[PATCH v4 1/4] gas: ld: libsframe: Support for SFrame FDEs without any FREs

[Jens Remus]

Allow SFrame sections without any FREs, that can occur if they solely
contain FDEs without any FREs.  For FDEs without and FREs set the
offset to the first FRE to zero.

libsframe/
	* sframe.c (sframe_encoder_write_sframe): Allow SFrame sections
	without any FREs.  For FDEs without any FREs set the offset to
	the first FRE to zero.

gas/
	* gen-sframe.c (output_sframe_funcdesc): For FDEs without any
	FREs set the offset to the first FRE to zero.

Signed-off-by: Jens Remus <jremus@linux.ibm.com>
---

Notes (jremus):
    Changes in V4:
    - Use ehp->sfh_num_fres instead of adding a new API to get the total
      number of FREs. (Indu)
    - Squash related assembler change from V3.
    - Reword commit subject and message.
    
    Changes in V3:
    - New patch.
    
    This patch is strictly no longer required.  Posting again to keep a
    copy for future reference, even if we decide not to make this change
    now.  For the time being we might prefer to error out in the linker
    when running into SFrame FDEs without any FREs.

 gas/gen-sframe.c   | 18 ++++++++++++------
 libsframe/sframe.c |  9 ++++++++-
 2 files changed, 20 insertions(+), 7 deletions(-)

diff --git a/gas/gen-sframe.c b/gas/gen-sframe.c
index d082b974be3f..acea1dc7dbb7 100644
--- a/gas/gen-sframe.c
+++ b/gas/gen-sframe.c
@@ -651,12 +651,18 @@ output_sframe_funcdesc (symbolS *start_of_fre_section,
 				  sfde_func_size));
 
   /* Offset to the first frame row entry.  */
-  exp.X_op = O_subtract;
-  exp.X_add_symbol = fre_symbol; /* Minuend.  */
-  exp.X_op_symbol = start_of_fre_section; /* Subtrahend.  */
-  exp.X_add_number = 0;
-  emit_expr (&exp, sizeof_member (sframe_func_desc_entry,
-				  sfde_func_start_fre_off));
+  if (sframe_fde->num_fres == 0)
+    /* SFrame FDEs without any FREs have a FRE offset of zero.  */
+    out_four (0);
+  else
+    {
+      exp.X_op = O_subtract;
+      exp.X_add_symbol = fre_symbol; /* Minuend.  */
+      exp.X_op_symbol = start_of_fre_section; /* Subtrahend.  */
+      exp.X_add_number = 0;
+      emit_expr (&exp, sizeof_member (sframe_func_desc_entry,
+				      sfde_func_start_fre_off));
+    }
 
   /* Number of FREs.  */
   out_four (sframe_fde->num_fres);
diff --git a/libsframe/sframe.c b/libsframe/sframe.c
index 824d1fd7ed99..9814a3ae4c1f 100644
--- a/libsframe/sframe.c
+++ b/libsframe/sframe.c
@@ -1880,7 +1880,7 @@ sframe_encoder_write_sframe (sframe_encoder_ctx *encoder)
      - buffers must be malloc'd by the caller.  */
   if ((contents == NULL) || (buf_size < hdr_size))
     return sframe_set_errno (&err, SFRAME_ERR_BUF_INVAL);
-  if (fr_info == NULL)
+  if (ehp->sfh_num_fres > 0 && fr_info == NULL)
     return sframe_set_errno (&err, SFRAME_ERR_FRE_INVAL);
 
   /* Write out the FRE table first.
@@ -1903,6 +1903,13 @@ sframe_encoder_write_sframe (sframe_encoder_ctx *encoder)
       fre_type = sframe_get_fre_type (fdep);
       num_fres = fdep->sfde_func_num_fres;
 
+      /* FDEs without any FDEs have a FRE offset of zero.  */
+      if (num_fres == 0)
+	fdep->sfde_func_start_fre_off = 0;
+
+      if (num_fres > 0 && fr_info == NULL)
+	return sframe_set_errno (&err, SFRAME_ERR_FRE_INVAL);
+
       for (j = 0; j < num_fres; j++)
 	{
 	  fre_index = global + j;
-- 
2.48.1