[Mesa-dev] [PATCH] egl/dri2: add a libname to dlopen for OpenBSD

[Jonathan Gray]

On Mon, Oct 17, 2016 at 12:39:11PM +0100, Emil Velikov wrote:
> On 17 October 2016 at 10:53, Eric Engestrom <eric.engestrom at imgtec.com> wrote:
> > On Sunday, 2016-10-16 16:38:35 +1100, Jonathan Gray wrote:
> >> On OpenBSD try to dlopen 'libglapi.so', ld.so will find
> >> the highest major/minor version and open it in this case.
> >>
> >> Avoids '#error Unknown glapi provider for this platform' at build time.
> >>
> >> Signed-off-by: Jonathan Gray <jsg at jsg.id.au>
> >
> > LGTM, and I guess the other *BSD will want the same since 7a9c92d0 broke
> > them too.
> >
> I'm not 100% sure about that. OpenBSD (unlike other BSD) did bump the
> major when the ABI breaks due to 'internal' changes - think of
> off_t/time_t on 32 vs 64bit systems and alike.
> 
> Unlike Linux kernel/distros, BSDs tend to be more relaxed when in
> comes to ABI, I believe. Don't quote me on that one ;-)

OpenBSD tends to favour simplified interfaces over backwards compatiblity
and is more like a research system in that respect.  As the kernel
and userland are one source tree ioctl compat largely doesn't exist.
System calls get deprecated and removed over the course of a few releases.
So we didn't go through the pain of duplicated systems calls for off_t
as mentioned, and don't go in for symbol versioning.  Just major.minor
library versioning, which is roughly symbol removals, major crank,
symbol additions minor crank.

I believe FreeBSD tends to go in for backwards compatibility more
but am not familiar with the details.  They also have a different ld.so.

Perhaps an else case for 'libglapi.so.0' would be appropriate for all
the other various unices instead of the #error ?

> 
> > Fixes: 7a9c92d071d010066349 ("egl/dri2: non-shared glapi cleanups")
> > Reviewed-by: Eric Engestrom <eric.engestrom at imgtec.com>
> >
> > Side note, I don't understand why we hardcode the version everywhere
> > (except Android). I can see it's been like that since that code was
> > added nearly 6 years ago (218381d9), but I couldn't find an explanation
> > in the logs, or any mention of it in the thread I found [1].
> > Emil, do you know?
> >
> The ABI must be stable. Since a) we (and linux distros in general)
> have the greater flexibility to "mix and match" components and b)
> glapi is/was used by xserver as well, the initial goal was that the
> ABI should not break, ever. See some the src/mapi changes by Brian
> Paul, which rework the nop calls due to different calling convention
> and stack corruption on Windows and the follow up fix to keep those
> Windows only and stable for everyone else
> be71bbfaa2ad201b570b56847a13328fc359d0ee.
> 
> Emil