Re: [PATCH v8 4/4] arm64: vdso32: Implement __vdso_futex_robust_try_unlock()

[Mark Rutland]

On Wed, Sep 16, 2026 at 10:11:01PM -0300, André Almeida wrote:
> Em 16/09/2026 11:28, Mark Rutland escreveu:
> > On Fri, Aug 21, 2026 at 06:50:45PM -0300, André Almeida wrote:
> > > Based on aarch64 implementation, provide a 32 bit entry point for
> > > this vDSO.
> > > 
> > > In order to keep compatibility with arm64_futex_robust_unlock_get_pop(),
> > > make sure to store the pop address at r2 and the compare result value
> > > at r3.
> > 
> > Before we add this to the compat vdso, we'll need to implement this on
> > arch/arm/.
> > 
> > Otherwise, my comments on the patch for the native vdso functions apply
> > here too.
> 
> Right, and the compat entry point at arch/arm64/ would point to the
> __vdso_futex_robust_list32_try_unlock implementation at arch/arm/?

So far we've had arm64 provide its own copy (which e.g. might use
sequences relying on ARMv8+ instructions), so I think we'd do the same
here.

The key thing is that 32-bit tasks on arm64 should see the same ABI as
native tasks on 32-bit arm. As there's a risk that 32-bit arm might have
some ABI quirks (e.g. due to older processors), we don't want to enable
features for compat tasks on arm64 before that's been implemented on
32-bit arm.

Mark.