ifunc resolving

[Zack Weinberg]

On Wed, Jan 20, 2021 at 4:33 AM Florian Weimer via Libc-alpha
<libc-alpha@sourceware.org> wrote:
> * Alan Modra via Libc-alpha:
> > On Tue, Jan 19, 2021 at 03:59:54PM +0100, Florian Weimer via Binutils wrote:
> > There is a third possibility.  If ld.so defers all irelative and other
> > relocations using ifunc symbols until all non-ifunc relocations have
> > been performed, globally, then ifunc resolvers would only have the
> > restriction that they not call other ifuncs.
> >
> > That idea was floated a very long time ago.  For some reason it is
> > too hard or too slow to do in ld.so.
>
> It's not too hard, I wrote a patch.  I didn't mention it because it was
> rejected.  It seemed about the only thing for which we had consensus. 8-/
>
> My patch did not find an appropriate order in all cases.  I think that's
> more or less unavoidable if IFUNC resolvers depend on relocations
> against other IFUNC resolvers.  It would have nicely covered all
> internal glibc uses at the time.

Every time this discussion comes up, I wonder how much it would help
if we completely scrapped the idea of lazy relocations.  Do what
LD_BIND_NOW=t does all the time.  Distributions are moving in this
direction already because that lets them turn on -z relro...

zw