[Bug dynamic-link/28218] ld.so: ifunc resolver calls a lazy PLT. When does it work?

["fweimer at redhat dot com" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=28218

Florian Weimer <fweimer at redhat dot com> changed:

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--- Comment #2 from Florian Weimer <fweimer at redhat dot com> ---
(In reply to Alan Modra from comment #1)
> > FreeBSD rtld resolves non-IRELATIVE relocations in all modules, then
> > IRELATIVE relocations in all modules.
> Yes, this is the correct way to do things, and the only general way to
> support cross-module ifunc resolvers that themselves might need to be
> relocated.  We have known this for a long time.  See for example
> https://gcc.gnu.org/legacy-ml/gcc-patches/2009-07/msg01307.html

Cross-module IFUNC resolvers that have relocation dependencies need more
deferral than just IRELATIVE relocations. Regular relocations which target an
IFUNC symbol need to be deferred, and copy relocations as well. Even that does
not completely address all cases.

My impression is that the glibc maintainers think that IFUNC resolvers must not
use have relocation dependencies. This could mean that they can only be
implemented in assembler on some targets.

Initial comments on a proposal were positive:
https://sourceware.org/legacy-ml/libc-alpha/2017-01/msg00468.html But I think
during later discussions, this approach was rejected.

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