Re: [PATCH v2 4/8] configure: Disable out-of-line atomic operations on Aarch64

[Akihiko Odaki <akihiko.odaki@gmail.com>]

On 2022/02/17 0:08, Philippe Mathieu-Daudé wrote:
> On 16/2/22 11:19, Richard Henderson wrote:
>> On 2/16/22 04:01, Philippe Mathieu-Daudé via wrote:
>>> GCC 10.1 introduced the -moutline-atomics option on Aarch64.
>>> This options is enabled by default, and triggers a link failure:
>>>
>>>    Undefined symbols for architecture arm64:
>>>      "___aarch64_cas1_acq_rel", referenced from:
>>>          _qmp_migrate_recover in migration_migration.c.o
>>>          _cpu_atomic_cmpxchgb_mmu in accel_tcg_cputlb.c.o
>>>          _cpu_atomic_fetch_sminb_mmu in accel_tcg_cputlb.c.o
>>>          _cpu_atomic_fetch_uminb_mmu in accel_tcg_cputlb.c.o
>>>          _cpu_atomic_fetch_smaxb_mmu in accel_tcg_cputlb.c.o
>>>          _cpu_atomic_fetch_umaxb_mmu in accel_tcg_cputlb.c.o
>>>          _cpu_atomic_smin_fetchb_mmu in accel_tcg_cputlb.c.o
>>>          ...
>>>      "___aarch64_ldadd4_acq_rel", referenced from:
>>>          _multifd_recv_new_channel in migration_multifd.c.o
>>>          _monitor_event in monitor_hmp.c.o
>>>          _handle_hmp_command in monitor_hmp.c.o
>>>          _colo_compare_finalize in net_colo-compare.c.o
>>>          _flatview_unref in softmmu_memory.c.o
>>>          _virtio_scsi_hotunplug in hw_scsi_virtio-scsi.c.o
>>>          _tcg_register_thread in tcg_tcg.c.o
>>>          ...
>>>      "___aarch64_swp4_acq", referenced from:
>>>          _qemu_spin_lock in softmmu_cpu-timers.c.o
>>>          _cpu_get_ticks in softmmu_cpu-timers.c.o
>>>          _qemu_spin_lock in softmmu_icount.c.o
>>>          _cpu_exec in accel_tcg_cpu-exec.c.o
>>>          _page_flush_tb_1.isra.0 in accel_tcg_translate-all.c.o
>>>          _page_entry_lock in accel_tcg_translate-all.c.o
>>>          _do_tb_phys_invalidate in accel_tcg_translate-all.c.o
>>>          ...
>>>
>>> QEMU implements its own atomic operations using C11 builtin helpers.
>>> Disable the GCC out-of-line atomic ops.
>>>
>>> Signed-off-by: Philippe Mathieu-Daudé<f4bug@amsat.org>
>>> ---
>>> Cc: Stefan Hajnoczi<stefanha@redhat.com>
>>> Cc: Paolo Bonzini<pbonzini@redhat.com>
>>>
>>> Clearly out of my understanding, but at least it links and the qtests
>>> pass.
>>> ---
>>>   configure | 12 ++++++++++++
>>>   1 file changed, 12 insertions(+)
>>
>> These should have been supplied by libgcc.a, which we're supposed to 
>> be linking against. Something is wrong with your installation.
> 
> I don't have gobjc/g++ installed, so ./configure defaulted to Clang to
> compile these languages, but compiled C files using GCC. At the end the
> Clang linker is used (the default c++ symlink).
> 
> Could there be a mismatch between Clang (-mno-outline-atomics) and GCC
> (-moutline-atomics)?

I think you have to instruct Clang to use libgcc instead of compiler-rt 
and link the objects with GCC. Here is the documentation of Clang about 
the runtime I could find:
https://clang.llvm.org/docs/Toolchain.html#libgcc-s-gnu