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

[Adhemerval Zanella Netto]

On 05/05/26 17:49, H.J. Lu wrote:
> 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.
I built the sparc64 toolchain using build-many-glibcs.py and vanilla branches:

* binutils: origin/binutils-2_46-branch (7db5c37036f2ddbf0db6199df6342f7945575623)
* gcc:      origin/releases/gcc-16 (3ddd3407b1d0a0f49a606ea95d5dd190dd6e2d31)
* glibc:    origin/release/2.43/master (e9517114acc77c0b8af9da6700107df16882b701)

No extra patch applied.