[Mesa-dev] VTK Offscreen Segfaults

tom fogal tfogal at sci.utah.edu
Thu Aug 5 16:07:07 PDT 2010

Brian Paul <brianp at vmware.com> writes:
> My other hunch is something is duplicated in the libOSMesa and libGL
> libraries that's causing things to blow up in general.

This is a good hunch.

I don't know how closely you've been following the thread, Brian, but
previously I brought up how it was important that link lines were:

  -lOSMesa -lGL

instead of:

  -lGL -lOSMesa

(where "GL" is Mesa's libGL")

With VisIt (which uses VTK), we found that we would get either blank
windows or crashes if we neglected to do this.  My /hunch/ (I never got
around to verifying) was that there is internal state in the libraries
which has the same symbol names, and since the symbols are stuffed into
a flat namespace, that's asking for trouble (both VisIt and VTK will
fiddle w/ OpeGL state).  Also, everything worked beautifully on OS X
w/o the above link line hack (Macs have a two-level symbol namespace,
at least by default).



also corroborates the `things are visible which shouldn't be' theory,
though it's a different issue than the blank window/crash, above.

Do note that both of these issues are from the pre-"-fvisibility=hidden
by default" days, which I was hoping/thinking would fix
things... haven't looked into it though.  It was also
previous to Dan's recent 'change how libOSMesa is linked' fix
(cbf30fce322506bd43692617de9d201533f41532)... but that commit is also
required to fix a Mac linking issue, so I wouldn't advocate throwing it
away for 7.8.


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