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
41using namespace llvm;
42
43// Use explicit storage to avoid accessing cl::opt in a signal handler.
44static bool DisableSymbolicationFlag = false;
45static ManagedStatic<std::string> CrashDiagnosticsDirectory;
46namespace {
47struct 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};
55struct 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
64void 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
73constexpr char DisableSymbolizationEnv[] = "LLVM_DISABLE_SYMBOLIZATION";
74constexpr char LLVMSymbolizerPathEnv[] = "LLVM_SYMBOLIZER_PATH";
75constexpr 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.
80struct CallbackAndCookie {
81  sys::SignalHandlerCallback Callback;
82  void *Cookie;
83  enum class Status { Empty, Initializing, Initialized, Executing };
84  std::atomic<Status> Flag;
85};
86
87static 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
91static std::array<CallbackAndCookie, MaxSignalHandlerCallbacks> &
92CallBacksToRun() {
93  static std::array<CallbackAndCookie, MaxSignalHandlerCallbacks> callbacks;
94  return callbacks;
95}
96
97// Signal-safe.
98void 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.
112static 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
127static 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.
134static 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.
141LLVM_ATTRIBUTE_USED
142static 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
256static bool printMarkupContext(raw_ostream &OS, const char *MainExecutableName);
257
258LLVM_ATTRIBUTE_USED
259static 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