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CrashHandler: be careful about crashing while handling

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Summary:
Looking at the current Apple-specific code for crash handling it does a few
silly things that I think we should avoid while handling crashes:

  * Try real hard not to allocate.
  * Set the global crash reporter string early so that any crash while
    generating the stack trace will still report some info.
  * Prevent reordering of operations in the current thread.

<rdar://problem/53503334>

Subscribers: hiraditya, jkorous, dexonsmith, llvm-commits, beanz, Bigcheese, thakis, lattner, jordan_rose

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D65235

llvm-svn: 367031
This commit is contained in:
JF Bastien 2019-07-25 16:07:41 +00:00
parent e3285696a8
commit 8aae65a906
1 changed files with 47 additions and 16 deletions
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63
lib/Support/PrettyStackTrace.cpp
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@ -121,31 +121,62 @@ extern "C" const char *__crashreporter_info__
asm(".desc ___crashreporter_info__, 0x10");
#endif
/// CrashHandler - This callback is run if a fatal signal is delivered to the
/// process, it prints the pretty stack trace.
static void setCrashLogMessage(const char *msg) {
#ifdef HAVE_CRASHREPORTERCLIENT_H
(void)CRSetCrashLogMessage(msg);
#elif HAVE_CRASHREPORTER_INFO
__crashreporter_info__ = msg;
#endif
// Don't reorder subsequent operations: whatever comes after might crash and
// we want the system crash handling to see the message we just set.
std::atomic_signal_fence(std::memory_order_seq_cst);
}
#ifdef __APPLE__
using CrashHandlerString = SmallString<2048>;
using CrashHandlerStringStorage =
std::aligned_storage<sizeof(CrashHandlerString),
alignof(CrashHandlerString)>::type;
static CrashHandlerStringStorage crashHandlerStringStorage;
#endif
/// This callback is run if a fatal signal is delivered to the process, it
/// prints the pretty stack trace.
static void CrashHandler(void *) {
#ifndef __APPLE__
// On non-apple systems, just emit the crash stack trace to stderr.
PrintCurStackTrace(errs());
#else
// Otherwise, emit to a smallvector of chars, send *that* to stderr, but also
// put it into __crashreporter_info__.
SmallString<2048> TmpStr;
// Emit the crash stack trace to a SmallString, put it where the system crash
// handling will find it, and also send it to stderr.
//
// The SmallString is fairly large in the hope that we don't allocate (we're
// handling a fatal signal, something is already pretty wrong, allocation
// might not work). Further, we don't use a magic static in case that's also
// borked. We leak any allocation that does occur because the program is about
// to die anyways. This is technically racy if we were handling two fatal
// signals, however if we're in that situation a race is the least of our
// worries.
auto &crashHandlerString =
*new (&crashHandlerStringStorage) CrashHandlerString;
// If we crash while trying to print the stack trace, we still want the system
// crash handling to have some partial information. That'll work out as long
// as the SmallString doesn't allocate. If it does allocate then the system
// crash handling will see some garbage because the inline buffer now contains
// a pointer.
setCrashLogMessage(crashHandlerString.c_str());
{
raw_svector_ostream Stream(TmpStr);
raw_svector_ostream Stream(crashHandlerString);
PrintCurStackTrace(Stream);
}
if (!TmpStr.empty()) {
#ifdef HAVE_CRASHREPORTERCLIENT_H
// Cast to void to avoid warning.
(void)CRSetCrashLogMessage(TmpStr.c_str());
#elif HAVE_CRASHREPORTER_INFO
__crashreporter_info__ = strdup(TmpStr.c_str());
#endif
errs() << TmpStr.str();
}
if (!crashHandlerString.empty()) {
setCrashLogMessage(crashHandlerString.c_str());
errs() << crashHandlerString.str();
} else
setCrashLogMessage("No crash information.");
#endif
}