[PATCH v2] libio: Properly link in libio functions in static binaries

[H.J. Lu]

On Fri, Aug 22, 2025 at 12:34 PM Adhemerval Zanella Netto
<adhemerval.zanella@linaro.org> wrote:
>
>
>
> On 22/08/25 16:04, H.J. Lu wrote:
> > On Fri, Aug 22, 2025 at 10:28 AM Xi Ruoyao <xry111@xry111.site> wrote:
> >>
> >> On Thu, 2025-08-21 at 16:57 -0700, H.J. Lu wrote:
> >>> 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
> >>>
> >>> static __typeof (name) *const name##_p __attribute__((used)) = name;
> >>>
> >>> This fixes BZ #33300.
> >>>
> >>> Signed-off-by: H.J. Lu <hjl.tools@gmail.com>
> >>
> >> Again:
> >>
> >> Tested-by: Xi Ruoyao <xry111@xry111.site>
> >>
> >> --
> >> Xi Ruoyao <xry111@xry111.site>
> >
> > I checked it in after testing s390x-linux-gnu with build-many-glibcs.py.
>
>
> I don't have a strong preference, and this fix seems fine; but Florian has
> asked if we can't just use SHF_GNU_RETAIN along with attribute ((used)) here.

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.