[Bug ld/22269] Undefined weak symbols isn't resolved to 0 in static PIE

[amodra at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=22269

--- Comment #11 from Alan Modra <amodra at gmail dot com> ---
> If there is a program bug:
> ...
> may lead to undesired behavior.

Quite so.

> -z dynamic-undefined-weak applies if there is a DT_NEEDED entry which
> may provide definition for undefined weak reference at run-time.  For static
> PIE, weak undefined should always be resolved to 0.

I agree, which is why I felt it was a good idea to default
link_info.dynamic_undefined_weak to 0 when link_info.nointerp.

Also, --no-dynamic-linker -z dynamic-undefined-weak probably ought to be an
error, or at least warn.

However, making that change (or explicitly passing -z nodynamic-undefined-weak)
results in x86 tests that fail, due to not generating a plt entry for the
undefined weak call.  No matter how I look at it, that is a bug in the x86
backend: link_info.dynamic_undefined_weak should not control the generation of
a plt entry.  (I'm also of the opinion that adding a plt entry for an undefined
weak without dynamic relocs is just bloat, but that's a separate issue and one
I don't care to argue about.)

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