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Create a sigaltstack when we register our signal handlers. Otherwise we'd very

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likely fail to produce a backtrace if we crash due to stack overflow.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@270273 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Richard Smith 2016-05-20 21:07:41 +00:00
parent 1c8492880e
commit ccdd1ce520
1 changed files with 31 additions and 0 deletions
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31
lib/Support/Unix/Signals.inc
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@ -28,6 +28,8 @@
# include <execinfo.h> // For backtrace().
#endif
#if HAVE_SIGNAL_H
// FIXME: We unconditionally use symbols from this header below. Do we really
// need a configure-time check for a POSIX-mandated header in lib/Support/Unix?
#include <signal.h>
#endif
#if HAVE_SYS_STAT_H
@ -106,6 +108,31 @@ static void RegisterHandler(int Signal) {
++NumRegisteredSignals;
}
// Hold onto the old alternate signal stack so that it's not reported as a leak.
// We don't make any attempt to remove our alt signal stack if we remove our
// signal handlers; that can't be done reliably if someone else is also trying
// to do the same thing.
static struct sigaltstack OldAltStack;
static void CreateSigAltStack() {
const size_t AltStackSize = MINSIGSTKSZ + 8192;
// If we're executing on the alternate stack, or we already have an alternate
// signal stack that we're happy with, there's nothing for us to do. Don't
// reduce the size, some other part of the process might need a larger stack
// than we do.
if (sigaltstack(nullptr, &OldAltStack) != 0 ||
OldAltStack.ss_flags & SS_ONSTACK ||
(OldAltStack.ss_sp && OldAltStack.ss_size >= AltStackSize))
return;
struct sigaltstack AltStack = {};
AltStack.ss_sp = malloc(AltStackSize);
AltStack.ss_size = AltStackSize;
if (sigaltstack(&AltStack, &OldAltStack) != 0)
free(AltStack.ss_sp);
}
static void RegisterHandlers() {
// We need to dereference the signals mutex during handler registration so
// that we force its construction. This is to prevent the first use being
@ -116,6 +143,10 @@ static void RegisterHandlers() {
// If the handlers are already registered, we're done.
if (NumRegisteredSignals != 0) return;
// Create an alternate stack for signal handling. This is necessary for us to
// be able to reliably handle signals due to stack overflow.
CreateSigAltStack();
for (auto S : IntSigs) RegisterHandler(S);
for (auto S : KillSigs) RegisterHandler(S);
}