[PATCH v2] AArch64: Cleanup PAC and BTI

[Wilco Dijkstra]

Hi Matthieu,

> I am not opposing this change but please, could you explain why we are
> doing this ?
> Is it because the minimum requirements to build glibc were increased to
> a newer version of binutils ?

Correct - I'll make this clearer in v3.

> Sorry to ask you to go beyond the original scope of this patch. Please
> could you fix this and use the AArch64 CFI directive instead of the
> SPARC one ? Feel free to do it in a separate patch.

Sure, that is easy to add.

> I noticed that the CFI instructions are not starting with a dot.
> I didn't know that it was supported. Any reason for preferring this ?

All cfi directives are #defines so they can be compiled out or adapted to
support different unwind directives.

> @@ -75,11 +75,7 @@ call_weak_fn:
>        .hidden _init
>        .type   _init, %function
>   _init:
> -#if HAVE_AARCH64_PAC_RET
> -     PACIASP
> -#else
> -     BTI_C
> -#endif
> +     paciasp

> Any reason for not adding the CFI along the signing ?

These are code fragments that combined by the linker to create the init and fini functions,
so there is no easy way to use unwind directives in a way that works.

Cheers,
Wilco