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//===--- CrashRecoveryContext.cpp - Crash Recovery ------------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
#include "llvm/Support/CrashRecoveryContext.h"
#include "llvm/ADT/SmallString.h"
#include "llvm/Config/config.h"
#include "llvm/Support/Mutex.h"
#include "llvm/Support/ThreadLocal.h"
#include "llvm/Support/ErrorHandling.h"
#include <setjmp.h>
#include <cstdio>
using namespace llvm;
namespace {
struct CrashRecoveryContextImpl;
static sys::ThreadLocal<const CrashRecoveryContextImpl> CurrentContext;
struct CrashRecoveryContextImpl {
CrashRecoveryContext *CRC;
std::string Backtrace;
::jmp_buf JumpBuffer;
volatile unsigned Failed : 1;
public:
CrashRecoveryContextImpl(CrashRecoveryContext *CRC) : CRC(CRC),
Failed(false) {
CurrentContext.set(this);
}
~CrashRecoveryContextImpl() {
CurrentContext.erase();
}
void HandleCrash() {
// Eliminate the current context entry, to avoid re-entering in case the
// cleanup code crashes.
CurrentContext.erase();
assert(!Failed && "Crash recovery context already failed!");
Failed = true;
// FIXME: Stash the backtrace.
// Jump back to the RunSafely we were called under.
longjmp(JumpBuffer, 1);
}
};
}
static sys::Mutex gCrashRecoveryContexMutex;
static bool gCrashRecoveryEnabled = false;
static sys::ThreadLocal<const CrashRecoveryContextCleanup>
tlIsRecoveringFromCrash;
CrashRecoveryContextCleanup::~CrashRecoveryContextCleanup() {}
CrashRecoveryContext::~CrashRecoveryContext() {
// Reclaim registered resources.
CrashRecoveryContextCleanup *i = head;
tlIsRecoveringFromCrash.set(head);
while (i) {
CrashRecoveryContextCleanup *tmp = i;
i = tmp->next;
tmp->cleanupFired = true;
tmp->recoverResources();
delete tmp;
}
tlIsRecoveringFromCrash.erase();
CrashRecoveryContextImpl *CRCI = (CrashRecoveryContextImpl *) Impl;
delete CRCI;
}
bool CrashRecoveryContext::isRecoveringFromCrash() {
return tlIsRecoveringFromCrash.get() != 0;
}
CrashRecoveryContext *CrashRecoveryContext::GetCurrent() {
if (!gCrashRecoveryEnabled)
return 0;
const CrashRecoveryContextImpl *CRCI = CurrentContext.get();
if (!CRCI)
return 0;
return CRCI->CRC;
}
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 = 0;
}
else {
cleanup->prev->next = cleanup->next;
if (cleanup->next)
cleanup->next->prev = cleanup->prev;
}
delete cleanup;
}
#ifdef LLVM_ON_WIN32
#include "Windows/Windows.h"
// 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. But that isn't likely
// to cause problems because nowhere in the project is SEH being
// used.
//
// Vectored exception handling is built on top of SEH, and so it
// works on a per-thread basis.
//
// 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.
//
// If we want to support as far back as Win2k, we could use the
// SetUnhandledExceptionFilter API, but there's a risk of that
// being entirely overwritten (it's not a chain).
static LONG CALLBACK ExceptionHandler(PEXCEPTION_POINTERS ExceptionInfo)
{
// Lookup the current thread local recovery object.
const CrashRecoveryContextImpl *CRCI = CurrentContext.get();
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.
// Handle the crash
const_cast<CrashRecoveryContextImpl*>(CRCI)->HandleCrash();
// 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 sys::ThreadLocal<const void> sCurrentExceptionHandle;
void CrashRecoveryContext::Enable() {
sys::ScopedLock L(gCrashRecoveryContexMutex);
if (gCrashRecoveryEnabled)
return;
gCrashRecoveryEnabled = true;
// 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.set(handle);
}
void CrashRecoveryContext::Disable() {
sys::ScopedLock L(gCrashRecoveryContexMutex);
if (!gCrashRecoveryEnabled)
return;
gCrashRecoveryEnabled = false;
PVOID currentHandle = const_cast<PVOID>(sCurrentExceptionHandle.get());
if (currentHandle) {
// Now we can remove the vectored exception handler from the chain
::RemoveVectoredExceptionHandler(currentHandle);
// Reset the handle in our thread-local set.
sCurrentExceptionHandle.set(NULL);
}
}
#else
// 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 to 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 int Signals[] = { SIGABRT, SIGBUS, SIGFPE, SIGILL, SIGSEGV, SIGTRAP };
static const unsigned NumSignals = sizeof(Signals) / sizeof(Signals[0]);
static struct sigaction PrevActions[NumSignals];
static void CrashRecoverySignalHandler(int Signal) {
// Lookup the current thread local recovery object.
const CrashRecoveryContextImpl *CRCI = CurrentContext.get();
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, 0);
if (CRCI)
const_cast<CrashRecoveryContextImpl*>(CRCI)->HandleCrash();
}
void CrashRecoveryContext::Enable() {
sys::ScopedLock L(gCrashRecoveryContexMutex);
if (gCrashRecoveryEnabled)
return;
gCrashRecoveryEnabled = true;
// 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]);
}
}
void CrashRecoveryContext::Disable() {
sys::ScopedLock L(gCrashRecoveryContexMutex);
if (!gCrashRecoveryEnabled)
return;
gCrashRecoveryEnabled = false;
// Restore the previous signal handlers.
for (unsigned i = 0; i != NumSignals; ++i)
sigaction(Signals[i], &PrevActions[i], 0);
}
#endif
bool CrashRecoveryContext::RunSafely(void (*Fn)(void*), void *UserData) {
// If crash recovery is disabled, do nothing.
if (gCrashRecoveryEnabled) {
assert(!Impl && "Crash recovery context already initialized!");
CrashRecoveryContextImpl *CRCI = new CrashRecoveryContextImpl(this);
Impl = CRCI;
if (setjmp(CRCI->JumpBuffer) != 0) {
return false;
}
}
Fn(UserData);
return true;
}
void CrashRecoveryContext::HandleCrash() {
CrashRecoveryContextImpl *CRCI = (CrashRecoveryContextImpl *) Impl;
assert(CRCI && "Crash recovery context never initialized!");
CRCI->HandleCrash();
}
const std::string &CrashRecoveryContext::getBacktrace() const {
CrashRecoveryContextImpl *CRC = (CrashRecoveryContextImpl *) Impl;
assert(CRC && "Crash recovery context never initialized!");
assert(CRC->Failed && "No crash was detected!");
return CRC->Backtrace;
}
//
namespace {
struct RunSafelyOnThreadInfo {
void (*UserFn)(void*);
void *UserData;
CrashRecoveryContext *CRC;
bool Result;
};
}
static void RunSafelyOnThread_Dispatch(void *UserData) {
RunSafelyOnThreadInfo *Info =
reinterpret_cast<RunSafelyOnThreadInfo*>(UserData);
Info->Result = Info->CRC->RunSafely(Info->UserFn, Info->UserData);
}
bool CrashRecoveryContext::RunSafelyOnThread(void (*Fn)(void*), void *UserData,
unsigned RequestedStackSize) {
RunSafelyOnThreadInfo Info = { Fn, UserData, this, false };
llvm_execute_on_thread(RunSafelyOnThread_Dispatch, &Info, RequestedStackSize);
return Info.Result;
}