /// Format a pointer value as hexadecimal. Zero pad it out so its always the
131 /// same width.
format_ptr(void * PC)132 static FormattedNumber format_ptr(void *PC) {
133   // Each byte is two hex digits plus 2 for the 0x prefix.
134   unsigned PtrWidth = 2 + 2 * sizeof(void *);
135   return format_hex((uint64_t)PC, PtrWidth);
136 }
137 
138 /// Helper that launches llvm-symbolizer and symbolizes a backtrace.
139 LLVM_ATTRIBUTE_USED
printSymbolizedStackTrace(StringRef Argv0,void ** StackTrace,int Depth,llvm::raw_ostream & OS)140 static bool printSymbolizedStackTrace(StringRef Argv0, void **StackTrace,
141                                       int Depth, llvm::raw_ostream &OS) {
142   if (DisableSymbolicationFlag || getenv(DisableSymbolizationEnv))
143     return false;
144 
145   // Don't recursively invoke the llvm-symbolizer binary.
146   if (Argv0.find("llvm-symbolizer") != std::string::npos)
147     return false;
148 
149   // FIXME: Subtract necessary number from StackTrace entries to turn return addresses
150   // into actual instruction addresses.
151   // Use llvm-symbolizer tool to symbolize the stack traces. First look for it
152   // alongside our binary, then in $PATH.
153   ErrorOr<std::string> LLVMSymbolizerPathOrErr = std::error_code();
154   if (const char *Path = getenv(LLVMSymbolizerPathEnv)) {
155     LLVMSymbolizerPathOrErr = sys::findProgramByName(Path);
156   } else if (!Argv0.empty()) {
157     StringRef Parent = llvm::sys::path::parent_path(Argv0);
158     if (!Parent.empty())
159       LLVMSymbolizerPathOrErr = sys::findProgramByName("llvm-symbolizer", Parent);
160   }
161   if (!LLVMSymbolizerPathOrErr)
162     LLVMSymbolizerPathOrErr = sys::findProgramByName("llvm-symbolizer");
163   if (!LLVMSymbolizerPathOrErr)
164     return false;
165   const std::string &LLVMSymbolizerPath = *LLVMSymbolizerPathOrErr;
166 
167   // If we don't know argv0 or the address of main() at this point, try
168   // to guess it anyway (it's possible on some platforms).
169   std::string MainExecutableName =
170       sys::fs::exists(Argv0) ? (std::string)std::string(Argv0)
171                              : sys::fs::getMainExecutable(nullptr, nullptr);
172   BumpPtrAllocator Allocator;
173   StringSaver StrPool(Allocator);
174   std::vector<const char *> Modules(Depth, nullptr);
175   std::vector<intptr_t> Offsets(Depth, 0);
176   if (!findModulesAndOffsets(StackTrace, Depth, Modules.data(), Offsets.data(),
177                              MainExecutableName.c_str(), StrPool))
178     return false;
179   int InputFD;
180   SmallString<32> InputFile, OutputFile;
181   sys::fs::createTemporaryFile("symbolizer-input", "", InputFD, InputFile);
182   sys::fs::createTemporaryFile("symbolizer-output", "", OutputFile);
183   FileRemover InputRemover(InputFile.c_str());
184   FileRemover OutputRemover(OutputFile.c_str());
185 
186   {
187     raw_fd_ostream Input(InputFD, true);
188     for (int i = 0; i < Depth; i++) {
189       if (Modules[i])
190         Input << Modules[i] << " " << (void*)Offsets[i] << "\n";
191     }
192   }
193 
194   Optional<StringRef> Redirects[] = {InputFile.str(), OutputFile.str(),
195                                      StringRef("")};
196   StringRef Args[] = {"llvm-symbolizer", "--functions=linkage", "--inlining",
197 #ifdef _WIN32
198                       // Pass --relative-address on Windows so that we don't
199                       // have to add ImageBase from PE file.
200                       // FIXME: Make this the default for llvm-symbolizer.
201                       "--relative-address",
202 #endif
203                       "--demangle"};
204   int RunResult =
205       sys::ExecuteAndWait(LLVMSymbolizerPath, Args, None, Redirects);
206   if (RunResult != 0)
207     return false;
208 
209   // This report format is based on the sanitizer stack trace printer.  See
210   // sanitizer_stacktrace_printer.cc in compiler-rt.
211   auto OutputBuf = MemoryBuffer::getFile(OutputFile.c_str());
212   if (!OutputBuf)
213     return false;
214   StringRef Output = OutputBuf.get()->getBuffer();
215   SmallVector<StringRef, 32> Lines;
216   Output.split(Lines, "\n");
217   auto CurLine = Lines.begin();
218   int frame_no = 0;
219   for (int i = 0; i < Depth; i++) {
220     auto PrintLineHeader = [&]() {
221       OS << right_justify(formatv("#{0}", frame_no++).str(),
222                           std::log10(Depth) + 2)
223          << ' ' << format_ptr(StackTrace[i]) << ' ';
224     };
225     if (!Modules[i]) {
226       PrintLineHeader();
227       OS << '\n';
228       continue;
229     }
230     // Read pairs of lines (function name and file/line info) until we
231     // encounter empty line.
232     for (;;) {
233       if (CurLine == Lines.end())
234         return false;
235       StringRef FunctionName = *CurLine++;
236       if (FunctionName.empty())
237         break;
238       PrintLineHeader();
239       if (!FunctionName.startswith("??"))
240         OS << FunctionName << ' ';
241       if (CurLine == Lines.end())
242         return false;
243       StringRef FileLineInfo = *CurLine++;
244       if (!FileLineInfo.startswith("??"))
245         OS << FileLineInfo;
246       else
247         OS << "(" << Modules[i] << '+' << format_hex(Offsets[i], 0) << ")";
248       OS << "\n";
249     }
250   }
251   return true;
252 }
253 
254 // Include the platform-specific parts of this class.
255 #ifdef LLVM_ON_UNIX
256 #include "Unix/Signals.inc"
257 #endif
258 #ifdef _WIN32
259 #include "Windows/Signals.inc"
260 #endif
261