Re: ld of binutils 2.12 appends two (garbage?) bytes

[Felix Kühling <fxkuehl at gmx dot de>]

On Sat, 11 May 2002 20:36:18 +0930
Alan Modra <amodra@bigpond.net.au> wrote:

> On Fri, May 10, 2002 at 04:56:10PM +0200, Felix Kühling wrote:
> > I'm assembling and linking a master boot record for the ia32
> > architecture which has to be exactly 446 bytes long. After upgrading
> > from binutils 2.10 to 2.12 it gets 2 bytes too long. I first assumed the
> > linker tried to make the length divisible by 4.
> 
> That's exactly what it does.
> 
> > But it does not append
> > zeros. Here is the end of the hexdump:
> 
> No, it appends NOPs in the .text section, and x86 gas chooses
> "mov %esi,%esi" as a two byte NOP.  I'm not sure what to do about

So gas is the bad guy :). As 'size' reported a text section length of
446 bytes I thought it was ld.

> fixing your particular problem.  Perhaps we should remove the
> record_alignment calls in tc-i386.c:md_begin.  They've been there for
> a very long time, as it's a good idea to align entry points into code,
> but not vital on x86.  Richard Henderson made some changes (see
> http://sources.redhat.com/ml/binutils/2000-12/msg00305.html) to pad
> out the end of sections to their alignment values, and this change in
> combination with the 4 byte alignment of .text causes your problem.
> 
> I'm tempted to remove
> 
>       /* The last subsegment gets an aligment corresponding to the
> 	 alignment of the section.  This allows proper nop-filling
> 	 at the end of code-bearing sections.  */
>       if (!frchainP->frch_next || frchainP->frch_next->frch_seg != now_seg)
> 	alignment = get_recorded_alignment (now_seg);
> 
> >from write.c:subsegs_finish.  Hmm, for those targets with minimum insn
> lengths, "#define SUB_SEGMENT_ALIGN MIN_INSN_ALIGN" and defining
> MIN_INSN_ALLIGN might be a good idea.  Richard?

Ok, I commented out the above lines and it works for me. Thanks for your
help.

> 
> -- 
> Alan Modra
> IBM OzLabs - Linux Technology Centre
> 

Regards,
   Felix

               __\|/__    ___     ___     ___
__Tschüß_______\_6 6_/___/__ \___/__ \___/___\___You can do anything,___
_____Felix_______\Ä/\ \_____\ \_____\ \______U___just not everything____
  fxkuehl@gmx.de    >o<__/   \___/   \___/        at the same time!