Re: vectorized CRC on ARM64

On Thu, Apr 02, 2026 at 10:53:24AM -0500, Nathan Bossart wrote:
> I think the new pg_comp_crc32_choose() is infinitely recursing on macOS
> because USE_ARMV8_CRC32C_WITH_RUNTIME_CHECK is not defined but
> pg_crc32c_armv8_available() returns false.  If I trace through that
> function, I see that it's going straight to the
> 
>     #else
>         return false;
>     #endif
> 
> at the end.  And sure enough, both HAVE_ELF_AUX_INFO and HAVE_GETAUXVAL
> aren't defined in pg_config.h.  I think we might need to use sysctlbyname()
> to determine PMULL support on macOS, but at this stage of the development
> cycle, I would probably lean towards just compiling in the sb8
> implementation.

Hm.  On second thought, that probably regresses macOS builds because it was
presumably using the armv8 path without runtime checks before...

-- 
nathan