Re: [PATCH 02/11] [gdb/macros] Handle 64-bit dwarf in gdb.base/fission-macro.exp

[Tom de Vries <tdevries@suse.de>]

On 5/21/24 17:44, Tom de Vries wrote:
> When enabling 64-bit dwarf in the test-case gdb.base/fission-macro.exp, we run
> into:
> ...
> (gdb) break -qualified main^M
> DW_MACRO_define_strx pointing outside of .debug_str.dwo section \
>    [in module fission-macro-5-640.dwo]^M
> (gdb) FAIL: gdb.base/fission-macro.exp: dwarf_version=5: dwarf_bits=64: \
>    gdb_breakpoint: set breakpoint at main
> ...
> 
> A dwarf-5 .debug_str_offsets section starts with a header consisting of:
> - an initial length (4 bytes for 32-bit and 12 bytes for 64-bit),
> - a 2 byte version string, and
> - 2 bytes padding
> so in total 8 bytes for 32-bit and 16 bytes for 64-bit.
> 
> This offset is calculated here in dwarf_decode_macros:
> ...
>        str_offsets_base = cu->header.addr_size;
> ...
> and in both cases this evaluates to 8.
> 
> So in the 64-bit case, we interpret the last 8 bytes of the header as an offset.
> 
> Fix this by computing str_offsets_base correctly for dwarf-5, for both the
> 32-bit and 64-bit case.
> 

I've combined this patch and "Handle v4 dwarf in 
gdb.base/fission-macro.exp", in other words 02/11 and 06/11 and 
resubmitted as 
https://sourceware.org/pipermail/gdb-patches/2025-January/214901.html .

I've also changed the code to use "cu->header.version" instead of 
"cu->per_cu->version ()". ( See also 
https://sourceware.org/pipermail/gdb-patches/2025-January/214886.html ).

Thanks,
- Tom

> Tested on x86_64-linux.
> 
> Tested test-case using a current gcc trunk build, and gcc 14.
> ---
>   gdb/dwarf2/read.c                        | 11 ++++++++++-
>   gdb/testsuite/gdb.base/fission-macro.exp |  2 +-
>   2 files changed, 11 insertions(+), 2 deletions(-)
> 
> diff --git a/gdb/dwarf2/read.c b/gdb/dwarf2/read.c
> index e8416905163..4884553000a 100644
> --- a/gdb/dwarf2/read.c
> +++ b/gdb/dwarf2/read.c
> @@ -21232,7 +21232,16 @@ dwarf_decode_macros (struct dwarf2_cu *cu, unsigned int offset,
>         str_offsets_section = &cu->dwo_unit->dwo_file
>   			       ->sections.str_offsets;
>         str_section = &cu->dwo_unit->dwo_file->sections.str;
> -      str_offsets_base = cu->header.addr_size;
> +      if (cu->per_cu->version () <= 4)
> +	str_offsets_base = cu->header.addr_size;
> +      else
> +	{
> +	  bfd *abfd = str_offsets_section->get_bfd_owner ();
> +	  unsigned int bytes_read = 0;
> +	  read_initial_length (abfd, str_offsets_section->buffer, &bytes_read, false);
> +	  const bool is_dwarf64 = bytes_read != 4;
> +	  str_offsets_base = is_dwarf64 ? 16 : 8;
> +	}
>       }
>     else
>       {
> diff --git a/gdb/testsuite/gdb.base/fission-macro.exp b/gdb/testsuite/gdb.base/fission-macro.exp
> index 705e3dd0c4b..4eb9c0efe21 100644
> --- a/gdb/testsuite/gdb.base/fission-macro.exp
> +++ b/gdb/testsuite/gdb.base/fission-macro.exp
> @@ -67,7 +67,7 @@ proc do_tests { dwarf_version dwarf_bits strict_dwarf } {
>   }
>   
>   foreach_with_prefix dwarf_version {5} {
> -    foreach_with_prefix dwarf_bits {32} {
> +    foreach_with_prefix dwarf_bits {32 64} {
>   	foreach_with_prefix strict_dwarf {0 1} {
>   	    do_tests $dwarf_version $dwarf_bits $strict_dwarf
>   	}