[Bug debug/98765] New: [11 Regression] stripping of LTO debug sections doesn't work anymore since switch to -gdwarf-5 by default

[Bug debug/98765] New: [11 Regression] stripping of LTO debug sections doesn't work anymore since switch to -gdwarf-5 by default

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98765

            Bug ID: 98765
           Summary: [11 Regression] stripping of LTO debug sections
                    doesn't work anymore since switch to -gdwarf-5 by
                    default
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: debug
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jakub at gcc dot gnu.org
  Target Milestone: ---

Testcase a.i:

# 0 "a.c"
# 1 "/var/tmp//"
# 0 "<built-in>"
# 0 "<command-line>"
# 1 "/usr/include/stdc-predef.h" 1 3 4
# 0 "<command-line>" 2
# 1 "a.c"
# 1 "a.h" 1
int
foo (void)
{
  return 0;
}
# 2 "a.c" 2

int
bar (void)
{
  return 0;
}

With gcc configured against latest binutils:
gcc -S -g -flto -ffat-lto-objects a.i
gcc -c a.s -o a.o
strip -p -R .gnu.lto_* -R .gnu.debuglto_* -N __gnu_lto_v1 a.o
strip: st3FEz69: symbol `.gnu.debuglto_.debug_line_str' required but not
present
strip: st3FEz69: no symbols

[Bug debug/98765] [11 Regression] stripping of LTO debug sections doesn't work anymore since switch to -gdwarf-5 by default

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98765

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2021-01-20
   Target Milestone|---                         |11.0
           Priority|P3                          |P1

[Bug debug/98765] [11 Regression] stripping of LTO debug sections doesn't work anymore since switch to -gdwarf-5 by default

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98765

--- Comment #1 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Seems to be a gcc bug to me:
        .section        .gnu.debuglto_.debug_info,"e",@progbits
...
        .long   .LASF0  # DW_AT_name: "a.c"
        .long   .LASF1  # DW_AT_comp_dir: "/var/tmp"
        .long   .Ldebug_line0   # DW_AT_stmt_list
...
        .section        .gnu.debuglto_.debug_line,"e",@progbits
.Ldebug_line0:
...
        .uleb128 0x3    # File names count
        .long   .LASF0  # File Entry: 0: "a.c"
        .byte   0
        .long   .LASF0  # File Entry: 0: "a.c"
        .byte   0
...
        .section        .gnu.debuglto_.debug_line_str,"eMS",@progbits,1
.LASF0:
        .string "a.c"
...
        .section        .debug_info,"",@progbits
.Ldebug_info1:
        .long   .LASF0  # DW_AT_name: "a.c"
        .long   .LASF1  # DW_AT_comp_dir: "/var/tmp"
        .quad   .Ltext0 # DW_AT_low_pc
        .quad   .Letext0-.Ltext0        # DW_AT_high_pc
        .long   .Ldebug_line1   # DW_AT_stmt_list

The references in .debug_info to .LASF0/.LASF1 labels from
.gnu.debuglto_.debug_line_str is what is incorrect.

[Bug debug/98765] [11 Regression] stripping of LTO debug sections doesn't work anymore since switch to -gdwarf-5 by default

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98765

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Assignee|unassigned at gcc dot gnu.org      |jakub at gcc dot gnu.org
             Status|NEW                         |ASSIGNED

[Bug debug/98765] [11 Regression] stripping of LTO debug sections doesn't work anymore since switch to -gdwarf-5 by default

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98765

--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
--- gcc/dwarf2out.c.jj  2021-01-20 08:32:09.612958930 +0100
+++ gcc/dwarf2out.c     2021-01-20 13:49:42.367772872 +0100
@@ -4733,7 +4733,9 @@ int
 reset_indirect_string (indirect_string_node **h, void *)
 {
   struct indirect_string_node *node = *h;
-  if (node->form == DW_FORM_strp || node->form == dwarf_FORM (DW_FORM_strx))
+  if (node->form == DW_FORM_strp
+      || node->form == DW_FORM_line_strp
+      || node->form == dwarf_FORM (DW_FORM_strx))
     {
       free (node->label);
       node->label = NULL;
fixes it but the string is then emitted into .debug_str rather than
.debug_line_str in the non-.gnu.debuglto_* case.

[Bug debug/98765] [11 Regression] stripping of LTO debug sections doesn't work anymore since switch to -gdwarf-5 by default

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98765

--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
--- gcc/dwarf2out.c.jj  2021-01-20 08:32:09.612958930 +0100
+++ gcc/dwarf2out.c     2021-01-20 14:15:14.735459774 +0100
@@ -4733,12 +4733,20 @@ int
 reset_indirect_string (indirect_string_node **h, void *)
 {
   struct indirect_string_node *node = *h;
-  if (node->form == DW_FORM_strp || node->form == dwarf_FORM (DW_FORM_strx))
+  if (node->form == DW_FORM_strp
+      || node->form == DW_FORM_line_strp
+      || node->form == dwarf_FORM (DW_FORM_strx))
     {
+      bool line_strp = node->form == DW_FORM_line_strp;
       free (node->label);
       node->label = NULL;
       node->form = (dwarf_form) 0;
       node->index = 0;
+      if (line_strp)
+       {
+         set_indirect_string (node);
+         node->form = DW_FORM_line_strp;
+       }
     }
   return 1;
 }
@@ -31395,10 +31403,7 @@ dwarf2out_finish (const char *filename)
       /* Remove indirect string decisions.  */
       debug_str_hash->traverse<void *, reset_indirect_string> (NULL);
       if (debug_line_str_hash)
-       {
-         debug_line_str_hash->traverse<void *, reset_indirect_string> (NULL);
-         debug_line_str_hash = NULL;
-       }
+       debug_line_str_hash->traverse<void *, reset_indirect_string> (NULL);
     }

 #if ENABLE_ASSERT_CHECKING
emits them in .debug_line_str, but emits also strings that aren't really
needed.

[Bug debug/98765] [11 Regression] stripping of LTO debug sections doesn't work anymore since switch to -gdwarf-5 by default

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98765

--- Comment #4 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jakub Jelinek <jakub@gcc.gnu.org>:

https://gcc.gnu.org/g:27c792895bd809115c1f70672835b7fdff74d318

commit r11-6820-g27c792895bd809115c1f70672835b7fdff74d318
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Wed Jan 20 18:51:04 2021 +0100

    debug: Fix up DWARF 5 -g -flto -ffat-lto-objects [PR98765]

    As mentioned in the PR, with -gdwarf-5 (or -g now) -flto -ffat-lto-objects,
    users can't strip the LTO sections with
    strip -p -R .gnu.lto_* -R .gnu.debuglto_* -N __gnu_lto_v1
    anymore when GCC is configured against recent binutils.

    The problem is that in that case .gnu.debuglto_.debug_line_str section is
    then used, which is fine for references to strings in .gnu.debuglto_.*
    sections, but not when those references are in .debug_info section too;
    those should really reference separate strings in .debug_line_str section.

    For .gnu.debuglto_.debug_str vs. .debug_str we handle it right, we
    reset_indirect_string the strings and thus force creation of new labels for
    the second time.
    But for DW_FORM_line_strp as the patch shows, there were multiple problems.
    First one was that reset_indirect_string, even when called through traverse
    on debug_line_str_hash, didn't do anything at all (fixed by first hunk).
    The second bug was that the DW_FORM_line_strp strings, which were supposed
    to be only visible through debug_line_str_hash, leaked into debug_str_hash
    (second hunk).
    And the third thing is that when we reset debug_line_str_hash, we should
    still make those strings DW_FORM_line_strp if they are accessed.
    One could do it by reinstantiating DW_FORM_line_strp right away in
    reset_indirect_string and not clear debug_line_str_hash, but that has the
    disadvantage that we then force emitting .debug_line_str strings that
aren't
    really needed - we need those from the CU DIEs' DW_AT_name and
    DW_AT_comp_dir attributes, but when emitting .debug_line section through
    assembler, we don't need to emit the strings we only needed for
    .gnu.debuglto_.debug_line which is always emitted by the compiler.

    2021-01-20  Jakub Jelinek  <jakub@redhat.com>

            PR debug/98765
            * dwarf2out.c (reset_indirect_string): Also reset indirect strings
            with DW_FORM_line_strp form.
            (prune_unused_types_update_strings): Don't add into debug_str_hash
            indirect strings with DW_FORM_line_strp form.
            (adjust_name_comp_dir): New function.
            (dwarf2out_finish): Call it on CU DIEs after resetting
            debug_line_str_hash.

[Bug debug/98765] [11 Regression] stripping of LTO debug sections doesn't work anymore since switch to -gdwarf-5 by default

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98765

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

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

--- Comment #5 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Fixed.