Re: BUG #15844: MIPS: remove .set mips2 in s_lock.h to fix r6 build

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: wzssyqa(at)gmail(dot)com
Cc: pgsql-bugs(at)lists(dot)postgresql(dot)org
Subject: Re: BUG #15844: MIPS: remove .set mips2 in s_lock.h to fix r6 build
Date: 2019-06-13 14:07:15
Message-ID: 7749.1560434835@sss.pgh.pa.us
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PG Bug reporting form <noreply(at)postgresql(dot)org> writes:
> MIPS r6 changes the encoding of LL/SC instruction,
> while the .set mips2 will force assembler to generate
> old encoding.
> This patch can fix this problem.

So I have a bunch of questions about this patch.

1. What problem is this actually solving? We have what I think are
reasonably modern MIPS machines in the buildfarm (frogfish,
topminnow) and they aren't complaining.

2. What toolchains define __mips_isa_rev at all? Seems like we could
be trading one portability issue for another one.

3. If we actually need something here, don't we need a run-time probe
rather than a compile-time check? Distro packagers, for example,
can't assume that their packages will be run on exactly the hardware
they build on.

regards, tom lane

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