[PATCH] libio: Properly link in libio functions in static binaries

[H.J. Lu]

On Mon, Aug 25, 2025 at 2:13 AM Florian Weimer <fweimer@redhat.com> wrote:
>
> * H. J. Lu:
>
> > On Thu, Aug 21, 2025 at 11:49 AM Florian Weimer <fweimer@redhat.com> wrote:
> >>
> >> * H. J. Lu:
> >>
> >> > commit 3020f72618e4f1d7338cd42b8bc7b2813e961b5a
> >> > Author: Adhemerval Zanella Netto <adhemerval.zanella@linaro.org>
> >> > Date:   Tue Dec 27 18:11:43 2022 -0300
> >> >
> >> >     libio: Remove the usage of __libc_IO_vtables
> >> >
> >> > added
> >> >
> >> >  #define libio_static_fn_required(name) __asm (".globl " #name);
> >> >
> >> > to link in libio functions in static binaries.  But there is no relocation
> >> > in
> >> >       .globl  _IO_file_open
> >> >
> >> > and "strip --strip-unneeded" will remove such unreferenced symbols which
> >> > breaks static binaries.  Redefine libio_static_fn_required to create a
> >> > reference to the required function with
> >> >
> >> >       .pushsection ".data.rel.ro.local","aw"
> >> > .L_IO_file_open:
> >> >       .dc.a   _IO_file_open
> >> >       .popsection
> >> >
> >> > This fixes BZ #33300.
> >>
> >> Is it possible to use SHF_RETAIN instead?
> >
> > SHF_GNU_RETAIN is used to keep an unused section for --gc-sections while
> > this one is to include an object from libc.a.  Even if the section with
> > _IO_file_doallocate is marked with SHF_GNU_RETAIN, it won't be linked in
> > without a reference to _IO_file_doallocate.
>
> Hmm.  The --strip-unneeded option says this:
>
>        --strip-unneeded
>            Remove all symbols that are not needed for relocation processing in
>            addition to debugging symbols and sections stripped by
>            --strip-debug.
>
> I think it's a user error to use this on libc.a.  What's the benefit of

Why can't --strip-unneeded be used on libc.a? If a symbol isn't used for
relocation processing, it is unused.

> using this option?
>
> Thanks,
> Florian
>


-- 
H.J.