[Bug debug/48176] New: .debug_aranges is no longer emitted

[Bug debug/48176] New: .debug_aranges is no longer emitted

[jan.kratochvil at redhat dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48176

           Summary: .debug_aranges is no longer emitted
           Product: gcc
           Version: 4.6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: debug
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: jan.kratochvil@redhat.com
            Target: x86_64-unknown-linux-gnu


echo 'main(){}' | gcc -x c - -g; readelf -WS a.out | grep debug_aranges

PASS - exists         - gcc (GCC) 4.5.3 20110318 (prerelease)
FAIL - does not exist - gcc (GCC) 4.7.0 20110318 (experimental)

elfutils relies on it:
https://bugzilla.redhat.com/show_bug.cgi?id=688532

Although GDB has never relied on it so there was a suggestion it could be
dropped in the favor of .gdb_index (generated and used by GDB itself).

[Bug debug/48176] .debug_aranges is no longer emitted

[pinskia at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48176

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> 2011-03-18 06:17:20 UTC ---
Hmm, maybe because the section would be empty, see PR 42288.

[Bug debug/48176] .debug_aranges is no longer emitted

[jan.kratochvil at redhat dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48176

Jan Kratochvil <jan.kratochvil at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |tromey at redhat dot com

--- Comment #2 from Jan Kratochvil <jan.kratochvil at redhat dot com> 2011-03-18 06:41:12 UTC ---
PR 42288 was for GDB and it can be closed I think.

I do not see why .debug_aranges would be empty - it contains valid information
with gcc-4.5 and even non-trivial such as with multiple CUs:

echo 'f(){}' | gcc -x c - -o 1.o -c -g; echo 'main(){}' | gcc 1.o -x c - -g;
readelf -WS a.out | grep debug_aranges

[Bug debug/48176] .debug_aranges is no longer emitted

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48176

--- Comment #3 from Richard Guenther <rguenth at gcc dot gnu.org> 2011-03-18 08:38:39 UTC ---
elfutils should be more forgiving

[Bug debug/48176] .debug_aranges is no longer emitted

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48176

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jakub at gcc dot gnu.org

--- Comment #4 from Jakub Jelinek <jakub at gcc dot gnu.org> 2011-03-18 08:43:35 UTC ---
See PR46704.

[Bug debug/48176] .debug_aranges is no longer emitted

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48176

--- Comment #5 from Jakub Jelinek <jakub at gcc dot gnu.org> 2011-03-18 09:00:59 UTC ---
I believe Eric's change was wrong actually, .debug_aranges section has useful
content even when !arange_table_in_use.  In particular, it describes .text and
.text.unlikely sections.

So IMHO we want:

--- gcc/dwarf2out.c2011-03-17 12:54:51.000000000 +0100
+++ gcc/dwarf2out.c2011-03-18 09:58:06.010366417 +0100
@@ -23664,7 +23664,7 @@ 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 (arange_table_in_use || text_section_used || cold_text_section_used)
     {
       switch_to_section (debug_aranges_section);
       output_aranges ();

I assume .debug_aranges isn't useful when no code has been emitted and after
all, we haven't been emitting it before either.  I'm unsure when exactly
would be fde_table_in_use different from
arange_table_in_use || text_section_used || cold_text_section_used
though.

[Bug debug/48176] [4.6/4.7 Regression] .debug_aranges is no longer emitted

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48176

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2011.03.18 09:01:37
   Target Milestone|---                         |4.6.0
            Summary|.debug_aranges is no longer |[4.6/4.7 Regression]
                   |emitted                     |.debug_aranges is no longer
                   |                            |emitted
     Ever Confirmed|0                           |1

[Bug debug/48176] [4.6/4.7 Regression] .debug_aranges is no longer emitted

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48176

--- Comment #6 from Jakub Jelinek <jakub at gcc dot gnu.org> 2011-03-18 09:08:41 UTC ---
And the PR42288 variant would be 
  if (info_section_emitted)
    {
      switch_to_section (debug_aranges_section);
      output_aranges ();
    }

[Bug debug/48176] [4.6/4.7 Regression] .debug_aranges is no longer emitted

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48176

--- Comment #7 from Jakub Jelinek <jakub at gcc dot gnu.org> 2011-03-18 09:20:37 UTC ---
I've tried a-charac.ads and fde_table_in_use is 0 in that case, so I wonder how
the PR46704 patch could stop emitting .debug_aranges in that case (unless there
was some bug that has been fixed since then).

[Bug debug/48176] [4.6/4.7 Regression] .debug_aranges is no longer emitted

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48176

--- Comment #8 from Jakub Jelinek <jakub at gcc dot gnu.org> 2011-03-18 09:32:13 UTC ---
If we want to be extra safe (and for 4.6 we need to be), I think
  if (fde_table_in_use && info_section_emitted)
or
  if ((arange_table_in_use || text_section_used || cold_text_section_used)
      && info_section_emitted)
are the conditions to use.  I think I prefer the latter, which is more explicit
on what it is testing, in particular output only if there will be any aranges
within the section actually emitted, and when there is a .Ldebug_info0 to point
the aranges to.

[Bug debug/48176] [4.6/4.7 Regression] .debug_aranges is no longer emitted

[ebotcazou at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48176

--- Comment #9 from Eric Botcazou <ebotcazou at gcc dot gnu.org> 2011-03-18 09:34:48 UTC ---
> I've tried a-charac.ads and fde_table_in_use is 0 in that case, so I wonder how
> the PR46704 patch could stop emitting .debug_aranges in that case (unless there
> was some bug that has been fixed since then).

You need to compile with -fkeep-inline-functions.

[Bug debug/48176] [4.6/4.7 Regression] .debug_aranges is no longer emitted

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48176

--- Comment #10 from Jakub Jelinek <jakub at gcc dot gnu.org> 2011-03-18 09:45:45 UTC ---
Thanks, I see.  fde_table_in_use is 2 then, arange_table_in_use is 0,
text_section_used 0 and cold_text_section_used 0.  So, the #c5 and both #c8
alternatives would fix this issue and not reintroduce the problem with
a-charac.ads -O2 -g -fkeep-inline-functions.
The only two functions in that CU are DECL_IGNORED, so begin_function debug
hook isn't called for them, just begin_prologue, and as the CU is empty
(DECL_IGNORED function are ignored for debug info) .debug_info isn't emitted
either.

[Bug debug/48176] [4.6/4.7 Regression] .debug_aranges is no longer emitted

[ebotcazou at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48176

--- Comment #11 from Eric Botcazou <ebotcazou at gcc dot gnu.org> 2011-03-18 09:51:26 UTC ---
> Thanks, I see.  fde_table_in_use is 2 then, arange_table_in_use is 0,
> text_section_used 0 and cold_text_section_used 0.  So, the #c5 and both #c8
> alternatives would fix this issue and not reintroduce the problem with
> a-charac.ads -O2 -g -fkeep-inline-functions.

What about testing ranges_by_label_in_use instead?

[Bug debug/48176] [4.6/4.7 Regression] .debug_aranges is no longer emitted

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48176

--- Comment #12 from Jakub Jelinek <jakub at gcc dot gnu.org> 2011-03-18 09:56:33 UTC ---
That is related to .debug_ranges, not .debug_aranges.
E.g. in the int main () { return 0; } case ranges_by_label_in_use is 0, not
surprisingly, we don't emit .debug_ranges in that case.  .debug_ranges is only
needed if some function or lexical block or inlined function doesn't have a
single range, but multiple ones.

[Bug debug/48176] [4.6/4.7 Regression] .debug_aranges is no longer emitted

[ebotcazou at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48176

--- Comment #13 from Eric Botcazou <ebotcazou at gcc dot gnu.org> 2011-03-18 10:05:32 UTC ---
> That is related to .debug_ranges, not .debug_aranges.

Ah, OK.  Your solution:

  (arange_table_in_use || text_section_used || cold_text_section_used)

seems indeed to be the best one, you might even want to write it as:

  (text_section_used || cold_text_section_used || arange_table_in_use)

to match the layout of output_aranges.  Thanks for debugging this.

[Bug debug/48176] [4.6/4.7 Regression] .debug_aranges is no longer emitted

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48176

--- Comment #14 from Jakub Jelinek <jakub at gcc dot gnu.org> 2011-03-18 16:18:12 UTC ---
Author: jakub
Date: Fri Mar 18 16:18:05 2011
New Revision: 171150

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=171150
Log:
    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.

Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/dwarf2out.c

[Bug debug/48176] [4.6/4.7 Regression] .debug_aranges is no longer emitted

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48176

--- Comment #15 from Jakub Jelinek <jakub at gcc dot gnu.org> 2011-03-18 16:22:10 UTC ---
Author: jakub
Date: Fri Mar 18 16:22:01 2011
New Revision: 171151

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=171151
Log:
    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.

Modified:
    branches/gcc-4_6-branch/gcc/ChangeLog
    branches/gcc-4_6-branch/gcc/dwarf2out.c

[Bug debug/48176] [4.6/4.7 Regression] .debug_aranges is no longer emitted

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48176

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |FIXED

--- Comment #16 from Jakub Jelinek <jakub at gcc dot gnu.org> 2011-03-18 19:11:54 UTC ---
Fixed.