libsframe: update the semantics of sframe_fre_get_ra_offset

Until now, sframe_fre_get_ra_offset () would return
SFRAME_ERR_FREOFFSET_NOPRESENT if the ABI uses fixed RA offset (e.g.,
AMD64).  A stack tracer, then, will call an explicit
sframe_decoder_get_fixed_ra_offset () to get the RA offset.

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

Adjustments need to be made to ensure the textual dump remains the same
as preivous.  Currently, e.g., if RA is not being tracked per FRE,
following is seen with objdump --sframe:

    STARTPC         CFA       FP        RA
    000000000000NNNN  sp+X      u         u

This patch changes the behavior of sframe_fre_get_ra_offset: it turns an
error into non-error.  This change will be included with the next
release of libsframe, where all exposed symbols will be versioned for
the first time.

libsframe/
	* sframe.c (sframe_fre_get_ra_offset): Return the fixed offset,
	if applicable.  Else return the RA offset from the FRE.
	* sframe-dump.c (dump_sframe_func_with_fres): Make adjustments
	to keep the textual dump same as previous.

2 files changed, 17 insertions, 9 deletions

diff --git a/libsframe/sframe-dump.c b/libsframe/sframe-dump.c
index 6d26639..2491b43 100644
--- a/libsframe/sframe-dump.c
+++ b/libsframe/sframe-dump.c
@@ -164,11 +164,15 @@ dump_sframe_func_with_fres (sframe_decoder_ctx *sfd_ctx,
 	strcpy (temp, "u");
       printf ("%-10s", temp);
 
-      /* Dump RA info.  */
-      if (err[2] == 0)
-	sprintf (temp, "c%+d", ra_offset);
-      else
+      /* Dump RA info.
+	 If an ABI does not track RA offset, e.g., AMD64, display a 'u',
+	 else display the offset d as 'c+-d'.  */
+      if (sframe_decoder_get_fixed_ra_offset(sfd_ctx)
+	  != SFRAME_CFA_FIXED_RA_INVALID)
 	strcpy (temp, "u");
+      else if (err[2] == 0)
+	sprintf (temp, "c%+d", ra_offset);
+
       /* Mark SFrame FRE's RA information with "[s]" if the RA is mangled
 	 with signature bits.  */
       const char *ra_mangled_p_str
diff --git a/libsframe/sframe.c b/libsframe/sframe.c
index 8837f87..3d1b557 100644
--- a/libsframe/sframe.c
+++ b/libsframe/sframe.c
@@ -665,11 +665,15 @@ int32_t
 sframe_fre_get_ra_offset (sframe_decoder_ctx *dctx,
 			  sframe_frame_row_entry *fre, int *errp)
 {
-  sframe_header *dhp = sframe_decoder_get_header (dctx);
-  /* If the RA offset was not being tracked, return an error code so the caller
-     can gather the fixed RA offset from the SFrame header.  */
-  if (dhp->sfh_cfa_fixed_ra_offset != SFRAME_CFA_FIXED_RA_INVALID)
-    return sframe_set_errno (errp, SFRAME_ERR_FREOFFSET_NOPRESENT);
+  int8_t ra_offset = sframe_decoder_get_fixed_ra_offset (dctx);
+  /* If the RA offset was not being tracked, return the fixed RA offset
+     from the SFrame header.  */
+  if (ra_offset != SFRAME_CFA_FIXED_RA_INVALID)
+    {
+      if (errp)
+	*errp = 0;
+      return ra_offset;
+    }
 
   /* Otherwise, get the RA offset from the FRE.  */
   return sframe_get_fre_offset (fre, SFRAME_FRE_RA_OFFSET_IDX, errp);