Re: PATCH: Store ELF section index for input file

[Alan Modra <amodra at bigpond dot net dot au>]

On Sat, Mar 19, 2005 at 09:57:01AM -0800, H. J. Lu wrote:
> On Sat, Mar 19, 2005 at 08:14:00PM +1030, Alan Modra wrote:
> > On Thu, Mar 17, 2005 at 12:58:27PM -0800, H. J. Lu wrote:
> > > @@ -4823,9 +4830,16 @@ _bfd_elf_section_from_bfd_section (bfd *
> > >    const struct elf_backend_data *bed;
> > >    int index;
> > >  
> > > -  if (elf_section_data (asect) != NULL
> > > -      && elf_section_data (asect)->this_idx != 0)
> > > -    return elf_section_data (asect)->this_idx;
> > > +  if (elf_section_data (asect) != NULL)
> > > +    {
> > > +      index = elf_section_data (asect)->this_idx;
> > > +      if (index != 0)
> > > +	{
> > > +	  Elf_Internal_Shdr **i_shdrp = elf_elfsections (abfd);
> > > +	  if (!i_shdrp || i_shdrp [index]->bfd_section == asect)
> > > +	    return index;
> > > +	}
> > > +    }
> > 
> > Please explain why this change is necessary.
> > 
> 
> _bfd_elf_section_from_bfd_section is called on input sections. When
> there are more than 64K input sections, linear search over a linked
> list can be very very slow. Since this_idx isn't used for input section
> and for input section, its bfd section is created from its ELF
> section index, we can use this_idx to store the ELF section index. The
> result is the linking time went from

No, I meant why that particular hunk.  You first posted a patch without
it, then just said it was needed, but not why.

> 966.01s user 0.81s system 99% cpu 16:06.87 total
> 
> to
> 
> 45.61s user 0.81s system 99% cpu 46.448 total
> 
> It is 20X speed up. I tested it with Linux kernel, binutils, gcc and
> glibc on ia32, ia64 and x86_64. There are no regressions.
> 
> BTW, it only solves the 64K input section problem. The 64K output
> sections is still very slow. bfd_section has a pointer to its BFD
> owner. Can we add a pointer to bfd_section, used_by_ld, which will
> be used by ld for lang_output_section_statement_type?

I think it might be worth investigating a larger change, not creating
lang_output_section_statemtents for orphans.  I'll look at this some
time when I have a free moment or two.

-- 
Alan Modra
IBM OzLabs - Linux Technology Centre