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