1 //===- Signals.cpp - Signal Handling support --------------------*- C++ -*-===//
2 //
3 //                     The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This file defines some helpful functions for dealing with the possibility of
11 // Unix signals occurring while your program is running.
12 //
13 //===----------------------------------------------------------------------===//
14 
15 #include "llvm/Support/Signals.h"
16 #include "llvm/ADT/STLExtras.h"
17 #include "llvm/ADT/StringRef.h"
18 #include "llvm/Config/llvm-config.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/FormatVariadic.h"
24 #include "llvm/Support/FormatAdapters.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 "llvm/Support/Options.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 cl::opt<bool, true>
44     DisableSymbolication("disable-symbolication",
45                          cl::desc("Disable symbolizing crash backtraces."),
46                          cl::location(DisableSymbolicationFlag), cl::Hidden);
47 
48 // Callbacks to run in signal handler must be lock-free because a signal handler
49 // could be running as we add new callbacks. We don't add unbounded numbers of
50 // callbacks, an array is therefore sufficient.
51 struct CallbackAndCookie {
52   sys::SignalHandlerCallback Callback;
53   void *Cookie;
54   enum class Status { Empty, Initializing, Initialized, Executing };
55   std::atomic<Status> Flag;
56 };
57 static constexpr size_t MaxSignalHandlerCallbacks = 8;
58 static CallbackAndCookie CallBacksToRun[MaxSignalHandlerCallbacks];
59 
60 // Signal-safe.
RunSignalHandlers()61 void sys::RunSignalHandlers() {
62   for (size_t I = 0; I < MaxSignalHandlerCallbacks; ++I) {
63     auto &RunMe = CallBacksToRun[I];
64     auto Expected = CallbackAndCookie::Status::Initialized;
65     auto Desired = CallbackAndCookie::Status::Executing;
66     if (!RunMe.Flag.compare_exchange_strong(Expected, Desired))
67       continue;
68     (*RunMe.Callback)(RunMe.Cookie);
69     RunMe.Callback = nullptr;
70     RunMe.Cookie = nullptr;
71     RunMe.Flag.store(CallbackAndCookie::Status::Empty);
72   }
73 }
74 
75 // Signal-safe.
insertSignalHandler(sys::SignalHandlerCallback FnPtr,void * Cookie)76 static void insertSignalHandler(sys::SignalHandlerCallback FnPtr,
77                                 void *Cookie) {
78   for (size_t I = 0; I < MaxSignalHandlerCallbacks; ++I) {
79     auto &SetMe = CallBacksToRun[I];
80     auto Expected = CallbackAndCookie::Status::Empty;
81     auto Desired = CallbackAndCookie::Status::Initializing;
82     if (!SetMe.Flag.compare_exchange_strong(Expected, Desired))
83       continue;
84     SetMe.Callback = FnPtr;
85     SetMe.Cookie = Cookie;
86     SetMe.Flag.store(CallbackAndCookie::Status::Initialized);
87     return;
88   }
89   report_fatal_error("too many signal callbacks already registered");
90 }
91 
92 static bool findModulesAndOffsets(void **StackTrace, int Depth,
93                                   const char **Modules, intptr_t *Offsets,
94                                   const char *MainExecutableName,
95                                   StringSaver &StrPool);
96 
97 /// Format a pointer value as hexadecimal. Zero pad it out so its always the
98 /// same width.
format_ptr(void * PC)99 static FormattedNumber format_ptr(void *PC) {
100   // Each byte is two hex digits plus 2 for the 0x prefix.
101   unsigned PtrWidth = 2 + 2 * sizeof(void *);
102   return format_hex((uint64_t)PC, PtrWidth);
103 }
104 
105 /// Helper that launches llvm-symbolizer and symbolizes a backtrace.
106 LLVM_ATTRIBUTE_USED
printSymbolizedStackTrace(StringRef Argv0,void ** StackTrace,int Depth,llvm::raw_ostream & OS)107 static bool printSymbolizedStackTrace(StringRef Argv0, void **StackTrace,
108                                       int Depth, llvm::raw_ostream &OS) {
109   if (DisableSymbolicationFlag)
110     return false;
111 
112   // Don't recursively invoke the llvm-symbolizer binary.
113   if (Argv0.find("llvm-symbolizer") != std::string::npos)
114     return false;
115 
116   // FIXME: Subtract necessary number from StackTrace entries to turn return addresses
117   // into actual instruction addresses.
118   // Use llvm-symbolizer tool to symbolize the stack traces. First look for it
119   // alongside our binary, then in $PATH.
120   ErrorOr<std::string> LLVMSymbolizerPathOrErr = std::error_code();
121   if (!Argv0.empty()) {
122     StringRef Parent = llvm::sys::path::parent_path(Argv0);
123     if (!Parent.empty())
124       LLVMSymbolizerPathOrErr = sys::findProgramByName("llvm-symbolizer", Parent);
125   }
126   if (!LLVMSymbolizerPathOrErr)
127     LLVMSymbolizerPathOrErr = sys::findProgramByName("llvm-symbolizer");
128   if (!LLVMSymbolizerPathOrErr)
129     return false;
130   const std::string &LLVMSymbolizerPath = *LLVMSymbolizerPathOrErr;
131 
132   // If we don't know argv0 or the address of main() at this point, try
133   // to guess it anyway (it's possible on some platforms).
134   std::string MainExecutableName =
135       Argv0.empty() ? sys::fs::getMainExecutable(nullptr, nullptr)
136                     : (std::string)Argv0;
137   BumpPtrAllocator Allocator;
138   StringSaver StrPool(Allocator);
139   std::vector<const char *> Modules(Depth, nullptr);
140   std::vector<intptr_t> Offsets(Depth, 0);
141   if (!findModulesAndOffsets(StackTrace, Depth, Modules.data(), Offsets.data(),
142                              MainExecutableName.c_str(), StrPool))
143     return false;
144   int InputFD;
145   SmallString<32> InputFile, OutputFile;
146   sys::fs::createTemporaryFile("symbolizer-input", "", InputFD, InputFile);
147   sys::fs::createTemporaryFile("symbolizer-output", "", OutputFile);
148   FileRemover InputRemover(InputFile.c_str());
149   FileRemover OutputRemover(OutputFile.c_str());
150 
151   {
152     raw_fd_ostream Input(InputFD, true);
153     for (int i = 0; i < Depth; i++) {
154       if (Modules[i])
155         Input << Modules[i] << " " << (void*)Offsets[i] << "\n";
156     }
157   }
158 
159   Optional<StringRef> Redirects[] = {StringRef(InputFile),
160                                      StringRef(OutputFile), StringRef("")};
161   StringRef Args[] = {"llvm-symbolizer", "--functions=linkage", "--inlining",
162 #ifdef _WIN32
163                       // Pass --relative-address on Windows so that we don't
164                       // have to add ImageBase from PE file.
165                       // FIXME: Make this the default for llvm-symbolizer.
166                       "--relative-address",
167 #endif
168                       "--demangle"};
169   int RunResult =
170       sys::ExecuteAndWait(LLVMSymbolizerPath, Args, None, Redirects);
171   if (RunResult != 0)
172     return false;
173 
174   // This report format is based on the sanitizer stack trace printer.  See
175   // sanitizer_stacktrace_printer.cc in compiler-rt.
176   auto OutputBuf = MemoryBuffer::getFile(OutputFile.c_str());
177   if (!OutputBuf)
178     return false;
179   StringRef Output = OutputBuf.get()->getBuffer();
180   SmallVector<StringRef, 32> Lines;
181   Output.split(Lines, "\n");
182   auto CurLine = Lines.begin();
183   int frame_no = 0;
184   for (int i = 0; i < Depth; i++) {
185     auto PrintLineHeader = [&]() {
186       OS << right_justify(formatv("#{0}", frame_no++).str(),
187                           std::log10(Depth) + 2)
188          << ' ' << format_ptr(StackTrace[i]) << ' ';
189     };
190     if (!Modules[i]) {
191       PrintLineHeader();
192       OS << '\n';
193       continue;
194     }
195     // Read pairs of lines (function name and file/line info) until we
196     // encounter empty line.
197     for (;;) {
198       if (CurLine == Lines.end())
199         return false;
200       StringRef FunctionName = *CurLine++;
201       if (FunctionName.empty())
202         break;
203       PrintLineHeader();
204       if (!FunctionName.startswith("??"))
205         OS << FunctionName << ' ';
206       if (CurLine == Lines.end())
207         return false;
208       StringRef FileLineInfo = *CurLine++;
209       if (!FileLineInfo.startswith("??"))
210         OS << FileLineInfo;
211       else
212         OS << "(" << Modules[i] << '+' << format_hex(Offsets[i], 0) << ")";
213       OS << "\n";
214     }
215   }
216   return true;
217 }
218 
219 // Include the platform-specific parts of this class.
220 #ifdef LLVM_ON_UNIX
221 #include "Unix/Signals.inc"
222 #endif
223 #ifdef _WIN32
224 #include "Windows/Signals.inc"
225 #endif
226