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