[Wayland-bugs] [Bug 74689] SIGSEGV weston-desktop-shell when specified background image missing

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=74689

--- Comment #5 from Neil Roberts <neil at linux.intel.com> ---
I bumped into this issue when using Mesa master and had a dig around. I think
it is related to the following Mesa commit although that isn't on the 10.0
branch so I'm not sure if I have exactly the same issue.

http://cgit.freedesktop.org/mesa/mesa/commit/?id=11baad35088dfd4bdabc1710df650

weston-desktop-shell creates at least two surfaces, one for the panel and one
for the background. The panel surface gets painted first. When eglMakeCurrent
is called for that the context's viewport will not have been set up yet so it
will call intel_prepare_render on it as expected. After that it will try to
paint the background surface and call eglMakeCurrent on that. The context's
viewport will have already been configured at this point so it won't call
intel_prepare_render. One of the things that intel_prepare_render does is call
intel_update_renderbuffers which causes the size in the gl_framebuffer to be
filled in. As this isn't called for the background surface the framebuffer's
size remains at 0,0. If there is no background image then the only drawing
operation that is done on the background surface is a glClear. However,
_mesa_Clear bails out very early on if the size of the framebuffer is 0,0 so
the call to glClear does nothing. Eventually eglSwapBuffers will be called on
this surface but it still won't have a size. eglSwapBuffers ends up calling
get_back_bo to ensure there is a back buffer. The size in the dri2_egl_surface
is still -1,-1. intel_region_alloc doesn't cope with this and ends up crashing.

I'm not sure what the best thing to do it. Maybe we need to cause
intel_prepare_render to be called at the start of _mesa_Clear?

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