Re: [RFC PATCH] futex: Introduce __vdso_robust_futex_unlock

[André Almeida]

Em 12/03/2026 15:40, Mathieu Desnoyers escreveu:
> On 2026-03-12 10:04, Mathieu Desnoyers wrote:
> > On 2026-03-12 09:46, André Almeida wrote:
> [...]
> > > First because we have FUTEX2_SIZE's, so uaddr could have different 
> > > size here.
>
> The robust futex ABI defines:
>
> #define FUTEX_OWNER_DIED        0x40000000
> #define FUTEX_WAITERS           0x80000000
>
> So how can a robust futex use a uaddr smaller than 32-bit ?
>
> And if the uaddr is 64-bit, I would expect those two values
> to be bits 63 and 62 (indexed from 0), but this contradicts
> the defines.
>
> What am I missing ?

Oh, I didn't realized that. So, for the current API, robust mutexes need 
to be 32bit integers. If everyone agrees on that, we can document this 
and let it be.

In the future we could something like FUTEX_OWNER_DIED_U64 and 
FUTEX_WAITERS_U64 to make it work correctly. But right now, robust 
futexes can only work with u32.