[PATCH v4 15/15] gas: Validate SFrame RA tracking and fixed RA offset

[Jens Remus]

Verify all architectures participating in SFrame generation do define
the mandatory SFrame return address (RA) tracking predicate function
sframe_ra_tracking_p. Do so by explicitly not testing for the macro
SFRAME_FRE_RA_TRACKING as otherwise required.

Verify that architectures not using SFrame RA tracking specify a valid
fixed RA offset.

gas/
	* gen-sframe.c (output_sframe_internal): Validate SFrame
	RA tracking and fixed RA offset.

Suggested-by: Indu Bhagat <indu.bhagat@oracle.com>
Signed-off-by: Jens Remus <jremus@linux.ibm.com>
---

Notes (jremus):
    Changes v3 -> v4:
    - Implement review feedback and suggestions from Indu.
    
    Changes v2 -> v3:
    - New patch.
    
    This could be made dependent on ENABLE_CHECKING (configure option
    --enable-checking).

 gas/gen-sframe.c | 14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/gas/gen-sframe.c b/gas/gen-sframe.c
index f83a64518c28..626dc33b71dc 100644
--- a/gas/gen-sframe.c
+++ b/gas/gen-sframe.c
@@ -667,12 +667,16 @@ output_sframe_internal (void)
      -fno-omit-frame-pointer is used.  */
   out_one (fixed_fp_offset);
 
-  /* Offset for the return address from CFA is fixed for some ABIs
-     (e.g., AMD64), output a SFRAME_CFA_FIXED_RA_INVALID otherwise.  */
-#ifdef sframe_ra_tracking_p
+  /* All ABIs participating in SFrame generation must define
+     sframe_ra_tracking_p.
+     When RA tracking (in FREs) is not needed (e.g., AMD64), SFrame assumes
+     the RA is going to be at a fixed offset from CFA.  Check that the fixed RA
+     offset is appropriately defined in all cases.  */
   if (!sframe_ra_tracking_p ())
-    fixed_ra_offset = sframe_cfa_ra_offset ();
-#endif
+    {
+      fixed_ra_offset = sframe_cfa_ra_offset ();
+      gas_assert (fixed_ra_offset != SFRAME_CFA_FIXED_RA_INVALID);
+    }
   out_one (fixed_ra_offset);
 
   /* None of the AMD64, or AARCH64 ABIs need the auxiliary header.
-- 
2.40.1