Re: [Valgrind-users] threads vs main and invalid stack writes

[Daniel S. <da...@co...>]

On Thu, 2013-07-04 at 11:07 -0700, John Reiser wrote:
> >     alloca(4096);
> >     __yell();
> 
> > 
> > (gdb) monitor get_vbits 0xffeffeed0 256
> > ________ ________ ________ ________ ________ ________ ________ ________
> > ________ ________ ________ ________ ________ ________ ________ ________
> > ________ ________ ________ ________ ________ ________ ________ ________
> > ________ ________ ________ ________ ________ ________ ________ ________
> > ________ ________ ________ ________ ffffffff ffffffff ffffffff ffffffff
> > ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff
> > ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff
> > ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff
> > Address 0xFFEFFEED0 len 256 has 144 bytes unaddressable
> > 
> > Any ideas? It seems to depend on:
> > 
> >  - Some (small) number of threads being spawned.
> >  - A > page-sized alloca().
> >  - Reasonably sized memset on top.
> >  - It's always the main thread which suffers.
> 
> Thank you for the small, reproducible testcase!
> 
> It's a bug in valgrind, so please file a bug report, and include the testcase.
> See the "Bug Reports" entry in the left column of the main page
> http://www.valgrind.org/ .

Okay, thank you.

I made https://bugs.kde.org/show_bug.cgi?id=321960

> Meanwhile the trivial workaround is to memset every result of alloca.

:D

> Oh, and "#include <string.h>"

Ah, sorry for that. A previous version only triggered while we had made
__yell a variadic function. Yeah, the above one had bad headers.

Thanks,
Daniel

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