Home Original page

IA32 TLS GD optimization issue

Jakub Jelinek jakub@redhat.com
Thu Nov 6 19:19:00 GMT 2003 
On Thu, Nov 06, 2003 at 09:49:51AM -0800, H. J. Lu wrote:
> The ia32 linker can optimize TLS GD to LE or IE. But they are not
> consistent. For GD -> LE, we can turn
> 
> 	leal foo(%reg), %eax; call ___tls_get_addr; nop
> 
> into
> 
> 	movl %gs:0, %eax; subl $foo@tpoff, %eax	# 6 byte form of subl
> 
> and
> 
> 	leal foo(%reg), %eax; call ___tls_get_addr
> 
> into
> 
> 	movl %gs:0, %eax; subl $foo@tpoff, %eax	# 5 byte form of subl
> 
> But for GD -> IE, we only support
> 
> 	leal foo(%reg), %eax; call ___tls_get_addr; nop
> 
> to
> 	movl %gs:0, %eax; subl $foo@gottpoff(%reg), %eax # 6 byte form of subl
> 
> since there is no 5 byte form for "subl $foo@gottpoff(%reg), %eax".

And the problem is?
Have you read http://people.redhat.com/drepper/tls.pdf ?

> Also I think this patch is needed for
> 
> 	leal foo(%reg), %eax; call ___tls_get_addr

No.  Look what line 2438 does.

> Should we support
> 
> 	leal foo(%reg), %eax; call ___tls_get_addr
> 
> at all? If yes, how should we fix it?

Can you explain what needs fixing?

> --- elf32-i386.c.tls	2003-11-04 09:43:23.000000000 -0800
> +++ elf32-i386.c	2003-11-06 09:45:57.000000000 -0800
> @@ -2473,6 +2473,7 @@ elf_i386_relocate_section (bfd *output_b
>  			     (5 byte form of subl).  */
>  			  memcpy (contents + rel->r_offset - 2,
>  				  "\x65\xa1\0\0\0\0\x2d\0\0\0", 11);
> +			  roff = rel->r_offset + 5;
>  			}
>  		    }
>  		  bfd_put_32 (output_bfd, tpoff (info, relocation),

	Jakub
More information about the Binutils mailing list