Re: Bug fix for glibc broke freebsd build in REL_11_STABLE

From: Andres Freund <andres(at)anarazel(dot)de>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Peter Eisentraut <peter(dot)eisentraut(at)2ndquadrant(dot)com>, Andrew Gierth <andrew(at)tao11(dot)riddles(dot)org(dot)uk>, Victor Wagner <vitus(at)wagner(dot)pp(dot)ru>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>
Subject: Re: Bug fix for glibc broke freebsd build in REL_11_STABLE
Date: 2018-09-05 18:15:49
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On 2018-09-05 14:08:11 -0400, Tom Lane wrote:
> Andres Freund <andres(at)anarazel(dot)de> writes:
> > On 2018-09-05 10:05:26 -0400, Tom Lane wrote:
> >> One thought is that maybe we should provide a way to override this,
> >> in case somebody really can't or doesn't want to use -msse2, and
> >> is willing to put up with platform-dependent float behavior.
> > IDK, people that are capable of making that decision can just hack
> > configure.
> "Just hacking configure" is a pretty high bar for most folk.

Sure. But being able to accurately judge whether you're ok that math
behaviour doesn't work as documented seems like a high bar too. And
this'd only be relevant if they insist on using clang rather than gcc.

> If you wanted to argue that the set of people who still want to run PG
> on pre-SSE2 hardware is the empty set, that'd be an easier sell
> really.

I think it's an empty set, yea, especially with clang.

> But what I'm really concerned about here, given that we're apparently
> talking about an ABI change, is that someone might want to run on a
> platform where the libraries insist on the x87 way.
> I'm actually a bit surprised to hear that you can just randomly add
> -msse2 on BSDen. Do they ship separate copies of libc et al to make
> that work?

I don't think we're talking about an ABI change - with -msse2 the
calling conventions are unchanged, the stuff just gets moved out of the
x87 registers into SSE ones / xmm for the actual math. Which in turn
solves our "80bit register" problem. There really shouldn't be any need
for libc6 itself to care.


Andres Freund

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