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

[Richard Henderson <richard.henderson@linaro.org>]

On 2/17/22 04:18, Philippe Mathieu-Daudé wrote:
> On 16/2/22 17:42, Akihiko Odaki wrote:
>> On 2022/02/17 0:08, Philippe Mathieu-Daudé wrote:
>>> On 16/2/22 11:19, Richard Henderson wrote:
>>>> 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).

This is another form of compiler mis-configuration.
If you don't have g++ to go with gcc, use --cxx=false to avoid picking up a different 
compiler.

>>> Could there be a mismatch between Clang (-mno-outline-atomics) and GCC
>>> (-moutline-atomics)?

I have no idea if those options do the same thing.

>> 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
> 
> Thanks for the pointer. And the next section is
> https://clang.llvm.org/docs/Toolchain.html#atomics-library :)
> 
>    Clang does not currently automatically link against libatomic when
>     using libgcc_s. You may need to manually add -latomic to support
>    this configuration when using non-native atomic operations (if you
>    see link errors referring to __atomic_* functions).
> 
> I'll try that.

-moutline-atomics is *not* the same as libatomic.
You should not need libatomic at all.


r~