Double size of sigaltstack to prevent overflow

[Hahnfeld]

Summary

On a crash printSymbolizedStackTrace(...) would need more memory than currently
allocated and therefore corrupts some data in front of sigaltstack.

[Hahnfeld]

Friendly ping...

[bcahoon]

I'm seeing the same problem, which is fixed with this patch. I'm seeing a hang when running llvm-lit with test/Bugpoint/crash-narrowfunctiontest.ll. The hang appears to be caused because data in the stack frame is corrupted, and the clear() method in a vector never returns, when executing CallBacksToRun->clear() in RunSignalHandlers().

This happens only when I build llvm in Debug mode. In Release mode, the problem doesn't occur. Also, if I build llvm in Debug mode, but compile only Signals.cpp with -O3, the failure doesn't occur.

I'm not sure how much stack space is needed on the alternate stack, though I tried MINSIGSTKSZ + 11264 and that works for me.

[Hahnfeld]

In D21222#470596, @bcahoon wrote:

I'm seeing the same problem, which is fixed with this patch. I'm seeing a hang when running llvm-lit with test/Bugpoint/crash-narrowfunctiontest.ll. The hang appears to be caused because data in the stack frame is corrupted, and the clear() method in a vector never returns, when executing CallBacksToRun->clear() in RunSignalHandlers().

This happens only when I build llvm in Debug mode. In Release mode, the problem doesn't occur. Also, if I build llvm in Debug mode, but compile only Signals.cpp with -O3, the failure doesn't occur.

I'm not sure how much stack space is needed on the alternate stack, though I tried MINSIGSTKSZ + 11264 and that works for me.

Yes, exactly. @rsmith is this ok to commit?

[Hahnfeld]

ping

[Hahnfeld]

Ping, I'd like to land this before branching for 3.9.

Thanks,
Jonas

[Hahnfeld]

ping

[Hahnfeld]

Ping! I'm not sure if there was any reasoning behind choosing this magic number...

[Hahnfeld]

Weekly ping...

[Hahnfeld]

Another ping for this one-liner...

[Hahnfeld]

Ping!

[Hahnfeld]

Has been done in rL279599

lib/Support/Unix/Signals.inc

 #if defined(HAVE_SIGALTSTACK)
 // 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 stack_t OldAltStack;
 
 static void CreateSigAltStack() {
-  const size_t AltStackSize = MINSIGSTKSZ + 8192;
+  const size_t AltStackSize = MINSIGSTKSZ + 16384;
 
   // 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))