[PATCH v5 1/2] x86-64: Save APX and Tile registers in ld.so trampoline

[H.J. Lu]

On Thu, Feb 15, 2024 at 1:39 PM Florian Weimer <fweimer@redhat.com> wrote:
>
> * Florian Weimer:
>
> > * H. J. Lu:
> >
> >> Add APX registers to STATE_SAVE_MASK so that APX and Tile registers are
> >> saved in ld.so trampoline.  This fixes BZ #31371.
> >
> > First APX is confusing?

What do you suggest?

> >
> > What's the impact on xsave_state_size and xsave_state_full_size?
> > I'm worried that the loader trampoline now overflows small stacks.
> > We used to have such problems in the past.
>
> It adds 8,256 bytes on one AMX-capable machine.  This will impact
> compatibility with existing software.  Stack usage is increased even if
> the application does not use AMX at all.

Also AMX may be enabled much later.

> I suggest to use a mechanism like STO_AARCH64_VARIANT_PCS to deal with
> AMX, and only add the APX flag for now.
>

I will drop Tile registers.


-- 
H.J.