[PATCH] Use 64-bit atomic on sem_t only with 8-byte alignment [BZ #33632]

[Andreas Schwab]

On Nov 16 2025, H.J. Lu wrote:

> commit 7fec8a5de6826ef9ae440238d698f0fe5a5fb372
> Author: Adhemerval Zanella <adhemerval.zanella@linaro.org>
> Date:   Thu Nov 13 14:26:08 2025 -0300
>
>     Revert __HAVE_64B_ATOMICS configure check
>
> uses 64-bit atomic operations on sem_t if 64-bit atomics are supported.
> But sem_t may be aligned to 32-bit on 32-bit architectures.  Add a macro,
> SEM_T_ALIGN, for sem_t alignment and use 64-bit atomic operations on sem_t
> only if 64-bit atomics are supported and SEM_T_ALIGN is at least 8-byte
> aligned.  This fixes BZ #33632.

It's not universally true that you need 8-byte alignment for 64-bit
atomic operation.

-- 
Andreas Schwab, schwab@linux-m68k.org
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