Re: CVS commit: src/sys/arch/aarch64

[Ryo Shimizu <ryo%nerv.org@localhost>]

>> Has any consideration be given to perhaps creating a new MACHINE_ARCH for this, or somehow otherwise decorating the ELF files to indicate their exec-ability?
>
>I am under the impression that PAC was designed to be forewards
>compatible, so older CPUs can execute code with this annotation. I don't
>whether it works in practice though.

Yes. That's right.
Even binaries compiled with "gcc -msign-return-address=all" work fine on
ARMv8.0-v8.2 CPUs. This is because the "paciasp" and "autiasp" instructions are
treated as "nop" on ARMv8.0-v8.2 CPUs.

Therefore, I don't think it's necessary to add detailed attributes to the ELF
header.

So, even if we default the PAC option right now, we won't have any problems.
But we might as well enable PAC by default after real ARMv8.3 hardware becomes
available easily.
(now tested on "qemu-system-aarch64 -cpu max")

-- 
ryo shimizu