[PATCH v2 4/4] dwarf2: store the RA state in CFI row

[Matthieu Longo]

On AArch64, the RA state informs the unwinder whether the return address
is mangled and how, or not. This information is encoded in a boolean in
the CFI row. This binary approach prevents from expressing more complex
configuration, as it is the case with PAuth_LR introduced in Armv9.5-A.

This patch addresses this limitation by replacing the boolean by an enum.

gcc/ChangeLog:

        * dwarf2cfi.cc
        (struct dw_cfi_row): Declare a new enum type to replace ra_mangled.
        (cfi_row_equal_p): Use ra_state instead of ra_mangled.
        (dwarf2out_frame_debug_cfa_negate_ra_state): Same.
        (change_cfi_row): Same.
---
 gcc/dwarf2cfi.cc | 24 ++++++++++++++++++------
 1 file changed, 18 insertions(+), 6 deletions(-)

diff --git a/gcc/dwarf2cfi.cc b/gcc/dwarf2cfi.cc
index f8d19d52429..1b94185a496 100644
--- a/gcc/dwarf2cfi.cc
+++ b/gcc/dwarf2cfi.cc
@@ -57,6 +57,15 @@ along with GCC; see the file COPYING3.  If not see
 #define DEFAULT_INCOMING_FRAME_SP_OFFSET INCOMING_FRAME_SP_OFFSET
 #endif
 
+
+/* Signing method used for return address authentication.
+   (AArch64 extension)  */
+typedef enum
+{
+  ra_no_signing = 0x0,
+  ra_signing_sp = 0x1,
+} ra_signing_method_t;
+
 /* A collected description of an entire row of the abstract CFI table.  */
 struct GTY(()) dw_cfi_row
 {
@@ -74,8 +83,8 @@ struct GTY(()) dw_cfi_row
   bool window_save;
 
   /* AArch64 extension for DW_CFA_AARCH64_negate_ra_state.
-     True if the return address is in a mangled state.  */
-  bool ra_mangled;
+     Enum which stores the return address state.  */
+  ra_signing_method_t ra_state;
 };
 
 /* The caller's ORIG_REG is saved in SAVED_IN_REG.  */
@@ -857,7 +866,7 @@ cfi_row_equal_p (dw_cfi_row *a, dw_cfi_row *b)
   if (a->window_save != b->window_save)
     return false;
 
-  if (a->ra_mangled != b->ra_mangled)
+  if (a->ra_state != b->ra_state)
     return false;
 
   return true;
@@ -1554,8 +1563,11 @@ dwarf2out_frame_debug_cfa_negate_ra_state (void)
 {
   dw_cfi_ref cfi = new_cfi ();
   cfi->dw_cfi_opc = DW_CFA_AARCH64_negate_ra_state;
+  cur_row->ra_state
+    = (cur_row->ra_state == ra_no_signing
+      ? ra_signing_sp
+      : ra_no_signing);
   add_cfi (cfi);
-  cur_row->ra_mangled = !cur_row->ra_mangled;
 }
 
 /* Record call frame debugging information for an expression EXPR,
@@ -2412,12 +2424,12 @@ change_cfi_row (dw_cfi_row *old_row, dw_cfi_row 
*new_row)
     {
       dw_cfi_ref cfi = new_cfi ();
 
-      gcc_assert (!old_row->ra_mangled && !new_row->ra_mangled);
+      gcc_assert (!old_row->ra_state && !new_row->ra_state);
       cfi->dw_cfi_opc = DW_CFA_GNU_window_save;
       add_cfi (cfi);
     }
 
-  if (old_row->ra_mangled != new_row->ra_mangled)
+  if (old_row->ra_state != new_row->ra_state)
     {
       dw_cfi_ref cfi = new_cfi ();
 
-- 
2.46.0