[AArch64][Libunwind] Add Support for FEAT_PAuthLR DWARF Instruction (#112171)

As part of FEAT_PAuthLR, a new DWARF Frame Instruction was introduced,
`DW_CFA_AARCH64_negate_ra_state_with_pc`. This instructs Libunwind that
the PC has been used with the signing instruction. This change includes
three commits
- Libunwind support for the newly introduced DWARF Instruction
- CodeGen Support for the DWARF Instructions
- Reversing the changes made in #96377. Due to
`DW_CFA_AARCH64_negate_ra_state_with_pc`'s requirements to be placed
immediately after the signing instruction, this would mean the CFI
Instruction location was not consistent with the generated location when
not using FEAT_PAuthLR. The commit reverses the changes and makes the
location consistent across the different branch protection options.
While this does have a code size effect, this is a negligible one.

For the ABI information, see here:
https://github.com/ARM-software/abi-aa/blob/853286c7ab66048e4b819682ce17f567b77a0291/aadwarf64/aadwarf64.rst#id23

1 files changed, 4 insertions, 0 deletions

diff --git a/llvm/lib/MC/MCDwarf.cpp b/llvm/lib/MC/MCDwarf.cpp
index 8ff097f..e058358 100644
--- a/llvm/lib/MC/MCDwarf.cpp
+++ b/llvm/lib/MC/MCDwarf.cpp
@@ -1381,6 +1381,10 @@ void FrameEmitterImpl::emitCFIInstruction(const MCCFIInstruction &Instr) {
     Streamer.emitInt8(dwarf::DW_CFA_AARCH64_negate_ra_state);
     return;
 
+  case MCCFIInstruction::OpNegateRAStateWithPC:
+    Streamer.emitInt8(dwarf::DW_CFA_AARCH64_negate_ra_state_with_pc);
+    return;
+
   case MCCFIInstruction::OpUndefined: {
     unsigned Reg = Instr.getRegister();
     Streamer.emitInt8(dwarf::DW_CFA_undefined);