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

[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.

-- 
H.J.