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//===--- 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>
using namespace llvm;
namespace {
struct CrashRecoveryContextImpl;
static LLVM_THREAD_LOCAL const CrashRecoveryContextImpl *CurrentContext;
struct CrashRecoveryContextImpl {
// When threads are disabled, this links up all active
// CrashRecoveryContextImpls. When threads are enabled there's one thread
// per CrashRecoveryContext and CurrentContext is a thread-local, so only one
// CrashRecoveryContextImpl is active per thread and this is always null.
const CrashRecoveryContextImpl *Next;
CrashRecoveryContext *CRC;
::jmp_buf JumpBuffer;
volatile unsigned Failed : 1;
unsigned SwitchedThread : 1;
unsigned ValidJumpBuffer : 1;
public:
CrashRecoveryContextImpl(CrashRecoveryContext *CRC) noexcept
: CRC(CRC), Failed(false), SwitchedThread(false), ValidJumpBuffer(false) {
Next = CurrentContext;
CurrentContext = this;
}
~CrashRecoveryContextImpl() {
if (!SwitchedThread)
CurrentContext = Next;
}
/// Called when the separate crash-recovery thread was finished, to
/// indicate that we don't need to clear the thread-local CurrentContext.
void setSwitchedThread() {
#if defined(LLVM_ENABLE_THREADS) && LLVM_ENABLE_THREADS != 0
SwitchedThread = true;
#endif
}
// If the function ran by the CrashRecoveryContext crashes or fails, then
// 'RetCode' represents the returned error code, as if it was returned by a
// process. 'Context' represents the signal type on Unix; on Windows, it is
// the ExceptionContext.
void HandleCrash(int RetCode, uintptr_t Context) {
// Eliminate the current context entry, to avoid re-entering in case the
// cleanup code crashes.
CurrentContext = Next;
assert(!Failed && "Crash recovery context already failed!");
Failed = true;
if (CRC->DumpStackAndCleanupOnFailure)
sys::CleanupOnSignal(Context);
CRC->RetCode = RetCode;
// Jump back to the RunSafely we were called under.
if (ValidJumpBuffer)
longjmp(JumpBuffer, 1);
// Otherwise let the caller decide of the outcome of the crash. Currently
// this occurs when using SEH on Windows with MSVC or clang-cl.
}
};
std::mutex &getCrashRecoveryContextMutex() {
static std::mutex CrashRecoveryContextMutex;
return CrashRecoveryContextMutex;
}
static bool gCrashRecoveryEnabled = false;
static LLVM_THREAD_LOCAL const CrashRecoveryContext *IsRecoveringFromCrash;
} // namespace
static void installExceptionOrSignalHandlers();
static void uninstallExceptionOrSignalHandlers();
CrashRecoveryContextCleanup::~CrashRecoveryContextCleanup() = default;
CrashRecoveryContext::CrashRecoveryContext() {
// On Windows, if abort() was previously triggered (and caught by a previous
// CrashRecoveryContext) the Windows CRT removes our installed signal handler,
// so we need to install it again.
sys::DisableSystemDialogsOnCrash();
}
CrashRecoveryContext::~CrashRecoveryContext() {
// Reclaim registered resources.
CrashRecoveryContextCleanup *i = head;
const CrashRecoveryContext *PC = IsRecoveringFromCrash;
IsRecoveringFromCrash = this;
while (i) {
CrashRecoveryContextCleanup *tmp = i;
i = tmp->next;
tmp->cleanupFired = true;
tmp->recoverResources();
delete tmp;
}
IsRecoveringFromCrash = PC;
CrashRecoveryContextImpl *CRCI = (CrashRecoveryContextImpl *) Impl;
delete CRCI;
}
bool CrashRecoveryContext::isRecoveringFromCrash() {
return IsRecoveringFromCrash != nullptr;
}
CrashRecoveryContext *CrashRecoveryContext::GetCurrent() {
if (!gCrashRecoveryEnabled)
return nullptr;
const CrashRecoveryContextImpl *CRCI = CurrentContext;
if (!CRCI)
return nullptr;
return CRCI->CRC;
}
void CrashRecoveryContext::Enable() {
std::lock_guard<std::mutex> L(getCrashRecoveryContextMutex());
// FIXME: Shouldn't this be a refcount or something?
if (gCrashRecoveryEnabled)
return;
gCrashRecoveryEnabled = true;
installExceptionOrSignalHandlers();
}
void CrashRecoveryContext::Disable() {
std::lock_guard<std::mutex> L(getCrashRecoveryContextMutex());
if (!gCrashRecoveryEnabled)
return;
gCrashRecoveryEnabled = false;
uninstallExceptionOrSignalHandlers();
}
void CrashRecoveryContext::registerCleanup(CrashRecoveryContextCleanup *cleanup)
{
if (!cleanup)
return;
if (head)
head->prev = cleanup;
cleanup->next = head;
head = cleanup;
}
void
CrashRecoveryContext::unregisterCleanup(CrashRecoveryContextCleanup *cleanup) {
if (!cleanup)
return;
if (cleanup == head) {
head = cleanup->next;
if (head)
head->prev = nullptr;
}
else {
cleanup->prev->next = cleanup->next;
if (cleanup->next)
cleanup->next->prev = cleanup->prev;
}
delete 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[] =
{ SIGABRT, SIGBUS, SIGFPE, SIGILL, SIGSEGV, SIGTRAP };
static const unsigned NumSignals = std::size(Signals);
static struct sigaction PrevActions[NumSignals];
static void CrashRecoverySignalHandler(int Signal) {
// Lookup the current thread local recovery object.
const CrashRecoveryContextImpl *CRCI = CurrentContext;
if (!CRCI) {
// We didn't find a crash recovery context -- this means either we got a
// signal on a thread we didn't expect it on, the application got a signal
// outside of a crash recovery context, or something else went horribly
// wrong.
//
// Disable crash recovery and raise the signal again. The assumption here is
// that the enclosing application will terminate soon, and we won't want to
// attempt crash recovery again.
//
// This call of Disable isn't thread safe, but it doesn't actually matter.
CrashRecoveryContext::Disable();
raise(Signal);
// The signal will be thrown once the signal mask is restored.
return;
}
// Unblock the signal we received.
sigset_t SigMask;
sigemptyset(&SigMask);
sigaddset(&SigMask, Signal);
sigprocmask(SIG_UNBLOCK, &SigMask, nullptr);
// Return the same error code as if the program crashed, as mentioned in the
// section "Exit Status for Commands":
// https://pubs.opengroup.org/onlinepubs/9699919799/xrat/V4_xcu_chap02.html
int RetCode = 128 + Signal;
// Don't consider a broken pipe as a crash (see clang/lib/Driver/Driver.cpp)
if (Signal == SIGPIPE)
RetCode = EX_IOERR;
if (CRCI)
const_cast<CrashRecoveryContextImpl *>(CRCI)->HandleCrash(RetCode, Signal);
}
static void installExceptionOrSignalHandlers() {
// Setup the signal handler.
struct sigaction Handler;
Handler.sa_handler = CrashRecoverySignalHandler;
Handler.sa_flags = 0;
sigemptyset(&Handler.sa_mask);
for (unsigned i = 0; i != NumSignals; ++i) {
sigaction(Signals[i], &Handler, &PrevActions[i]);
}
}
static void uninstallExceptionOrSignalHandlers() {
// Restore the previous signal handlers.
for (unsigned i = 0; i != NumSignals; ++i)
sigaction(Signals[i], &PrevActions[i], nullptr);
}
#endif // !_WIN32
bool CrashRecoveryContext::RunSafely(function_ref<void()> Fn) {
// If crash recovery is disabled, do nothing.
if (gCrashRecoveryEnabled) {
assert(!Impl && "Crash recovery context already initialized!");
CrashRecoveryContextImpl *CRCI = new CrashRecoveryContextImpl(this);
Impl = CRCI;
CRCI->ValidJumpBuffer = true;
if (setjmp(CRCI->JumpBuffer) != 0) {
return false;
}
}
Fn();
return true;
}
#endif // !_MSC_VER
[[noreturn]] void CrashRecoveryContext::HandleExit(int RetCode) {
#if defined(_WIN32)
// Since the exception code is actually of NTSTATUS type, we use the
// Microsoft-recommended 0xE prefix, to signify that this is a user error.
// This value is a combination of the customer field (bit 29) and severity
// field (bits 30-31) in the NTSTATUS specification.
::RaiseException(0xE0000000 | RetCode, 0, 0, NULL);
#else
// On Unix we don't need to raise an exception, we go directly to
// HandleCrash(), then longjmp will unwind the stack for us.
CrashRecoveryContextImpl *CRCI = (CrashRecoveryContextImpl *)Impl;
assert(CRCI && "Crash recovery context never initialized!");
CRCI->HandleCrash(RetCode, 0 /*no sig num*/);
#endif
llvm_unreachable("Most likely setjmp wasn't called!");
}
bool CrashRecoveryContext::isCrash(int RetCode) {
#if defined(_WIN32)
// On Windows, the code is interpreted as NTSTATUS. The two high bits
// represent the severity. Values starting with 0x80000000 are reserved for
// "warnings"; values of 0xC0000000 and up are for "errors". In practice, both
// are interpreted as a non-continuable signal.
unsigned Code = ((unsigned)RetCode & 0xF0000000) >> 28;
if (Code != 0xC && Code != 8)
return false;
#else
// On Unix, signals are represented by return codes of 128 or higher.
// Exit code 128 is a reserved value and should not be raised as a signal.
if (RetCode <= 128)
return false;
#endif
return true;
}
bool CrashRecoveryContext::throwIfCrash(int RetCode) {
if (!isCrash(RetCode))
return false;
#if defined(_WIN32)
::RaiseException(RetCode, 0, 0, NULL);
#else
llvm::sys::unregisterHandlers();
raise(RetCode - 128);
#endif
return true;
}
// FIXME: Portability.
static void setThreadBackgroundPriority() {
#ifdef __APPLE__
setpriority(PRIO_DARWIN_THREAD, 0, PRIO_DARWIN_BG);
#endif
}
static bool hasThreadBackgroundPriority() {
#ifdef __APPLE__
return getpriority(PRIO_DARWIN_THREAD, 0) == 1;
#else
return false;
#endif
}
namespace {
struct RunSafelyOnThreadInfo {
function_ref<void()> Fn;
CrashRecoveryContext *CRC;
bool UseBackgroundPriority;
bool Result;
};
} // namespace
static void RunSafelyOnThread_Dispatch(void *UserData) {
RunSafelyOnThreadInfo *Info =
reinterpret_cast<RunSafelyOnThreadInfo*>(UserData);
if (Info->UseBackgroundPriority)
setThreadBackgroundPriority();
Info->Result = Info->CRC->RunSafely(Info->Fn);
}
bool CrashRecoveryContext::RunSafelyOnThread(function_ref<void()> Fn,
unsigned RequestedStackSize) {
bool UseBackgroundPriority = hasThreadBackgroundPriority();
RunSafelyOnThreadInfo Info = { Fn, this, UseBackgroundPriority, false };
llvm::thread Thread(RequestedStackSize == 0
? std::nullopt
: std::optional<unsigned>(RequestedStackSize),
RunSafelyOnThread_Dispatch, &Info);
Thread.join();
if (CrashRecoveryContextImpl *CRC = (CrashRecoveryContextImpl *)Impl)
CRC->setSwitchedThread();
return Info.Result;
}