[opensource-dev] Debugging Snowstorm under Linux x64 with GDB locks the whole X session

Aleric Inglewood aleric.inglewood at gmail.com
Wed Dec 29 10:19:33 PST 2010


Hi NickyP,

yes, this is a "known" problem: the viewer sometimes locks the X display,
if then you halt it in the debugger you're toast.

I worked around this by running the debugger from different X display.
That can be a second X running on the same PC (ie second video card)
or just another PC with it's own videocard and X server.

Assuming the latter, you'd open an xterm on the second PC,
login (using ssh for example) to the PC running the viewer and
then setting DISPLAY to the display of the PC running the viewer
of course ;) (ie: export DISPLAY=hikaru:0.0, where hikaru is the
name of my PC running the viewer). Then start gdb as usual.

For this to work however, you must configure X to allow connections
from that other PC. In order to test if that part works I'd first try
running xterm instead of gdb+viewer ;). You probably need to
change a configuration on the gdm login screen (sorry I forgot)
to get X to listen on port 6000 at ALL (check with netstat) and
then you need to give your other PC access by running xhost).

On Wed, Dec 29, 2010 at 5:51 PM, Nicky D. <sl.nicky.ml at googlemail.com> wrote:
> Hello,
>
> did anyone ever have the following problem? I start snowstorm directly
> under gdb, run it. Then after a while (mostly after SL login) my
> machine GUI locks up.
>
> I cannot use any X programs anymore, if I run mplayer it will stop
> playing music. Neither can I kill the X server or switch session. But
> I can ssh into the
> machine. There I see the snowstorm binary taking all CPU time. Once I
> kill snowstorm and gdb via this ssh login everything will be good
> again.
>
> I get a hunch that this has to do with the threads snowstorm creates.
> As the last thing I usually see in the gdb output is a line 'Thread
> .... created'. Of course
> this could be a coincidence.
>
> This is a very annoying issue, as it makes debugging Snowstorm
> (actually it seems to affect all V2 based viewers) nearly impossible.
>
> The GDB version I use is 'GNU gdb (Gentoo 7.2 p1) 7.2'. Kernel is
> 2.6.36-gentoo-r3. Snowstorm is synced to the latest changes.
>
> For snowstorm and kernel I already tried different versions. It did
> not help at all. I even tried Phoenix-Firestorm, same result.
>
> Has anyone ever seen something like this, or got a slight idea what I might try?
> Can the threads in snowstorm be temporarily disabled to make sure they
> are either causing or not causing this?
>
> Cheers,
>   Nicky
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