[llvm] [AArch64][PAC] Introduce AArch64::PAC pseudo instruction (PR #146488)

[Daniil Kovalev via llvm-commits]

https://github.com/kovdan01 approved this pull request.

This looks reasonable, thanks! I have no objections merging this.

A couple of thoughts regarding discussion about performance overhead. It would be very nice to have no overhead compared to current implementation, and it looks like that this could be achieved using an approach similar to #132857. But I agree with @atrosinenko that in most cases there is no overhead. So, we have the following points:

- this PR is beneficial for security;
- the performance overhead is not observed for the majority of the cases;
- we have this PR included in 21.x release milestone.

Given that, I think it's worth merging even w/o fixing the performance overhead. But, if we do so, it's definitely worth fixing that in a follow-up patch. My point is that security-affecting updates should be better merged sooner than later :)


https://github.com/llvm/llvm-project/pull/146488