Xorg segmentation fault when drawing PolyArcs (under kicad)

Renato Caldas seventhguardian at gmail.com
Wed Oct 21 01:18:03 PDT 2009

2009/10/20 Renato Caldas <seventhguardian at gmail.com>:
> 2009/10/20 Renato Caldas <seventhguardian at gmail.com>:
>> Hello,
>> Thanks for looking into this!
>> 2009/10/20 Michel Dänzer <michel at daenzer.net>:
>>> On Mon, 2009-10-12 at 20:12 +0100, Renato Caldas wrote:
>>>> Hello,
>>>> First of all, I'm not subscribed to this list, so please include my
>>>> e-mail in the CC.
>>>> When using (trying to use...), kicad I managed to get consistent Xorg
>>>> segmentation faults. I've filed a bug report on fedora's bugzilla:
>>>> https://bugzilla.redhat.com/show_bug.cgi?id=528475. There I've
>>>> included a very basic test case that works all the time. In the
>>>> meantime, I've also got my hands dirty, and tried to debug Xorg using
>>>> gdb.
>>>> The symptom is that the function fbBltOne is called with src=0x0, so
>>>> Xorg segfaults as soon as it tries to use src (in LoadBits; at
>>>> fb/fbbltone.c:292).
>>>> I've traced its value back to fbPushPixels, where it is created and
>>>> fed to the function chain, in the macro fbGetStipDrawable (defined at
>>>> fb/fb.h:720).
>>>> Here pDrawable->type seems to be DRAWABLE_PIXMAP, so _pPix is simply
>>>> cast from pDrawable. Then the _pPix -> devPrivate.ptr is used as
>>>> "src", after a couple of castings and copying around.
>>> Please provide a full backtrace ('bt full' in gdb) from when the crash
>>> occurs.
>> Attached. I've also attached it to the bug report, just in case.
>>> If you're using EXA, the problem is most likely that some code path
>>> isn't calling exaPrepareAccess(Reg) for the pixmap in question before
>>> calling down to the fb module.

It seems that the code path is calling exaPrepareAccess:

in ExaCheckPolyArc:

exaPrepareAccess (pDrawable, EXA_PREPARE_DEST);
exaPrepareAccessGC (pGC);
pGC->ops->PolyArc (pDrawable, pGC, narcs, pArcs);

but there's possibly something wrong there.


>> I am using EXA. I'll try enabling XAA and report back.
> Nouveau doesn't support XAA, but I've disabled the acceleration. It
> doesn't crash anymore, so you must be correct :) I'll try to figure
> out a patch.
> Everything is slow now, but at least I can do some work. Thanks!
> Cheers,
>  Renato
>> Thanks,
>>  Renato

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