[llvm-dev] [lld] elf linker creates undefined empty symbol

Sean Silva via llvm-dev llvm-dev at lists.llvm.org
Thu Feb 23 01:14:36 PST 2017

On Wed, Feb 22, 2017 at 6:14 AM, Rafael Avila de Espindola <
rafael.espindola at gmail.com> wrote:

> Sean Silva <chisophugis at gmail.com> writes:
> >> When __libc_start_main is hidden, it doesn't end up in the dynamic
> symbol
> >> table and so we use the default DynsymIndex of 0.
> >>
> >
> >
> > I think BFD is doing the right thing. The `extern_weak hidden` is
> resolved
> > to null since by virtue of being hidden it doesn't refer to the function
> in
> > libc.so (and there is no definition in the executable). For some reason,
> > LLD thinks that it needs to resolve __libc_start_main dynamically and
> > things go horribly wrong. Rafael, what do you think?
> If it is hidden it should really not end up in the dynamic symbol
> table. I will try to take a look at your reproducible latter in the day.

FWIW, gold issues an error:

/usr/bin/ld.gold: error: hidden symbol '__libc_start_main' is not defined
/usr/bin/ld.gold: error: hidden symbol '__libc_start_main' is not defined

In theory `extern_weak hidden` could still fail to have a local definition
and then it would resolve to 0 due to being weak, which is what BFD does.
But `extern_weak hidden` is still pretty questionable. E.g. in the original
case that Carlo ran into, this was not the expected behavior (and this
error may have saved him some time actually).

-- Sean Silva

> Cheers,
> Rafael
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