CrashRecoveryContext.cpp | Explore in Territory

//===--- CrashRecoveryContext.cpp - Crash Recovery ------------------------===//
//
// 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
//
//===----------------------------------------------------------------------===//

#include "llvm/Support/CrashRecoveryContext.h"
#include "llvm/Config/llvm-config.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/ExitCodes.h"
#include "llvm/Support/Signals.h"
#include "llvm/Support/thread.h"
#include <cassert>
#include <mutex>
#include <setjmp.h>

usingnamespacellvm;

namespace {

struct CrashRecoveryContextImpl;
static LLVM_THREAD_LOCAL const CrashRecoveryContextImpl *CurrentContext;

struct CrashRecoveryContextImpl { … };

std::mutex &getCrashRecoveryContextMutex() { … }

static bool gCrashRecoveryEnabled = …;

static LLVM_THREAD_LOCAL const CrashRecoveryContext *IsRecoveringFromCrash;

} // namespace

static void installExceptionOrSignalHandlers();
static void uninstallExceptionOrSignalHandlers();

CrashRecoveryContextCleanup::~CrashRecoveryContextCleanup() = default;

CrashRecoveryContext::CrashRecoveryContext() { … }

CrashRecoveryContext::~CrashRecoveryContext() { … }

bool CrashRecoveryContext::isRecoveringFromCrash() { … }

CrashRecoveryContext *CrashRecoveryContext::GetCurrent() { … }

void CrashRecoveryContext::Enable() { … }

void CrashRecoveryContext::Disable() { … }

void CrashRecoveryContext::registerCleanup(CrashRecoveryContextCleanup *cleanup)
{ … }

void
CrashRecoveryContext::unregisterCleanup(CrashRecoveryContextCleanup *cleanup) { … }

#if defined(_MSC_VER)

#include <windows.h> // for GetExceptionInformation

// If _MSC_VER is defined, we must have SEH. Use it if it's available. It's way
// better than VEH. Vectored exception handling catches all exceptions happening
// on the thread with installed exception handlers, so it can interfere with
// internal exception handling of other libraries on that thread. SEH works
// exactly as you would expect normal exception handling to work: it only
// catches exceptions if they would bubble out from the stack frame with __try /
// __except.

static void installExceptionOrSignalHandlers() {}
static void uninstallExceptionOrSignalHandlers() {}

// We need this function because the call to GetExceptionInformation() can only
// occur inside the __except evaluation block
static int ExceptionFilter(_EXCEPTION_POINTERS *Except) {
  // Lookup the current thread local recovery object.
  const CrashRecoveryContextImpl *CRCI = CurrentContext;

  if (!CRCI) {
    // Something has gone horribly wrong, so let's just tell everyone
    // to keep searching
    CrashRecoveryContext::Disable();
    return EXCEPTION_CONTINUE_SEARCH;
  }

  int RetCode = (int)Except->ExceptionRecord->ExceptionCode;
  if ((RetCode & 0xF0000000) == 0xE0000000)
    RetCode &= ~0xF0000000; // this crash was generated by sys::Process::Exit

  // Handle the crash
  const_cast<CrashRecoveryContextImpl *>(CRCI)->HandleCrash(
      RetCode, reinterpret_cast<uintptr_t>(Except));

  return EXCEPTION_EXECUTE_HANDLER;
}

#if defined(__clang__) && defined(_M_IX86)
// Work around PR44697.
__attribute__((optnone))
#endif
bool CrashRecoveryContext::RunSafely(function_ref<void()> Fn) {
  if (!gCrashRecoveryEnabled) {
    Fn();
    return true;
  }
  assert(!Impl && "Crash recovery context already initialized!");
  Impl = new CrashRecoveryContextImpl(this);
  __try {
    Fn();
  } __except (ExceptionFilter(GetExceptionInformation())) {
    return false;
  }
  return true;
}

#else // !_MSC_VER

#if defined(_WIN32)
// This is a non-MSVC compiler, probably mingw gcc or clang without
// -fms-extensions. Use vectored exception handling (VEH).
//
// On Windows, we can make use of vectored exception handling to catch most
// crashing situations.  Note that this does mean we will be alerted of
// exceptions *before* structured exception handling has the opportunity to
// catch it. Unfortunately, this causes problems in practice with other code
// running on threads with LLVM crash recovery contexts, so we would like to
// eventually move away from VEH.
//
// Vectored works on a per-thread basis, which is an advantage over
// SetUnhandledExceptionFilter. SetUnhandledExceptionFilter also doesn't have
// any native support for chaining exception handlers, but VEH allows more than
// one.
//
// The vectored exception handler functionality was added in Windows
// XP, so if support for older versions of Windows is required,
// it will have to be added.

#include "llvm/Support/Windows/WindowsSupport.h"

static LONG CALLBACK ExceptionHandler(PEXCEPTION_POINTERS ExceptionInfo)
{
  // DBG_PRINTEXCEPTION_WIDE_C is not properly defined on all supported
  // compilers and platforms, so we define it manually.
  constexpr ULONG DbgPrintExceptionWideC = 0x4001000AL;
  switch (ExceptionInfo->ExceptionRecord->ExceptionCode)
  {
  case DBG_PRINTEXCEPTION_C:
  case DbgPrintExceptionWideC:
  case 0x406D1388:  // set debugger thread name
    return EXCEPTION_CONTINUE_EXECUTION;
  }

  // Lookup the current thread local recovery object.
  const CrashRecoveryContextImpl *CRCI = CurrentContext;

  if (!CRCI) {
    // Something has gone horribly wrong, so let's just tell everyone
    // to keep searching
    CrashRecoveryContext::Disable();
    return EXCEPTION_CONTINUE_SEARCH;
  }

  // TODO: We can capture the stack backtrace here and store it on the
  // implementation if we so choose.

  int RetCode = (int)ExceptionInfo->ExceptionRecord->ExceptionCode;
  if ((RetCode & 0xF0000000) == 0xE0000000)
    RetCode &= ~0xF0000000; // this crash was generated by sys::Process::Exit

  // Handle the crash
  const_cast<CrashRecoveryContextImpl *>(CRCI)->HandleCrash(
      RetCode, reinterpret_cast<uintptr_t>(ExceptionInfo));

  // Note that we don't actually get here because HandleCrash calls
  // longjmp, which means the HandleCrash function never returns.
  llvm_unreachable("Handled the crash, should have longjmp'ed out of here");
}

// Because the Enable and Disable calls are static, it means that
// there may not actually be an Impl available, or even a current
// CrashRecoveryContext at all.  So we make use of a thread-local
// exception table.  The handles contained in here will either be
// non-NULL, valid VEH handles, or NULL.
static LLVM_THREAD_LOCAL const void* sCurrentExceptionHandle;

static void installExceptionOrSignalHandlers() {
  // We can set up vectored exception handling now.  We will install our
  // handler as the front of the list, though there's no assurances that
  // it will remain at the front (another call could install itself before
  // our handler).  This 1) isn't likely, and 2) shouldn't cause problems.
  PVOID handle = ::AddVectoredExceptionHandler(1, ExceptionHandler);
  sCurrentExceptionHandle = handle;
}

static void uninstallExceptionOrSignalHandlers() {
  PVOID currentHandle = const_cast<PVOID>(sCurrentExceptionHandle);
  if (currentHandle) {
    // Now we can remove the vectored exception handler from the chain
    ::RemoveVectoredExceptionHandler(currentHandle);

    // Reset the handle in our thread-local set.
    sCurrentExceptionHandle = NULL;
  }
}

#else // !_WIN32

// Generic POSIX implementation.
//
// This implementation relies on synchronous signals being delivered to the
// current thread. We use a thread local object to keep track of the active
// crash recovery context, and install signal handlers to invoke HandleCrash on
// the active object.
//
// This implementation does not attempt to chain signal handlers in any
// reliable fashion -- if we get a signal outside of a crash recovery context we
// simply disable crash recovery and raise the signal again.

#include <signal.h>

static const int Signals[] = …;
static const unsigned NumSignals = …;
static struct sigaction PrevActions[NumSignals];

static void CrashRecoverySignalHandler(int Signal) { … }

static void installExceptionOrSignalHandlers() { … }

static void uninstallExceptionOrSignalHandlers() { … }

#endif // !_WIN32

bool CrashRecoveryContext::RunSafely(function_ref<void()> Fn) { … }

#endif // !_MSC_VER

[[noreturn]] void CrashRecoveryContext::HandleExit(int RetCode) { … }

bool CrashRecoveryContext::isCrash(int RetCode) { … }

bool CrashRecoveryContext::throwIfCrash(int RetCode) { … }

// FIXME: Portability.
static void setThreadBackgroundPriority() { … }

static bool hasThreadBackgroundPriority() { … }

namespace {
struct RunSafelyOnThreadInfo { … };
} // namespace

static void RunSafelyOnThread_Dispatch(void *UserData) { … }
bool CrashRecoveryContext::RunSafelyOnThread(function_ref<void()> Fn,
                                             unsigned RequestedStackSize) { … }
llvm/llvm/lib/Support/CrashRecoveryContext.cpp
