[llvm] [PAC][CodeGen][ELF][AArch64] Support signed GOT (PR #105798)

[Daniil Kovalev via llvm-commits]

kovdan01 wrote:

Comments regarding latest update:

1. For emitting check sequence after auth instruction when no FPAC, use `emitPtrauthCheckAuthenticatedValue` introduced in #110702. See 118e2fb4dd1504fda4732bf069dbfcdb0edff5aa

2. When handling extern weak symbols during `LOADgotAUTH` expansion, check the pointer against null before auth instruction (null pointer is not signed and should not be authenticated). See 9a5f1ef5a92507bc6760f81f93faa5938f78eba1

3. In `LOADgotAUTH` expansion, emit check sequence just like it is done before resign in `LOADgotPAC` expansion. Though `LOADgotAUTH` does not contain resign, we do not know how the authenticated pointer would be used in code later, so we should conservatively emit check sequence in `LOADgotAUTH` right after auth instruction. See 61bae48816e81d9f8adc4f5af0e290c047466c96



https://github.com/llvm/llvm-project/pull/105798