Re: [PATCH][gdb/symtab] Remove superfluous end-of-sequence marker

[Bernd Edlinger <bernd.edlinger@hotmail.de>]

On 1/4/21 2:59 PM, Tom de Vries wrote:
> Hi,
> 
> While working on PR26935 I noticed that when running test-case
> gdb.base/morestack.exp with target board unix/-m32/-fPIE/-pie and ld linker,
> I get this linetable fragment for morestack.S using readelf -wL:
> ...
> CU: ../../../../libgcc/config/i386/morestack.S:
> Line number    Starting address    View    Stmt
> 109               0xc9c               x
>   ...
> 838               0xe03               x
>   -               0xe04
> 
> 636                   0               x
> 637                 0x3               x
>   -                 0x4
> ...
> but with "maint info line-table" I get:
> ...
> INDEX  LINE   ADDRESS            IS-STMT
> 0      END    0x00000004         Y
> 1      109    0x00000c9c         Y
>   ...
> 110    838    0x00000e03         Y
> 111    END    0x00000e04         Y
> ...
> 
> So, apparently the entries with addresses 0x0 and 0x3 are filtered out
> because the addresses are out of range, but the same doesn't happen with the
> end-of-seq terminator.
> 
> Fix this by filtering out end-of-seq terminators that do not actually
> terminate anything.
> 
> Tested on x86_64-linux.
> 
> Any comments?
> 
> Thanks,
> - Tom
> 
> [gdb/symtab] Remove superfluous end-of-sequence marker
> 
> gdb/ChangeLog:
> 
> 2021-01-04  Tom de Vries  <tdevries@suse.de>
> 
> 	* buildsym.c (buildsym_compunit::record_line): Filter out end-of-seq
> 	terminators that do not terminate anything.
> 
> gdb/testsuite/ChangeLog:
> 
> 2021-01-04  Tom de Vries  <tdevries@suse.de>
> 
> 	* gdb.dwarf2/dw2-out-of-range-end-of-seq.exp: New file.
> 
> ---
>  gdb/buildsym.c                                     |  8 ++
>  .../gdb.dwarf2/dw2-out-of-range-end-of-seq.exp     | 94 ++++++++++++++++++++++
>  2 files changed, 102 insertions(+)
> 
> diff --git a/gdb/buildsym.c b/gdb/buildsym.c
> index 1d8c579b7b8..245aecf0c38 100644
> --- a/gdb/buildsym.c
> +++ b/gdb/buildsym.c
> @@ -714,6 +714,14 @@ buildsym_compunit::record_line (struct subfile *subfile, int line,
>  	    break;
>  	  subfile->line_vector->nitems--;
>  	}
> +
> +      /* Ignore an end-of-sequence marker marking an empty sequence.  */
> +      struct linetable_entry *last
> +	= (subfile->line_vector->nitems == 0
> +	   ? nullptr
> +	   : &subfile->line_vector->item[subfile->line_vector->nitems - 1]);
> +      if (last == nullptr || last->line == 0)
> +	return;
>      }
>  

What you want to achieve here can probably be done more easily this way:

diff --git a/gdb/buildsym.c b/gdb/buildsym.c
index 1d8c579..dda83f7 100644
--- a/gdb/buildsym.c
+++ b/gdb/buildsym.c
@@ -710,6 +710,8 @@ struct blockvector *
       while (subfile->line_vector->nitems > 0)
        {
          e = subfile->line_vector->item + subfile->line_vector->nitems - 1;
+         if (e->line == 0)
+           return;
          if (e->pc != pc)
            break;
          subfile->line_vector->nitems--;


I wonder however where the out-of-range line entries are filtered away.
Would it be better to filter the end of sequence markers there?


Bernd.