fix: Link `atomic` into LLVMOrcJIT on platforms without hardware support for atomics

[414owen]

Summary

When linking LLVMOrcJit on ARMv6, I get an error about a missing reference to __atomic_fetch_add_8.

This seems to be because on platforms without hardware support, we need to link in atomic.

The full error is below:

[ 66%] Linking CXX shared library ../../libLLVMOrcJIT.so
/usr/bin/ld: CMakeFiles/LLVMOrcJIT.dir/ObjectLinkingLayer.cpp.o: in function `llvm::orc::ObjectLinkingLayer::add(llvm::IntrusiveRefCntPtr<llvm::orc::ResourceTracker>, std::unique_ptr<llvm::jitlink::LinkGraph, std::default_delete<llvm::jitlink::LinkGraph> >)':
ObjectLinkingLayer.cpp:(.text._ZN4llvm3orc18ObjectLinkingLayer3addENS_18IntrusiveRefCntPtrINS0_15ResourceTrackerEEESt10unique_ptrINS_7jitlink9LinkGraphESt14default_deleteIS7_EE+0x3e0): undefined reference to `__atomic_fetch_add_8'
collect2: error: ld returned 1 exit status
gmake[2]: *** [lib/ExecutionEngine/Orc/CMakeFiles/LLVMOrcJIT.dir/build.make:659: lib/libLLVMOrcJIT.so.14] Error 1
gmake[1]: *** [CMakeFiles/Makefile2:13868: lib/ExecutionEngine/Orc/CMakeFiles/LLVMOrcJIT.dir/all] Error 2
gmake: *** [Makefile:171: all] Error 2

[414owen]

Added better git commit description

[lhames]

Thanks very much @414owen!

Do you have commit access? If not then please just let me know what name and email you'd like me to use for attribution and I can commit on your behalf.

[414owen]

Hi @lhames,
No, I don't have commit access (I created an account just to post this diff really).
You can use "Owen Shepherd <[e-mail]>" for the attribution.

I let the build run for a bit and got another similar error, but I'm not sure which cmake file to add the fix to in the next case:

[ 70%] Linking CXX shared library ../../../lib/liblldCOFF.so
/usr/bin/ld: CMakeFiles/lldCOFF.dir/DebugTypes.cpp.o: in function `void llvm::function_ref<void (unsigned int)>::callback_fn<lld::coff::TypeMerger::mergeTypesWithGHash()::{lambda(unsigned int)#3}>(int, unsigned int)':
DebugTypes.cpp:(.text._ZN4llvm12function_refIFvjEE11callback_fnIZN3lld4coff10TypeMerger19mergeTypesWithGHashEvEUljE1_EEvij+0x11c): undefined reference to `__atomic_load_8'
/usr/bin/ld: DebugTypes.cpp:(.text._ZN4llvm12function_refIFvjEE11callback_fnIZN3lld4coff10TypeMerger19mergeTypesWithGHashEvEUljE1_EEvij+0x1e4): undefined reference to `__atomic_compare_exchange_8'
collect2: error: ld returned 1 exit status
gmake[2]: *** [tools/lld/COFF/CMakeFiles/lldCOFF.dir/build.make:380: lib/liblldCOFF.so.14] Error 1
gmake[1]: *** [CMakeFiles/Makefile2:17562: tools/lld/COFF/CMakeFiles/lldCOFF.dir/all] Error 2
gmake: *** [Makefile:171: all] Error 2

Any pointers?

[lhames]

My first guess would be llvm-project/lld/COFF/CMakeLists.txt, but it's worth double-checking that with an LLD reviewer.

I'm just rebuilding to test this locally now and hope to have it committed shortly.

[thesamesam]

You should be able to use the mechanism from https://github.com/llvm/llvm-project/commit/fa981b541365190ae646d2dce575706cd0626cf7 instead for both the original change here and any future changes?

llvm/lib/ExecutionEngine/Orc/CMakeLists.txt

+if (NOT HAVE_CXX_ATOMICS64_WITHOUT_LIB)
+  set (atomic_lib atomic)
+endif()
+
 if( CMAKE_HOST_UNIX AND HAVE_LIBRT )
   set(rt_lib rt)
 endif()
 
 add_llvm_component_library(LLVMOrcJIT
   COFFVCRuntimeSupport.cpp
   COFFPlatform.cpp
   CompileOnDemandLayer.cpp
add_llvm_component_library(LLVMOrcJIT
   ${LLVM_MAIN_INCLUDE_DIR}/llvm/ExecutionEngine/Orc
 
   DEPENDS
   intrinsics_gen
 
   LINK_LIBS
   ${LLVM_PTHREAD_LIB}
   ${rt_lib}
+  ${atomic_lib}
 
   LINK_COMPONENTS
   Core
   ExecutionEngine
   JITLink
   Object
   OrcShared
   OrcTargetProcess