[Bug debug/48041] New: dwarf2out emits unnecessary null byte in empty .debug_abbrev section

["mark at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48041

           Summary: dwarf2out emits unnecessary null byte in empty
                    .debug_abbrev section
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: debug
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: mark@gcc.gnu.org


Detected by the elfutils dwarflint tool.

Example:
$ echo > empty.c 
$ gcc -g -c empty.c 
$ readelf -x .debug_abbrev empty.o
Hex dump of section '.debug_abbrev':
  0x00000000 00                                  .

Although harmless it might add up if a project has a lot of objects without any
real debuginfo in them. There might not actually be many such projects though.

The fix seems easy:

Index: gcc/dwarf2out.c
===================================================================
--- gcc/dwarf2out.c    (revision 170813)
+++ gcc/dwarf2out.c    (working copy)
@@ -11058,7 +11058,8 @@
     }

   /* Terminate the table.  */
-  dw2_asm_output_data (1, 0, NULL);
+  if (abbrev_die_table_in_use > 1)
+    dw2_asm_output_data (1, 0, NULL);
 }

 /* Output a symbol we can use to refer to this DIE from another CU.  */

Bootstraps fine on x86_64-gnu-linux and no regressions seen with make check -k

I'll submit it to gcc-patches when the tree opens up again for stage one.