[llvm] [llvm-exegesis][AArch64] Disable pauth and ldgm as unsupported instructions fixed (PR #136868)

[Peter Collingbourne via llvm-commits]

pcc wrote:

I'm guessing that the issue is that this change is disabling the IA key while a stack frame built with return PAC has a signed return address. The AUTIASP will act as a NOP and the RET instruction will branch to the signed address, causing the segfault observed in https://github.com/llvm/llvm-project/pull/136868#issuecomment-2852231883 . Also, if llvm-exegesis is run on a system that supports PAuth ABI, this prctl will lead to a crash on the next indirect or virtual call.

PR_PAC_SET_ENABLED_KEYS isn't really meant to be used by normal user applications, so I'm not sure if there's a good way to make this work. Maybe you could prevent llvm-exegesis from generating AUT instructions for now?

https://github.com/llvm/llvm-project/pull/136868