Re: [Mesa3d-dev] Segmentation Fault in shade_rastpos

[Brian P. <br...@va...>]

Allen Barnett wrote:
> 
> Brian Paul wrote:
> >
> > Allen Barnett wrote:
> > >
> > > Hi,
> > >
> > > I'm getting a segmentation fault in the Mesa function shade_rastpos()
> > > when lighting is turned on and if no other drawing precedes a call to
> > > RasterPos2i(). Attached is a sample program which demonstrates the
> > > problem. I'm using Mesa 3.5.1 on RedHat 7.1/i386.
> >
> > Hmmm, your test program runs fine here.  Can you get a stack trace
> > with your debugger?
> 
> Sorry, I pressed the send button before I reverted the attached code to
> its failure mode in my original message. Did you test it with the quad
> drawing commented out as below?
> 
> > void display ( void )
> > {
> > #if 0
> >  glBegin( GL_QUADS );
> >  glVertex2i( 0, 0 );
> >  glVertex2i( 50, 0 );
> >  glVertex2i( 50, 50 );
> >  glVertex2i( 0, 50 );
> >  glEnd();
> > #endif
> >
> >  glRasterPos2i( 0, 0 );
> > }
> 
> The output from the debugger is below.

I've checked in a fix for this problem.  Here's the diff:

diff -r1.28 rastpos.c
133a134,136
>    if (!ctx->_ShineTable[0] || !ctx->_ShineTable[1])
>       _mesa_validate_all_lighting_tables( ctx );
> 


> And another question(s): How do you debug Mesa with GDB? I guess I don't
> understand how to get it to compile without optimization (a ./configure
> option?) and if I have to build and link with a static archive library
> instead of a shared object? Any tips would be helpful.

I always use the old-style Makefiles when debugging/developing.  Try this:

cd src
make -f Makefile.X11 clean
make -f Makefile.X11 linux-debug

When running with gdb and using a shared libGL.so, you can't set breakpoints
in the Mesa code until the program has begun executing.  To work around that,
first set a breakpoint in main(), then run.  When gdb stops in main() you
can then set breakpoints elsewhere in Mesa.

-Brian