[PATCH] Emit .debug_aranges when needed (PR debug/48176)

[Jakub Jelinek]

Hi!

Eric changed dwarf2out_finish in January to fix PR46704, unfortunately
that change means we often don't emit .debug_aranges at all even when it
should be present and is needed for e.g. elfutils.
In PR46704 there were 2 DECL_IGNORED functions with -O2 -g
-fkeep-inline-functions, so fde_table_in_use was 2, but .debug_info
section wasn't emitted as it was empty and thus .debug_aranges referenced
non-existent .Ldebug_info0 symbol.
arange_table_in_use is often 0, in particular if all emitted functions
are only in .text/.text.unlikely sections.  .debug_aranges contains
first range of .text the current CU covers, then range of .text.unlikely
and only afterwards the other ranges (arange_table_in_use is count of
those).

The following patch fixes it by emitting .debug_aranges whenever it will
be non-empty (and the extra && info_section_emitted is just to make sure
.Ldebug_info0 can be used too).  If you want, for 4.7+ I think
we could just use
  if (text_section_used || cold_text_section_used || arange_table_in_use)
    {
      gcc_assert (info_section_emitted);
...

Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk/4.6?

2011-03-18  Jakub Jelinek  <jakub@redhat.com>

	PR debug/48176
	* dwarf2out.c (dwarf2out_finish): Call output_aranges even when
	arange_table_in_use is 0, but either text_section_used or
	cold_text_section_used is true.  Don't call it if
	!info_section_emitted.

--- gcc/dwarf2out.c.jj	2011-03-17 21:34:34.000000000 +0100
+++ gcc/dwarf2out.c	2011-03-18 10:50:33.303546024 +0100
@@ -23667,7 +23667,8 @@ dwarf2out_finish (const char *filename)
 
   /* Output the address range information.  We only put functions in the arange
      table, so don't write it out if we don't have any.  */
-  if (arange_table_in_use)
+  if ((text_section_used || cold_text_section_used || arange_table_in_use)
+      && info_section_emitted)
     {
       switch_to_section (debug_aranges_section);
       output_aranges ();

	Jakub