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diff --git a/llvm/lib/Support/Signals.cpp b/llvm/lib/Support/Signals.cpp
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+//===- Signals.cpp - Signal Handling support --------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This file defines some helpful functions for dealing with the possibility of
+// Unix signals occurring while your program is running.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Support/Signals.h"
+#include "llvm/ADT/STLExtras.h"
+#include "llvm/ADT/StringRef.h"
+#include "llvm/Config/llvm-config.h"
+#include "llvm/Support/ErrorOr.h"
+#include "llvm/Support/FileSystem.h"
+#include "llvm/Support/FileUtilities.h"
+#include "llvm/Support/Format.h"
+#include "llvm/Support/FormatVariadic.h"
+#include "llvm/Support/FormatAdapters.h"
+#include "llvm/Support/ManagedStatic.h"
+#include "llvm/Support/MemoryBuffer.h"
+#include "llvm/Support/Mutex.h"
+#include "llvm/Support/Program.h"
+#include "llvm/Support/StringSaver.h"
+#include "llvm/Support/raw_ostream.h"
+#include "llvm/Support/Options.h"
+#include <vector>
+
+//===----------------------------------------------------------------------===//
+//=== WARNING: Implementation here must contain only TRULY operating system
+//===          independent code.
+//===----------------------------------------------------------------------===//
+
+using namespace llvm;
+
+// Use explicit storage to avoid accessing cl::opt in a signal handler.
+static bool DisableSymbolicationFlag = false;
+static cl::opt<bool, true>
+    DisableSymbolication("disable-symbolication",
+                         cl::desc("Disable symbolizing crash backtraces."),
+                         cl::location(DisableSymbolicationFlag), cl::Hidden);
+
+// Callbacks to run in signal handler must be lock-free because a signal handler
+// could be running as we add new callbacks. We don't add unbounded numbers of
+// callbacks, an array is therefore sufficient.
+struct CallbackAndCookie {
+  sys::SignalHandlerCallback Callback;
+  void *Cookie;
+  enum class Status { Empty, Initializing, Initialized, Executing };
+  std::atomic<Status> Flag;
+};
+static constexpr size_t MaxSignalHandlerCallbacks = 8;
+static CallbackAndCookie CallBacksToRun[MaxSignalHandlerCallbacks];
+
+// Signal-safe.
+void sys::RunSignalHandlers() {
+  for (size_t I = 0; I < MaxSignalHandlerCallbacks; ++I) {
+    auto &RunMe = CallBacksToRun[I];
+    auto Expected = CallbackAndCookie::Status::Initialized;
+    auto Desired = CallbackAndCookie::Status::Executing;
+    if (!RunMe.Flag.compare_exchange_strong(Expected, Desired))
+      continue;
+    (*RunMe.Callback)(RunMe.Cookie);
+    RunMe.Callback = nullptr;
+    RunMe.Cookie = nullptr;
+    RunMe.Flag.store(CallbackAndCookie::Status::Empty);
+  }
+}
+
+// Signal-safe.
+static void insertSignalHandler(sys::SignalHandlerCallback FnPtr,
+                                void *Cookie) {
+  for (size_t I = 0; I < MaxSignalHandlerCallbacks; ++I) {
+    auto &SetMe = CallBacksToRun[I];
+    auto Expected = CallbackAndCookie::Status::Empty;
+    auto Desired = CallbackAndCookie::Status::Initializing;
+    if (!SetMe.Flag.compare_exchange_strong(Expected, Desired))
+      continue;
+    SetMe.Callback = FnPtr;
+    SetMe.Cookie = Cookie;
+    SetMe.Flag.store(CallbackAndCookie::Status::Initialized);
+    return;
+  }
+  report_fatal_error("too many signal callbacks already registered");
+}
+
+static bool findModulesAndOffsets(void **StackTrace, int Depth,
+                                  const char **Modules, intptr_t *Offsets,
+                                  const char *MainExecutableName,
+                                  StringSaver &StrPool);
+
+/// Format a pointer value as hexadecimal. Zero pad it out so its always the
+/// same width.
+static FormattedNumber format_ptr(void *PC) {
+  // Each byte is two hex digits plus 2 for the 0x prefix.
+  unsigned PtrWidth = 2 + 2 * sizeof(void *);
+  return format_hex((uint64_t)PC, PtrWidth);
+}
+
+/// Helper that launches llvm-symbolizer and symbolizes a backtrace.
+LLVM_ATTRIBUTE_USED
+static bool printSymbolizedStackTrace(StringRef Argv0, void **StackTrace,
+                                      int Depth, llvm::raw_ostream &OS) {
+  if (DisableSymbolicationFlag)
+    return false;
+
+  // Don't recursively invoke the llvm-symbolizer binary.
+  if (Argv0.find("llvm-symbolizer") != std::string::npos)
+    return false;
+
+  // FIXME: Subtract necessary number from StackTrace entries to turn return addresses
+  // into actual instruction addresses.
+  // Use llvm-symbolizer tool to symbolize the stack traces. First look for it
+  // alongside our binary, then in $PATH.
+  ErrorOr<std::string> LLVMSymbolizerPathOrErr = std::error_code();
+  if (!Argv0.empty()) {
+    StringRef Parent = llvm::sys::path::parent_path(Argv0);
+    if (!Parent.empty())
+      LLVMSymbolizerPathOrErr = sys::findProgramByName("llvm-symbolizer", Parent);
+  }
+  if (!LLVMSymbolizerPathOrErr)
+    LLVMSymbolizerPathOrErr = sys::findProgramByName("llvm-symbolizer");
+  if (!LLVMSymbolizerPathOrErr)
+    return false;
+  const std::string &LLVMSymbolizerPath = *LLVMSymbolizerPathOrErr;
+
+  // If we don't know argv0 or the address of main() at this point, try
+  // to guess it anyway (it's possible on some platforms).
+  std::string MainExecutableName =
+      sys::fs::exists(Argv0) ? (std::string)Argv0
+                             : sys::fs::getMainExecutable(nullptr, nullptr);
+  BumpPtrAllocator Allocator;
+  StringSaver StrPool(Allocator);
+  std::vector<const char *> Modules(Depth, nullptr);
+  std::vector<intptr_t> Offsets(Depth, 0);
+  if (!findModulesAndOffsets(StackTrace, Depth, Modules.data(), Offsets.data(),
+                             MainExecutableName.c_str(), StrPool))
+    return false;
+  int InputFD;
+  SmallString<32> InputFile, OutputFile;
+  sys::fs::createTemporaryFile("symbolizer-input", "", InputFD, InputFile);
+  sys::fs::createTemporaryFile("symbolizer-output", "", OutputFile);
+  FileRemover InputRemover(InputFile.c_str());
+  FileRemover OutputRemover(OutputFile.c_str());
+
+  {
+    raw_fd_ostream Input(InputFD, true);
+    for (int i = 0; i < Depth; i++) {
+      if (Modules[i])
+        Input << Modules[i] << " " << (void*)Offsets[i] << "\n";
+    }
+  }
+
+  Optional<StringRef> Redirects[] = {StringRef(InputFile),
+                                     StringRef(OutputFile), StringRef("")};
+  StringRef Args[] = {"llvm-symbolizer", "--functions=linkage", "--inlining",
+#ifdef _WIN32
+                      // Pass --relative-address on Windows so that we don't
+                      // have to add ImageBase from PE file.
+                      // FIXME: Make this the default for llvm-symbolizer.
+                      "--relative-address",
+#endif
+                      "--demangle"};
+  int RunResult =
+      sys::ExecuteAndWait(LLVMSymbolizerPath, Args, None, Redirects);
+  if (RunResult != 0)
+    return false;
+
+  // This report format is based on the sanitizer stack trace printer.  See
+  // sanitizer_stacktrace_printer.cc in compiler-rt.
+  auto OutputBuf = MemoryBuffer::getFile(OutputFile.c_str());
+  if (!OutputBuf)
+    return false;
+  StringRef Output = OutputBuf.get()->getBuffer();
+  SmallVector<StringRef, 32> Lines;
+  Output.split(Lines, "\n");
+  auto CurLine = Lines.begin();
+  int frame_no = 0;
+  for (int i = 0; i < Depth; i++) {
+    auto PrintLineHeader = [&]() {
+      OS << right_justify(formatv("#{0}", frame_no++).str(),
+                          std::log10(Depth) + 2)
+         << ' ' << format_ptr(StackTrace[i]) << ' ';
+    };
+    if (!Modules[i]) {
+      PrintLineHeader();
+      OS << '\n';
+      continue;
+    }
+    // Read pairs of lines (function name and file/line info) until we
+    // encounter empty line.
+    for (;;) {
+      if (CurLine == Lines.end())
+        return false;
+      StringRef FunctionName = *CurLine++;
+      if (FunctionName.empty())
+        break;
+      PrintLineHeader();
+      if (!FunctionName.startswith("??"))
+        OS << FunctionName << ' ';
+      if (CurLine == Lines.end())
+        return false;
+      StringRef FileLineInfo = *CurLine++;
+      if (!FileLineInfo.startswith("??"))
+        OS << FileLineInfo;
+      else
+        OS << "(" << Modules[i] << '+' << format_hex(Offsets[i], 0) << ")";
+      OS << "\n";
+    }
+  }
+  return true;
+}
+
+// Include the platform-specific parts of this class.
+#ifdef LLVM_ON_UNIX
+#include "Unix/Signals.inc"
+#endif
+#ifdef _WIN32
+#include "Windows/Signals.inc"
+#endif