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

["Philippe Mathieu-Daudé" <philippe.mathieu.daude@gmail.com>]

On 18/2/22 16:36, Paolo Bonzini wrote:
> On 2/18/22 02:46, Richard Henderson wrote:
>>>>>
>>>>> 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.
> 
> This would be the kind of problem that this test is trying to cover:
> 
>      if do_cxx $CXXFLAGS $EXTRA_CXXFLAGS $CONFIGURE_CXXFLAGS 
> $QEMU_CXXFLAGS -o $TMPE $TMPCXX $TMPO $QEMU_LDFLAGS; then
>          # C++ compiler $cxx works ok with C compiler $cc
>          :
>      else
>          echo "C++ compiler $cxx does not work with C compiler $cc"
>          echo "Disabling C++ specific optional code"
>          cxx=
>      fi
> 
> In the past it detected issues with libasan/libtsan incompatibilities.
> We should either add a test for atomic operations, or just drop the
> test.

We shouldn't assume gcc is GCC:

$ c++ --version
Apple clang version 13.0.0 (clang-1300.0.29.30)
Target: arm64-apple-darwin21.3.0
Thread model: posix
InstalledDir: 
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin

$ g++ --version
Configured with: --prefix=/Applications/Xcode.app/Contents/Developer/usr 
--with-gxx-include-dir=/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/4.2.1
Apple clang version 13.0.0 (clang-1300.0.29.30)
Target: arm64-apple-darwin21.3.0
Thread model: posix
InstalledDir: 
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin

$ gcc --version
Configured with: --prefix=/Applications/Xcode.app/Contents/Developer/usr 
--with-gxx-include-dir=/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/4.2.1
Apple clang version 13.0.0 (clang-1300.0.29.30)
Target: arm64-apple-darwin21.3.0
Thread model: posix
InstalledDir: 
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin

$ clang --version
Apple clang version 13.0.0 (clang-1300.0.29.30)
Target: arm64-apple-darwin21.3.0
Thread model: posix
InstalledDir: 
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin