[PATCH 3/4] libdwfl, aarch64: Demangle return addresses using a PAC mask

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

Demangle mangled return addresses on AARCH64. The value of the masks is
stored in the struct Dwfl_Thread.

Signed-off-by: German Gomez <german.gomez@arm.com>
---
 libdwfl/dwfl_frame.c   |  3 +++
 libdwfl/frame_unwind.c | 14 +++++++++++++-
 libdwfl/libdwflP.h     |  7 +++++++
 3 files changed, 23 insertions(+), 1 deletion(-)

diff --git a/libdwfl/dwfl_frame.c b/libdwfl/dwfl_frame.c
index 77e0c5cb..88972d8e 100644
--- a/libdwfl/dwfl_frame.c
+++ b/libdwfl/dwfl_frame.c
@@ -270,6 +270,8 @@ dwfl_getthreads (Dwfl *dwfl, int (*callback) (Dwfl_Thread *thread, void *arg),
   thread.process = process;
   thread.unwound = NULL;
   thread.callbacks_arg = NULL;
+  thread.aarch64.pauth_insn_mask = 0;
+
   for (;;)
     {
       thread.tid = process->callbacks->next_thread (dwfl,
@@ -340,6 +342,7 @@ getthread (Dwfl *dwfl, pid_t tid,
       thread.process = process;
       thread.unwound = NULL;
       thread.callbacks_arg = NULL;
+      thread.aarch64.pauth_insn_mask = 0;
 
       if (process->callbacks->get_thread (dwfl, tid, process->callbacks_arg,
 					  &thread.callbacks_arg))
diff --git a/libdwfl/frame_unwind.c b/libdwfl/frame_unwind.c
index 9ac33833..839d1eff 100644
--- a/libdwfl/frame_unwind.c
+++ b/libdwfl/frame_unwind.c
@@ -610,7 +610,19 @@ handle_cfi (Dwfl_Frame *state, Dwarf_Addr pc, Dwarf_CFI *cfi, Dwarf_Addr bias)
 
       /* Some architectures encode some extra info in the return address.  */
       if (regno == frame->fde->cie->return_address_register)
-	regval &= ebl_func_addr_mask (ebl);
+	{
+	  regval &= ebl_func_addr_mask (ebl);
+
+	  /* In aarch64, pseudo-register RA_SIGN_STATE indicates whether the 
+	     return address needs demangling using the PAC mask from the
+	     thread. */
+	  if (cfi->e_machine == EM_AARCH64 &&
+	      frame->nregs > DW_AARCH64_RA_SIGN_STATE &&
+	      frame->regs[DW_AARCH64_RA_SIGN_STATE].value & 0x1)
+	    {
+	      regval &= ~(state->thread->aarch64.pauth_insn_mask);
+	    }
+	}
 
       /* This is another strange PPC[64] case.  There are two
 	 registers numbers that can represent the same DWARF return
diff --git a/libdwfl/libdwflP.h b/libdwfl/libdwflP.h
index 7503a627..d3fe8118 100644
--- a/libdwfl/libdwflP.h
+++ b/libdwfl/libdwflP.h
@@ -244,6 +244,12 @@ struct Dwfl_Thread
   /* Bottom (innermost) frame while we're initializing, NULL afterwards.  */
   Dwfl_Frame *unwound;
   void *callbacks_arg;
+
+  /* Data for handling AARCH64 (currently limited to demangling PAC from
+     return addresses). */
+  struct {
+    Dwarf_Addr pauth_insn_mask;
+  } aarch64;
 };
 
 /* See its typedef in libdwfl.h.  */
@@ -782,6 +788,7 @@ INTDECL (dwfl_thread_tid)
 INTDECL (dwfl_frame_thread)
 INTDECL (dwfl_thread_state_registers)
 INTDECL (dwfl_thread_state_register_pc)
+INTDECL (dwfl_thread_state_aarch64_pauth)
 INTDECL (dwfl_getthread_frames)
 INTDECL (dwfl_getthreads)
 INTDECL (dwfl_thread_getframes)
-- 
2.25.1