Re: [PATCH] arm64: compat: Keep alignment address arithmetic 32-bit

[Arnd Bergmann]

On Tue, Aug 18, 2026, at 05:22, Karl Mehltretter wrote:
> On Mon, Aug 17, 2026 at 11:15:33AM +0100, Arnd Bergmann wrote:
<
> The 4 GiB wraparound case is possible with a rather unusual arm64
> kernel configuration, and correctly handling an individual word
> crossing the boundary would require byte accesses. That seems too
> contrived to justify the extra complexity here.

I don't understand, what is special about the configuration?
Isn't this exactly the case you were trying to address with
the compat_ptr() hack?

> Just to be sure by "both instances" do you mean the nr_regs
> declarations in both arch/arm64/kernel/compat_alignment.c and
> arch/arm/mm/alignment.c?

Yes

> Changing nr_regs in arm32 alignment.c would not change the generated
> code and I guess probably not be backported, so that would create a
> divergence with stable kernels.
>
> Would you prefer changing both files, or only the arm64 implementation?

I would suggest doing only a small change to arm64.

     Arnd