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From: "vries at gcc dot gnu.org" <sourceware-bugzilla@sourceware.org>
To: gdb-prs@sourceware.org
Subject: [Bug symtab/31689] New: [gdb/symtab] PR gas/29517 workaround, dwarf2
 case
Date: Wed, 01 May 2024 13:14:07 +0000
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https://sourceware.org/bugzilla/show_bug.cgi?id=3D31689

            Bug ID: 31689
           Summary: [gdb/symtab] PR gas/29517 workaround, dwarf2 case
           Product: gdb
           Version: HEAD
            Status: NEW
          Severity: normal
          Priority: P2
         Component: symtab
          Assignee: unassigned at sourceware dot org
          Reporter: vries at gcc dot gnu.org
  Target Milestone: ---

Consider the following example:
...
$ gcc -g ~/data/hello.c
$ gcc -g hello.s -c
$ readelf -wi hello.o
Contents of the .debug_info section:

  Compilation Unit @ offset 0:
   Length:        0x41 (32-bit)
   Version:       2
   Abbrev Offset: 0
   Pointer Size:  8
 <0><b>: Abbrev Number: 1 (DW_TAG_compile_unit)
    <c>   DW_AT_stmt_list   : 0
    <10>   DW_AT_low_pc      : 0
    <18>   DW_AT_high_pc     : 0x15
    <20>   DW_AT_name        : (indirect string, offset: 0): hello.s
    <24>   DW_AT_comp_dir    : (indirect string, offset: 0x8): /home/vries/=
gdb
    <28>   DW_AT_producer    : (indirect string, offset: 0x18): GNU AS 2.41=
.0
    <2c>   DW_AT_language    : 32769    (MIPS assembler)
 <1><2e>: Abbrev Number: 2 (DW_TAG_subprogram)
    <2f>   DW_AT_name        : (indirect string, offset: 0x26): main
    <33>   DW_AT_external    : 1
    <34>   DW_AT_low_pc      : 0
    <3c>   DW_AT_high_pc     : 0x15
 <1><44>: Abbrev Number: 0
...

The return type of main is incorrect.  It doesn't have a DW_AT_type attribu=
te,
and consequently the return type is void.

This is PR gas/29517.  There is a fix for this, added in gas 2.40.

We can see that gas 2.41 is used.  So the fix is present in the assembler u=
sed.

However, the fix only works for dwarf3 and later, because it requires
DW_TAG_unspecified type, and the CU dwarf version is 2, due to:
...
$ gcc -g hello.s -c -v 2>&1 | grep "/as " | sed 's%.*/as %as %'
as --gdwarf2 -v --64 -o hello.o hello.s
...

A workaround for this problem was added here:
...
commit 1d45d90934b10862c00a22bcf4075815a785001b
Author: Tom de Vries <tdevries@suse.de>
Date:   Mon Oct 16 16:32:28 2023 +0200

    [gdb/symtab] Work around PR gas/29517
...
but that one is only active for gas 2.39.

For dwarf2, it should be active for gas >=3D 2.39.

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