Re: Don't understand valgrind output

[Thomas Stover <thomas wsinnovations com>]

> Date: Sun, 14 Oct 2007 10:24:14 -0400 (EDT)
> From: Allin Cottrell <cottrell wfu edu>
> Subject: Re: Don't understand valgrind output
> To: Michael Lamothe <michael lamothe gmail com>
> Cc: gtk-app-devel-list gnome org
> Message-ID:
>         <alpine LRH 0 9999 0710141020570 30351 ricardo ecn wfu edu>
> Content-Type: TEXT/PLAIN; charset=US-ASCII
>
> On Sat, 13 Oct 2007, Michael Lamothe wrote:
>
>   
> > I have been struggling with application freezes in my application for
> > about 2 months and I was hoping that I could get some help.  I've been
> > cleaning the application up with errors reported by valgrind but can't
> > seem to work out what this means.  Can anyone shed some light on this?
> >  Should I just ignore this memory error?
> >
> > ==13801== Syscall param write(buf) points to uninitialised byte(s)
> > ==13801==    at 0x40007F2: (within /lib/ld-2.5.so)
> > ==13801==    by 0x4B6D64E: _X11TransWrite (in /usr/lib/libX11.so.6.2.0)
> >     
>
> I don't think this has anything to do with your application as 
> such.  Valgrind is complaining about apparently uninitialized data 
> in regard to XOpenDisplay.  
>
> Allin Cottrell
>
>   
Yes this happens to me also. It is almost certainly not your 
application. Valgrind normally finds all sorts of errors that are 
effectively not really errors for one reason or another. Example: the C 
library not 100% free()ing something before exit. There is some sort of 
internal valgrind database that is used to suppress this stuff. This 
internal suppression does not always work due to subtleties like 
valgrind build time / application run time gcc/libc mismatches. For 
instance, on the latest 64bit ubuntu, there are dozens of such errors 
that I am not suppose to see, and so I just "know" that certain libc 
based errors can be ignored. Every time I valgrind a gtk app, I get all 
sorts of things like you are seeing with xlib and gtk libs. Whether or 
not these are real problems or ignorable, I don't know. They don't seem 
to cause any runtime issues though. I'm getting the impression that not 
many gtk people use valgrind, since perhapses these errors also could be 
added to the suppression database.

Btw: if your application truly is "freezing" and not crashing with a 
core dump, then you most likely are caught in an infinite loop, or have 
some blocking IO that is being incorrectly handled. Just look at the cpu 
usage of the app next time it freezes. That will be a dead give away 
about the loop.