[Mesa-dev] [Bug 99781] Some Unity games fail assertion on startup in glXCreateContextAttribsARB

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=99781

--- Comment #12 from Uli Schlachter <psychon at znc.in> ---
I took a look at this and I would guess that the bug is in mesa. However, I do
not want to built mesa myself and thus I will not test my theory.

The function __glXSendError() in mesa's src/glx/glx_error.c invents an X11
protocol error out of thin air. For the sequence number it uses dpy->request.
This is the sequence number of the last request that was sent. _XError() will
then update dpy->last_request_read based on the sequence number of the error
that just "came in".

If now another something comes in with a sequence number less than
dpy->last_request_read, since sequence numbers are monotonically increasing,
widen() will incorrectly add 1<<32 to the sequence number and things might go
downhill afterwards.

At least that's my theory. If my theory is right, changing mesa's
__glXSendError() to use dpy->last_request_read instead of dpy->request should
fix things.

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