Problem with string merging and PC relative relocations

[Andreas Jaeger]

Andreas Schwab <schwab@suse.de> writes:

> Jakub Jelinek <jakub@redhat.com> writes:
>
> |> On Mon, Feb 11, 2002 at 06:27:13PM +0100, Andreas Jaeger wrote:
> |> > 
> |> > Andreas Schwab and myself looked closer into this message on x86-64:
> |> > 
> |> > x86_64-unknown-linux-ld: /abuild/aj/build/elf/librtld.os: access beyond end of merged section (-4 + 0)
> |> > 
> |> > We've located this relocation in dl-cache.os (part of glibc):
> |> >  216:   48 8d 3d 00 00 00 00    lea    0(%rip),%rdi        # 21d <_dl_load_cache_lookup+0x12d>
> |> >                         219: R_X86_64_PC32      .rodata.str1.1+0xfffffffffffffffc
> |> > 
> |> > The problem is the PC-relative addressing here.  The offset
> |> > compensates for the fact that the addressing is relative to the *next*
> |> > instruction.  So, it is not really an offset into the string section -
> |> > and should not be treated as such.
> |> 
> |> This should not happen.
> |> Only local relocs against SHF_MERGE section with zero addend should be
> |> converted to STT_SECTION + addend.
> |> This is what gas/write.c (adjust_reloc_syms):
> |>         /* Never adjust a reloc against local symbol in a merge section
> |>            with non-zero addend.  */
> |>         if ((symsec->flags & SEC_MERGE) && fixp->fx_offset)
> |>           {
> |>             symbol_mark_used_in_reloc (fixp->fx_addsy);
> |>             goto done;
> |>           }
> |> 
> |> is for. If you modify the addend later in tc-*, you need to care about it in
> |> your tc-* files.
>
> This should fix the problem:

It does indeed.  Now we get a reference for a symbol inside the rodata
section:

 216:   48 8d 3d 00 00 00 00    lea    0(%rip),%rdi        # 21d <_dl_load_cache
_lookup+0x12d>
                        219: R_X86_64_PC32      .LC7+0xfffffffffffffffc

Jakub, does this look ok?

Andreas

> 2002-02-12  Andreas Schwab  <schwab@suse.de>
>
> 	* config/tc-i386.c (tc_i386_fix_adjustable): Don't adjust
> 	pc-relative relocations to merge sections in 64-bit mode.
>
> --- gas/config/tc-i386.c.~1.109.~	Tue Feb 12 10:30:44 2002
> +++ gas/config/tc-i386.c	Tue Feb 12 18:04:13 2002
> @@ -1178,7 +1178,12 @@
>    /* Prevent all adjustments to global symbols, or else dynamic
>       linking will not work correctly.  */
>    if (S_IS_EXTERNAL (fixP->fx_addsy)
> -      || S_IS_WEAK (fixP->fx_addsy))
> +      || S_IS_WEAK (fixP->fx_addsy)
> +      /* Don't adjust pc-relative references to merge sections in 64-bit
> +	 mode.  */
> +      || (use_rela_relocations
> +	  && (S_GET_SEGMENT (fixP->fx_addsy)->flags & SEC_MERGE) != 0
> +	  && fixP->fx_pcrel))
>      return 0;
>  #endif
>    /* adjust_reloc_syms doesn't know about the GOT.  */
>
> Andreas.

-- 
 Andreas Jaeger
  SuSE Labs aj@suse.de
   private aj@arthur.inka.de
    http://www.suse.de/~aj