[PATCH 2/2] libsframe: update the semantics of sframe_fre_get_fp_offset

[Indu Bhagat <indu.bhagat@oracle.com>]

Until now, sframe_fre_get_fp_offset () would return
SFRAME_ERR_FREOFFSET_NOPRESENT if the ABI uses fixed FP offset.  A stack
tracer, then, would call an explicit sframe_decoder_get_fixed_fp_offset ()
to get the FP offset.

On second look, it appears to make sense to hide these details of
whether the FP offset is fixed or not in an ABI from the consumer.  Now,
with the changed semantics, the call to sframe_fre_get_fp_offset () will
fetch the fixed FP offset if applicable, or get the FP offset from FRE
when there is no fixed FP offset.

This patch changes the behavior of sframe_fre_get_fp_offset (): it turns
an error into non-error.  This change is deemed a compatible ABI change,
because it should not break consumers unless they were relying on the
error; the latter seems unlikely.  Hence, this change of semantics of
the API does not require symbol versioning to accompany.

libsframe/
	* sframe.c (sframe_fre_get_fp_offset): Return the fixed offset, if
	applicable. Else return the FP offset from the FRE.
---
 libsframe/sframe.c | 17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/libsframe/sframe.c b/libsframe/sframe.c
index 8d9d194a8a8..ba70bba294f 100644
--- a/libsframe/sframe.c
+++ b/libsframe/sframe.c
@@ -644,16 +644,21 @@ sframe_fre_get_fp_offset (sframe_decoder_ctx *dctx,
 			  sframe_frame_row_entry *fre, int *errp)
 {
   uint32_t fp_offset_idx = 0;
-  sframe_header *dhp = sframe_decoder_get_header (dctx);
-  /* If the FP offset is not being tracked, return an error code so the caller
-     can gather the fixed FP offset from the SFrame header.  */
-  if (dhp->sfh_cfa_fixed_fp_offset != SFRAME_CFA_FIXED_FP_INVALID)
-    return sframe_set_errno (errp, SFRAME_ERR_FREOFFSET_NOPRESENT);
+  int8_t fp_offset = sframe_decoder_get_fixed_fp_offset (dctx);
+  /* If the FP offset is not being tracked, return the fixed FP offset
+     from the SFrame header.  */
+  if (fp_offset != SFRAME_CFA_FIXED_FP_INVALID)
+    {
+      if (errp)
+	*errp = 0;
+      return fp_offset;
+    }
 
   /* In some ABIs, the stack offset to recover RA (using the CFA) from is
      fixed (like AMD64).  In such cases, the stack offset to recover FP will
      appear at the second index.  */
-  fp_offset_idx = ((dhp->sfh_cfa_fixed_ra_offset != SFRAME_CFA_FIXED_RA_INVALID)
+  fp_offset_idx = ((sframe_decoder_get_fixed_ra_offset (dctx)
+		    != SFRAME_CFA_FIXED_RA_INVALID)
 		   ? SFRAME_FRE_RA_OFFSET_IDX
 		   : SFRAME_FRE_FP_OFFSET_IDX);
   return sframe_get_fre_offset (fre, fp_offset_idx, errp);
-- 
2.39.2