ABI Changes (was Re: Graphics Driver Frameworks and Security)

[Matthias Hopf]

Andy,

Egbert doesn't have internet connection ATM, that's why he's not really
responsive at the moment. I just phoned him and can tell his point of
view about your major concern:

On May 16, 06 23:00:56 -0700, Andy Ritger wrote:
>     - Field alignment within the DrawableRec data structure on 64-bit
>       platforms (bug 6924); this change was made as part of the
>       fix for bug 6438.  This change seems unfortunate, because A)
>       DrawableRec is so pervasive throughout the whole X server and
>       drivers, it is hard to abstract away the ABI differences,
>       B) bug 6438 really could have been fixed without changing
>       the ABI (DrawableRec could have been padded to retain the
>       same alignment after the fix), C) there seemed to be some
>       awareness that the change would alter the ABI, yet there was
>       no announcement or reving of the ABI version.
> 
>       It may be dangerously close to 7.1 release, but I would like
>       to suggest padding the DrawableRec data structure such that the
>       id field is still only 32-bits, as it is now (and therefore
>       still fixes bug 6438), but that the fields retain the same
>       alignment that they had previously.  Either Aaron Plattner
>       or I will provide a patch to bug 6924.

Egbert's point of view is (AFAIU) that in the long term the current solution is
the right one, removing as many #ifdefs as possible.

He doesn't have any issues with a temporary solution that uses 32 bits
always, as long as everything works not only for 32/64 bit but also for
both endianess.

But he also assures that there are more, similar issues, that have to be
addressed, so there *will* be some pain for binary only graphics
drivers, but these changes could well be combined in (hopefully) a
single ABI breakage. Still, the ABI is more likely to change nowadays
compared to former development cycles.

However, as 7.1 is pretty close, final judgment whether some patch will
go in or not before 7.1 is rolled can only be made by the release
manager.

CU

Matthias

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