Re: ARM mapping symbols and --strip-unneeded

["Richard Earnshaw (lists)" <Richard dot Earnshaw at arm dot com>]

On 29/06/16 10:24, Nick Clifton wrote:
> Hi Richard,
> 
>> Might be safer to use strncmp (sym, type, 2) since 'extended' mapping
>> symbols can be produced by some tools.
> 
> We might as well extract mapping symbol determination into a separate
> function - I have a feeling that it is going to be needed again in the
> future.  So what do you think of this patch ?
> 

Even better.  Thanks.

R.


> Cheers
>   Nick
> 
> diff --git a/bfd/elf32-arm.c b/bfd/elf32-arm.c
> index 04e776c..105e3cc 100644
> --- a/bfd/elf32-arm.c
> +++ b/bfd/elf32-arm.c
> @@ -18266,6 +18266,28 @@ elf32_arm_copy_special_section_fields (const bfd *ibfd ATTRIBUTE_UNUSED,
>    return FALSE;
>  }
>  
> +/* Returns TRUE if NAME is an ARM mapping symbol.
> +   Traditionally the symbols $a, $d and $t have been used.
> +   The ARM ELF standard also defines $x (for A64 code).  It also allows a
> +   period initiated suffix to be added to the symbol: "$[adtx]\.[:sym_char]+".
> +   Other tools might also produce $b (Thumb BL), $f, $p, $m and $v, but we do
> +   not support them here.  $t.x indicates the start of ThumbEE instructions.  */
> +
> +static bfd_boolean
> +is_mapping_symbol (const char * name)
> +{
> +  return name != NULL /* Paranoia.  */
> +    && name[0] == '$' /* Note: if objcopy --prefix-symbols has been used then
> +			 the mapping symbols could have acquired a prefix.
> +			 We do not support this here, since such symbols no
> +			 longer conform to the ARM ELF ABI.  */
> +    && (name[1] == 'a' || name[1] == 'd' || name[1] == 't' || name[1] == 'x')
> +    && (name[2] == 0 || name[2] == '.');
> +  /* FIXME: Strictly speaking the symbol is only a valid mapping symbol if
> +     any characters that follow the period are legal characters for the body
> +     of a symbol's name.  For now we just assume that this is the case.  */
> +}
> +
>  /* Make sure that mapping symbols in object files are not removed via the
>     "strip --strip-unneeded" tool.  These symbols are needed in order to
>     correctly generate interworking veneers, and for byte swapping code
> @@ -18276,11 +18298,8 @@ static void
>  elf32_arm_backend_symbol_processing (bfd *abfd, asymbol *sym)
>  {
>    if (((abfd->flags & (EXEC_P | DYNAMIC)) == 0)
> -      && sym->name != NULL
>        && sym->section != bfd_abs_section_ptr
> -      && (strcmp (sym->name, "$a") == 0
> -	  || strcmp (sym->name, "$t") == 0
> -	  || strcmp (sym->name, "$d") == 0))
> +      && is_mapping_symbol (sym->name))
>      sym->flags |= BSF_KEEP;
>  }
>