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

[Florian Weimer]

* 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'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.

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

Thanks,
Florian