Re: [PATCH v1 2/2] rseq: slice ext: Ensure rseq feature size differs from original rseq size

[Mathieu Desnoyers <mathieu.desnoyers@efficios.com>]

On 2026-02-18 11:52, Mathieu Desnoyers wrote:
[...]
> 
> The effect of this change is to increase the size and alignment of
> the rseq area from 32 to 64 bytes before we actually have fields using
> that memory.
> 
[...]
> -} __attribute__((aligned(4 * sizeof(__u64))));
> +} __attribute__((aligned(8 * sizeof(__u64))));

Actually bumping the alignment from 32 to 64 is not correct here,
because the kernel still has to deal with legacy userspace which
align struct rseq on 32 bytes only.

What I can do instead is change the value returned by
getauxval(AT_RSEQ_ALIGN) from 32 to 64, thus requesting
that newer userspace align its allocation on 64-byte.

I'll prepare an updated patch series.

Thanks,

Mathieu

-- 
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com