Re: [PATCH v2] gdb: work around negative DW_AT_data_member_location GCC 11 bug

[Lancelot SIX via Gdb-patches <gdb-patches@sourceware.org>]

Hi,

I have minor comments below:

> diff --git a/gdb/dwarf2/cu.c b/gdb/dwarf2/cu.c
> index 019165f6e6c5..20aecd4da4d6 100644
> --- a/gdb/dwarf2/cu.c
> +++ b/gdb/dwarf2/cu.c
> @@ -31,7 +31,8 @@ dwarf2_cu::dwarf2_cu (dwarf2_per_cu_data *per_cu,
>      has_loclist (false),
>      checked_producer (false),
>      producer_is_gxx_lt_4_6 (false),
> -    producer_is_gcc_lt_4_3 (false),
> +	producer_is_gcc_lt_4_3 (false),
> +	producer_is_gcc_11 (false),
   ^

You seem to be changing the indentation here (this changes 4 spaces for
1 tab).


>      producer_is_icc (false),
>      producer_is_icc_lt_14 (false),
>      producer_is_codewarrior (false),
> diff --git a/gdb/dwarf2/cu.h b/gdb/dwarf2/cu.h
> index 078479a56988..bce0a3de63a4 100644
> --- a/gdb/dwarf2/cu.h
> +++ b/gdb/dwarf2/cu.h
> @@ -253,6 +253,7 @@ struct dwarf2_cu
>    bool checked_producer : 1;
>    bool producer_is_gxx_lt_4_6 : 1;
>    bool producer_is_gcc_lt_4_3 : 1;
> +  bool producer_is_gcc_11 : 1;
>    bool producer_is_icc : 1;
>    bool producer_is_icc_lt_14 : 1;
>    bool producer_is_codewarrior : 1;
> diff --git a/gdb/dwarf2/read.c b/gdb/dwarf2/read.c
> index f7cb95b40cba..1a749eac334f 100644
> --- a/gdb/dwarf2/read.c
> +++ b/gdb/dwarf2/read.c
> @@ -14320,6 +14320,7 @@ check_producer (struct dwarf2_cu *cu)
>      {
>        cu->producer_is_gxx_lt_4_6 = major < 4 || (major == 4 && minor < 6);
>        cu->producer_is_gcc_lt_4_3 = major < 4 || (major == 4 && minor < 3);
> +      cu->producer_is_gcc_11 = major == 11;
>      }
>    else if (producer_is_icc (cu->producer, &major, &minor))
>      {
> @@ -14464,6 +14465,19 @@ handle_member_location (struct die_info *die, struct dwarf2_cu *cu,
>        if (attr->form_is_constant ())
>  	{
>  	  LONGEST offset = attr->constant_value (0);
> +
> +	  /* Work around this GCC 11 bug, where it would erroneously use -1
> +	     data member locations, instead of 0:
> +
> +	       Negative DW_AT_data_member_location
> +	       https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101378
> +	     */
> +	  if (offset == -1 && cu->producer_is_gcc_11)
> +	    {
> +	      complaint (_("DW_AT_data_member_location value of -1, assuming 0"));
> +	      offset = 0;
> +	    }
> +
>  	  field->set_loc_bitpos (offset * bits_per_byte);
>  	}
>        else if (attr->form_is_section_offset ())
> diff --git a/gdb/testsuite/gdb.dwarf2/negative-data-member-location.c b/gdb/testsuite/gdb.dwarf2/negative-data-member-location.c
> new file mode 100644
> index 000000000000..4871b2f12036
> --- /dev/null
> +++ b/gdb/testsuite/gdb.dwarf2/negative-data-member-location.c
> @@ -0,0 +1,29 @@
> +/* Copyright (C) 2021 Free Software Foundation, Inc.

The year needs to be updated to 2021-2022.

> +
> +   This file is part of GDB.
> +
> +   This program is free software; you can redistribute it and/or modify
> +   it under the terms of the GNU General Public License as published by
> +   the Free Software Foundation; either version 3 of the License, or
> +   (at your option) any later version.
> +
> +   This program is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> +   GNU General Public License for more details.
> +
> +   You should have received a copy of the GNU General Public License
> +   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
> +
> +struct the_struct
> +{
> +  char x[4];
> +};
> +
> +struct the_struct s = { { 0x11, 0x22, 0x22, 0x11 } };
> +
> +int
> +main (void)
> +{
> +  return 0;
> +}
> diff --git a/gdb/testsuite/gdb.dwarf2/negative-data-member-location.exp b/gdb/testsuite/gdb.dwarf2/negative-data-member-location.exp
> new file mode 100644
> index 000000000000..9d05f208958b
> --- /dev/null
> +++ b/gdb/testsuite/gdb.dwarf2/negative-data-member-location.exp
> @@ -0,0 +1,77 @@
> +# Copyright 2021 Free Software Foundation, Inc.
Same, update the year from 2021 to 2021-2022.

Best,
Lancelot.