[Bug 765713] compositor: Crashes on Windows with ORC when doing pixel-aspect-ratio conversion

[GStreamer (GNOME Bugzilla)]

https://bugzilla.gnome.org/show_bug.cgi?id=765713

Sebastian Dröge (slomo) <slomo at coaxion.net> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
                 CC|                            |ds at schleef.org
          Component|gst-plugins-bad             |orc
         Resolution|---                         |FIXED

--- Comment #1 from Sebastian Dröge (slomo) <slomo at coaxion.net> ---
commit bec7ebea1935c112f5b4b30fc3c47626ac99c940
Author: Sebastian Dröge <sebastian at centricular.com>
Date:   Wed Aug 24 19:11:18 2016 +0300

    orcx86: Fix generation of ModR/M / SIB bytes for the EBP, R12, R13
registers

    See http://wiki.osdev.org/X86-64_Instruction_Encoding#ModR.2FM

    ESP and R12 are to be handled exactly the same, that is the addressing is
    done with SIB instead of directly.

    EBP and R13 have a special case for Mod 00, where they're expecting RIP/EIP
    plus 32 bit displacement. If we handle them like all other registers, we
would
    instead of addressing offset 0, address something relative to the
instruction
    pointer and make part of the following instruction the 32 bit displacement.

    Instead of using Mod 00 for offset 0 like for all other registers, we use
Mod
    01 and a 8 bit displacement of 0.

    On Windows this rather low-level bug caused problems at a rather
    high-level in the ORC video conversion code, where a movdqu was eating the
    following paddw instruction and tried to load data from a rather random
memory
    location.

    For whatever reason this didn't cause any other big problems in other ORC
    generated code, and it also only seemed to have caused problems on Windows.

    https://bugzilla.gnome.org/show_bug.cgi?id=765713

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