Created attachment 28886 [details]
test case

If for instance,
       glBegin(GL_LINES);
       glEnd();
is repeated (64 times here) mesa will crash with

Program received signal SIGFPE, Arithmetic exception.
0x0109d5a0 in vbo_exec_vtx_flush (exec=0x809fc98, unmap=0 '\0')

because exec->vtx.vertex_size = 0 and we get a division by zero. Not that this is a useful construct, but it happens in some programs and did not crash before. http://www.opengl.org/documentation/specs/man_pages/hardcopy/GL/html/gl/begin.html says "Lines, triangles,	quadrilaterals,	and polygons that	are incompletely specified are not drawn."

The attached test program demonstrates the crash (it is based on the example in http://glprogramming.com/red/chapter01.html :) )