[PATCH] Link static C++ tests against libatomic.a if needed

[H.J. Lu]

On Tue, May 5, 2026 at 8:36 PM Adhemerval Zanella Netto
<adhemerval.zanella@linaro.org> wrote:
>
>
>
> On 05/05/26 09:33, H.J. Lu wrote:
> > On Tue, May 5, 2026 at 8:27 PM Adhemerval Zanella Netto
> > <adhemerval.zanella@linaro.org> wrote:
> >>
> >>
> >>
> >> On 04/05/26 22:50, H.J. Lu wrote:
> >>> On Tue, May 5, 2026 at 9:42 AM Sam James <sam@gentoo.org> wrote:
> >>>>
> >>>> "H.J. Lu" <hjl.tools@gmail.com> writes:
> >>>>
> >>>>> On Mon, May 4, 2026 at 10:33 AM H.J. Lu <hjl.tools@gmail.com> wrote:
> >>>>>>
> >>>>>> Define cxx-static-link-libatomic to -latomic if DT_NEEDED entries in
> >>>>>> libstdc++.so include libatomic.so.  Update link-extra-libs-static to
> >>>>>> include $(cxx-static-link-libatomic) if -lstdc++ is used.
> >>>>>>
> >>>>>> Tested with sparcv8-linux-gnu-leon3 and sparcv9-linux-gnu using
> >>>>>> uild-many-glibcs.py.  This fixes BZ #34121.
> >>>>>>
> >>>>>
> >>>>> FWIW, sparc g++ does pass -latomic_asneeded to ld.  But glibc tests
> >>>>> are built with -nostdlib -nostartfiles using gcc, not g++.
> >>>>
> >>>> https://inbox.sourceware.org/gcc-patches/CACb0b4m+ex47Tpyp1qvW9+0p4onyEvsfXeXE_4zZrteMO5q5EQ@mail.gmail.com/
> >>>>
> >>>> I don't remember what happened with that, there were a few issues with
> >>>> the libatomic autolinking so I lost track.
> >>>
> >>> One way to fix the gcc is to create libstdc++.a as linker script, similar to
> >>>
> >>> [hjl@gnu-tgl-3 x86-glibc]$ cat /usr/lib64/libm.a
> >>> /* GNU ld script
> >>> */
> >>> OUTPUT_FORMAT(elf64-x86-64)
> >>> GROUP ( /usr/lib64/libm-2.43.a /usr/lib64/libmvec.a )
> >>> [hjl@gnu-tgl-3 x86-glibc]$
> >>>
> >>> to include libatomic.a in libstdc++.a if needed.  But I don't know if it works
> >>> everywhere.
> >>>
> >>
> >> It seems gcc-16 has another issue, it also fails on building glibc after a bootstrap
> >> with build-many-glibcs.py with:
> >>
> >> [..-m32 -mlong-double-128 -mcpu=v9 -o /home/azanella/Projects/glibc/build/sparcv9-linux-gnu-gcc16/support/links-dso-program -pie  -Wl,-O1 -nostdlib -nostartfiles [...]
> >> [...]/sparc64-linux-gnu/sparc64-glibc-linux-gnu/bin/ld: [...]/sparc64-linux-gnu/bin/../lib/gcc/sparc64-glibc-linux-gnu/16.1.1/../../../../sparc64-glibc-linux-gnu/lib/../lib/libstdc++.so: undefined reference to `__atomic_fetch_add_4@LIBATOMIC_1.0'
> >> [...]//sparc64-glibc-lisparc64-linux-gnunux-gnu/bin/ld: [...]/sparc64-linux-gnu/bin/../lib/gcc/sparc64-glibc-linux-gnu/16.1.1/../../../../sparc64-glibc-linux-gnu/lib/../lib/libstdc++.so: undefined reference to `__atomic_fetch_sub_4@LIBATOMIC_1.0'
> >>
> >> And dumping the linker invocation, it shows another issue:
> >>
> >> ld: warning: libatomic.so.1, needed by [...]/sparc64-linux-gnu/bin/../lib/gcc/sparc64-glibc-linux-gnu/16.1.1/../../../../sparc64-glibc-linux-gnu/lib/../lib/libstdc++.so, not found (try using -rpath or -rpath-link)
> >
> > Which version of binutils are you using?  Binutils master branch works
> > for me for sparc64-glibc-linux-gnu.
>
> It is a pretty recent one:
>
> $ ./bin/sparc64-glibc-linux-gnu-ld -v
> GNU ld (GNU Binutils) 2.46.0.20260504

This shouldn't happen since __atomic_fetch_sub_4 is only referenced
inside of libstdc++.so.  Why can't ld find libatomic.so.1? Mine has

[hjl@gnu-zen4-1 lib]$ pwd
/export/build/gnu/tools-build/glibc-many/install/compilers/sparc64-linux-gnu/sparc64-glibc-linux-gnu/lib
[hjl@gnu-zen4-1 lib]$ ls
ldscripts              libgomp.la        libstdc++exp.a
libatomic.a            libgomp.so        libstdc++exp.la
libatomic_asneeded.a   libgomp.so.1      libstdc++fs.a
libatomic_asneeded.so  libgomp.so.1.0.0  libstdc++fs.la
libatomic.la           libgomp.spec      libstdc++.la
libatomic.so           libitm.a          libstdc++.modules.json
libatomic.so.1         libitm.la         libstdc++.so
libatomic.so.1.2.0     libitm.so         libstdc++.so.6
libgcc_s_asneeded.so   libitm.so.1       libstdc++.so.6.0.35
libgcc_s.so            libitm.so.1.0.0   libstdc++.so.6.0.35-gdb.py
libgcc_s.so.1          libitm.spec       libsupc++.a
libgomp.a              libstdc++.a       libsupc++.la
[hjl@gnu-zen4-1 lib]$ file libatomic.so.1.2.0
libatomic.so.1.2.0: ELF 32-bit MSB shared object, SPARC32PLUS, V8+
Required, total store ordering, version 1 (SYSV), dynamically linked,
with debug_info, not stripped
[hjl@gnu-zen4-1 lib]$

Something seems wrong in your setup.

> >
> >> It seems now that libstdc++.so is dynamic linker against libatomic.so:
> >>
> >> $ readelf -d ./sparc64-glibc-linux-gnu/lib/libstdc++.so | grep NEEDED
> >>  0x00000001 (NEEDED)                     Shared library: [libm.so.6]
> >>  0x00000001 (NEEDED)                     Shared library: [libatomic.so.1]
> >>  0x00000001 (NEEDED)                     Shared library: [libc.so.6]
> >>  0x00000001 (NEEDED)                     Shared library: [ld-linux.so.2]
> >>  0x00000001 (NEEDED)                     Shared library: [libgcc_s.so.1]
> >>
> >> Where previously (gcc-15) it seems to be statically linked:
> >>
> >> $ readelf -d ./sparc64-glibc-linux-gnu/lib/libstdc++.so | grep NEEDED
> >>  0x00000001 (NEEDED)                     Shared library: [libm.so.6]
> >>  0x00000001 (NEEDED)                     Shared library: [libc.so.6]
> >>  0x00000001 (NEEDED)                     Shared library: [ld-linux.so.2]
> >>  0x00000001 (NEEDED)                     Shared library: [libgcc_s.so.1]
> >>
> >
> >
>


-- 
H.J.