[PATCH 2/4] libdw, aarch64: Implement DW_CFA_AARCH64_negate_ra_state CFI instruction

[German Gomez <german.gomez@arm.com>]

Implement DW_CFA_AARCH64_negate_ra_state in accordance with the DWARF
AARCH64 ABI [1].

Followup commits will use the value of this register to remove the PAC
from return addresses.

[1] https://github.com/ARM-software/abi-aa/blob/main/aadwarf64/aadwarf64.rst#44call-frame-instructions

Signed-off-by: German Gomez <german.gomez@arm.com>
---
 libdw/cfi.c | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/libdw/cfi.c b/libdw/cfi.c
index a73fb03f..f985b4d8 100644
--- a/libdw/cfi.c
+++ b/libdw/cfi.c
@@ -125,6 +125,15 @@ execute_cfi (Dwarf_CFI *cache,
     fs->regs[regno].value = (r_value);			\
   } while (0)
 
+  /* The AARCH64 DWARF ABI states that register 34 (ra_sign_state) must
+     be initialized to 0. So do it before executing the CFI. */
+  if (cache->e_machine == EM_AARCH64)
+    {
+      if (unlikely (! enough_registers (DW_AARCH64_RA_SIGN_STATE, &fs, &result)))
+	goto out;
+      fs->regs[DW_AARCH64_RA_SIGN_STATE].value = 0;
+    }
+
   while (program < end)
     {
       uint8_t opcode = *program++;
@@ -355,7 +364,10 @@ execute_cfi (Dwarf_CFI *cache,
 	    {
 	      /* Toggles the return address state, indicating whether
 		 the return address is encrypted or not on
-		 aarch64. XXX not handled yet.  */
+		 aarch64. */
+	      if (unlikely (! enough_registers (DW_AARCH64_RA_SIGN_STATE, &fs, &result)))
+		goto out;
+	      fs->regs[DW_AARCH64_RA_SIGN_STATE].value ^= 0x1;
 	    }
 	  else
 	    {
-- 
2.25.1