[PATCH v7 1/2] x86-64: Save APX registers in ld.so trampoline

[H.J. Lu]

On Fri, Feb 16, 2024 at 3:51 AM Florian Weimer <fweimer@redhat.com> wrote:
>
> * Noah Goldstein:
>
> >> +/* Save SSE, AVX, AVX512, mask, bound and APX registers.  Bound and APX
> >> +   registers are mutually exclusive.  */
> >> +# define STATE_SAVE_MASK               \
> >> +  ((1 << X86_XSTATE_SSE_ID)            \
> >> +   | (1 << X86_XSTATE_AVX_ID)          \
> >> +   | (1 << X86_XSTATE_BNDREGS_ID)      \
> >> +   | (1 << X86_XSTATE_K_ID)            \
> >> +   | (1 << X86_XSTATE_ZMM_H_ID)        \
> >> +   | (1 << X86_XSTATE_ZMM_ID)          \
> >> +   | (1 << X86_XSTATE_APX_F_ID))
>
> > Need tile here?
>
> We can't save the AMX state because it's too big and will overflow
> existing stacks.  This change is immediately active on systems with AMX,
> even for old applications which do not know about AMX at all.
>
>

Another problem is that AMX is enabled by a syscall.  When ld.so checks
the xsave mask, AMX state may not be active at the time.

-- 
H.J.