Re: [PATCH] Initialize the entire obstack struct [BZ #17919]

[Mark Wielaard]

On Tue, 2015-02-03 at 13:14 -0500, Carlos O'Donell wrote:
> On 02/03/2015 01:14 PM, Carlos O'Donell wrote:
> > However, I see that GCC thinks this is a valgrind bug.
> > 
> > If valgrind is simply looking at the comparison to make
> > the warning then it falls into the 'false positive' category.
> > In which case I think Valgrind should set up an exception for
> > this warning on s390.
> 
> To be clear, I think nothing needs to be done now except file
> an upstream valgrind PR.

Yes please:
https://bugs.kde.org/enter_bug.cgi?product=valgrind&format=guided

This sounds a bit like https://bugs.kde.org/show_bug.cgi?id=308427 "s390
memcheck reports tsearch conditional jump or move depends on
uninitialized value". But that bug got fixed some time ago and should
not be in the latest version of valgrind. It does contain a nice
description of how best to report such an issue.

Just run under valgrind with --vgdb-error=0 and then attach with gdb,
through target remote | vgdb. Please include the disassembly output from
gdb around the code that produces the warning. And if possible use the
valgrind gdb monitor commands to figure out which bits valgrind thinks
are (un)defined.
http://valgrind.org/docs/manual/mc-manual.html#mc-manual.monitor-commands

Thanks,

Mark