Horton

Re: Detection of hadware feature => please do not use signal

Tom Lane <tgl@sss.pgh.pa.us>

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Thomas Munro <thomas.munro@gmail.com>
Cc: Heikki Linnakangas <hlinnaka@iki.fi>, Bastien Roucariès <rouca@debian.org>, pgsql-bugs@lists.postgresql.org
Date: 2024-11-25T15:41:37Z
Lists: pgsql-bugs 
I wrote:
> I also confirmed that our existing code works on Fedora 30 armv7l
> (also hard-float) with gcc 9.3.1.  That's the only other ARM32
> image I have at hand :-(

> So yeah, it would seem they broke it between 10.2.1 and 10.5.0.

After discussion with the gcc folk (see bug report linked upthread)
it emerges that there was indeed a change somewhere in that time
frame.  It used to be that if the platform defaults were
"-march=A -mfpu=X" then writing "-march=B" on the command line
would still leave you with "-mfpu=X", possibly a nonsensical
combination.  So now they ignore any build-time default, with
the effect that writing just "-march=armv8-a+crc" selects soft
float, which fails on platforms that require hard-float ABI.
(I didn't ask whether this was the same change prompted by the
other bug report you found, but perhaps it was.)

Also, there's no +fp option for "-march=armv8-a" because the
ARMv8 specs require chips to implement both or neither of FP
and SIMD.  So the idiomatic thing for us to write is not a
separate -mfpu spec but "-march=armv8-a+crc+simd".  I'll
adjust my patch to do it like that and push later today.

			regards, tom lane

Commits

  1. Update configure probes for CFLAGS needed for ARM CRC instructions.

  2. Support runtime CRC feature probing on NetBSD/ARM using sysctl().

  3. Use auxv to check for CRC32 instructions on ARM.

  4. Improve our method for probing the availability of ARM CRC instructions.