Re: libbfd: Guess the architecture of an executable file with libbfd

[Emmanuel Fleury <fleury at labri dot fr>]

On 05/23/2013 05:35 AM, Alan Modra wrote:
>
>> By the way, the confusion seems to be between:
>>
>> elf32-littlearm
>>  (header little endian, data little endian)
>>   arm
>> elf32-littlearm-symbian
>>  (header little endian, data little endian)
>>   arm
>> elf32-littlearm-vxworks
>>  (header little endian, data little endian)
>>   arm
> 
> Add elf32-littlearm-nacl to that list with current binutils.

Yes, I was using 2.22 on my first attempt.

> I've been meaning to do something about this ever since I wrote
> http://sourceware.org/ml/binutils/2013-01/msg00448.html.  The first
> hunk in the following patch stops bfd choosing a generic ELF target
> (like elf32-little) when another target is a better match
> (eg. elf32-littlearm).  The last hunk effectively banishes "File
> format is ambiguous" errors for ELF.  This might be a little
> controversial, but if vxworks, symbian and nacl are confused by
> using the more general machine specific ELF target then they really
> should have specified OS_ABI or implemented target object_p, archive_p
> and core_file_p functions.
> 
> 	* format.c (bfd_check_format_matches): Don't match a target in
> 	targ_selvecs if some other target is a better match.  If
> 	targets implement match priority, fall back to the first of
> 	the best matches.
> 
> Index: bfd/format.c
> ===================================================================
> RCS file: /cvs/src/src/bfd/format.c,v
> retrieving revision 1.32
> diff -u -p -r1.32 format.c
> --- bfd/format.c	28 Jan 2013 07:58:16 -0000	1.32
> +++ bfd/format.c	23 May 2013 02:14:17 -0000
> @@ -376,6 +376,9 @@ bfd_check_format_matches (bfd *abfd, bfd
>  	}
>      }
>  
> +  /* We have more than one equally good match.  If any of the best
> +     matches is a target in config.bfd targ_defvec or targ_selvecs,
> +     choose it.  */
>    if (match_count > 1)
>      {
>        const bfd_target * const *assoc = bfd_associated_vector;
> @@ -385,7 +388,8 @@ bfd_check_format_matches (bfd *abfd, bfd
>  	  int i = match_count;
>  
>  	  while (--i >= 0)
> -	    if (matching_vector[i] == right_targ)
> +	    if (matching_vector[i] == right_targ
> +		&& right_targ->match_priority <= best_match)
>  	      break;
>  
>  	  if (i >= 0)
> @@ -396,6 +400,22 @@ bfd_check_format_matches (bfd *abfd, bfd
>  	}
>      }
>  
> +  /* We still have more than one equally good match, and at least some
> +     of the targets support match priority.  Choose the first of the
> +     best matches.  */
> +  if (match_count > 1 && best_count != match_count)
> +    {
> +      int i;
> +
> +      for (i = 0; i < match_count; i++)
> +	{
> +	  right_targ = matching_vector[i];
> +	  if (right_targ->match_priority <= best_match)
> +	    break;
> +	}
> +      match_count = 1;
> +    }
> +
>    /* There is way too much undoing of half-known state here.  We
>       really shouldn't iterate on live bfd's.  Note that saving the
>       whole bfd and restoring it would be even worse; the first thing
> 

I applied the patch on a 2.23 and it worked fine for my case.

Thanks a lot !

Regards
-- 
Emmanuel Fleury

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