aarch64: Save/Restore PAC keys

[Keno]

Should fix #3568.

[Keno]

We'll look into getting a buildkite agent set up on an M1, so we can actually test this.

[Keno]

Seeing the following test failures on an M1 with this PR on Fedora Asahi Remix, so I think it's mostly working:

        1128 - vdso_clock_gettime_stack (Failed)
        1132 - vdso_time_stack (Failed)
        1230 - fork_exec_info_thr (Failed)
        1231 - fork_exec_info_thr-no-syscallbuf (Failed)
        1260 - record_replay (Failed)
        1261 - record_replay-no-syscallbuf (Failed)
        1266 - replay_serve_files (Failed)
        1267 - replay_serve_files-no-syscallbuf (Failed)
        1346 - vfork_done_clone (Failed)
        1347 - vfork_done_clone-no-syscallbuf (Failed)

[Keno]

I guess to fix record_replay, I should add ptrace emulation support for these regsets.

[GitMensch]

From the testing that Ben did rr replay chrashes without and works with this PR included - is there anything that needs to be done now or can this be pulled in and follow-up PRs be created for things that are considered to be missing?

[GitMensch]

Friendly ping @Keno to possibly merge as is (existing tests that failed before on aarch64 now pass) and add follow-up PRs if/as necessary.

[Keno]

I was hoping to get the M1 buildkite up, so we can actually test this. Let me follow up on that.

[BenWibking]

@Keno Just wanted to ping about this. Is the testing infrastructure in place for this now?

[pcc]

Ping; this also fixed my PAC issue.

Note that in addition to the keys themselves, we'll also need to save/restore the key enabled state, which is available via NT_ARM_PAC_ENABLED_KEYS.

[jvoisin]

Yup, fixing things here as well :)