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[1/2] libsframe: update the semantics of sframe_fre_get_ra_offset

Message ID 20230608044935.4183325-2-indu.bhagat@oracle.com
State Accepted
Headers
Series libsframe: changes to semantics of two existing APIs |

Checks

Context Check Description
snail/binutils-gdb-check success Github commit url

Commit Message

Indu Bhagat June 8, 2023, 4:49 a.m. UTC 
  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.

This patch changes the behavior of sframe_fre_get_ra_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 does
not require symbol versioning to accompany.

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

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.
---
 libsframe/sframe-dump.c | 12 ++++++++----
 libsframe/sframe.c      | 14 +++++++++-----
 2 files changed, 17 insertions(+), 9 deletions(-)
diff mbox series

Patch

diff --git a/libsframe/sframe-dump.c b/libsframe/sframe-dump.c
index 6d266392cd7..2491b4391f3 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 a5f4a7f6519..8d9d194a8a8 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);