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glDrawBuffer crashes in case of surfaceless context

Submitted by Volker Vogelhuber

Assigned to Default DRI bug account

Link to original bug (#102574)

Description

I've created a surfaceless OpenGL context using the EGL_KHR_surfaceless_context extension together with eglGetPlatformDisplay/EGL_PLATFORM_GBM_MESA. In this scenario there seem to be no valid default framebuffer which is Ok, as I'm normally only render to FBOs with textures bound. Due to an error on my side I called glDrawBuffer with GL_FRONT_LEFT while no FBO was bound.

This result in a crash in intel_buffers.c because in intelDrawBuffer() dri2InvalidateDrawable is called with a null pointer which is not checked in dri2InvalidateDrawable() or anywhere before.

While the root cause for triggering the error is on my side, I think it may be better to raise an error instead of crashing. So I propose to add a check to brw->driContext->driDrawablePriv within intelDrawBuffer. Probably if the driDrawablePriv is nullptr one should not call intel_prepare_render either.

Mesa 17.1 with Kernel 4.9.6 on Intel Apollo Lake GPU

Version: 17.1

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