Re: [PATCH] [gdb/symtab] Error out for .debug_types section in dwz file

[Guinevere Larsen <blarsen@redhat.com>]

On 12/09/2023 10:43, Tom de Vries via Gdb-patches wrote:
> There are two methods to factor out type information in a dwarf4 executable:
> - use -fdebug-info-types to generate type units in a .debug_types section, and
> - use dwz to create partial units.
>
> The dwz method has an extra benefit: it also allows to factor out information
> between executables into a newly created .dwz file, pointed to by a
> .gnu_debugaltlink section.
>
> There is nothing prohibiting a .gnu_debugaltlink file to contain a
> .debug_types section.
>
> It's just not generated by dwz or any other tool atm, and consequently gdb has
> no support for it.  Enhancement PR symtab/30838 is open about the lack of
> support.
>
> Make the current situation explicit by emitting a dwarf error:
> ...
> (gdb) file struct-with-sig-2^M
> Reading symbols from struct-with-sig-2...^M
> Dwarf Error: .debug_types section not supported in dwz file^M
> ...
> and add an assert in write_gdbindex:
> ...
> +      /* See enhancement PR symtab/30838.  */
> +      gdb_assert (!(per_cu->is_dwz && per_cu->is_debug_types));
> ...
> to clarify why we can use:
> ...
>        data_buf &cu_list = (per_cu->is_debug_types
>                             ? types_cu_list
>                             : per_cu->is_dwz ? dwz_cu_list : objfile_cu_list);
> ...
>
> The test-case is a modified copy from gdb.dwarf2/struct-with-sig.exp, so it
> keeps the copyright years range.
>
> Tested on x86_64-linux.
>
> Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=30838
> ---

Hi! I tested this patch and it does not add any regression, and properly 
detects the situation.

Tested-By: Guinevere Larsen <blarsen@redhat.com>

-- 
Cheers,
Guinevere Larsen
She/Her/Hers

>   gdb/dwarf2/dwz.c                              |   5 +
>   gdb/dwarf2/dwz.h                              |   1 +
>   gdb/dwarf2/index-write.c                      |   3 +
>   gdb/dwarf2/read.c                             |   6 +
>   .../gdb.dwarf2/struct-with-sig-2.exp          | 128 ++++++++++++++++++
>   5 files changed, 143 insertions(+)
>   create mode 100644 gdb/testsuite/gdb.dwarf2/struct-with-sig-2.exp
>
> diff --git a/gdb/dwarf2/dwz.c b/gdb/dwarf2/dwz.c
> index 447c942da6a..bd2bcb91d83 100644
> --- a/gdb/dwarf2/dwz.c
> +++ b/gdb/dwarf2/dwz.c
> @@ -91,6 +91,11 @@ locate_dwz_sections (bfd *abfd, asection *sectp, dwz_file *dwz_file)
>         dwz_file->debug_names.s.section = sectp;
>         dwz_file->debug_names.size = bfd_section_size (sectp);
>       }
> +  else if (dwarf2_elf_names.types.matches (sectp->name))
> +    {
> +      dwz_file->types.s.section = sectp;
> +      dwz_file->types.size = bfd_section_size (sectp);
> +    }
>   }
>   
>   /* Attempt to find a .dwz file (whose full path is represented by
> diff --git a/gdb/dwarf2/dwz.h b/gdb/dwarf2/dwz.h
> index 232b4dbce01..5f61b5e1216 100644
> --- a/gdb/dwarf2/dwz.h
> +++ b/gdb/dwarf2/dwz.h
> @@ -48,6 +48,7 @@ struct dwz_file
>     struct dwarf2_section_info macro {};
>     struct dwarf2_section_info gdb_index {};
>     struct dwarf2_section_info debug_names {};
> +  struct dwarf2_section_info types {};
>   
>     /* The dwz's BFD.  */
>     gdb_bfd_ref_ptr dwz_bfd;
> diff --git a/gdb/dwarf2/index-write.c b/gdb/dwarf2/index-write.c
> index 11f254e263a..7e2f77e3642 100644
> --- a/gdb/dwarf2/index-write.c
> +++ b/gdb/dwarf2/index-write.c
> @@ -1211,6 +1211,9 @@ write_gdbindex (dwarf2_per_bfd *per_bfd, cooked_index *table,
>         const auto insertpair = cu_index_htab.emplace (per_cu, counter);
>         gdb_assert (insertpair.second);
>   
> +      /* See enhancement PR symtab/30838.  */
> +      gdb_assert (!(per_cu->is_dwz && per_cu->is_debug_types));
> +
>         /* The all_units list contains CUs read from the objfile as well as
>   	 from the eventual dwz file.  We need to place the entry in the
>   	 corresponding index.  */
> diff --git a/gdb/dwarf2/read.c b/gdb/dwarf2/read.c
> index 98bedbc5d49..cd4005fb7b2 100644
> --- a/gdb/dwarf2/read.c
> +++ b/gdb/dwarf2/read.c
> @@ -5314,6 +5314,12 @@ create_all_units (dwarf2_per_objfile *per_objfile)
>         dwz->line.read (objfile);
>         read_comp_units_from_section (per_objfile, &dwz->info, &dwz->abbrev, 1,
>   				    types_htab, rcuh_kind::COMPILE);
> +
> +      if (!dwz->types.empty ())
> +	{
> +	  /* See enhancement PR symtab/30838.  */
> +	  error (_("Dwarf Error: .debug_types section not supported in dwz file"));
> +	}
>       }
>   
>     per_objfile->per_bfd->signatured_types = std::move (types_htab);
> diff --git a/gdb/testsuite/gdb.dwarf2/struct-with-sig-2.exp b/gdb/testsuite/gdb.dwarf2/struct-with-sig-2.exp
> new file mode 100644
> index 00000000000..f6877fc6a17
> --- /dev/null
> +++ b/gdb/testsuite/gdb.dwarf2/struct-with-sig-2.exp
> @@ -0,0 +1,128 @@
> +# Copyright 2020-2023 Free Software Foundation, Inc.
> +
> +# 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/>.
> +
> +# Variant of struct-with-sig.exp where TUs are in .gnu_debugaltlink file.
> +
> +load_lib dwarf.exp
> +
> +# This test can only be run on targets which support DWARF-2 and use gas.
> +require dwarf2_support
> +
> +standard_testfile main-foo.c .S .S
> +
> +set build_id [string repeat ff 20]
> +
> +# Make some DWARF for the dwz file.
> +set asm_file [standard_output_file $srcfile2]
> +Dwarf::assemble $asm_file {
> +    build_id $::build_id
> +
> +    tu {} 0x0000000000000001 the_type_i {
> +	type_unit {} {
> +	    declare_labels int_type
> +
> +	    the_type_i: structure_type {
> +		{name s}
> +		{byte_size 4 sdata}
> +	    } {
> +		member {
> +		    {name i}
> +		    {type :$int_type}
> +		}
> +	    }
> +	    int_type: base_type {
> +		{name int}
> +		{encoding @DW_ATE_signed}
> +		{byte_size 4 sdata}
> +	    }
> +	}
> +    }
> +
> +    tu {} 0x0000000000000002 the_type_j {
> +	type_unit {} {
> +	    declare_labels int_type
> +
> +	    the_type_j: structure_type {
> +		{name s}
> +		{byte_size 4 sdata}
> +	    } {
> +		member {
> +		    {name j}
> +		    {type :$int_type}
> +		}
> +	    }
> +	    int_type: base_type {
> +		{name int}
> +		{encoding @DW_ATE_signed}
> +		{byte_size 4 sdata}
> +	    }
> +	}
> +    }
> +}
> +
> +# We're using an object instead of executable here to keep cc-with-tweaks.sh
> +# from modifying it.  It also means we can set the build-id, rather than
> +# having to extract it.
> +if { [gdb_compile $asm_file $binfile.dwz object {nodebug}] != "" } {
> +    return -1
> +}
> +
> +set host_dwz_file [gdb_remote_download host $binfile.dwz]
> +
> +# Make some DWARF for the executable.
> +set asm_file [standard_output_file $srcfile3]
> +Dwarf::assemble $asm_file {
> +    gnu_debugaltlink $::host_dwz_file $::build_id
> +
> +    cu {} {
> +	compile_unit {
> +	    {DW_AT_language @DW_LANG_C}
> +	    {DW_AT_name main.c}
> +	} {
> +	    structure_type {
> +		{name s}
> +		{signature 0x0000000000000001 ref_sig8}
> +		{declaration 1 flag}
> +	    }
> +	    DW_TAG_subprogram {
> +		{MACRO_AT_func {main}}
> +	    }
> +	}
> +    }
> +
> +    cu {} {
> +	compile_unit {
> +	    {DW_AT_language @DW_LANG_C}
> +	    {DW_AT_name     foo.c}
> +	} {
> +	    structure_type {
> +		{name s}
> +		{signature 0x0000000000000002 ref_sig8}
> +		{declaration 1 flag}
> +	    }
> +	    DW_TAG_subprogram {
> +		{MACRO_AT_func {foo}}
> +	    }
> +	}
> +    }
> +}
> +
> +if { [prepare_for_testing "failed to prepare" ${testfile} \
> +	  [list $srcfile $asm_file] {nodebug}] } {
> +    return -1
> +}
> +
> +set re "Dwarf Error: .debug_types section not supported in dwz file"
> +gdb_assert { [regexp $re $gdb_file_cmd_msg] } "Dwarf Error message"
>
> base-commit: 318d3bda5cad124bd11eebb0349d0f183ba625b1