[cfe-dev] Libcxx cmake warning "Host compiler must support std::atomic!"

Wed Mar 27 14:56:56 PDT 2019

libc++-dev is probably a better list for this discussion. Moving cfe-dev to BCC...

> On Mar 27, 2019, at 2:53 PM, Brian M. Rzycki <brzycki at gmail.com> wrote:
> 
> I've bisected down the previously mentioned commit deltas to the following commit. This is the first instance of the warning message.
> 
> https://github.com/llvm/llvm-project/commit/21450545d14 <https://github.com/llvm/llvm-project/commit/21450545d14> 
> 
> [libc++] decoupling Freestanding atomic<T> from libatomic.a
> This patch introduces non-lockfree atomics that do not require using
> an external libatomic. This work is done with the long-term goal of
> allowing the use of <atomic> in freestanding environments.
> 
> Thanks to Olivier Giroux for the patch.
> Differential Revision: https://reviews.llvm.org/D56913 <https://reviews.llvm.org/D56913>
>  
> llvm-svn: 355318
>  
> 
> On Wed, Mar 27, 2019 at 3:43 PM Brian M. Rzycki <brzycki at gmail.com <mailto:brzycki at gmail.com>> wrote:
> Sorry, I wasn't clear. I meant the change is somewhere between those two commits: those are two nightly builds 24 hours apart.
> 
> On Wed, Mar 27, 2019 at 3:08 PM JF Bastien <jfbastien at apple.com <mailto:jfbastien at apple.com>> wrote:
> 
> 
>> On Mar 27, 2019, at 12:59 PM, Brian M. Rzycki via cfe-dev <cfe-dev at lists.llvm.org <mailto:cfe-dev at lists.llvm.org>> wrote:
>> 
>> Hello Krzysztof,
>> 
>> I've seen these errors in our nightly builds as well and noticed them when tracking down a different set of build breaks last month. I don't honestly know if they can be safely ignored. Our nightly compilers work for our testing even with the errors. I would be interested in knowing what this means and if it impacts us though.
>> 
>> I did a little digging and found when we started seeing the messages. These SHAs are from the LLVM monorepo (https://github.com/llvm/llvm-project.git <https://github.com/llvm/llvm-project.git>). We started seeing them in our builds 2019-March-05. I don't have the exact commit but may have time tomorrow to dig in a bit more.
>> 
>> b306ef12f04635-master (llvm-svn: 355299) # clean
>> 81dbc02671b223-master (llvm-svn: 355375) # emits "Host compiler must support std::atomic!”
> 
> This change?
> https://github.com/llvm/llvm-project/commit/81dbc02671b223 <https://github.com/llvm/llvm-project/commit/81dbc02671b223>
> It’s an LLDB commit, doesn’t seem related. Maybe an adjacent change was the root cause?
> 
> 
>> On Wed, Mar 27, 2019 at 1:20 PM Krzysztof Parzyszek via cfe-dev <cfe-dev at lists.llvm.org <mailto:cfe-dev at lists.llvm.org>> wrote:
>> I'm seeing the following warning during cmake. I'm not sure when it started. Is this a known issue? Can it be safely ignored?
>> 
>> CMake Warning at projects/libcxx/cmake/Modules/CheckLibcxxAtomic.cmake:49 (message):
>>   Host compiler must support std::atomic!
>> Call Stack (most recent call first):
>>   projects/libcxx/cmake/config-ix.cmake:63 (include)
>>   projects/libcxx/CMakeLists.txt:476 (include)
>> 
>> It's also showing up in the upstream bots:
>> http://lab.llvm.org:8011/builders/libcxx-libcxxabi-x86_64-linux-debian/builds/1189/steps/cmake/logs/stdio <http://lab.llvm.org:8011/builders/libcxx-libcxxabi-x86_64-linux-debian/builds/1189/steps/cmake/logs/stdio>
>> 
>> The linker errors (in my cmake) are actually:
>> CMakeFiles/cmTC_354e0.dir/src.cxx.o: In function `__clang_call_terminate':
>> src.cxx:(.text.__clang_call_terminate[__clang_call_terminate]+0x2): undefined reference to `__cxa_begin_catch'
>> src.cxx:(.text.__clang_call_terminate[__clang_call_terminate]+0xb): undefined reference to `std::terminate()'
>> CMakeFiles/cmTC_354e0.dir/src.cxx.o:(.data.DW.ref.__gxx_personality_v0[DW.ref.__gxx_personality_v0]+0x0): undefined reference to `__gxx_personality_v0'
>> clang-8: error: linker command failed with exit code 1 (use -v to see invocation)
>> CMakeFiles/cmTC_354e0.dir/build.make:97: recipe for target 'cmTC_354e0' failed
>> 
>> -- 
>> Krzysztof Parzyszek  kparzysz at quicinc.com <mailto:kparzysz at quicinc.com>   LLVM compiler development
>> 
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