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 <cmath>
34 #include <vector>
35 
36 //===----------------------------------------------------------------------===//
37 //=== WARNING: Implementation here must contain only TRULY operating system
38 //===          independent code.
39 //===----------------------------------------------------------------------===//
40 
41 using namespace llvm;
42 
43 // Use explicit storage to avoid accessing cl::opt in a signal handler.
44 static bool DisableSymbolicationFlag = false;
45 static ManagedStatic<std::string> CrashDiagnosticsDirectory;
46 namespace {
47 struct CreateDisableSymbolication {
48   static void *call() {
49     return new cl::opt<bool, true>(
50         "disable-symbolication",
51         cl::desc("Disable symbolizing crash backtraces."),
52         cl::location(DisableSymbolicationFlag), cl::Hidden);
53   }
54 };
55 struct CreateCrashDiagnosticsDir {
56   static void *call() {
57     return new cl::opt<std::string, true>(
58         "crash-diagnostics-dir", cl::value_desc("directory"),
59         cl::desc("Directory for crash diagnostic files."),
60         cl::location(*CrashDiagnosticsDirectory), cl::Hidden);
61   }
62 };
63 } // namespace
64 void llvm::initSignalsOptions() {
65   static ManagedStatic<cl::opt<bool, true>, CreateDisableSymbolication>
66       DisableSymbolication;
67   static ManagedStatic<cl::opt<std::string, true>, CreateCrashDiagnosticsDir>
68       CrashDiagnosticsDir;
69   *DisableSymbolication;
70   *CrashDiagnosticsDir;
71 }
72 
73 constexpr char DisableSymbolizationEnv[] = "LLVM_DISABLE_SYMBOLIZATION";
74 constexpr char LLVMSymbolizerPathEnv[] = "LLVM_SYMBOLIZER_PATH";
75 constexpr char EnableSymbolizerMarkupEnv[] = "LLVM_ENABLE_SYMBOLIZER_MARKUP";
76 
77 // Callbacks to run in signal handler must be lock-free because a signal handler
78 // could be running as we add new callbacks. We don't add unbounded numbers of
79 // callbacks, an array is therefore sufficient.
80 struct CallbackAndCookie {
81   sys::SignalHandlerCallback Callback;
82   void *Cookie;
83   enum class Status { Empty, Initializing, Initialized, Executing };
84   std::atomic<Status> Flag;
85 };
86 
87 static constexpr size_t MaxSignalHandlerCallbacks = 8;
88 
89 // A global array of CallbackAndCookie may not compile with
90 // -Werror=global-constructors in c++20 and above
91 static std::array<CallbackAndCookie, MaxSignalHandlerCallbacks> &
92 CallBacksToRun() {
93   static std::array<CallbackAndCookie, MaxSignalHandlerCallbacks> callbacks;
94   return callbacks;
95 }
96 
97 // Signal-safe.
98 void sys::RunSignalHandlers() {
99   for (CallbackAndCookie &RunMe : CallBacksToRun()) {
100     auto Expected = CallbackAndCookie::Status::Initialized;
101     auto Desired = CallbackAndCookie::Status::Executing;
102     if (!RunMe.Flag.compare_exchange_strong(Expected, Desired))
103       continue;
104     (*RunMe.Callback)(RunMe.Cookie);
105     RunMe.Callback = nullptr;
106     RunMe.Cookie = nullptr;
107     RunMe.Flag.store(CallbackAndCookie::Status::Empty);
108   }
109 }
110 
111 // Signal-safe.
112 static void insertSignalHandler(sys::SignalHandlerCallback FnPtr,
113                                 void *Cookie) {
114   for (CallbackAndCookie &SetMe : CallBacksToRun()) {
115     auto Expected = CallbackAndCookie::Status::Empty;
116     auto Desired = CallbackAndCookie::Status::Initializing;
117     if (!SetMe.Flag.compare_exchange_strong(Expected, Desired))
118       continue;
119     SetMe.Callback = FnPtr;
120     SetMe.Cookie = Cookie;
121     SetMe.Flag.store(CallbackAndCookie::Status::Initialized);
122     return;
123   }
124   report_fatal_error("too many signal callbacks already registered");
125 }
126 
127 static bool findModulesAndOffsets(void **StackTrace, int Depth,
128                                   const char **Modules, intptr_t *Offsets,
129                                   const char *MainExecutableName,
130                                   StringSaver &StrPool);
131 
132 /// Format a pointer value as hexadecimal. Zero pad it out so its always the
133 /// same width.
134 static FormattedNumber format_ptr(void *PC) {
135   // Each byte is two hex digits plus 2 for the 0x prefix.
136   unsigned PtrWidth = 2 + 2 * sizeof(void *);
137   return format_hex((uint64_t)PC, PtrWidth);
138 }
139 
140 /// Helper that launches llvm-symbolizer and symbolizes a backtrace.
141 LLVM_ATTRIBUTE_USED
142 static bool printSymbolizedStackTrace(StringRef Argv0, void **StackTrace,
143                                       int Depth, llvm::raw_ostream &OS) {
144   if (DisableSymbolicationFlag || getenv(DisableSymbolizationEnv))
145     return false;
146 
147   // Don't recursively invoke the llvm-symbolizer binary.
148   if (Argv0.contains("llvm-symbolizer"))
149     return false;
150 
151   // FIXME: Subtract necessary number from StackTrace entries to turn return addresses
152   // into actual instruction addresses.
153   // Use llvm-symbolizer tool to symbolize the stack traces. First look for it
154   // alongside our binary, then in $PATH.
155   ErrorOr<std::string> LLVMSymbolizerPathOrErr = std::error_code();
156   if (const char *Path = getenv(LLVMSymbolizerPathEnv)) {
157     LLVMSymbolizerPathOrErr = sys::findProgramByName(Path);
158   } else if (!Argv0.empty()) {
159     StringRef Parent = llvm::sys::path::parent_path(Argv0);
160     if (!Parent.empty())
161       LLVMSymbolizerPathOrErr = sys::findProgramByName("llvm-symbolizer", Parent);
162   }
163   if (!LLVMSymbolizerPathOrErr)
164     LLVMSymbolizerPathOrErr = sys::findProgramByName("llvm-symbolizer");
165   if (!LLVMSymbolizerPathOrErr)
166     return false;
167   const std::string &LLVMSymbolizerPath = *LLVMSymbolizerPathOrErr;
168 
169   // If we don't know argv0 or the address of main() at this point, try
170   // to guess it anyway (it's possible on some platforms).
171   std::string MainExecutableName =
172       sys::fs::exists(Argv0) ? (std::string)std::string(Argv0)
173                              : sys::fs::getMainExecutable(nullptr, nullptr);
174   BumpPtrAllocator Allocator;
175   StringSaver StrPool(Allocator);
176   std::vector<const char *> Modules(Depth, nullptr);
177   std::vector<intptr_t> Offsets(Depth, 0);
178   if (!findModulesAndOffsets(StackTrace, Depth, Modules.data(), Offsets.data(),
179                              MainExecutableName.c_str(), StrPool))
180     return false;
181   int InputFD;
182   SmallString<32> InputFile, OutputFile;
183   sys::fs::createTemporaryFile("symbolizer-input", "", InputFD, InputFile);
184   sys::fs::createTemporaryFile("symbolizer-output", "", OutputFile);
185   FileRemover InputRemover(InputFile.c_str());
186   FileRemover OutputRemover(OutputFile.c_str());
187 
188   {
189     raw_fd_ostream Input(InputFD, true);
190     for (int i = 0; i < Depth; i++) {
191       if (Modules[i])
192         Input << Modules[i] << " " << (void*)Offsets[i] << "\n";
193     }
194   }
195 
196   std::optional<StringRef> Redirects[] = {InputFile.str(), OutputFile.str(),
197                                           StringRef("")};
198   StringRef Args[] = {"llvm-symbolizer", "--functions=linkage", "--inlining",
199 #ifdef _WIN32
200                       // Pass --relative-address on Windows so that we don't
201                       // have to add ImageBase from PE file.
202                       // FIXME: Make this the default for llvm-symbolizer.
203                       "--relative-address",
204 #endif
205                       "--demangle"};
206   int RunResult =
207       sys::ExecuteAndWait(LLVMSymbolizerPath, Args, std::nullopt, Redirects);
208   if (RunResult != 0)
209     return false;
210 
211   // This report format is based on the sanitizer stack trace printer.  See
212   // sanitizer_stacktrace_printer.cc in compiler-rt.
213   auto OutputBuf = MemoryBuffer::getFile(OutputFile.c_str());
214   if (!OutputBuf)
215     return false;
216   StringRef Output = OutputBuf.get()->getBuffer();
217   SmallVector<StringRef, 32> Lines;
218   Output.split(Lines, "\n");
219   auto CurLine = Lines.begin();
220   int frame_no = 0;
221   for (int i = 0; i < Depth; i++) {
222     auto PrintLineHeader = [&]() {
223       OS << right_justify(formatv("#{0}", frame_no++).str(),
224                           std::log10(Depth) + 2)
225          << ' ' << format_ptr(StackTrace[i]) << ' ';
226     };
227     if (!Modules[i]) {
228       PrintLineHeader();
229       OS << '\n';
230       continue;
231     }
232     // Read pairs of lines (function name and file/line info) until we
233     // encounter empty line.
234     for (;;) {
235       if (CurLine == Lines.end())
236         return false;
237       StringRef FunctionName = *CurLine++;
238       if (FunctionName.empty())
239         break;
240       PrintLineHeader();
241       if (!FunctionName.starts_with("??"))
242         OS << FunctionName << ' ';
243       if (CurLine == Lines.end())
244         return false;
245       StringRef FileLineInfo = *CurLine++;
246       if (!FileLineInfo.starts_with("??"))
247         OS << FileLineInfo;
248       else
249         OS << "(" << Modules[i] << '+' << format_hex(Offsets[i], 0) << ")";
250       OS << "\n";
251     }
252   }
253   return true;
254 }
255 
256 static bool printMarkupContext(raw_ostream &OS, const char *MainExecutableName);
257 
258 LLVM_ATTRIBUTE_USED
259 static bool printMarkupStackTrace(StringRef Argv0, void **StackTrace, int Depth,
260                                   raw_ostream &OS) {
261   const char *Env = getenv(EnableSymbolizerMarkupEnv);
262   if (!Env || !*Env)
263     return false;
264 
265   std::string MainExecutableName =
266       sys::fs::exists(Argv0) ? std::string(Argv0)
267                              : sys::fs::getMainExecutable(nullptr, nullptr);
268   if (!printMarkupContext(OS, MainExecutableName.c_str()))
269     return false;
270   for (int I = 0; I < Depth; I++)
271     OS << format("{{{bt:%d:%#016x}}}\n", I, StackTrace[I]);
272   return true;
273 }
274 
275 // Include the platform-specific parts of this class.
276 #ifdef LLVM_ON_UNIX
277 #include "Unix/Signals.inc"
278 #endif
279 #ifdef _WIN32
280 #include "Windows/Signals.inc"
281 #endif
282