Horton

Re: Invalid control file checksum with AVX-512 during initdb on a clang19 -O0 build

John Naylor <johncnaylorls@gmail.com>

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From: John Naylor <johncnaylorls@gmail.com>
To: Nathan Bossart <nathandbossart@gmail.com>
Cc: Soumyadeep Chakraborty <soumyadeep2007@gmail.com>, PostgreSQL mailing lists <pgsql-bugs@lists.postgresql.org>
Date: 2025-06-12T06:57:01Z
Lists: pgsql-bugs

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Workaround code generation bug in clang

  2. Don't reduce output request size on non-Unix-socket connections.

Attachments

On Thu, Jun 12, 2025 at 4:42 AM Nathan Bossart <nathandbossart@gmail.com> wrote:
>
> (I've CC'd the committer of the feature.)
>
> On Wed, Jun 11, 2025 at 11:10:31AM -0700, Soumyadeep Chakraborty wrote:
> > Note that this only reproduces with clang-19 -O0 and NOT -O3. I haven't
> > tried with other versions of clang.
> >
> > OTOH, gcc-14 is cool with both -O0 and -O3, with AVX-512 getting picked
> > for both cases, for CRC instructions.
>
> I'm wondering if there's anything else this could be besides a compiler
> bug.  It's interesting that -O0 is the broken case.  Have you tried looking
> for differences in the assembly code?

Hmm, clang at -O0 is the same in versions 18, 19, and 20. The change
from v17 is easy enough to workaround as in the attached, which
produces identical output as master at -O2. Does this fix it for you?
If that's not it, it may be more difficult, as the change at -O0 from
v16 to v17 is large, so it's hard to see what's going on.

-- 
John Naylor
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