Re: Include ppc64le build type for back branches

Robert Haas <robertmhaas@gmail.com> writes:
> I don't really want to get into an argument about this, but is the
> reason we haven't updated config.guess and config.sub in the past that
> it presents an actual stability risk, or just that nobody's asked
> before?  Because the first one is a good reason not to do it now, but
> the second one isn't.

Well, I see at least one case in the git history where we explicitly
declined to update config.guess/config.sub:

Author: Tom Lane <tgl@sss.pgh.pa.us>
Branch: master Release: REL9_3_BR [5c7603c31] 2013-06-04 15:42:02 -0400
Branch: REL9_2_STABLE Release: REL9_2_5 [612ecf311] 2013-06-04 15:42:21 -0400

    Add ARM64 (aarch64) support to s_lock.h.

    Use the same gcc atomic functions as we do on newer ARM chips.
    (Basically this is a copy and paste of the __arm__ code block,
    but omitting the SWPB option since that definitely won't work.)

    Back-patch to 9.2.  The patch would work further back, but we'd also
    need to update config.guess/config.sub in older branches to make them
    build out-of-the-box, and there hasn't been demand for it.

    Mark Salter


More generally, I think "does updating config.guess, in itself, pose
a stability risk" is a false statement of the issue.  The real issue is
do we want to start supporting a new platform in 9.1-9.3; that is, IMO
if we accept this request then we are buying into doing *whatever is
needed* to support ppc64le on those branches.  Maybe that will stop with
config.guess/config.sub, or maybe it won't.

Setting this precedent will also make it quite hard to reject future
requests to back-patch support for other new platforms.

I'm not planning to go to war about this issue either.  But I do think
there's a slippery-slope hazard here, and we should be prepared for
the logical consequences of accepting such a request.  Or if we're
going to have a policy allowing this request but not every such request,
somebody had better enunciate what that policy is.

                        regards, tom lane

(BTW, so far as direct stability hazards go, I would guess that the
key question is how much version skew can be tolerated between autoconf
and config.guess/config.sub. I have no idea about that; Peter E. might.
But I do note that pre-9.4 branches use an older autoconf version.)