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Re: more prelink
On Sun, Sep 29, 2002 at 11:30:01PM +0200, Jakub Jelinek wrote:
> On Fri, Sep 27, 2002 at 11:39:06PM -0400, Jack Howarth wrote:
> > Jakub,
> > I think I have stumbled over another issue with prelink that
> > could be problematic unless addressed. Currently the glibc srpms
> > are using a postinst script to prelink libc.so.6 with the
> > --reloc-only flag so it is relinked to the specified base address.
> > If I do that on entropy with...
> >
> > /usr/sbin/prelink --reloc-only=0x40000 /lib/libc-2.2.94.so
>
> I'm terribly sorry to say, but now that I think about it, --reloc-only
> for libc.so makes no sense on ppc/x86-64/sparc* etc. Sorry for
> forgotting about this.
> It speeds things up on REL or ELF_MACHINE_REL_RELATIVE arches only.
> ELF_MACHINE_REL_RELATIVE are those where R_*_RELATIVE relocs have the
> addend in *r_offset. ppc/x86-64/sparc* usually have zero there.
> Even if I changed back binutils to put addend to both r_addend and *r_offset
> on ppc, ELF_MACHINE_REL_RELATIVE could not be defined because there are
> already many -z combreloc binaries and libraries out there I think
> and they'd suddenly fail in weird ways.
> R_*_RELATIVE relocs can be skipped on the other
> arches (ppc, x86-64, sparc*, ...) if the library is prelinked, not
> just prelink -r'ed. Then it guarantees *r_offset has the proper value.
How big is the performance difference? If it's worthwhile, we could
add (say) a dynamic tag which guarantees us that the binary has this
property.
[Didn't you change binutils to do this on PPC a couple of weeks ago?
When making it put a predictable value there?]
--
Daniel Jacobowitz
MontaVista Software Debian GNU/Linux Developer