[PATCH] D68964: cmake/modules/CheckAtomic.cmake: catch false positives in RISC-V

[Gokturk Yuksek via Phabricator via llvm-commits]

gokturk added a comment.

Please do not merge.

I do not see how the result of this check is propagated to LDFLAGS by the build system. Even after this patch, the build fails the same way:

  /usr/lib/gcc/riscv64-unknown-linux-gnu/9.1.0/../../../../riscv64-unknown-linux-gnu/bin/ld: tools/dsymutil/CMakeFiles/dsymutil.dir/dsymutil.cpp.o: in function `.LEHB79':
  dsymutil.cpp:(.text._ZNSt17_Function_handlerIFvvESt5_BindIFZ4mainEUlSt10shared_ptrIN4llvm14raw_fd_ostreamEENS3_8dsymutil11LinkOptionsEE_S5_S7_EEE9_M_invokeERKSt9_Any_data+0x168): undefined reference to `__atomic_fetch_and_1'
  /usr/lib/gcc/riscv64-unknown-linux-gnu/9.1.0/../../../../riscv64-unknown-linux-gnu/bin/ld: tools/dsymutil/CMakeFiles/dsymutil.dir/dsymutil.cpp.o: in function `.L0 ':
  dsymutil.cpp:(.text._ZNSt17_Function_handlerIFvvESt5_BindIFZ4mainEUlSt10shared_ptrIN4llvm14raw_fd_ostreamEENS3_8dsymutil11LinkOptionsEE_S5_S7_EEE9_M_invokeERKSt9_Any_data+0x2ee): undefined reference to `__atomic_fetch_and_1'
  /usr/lib/gcc/riscv64-unknown-linux-gnu/9.1.0/../../../../riscv64-unknown-linux-gnu/bin/ld: dsymutil.cpp:(.text.startup.main+0xefc): undefined reference to `__atomic_fetch_and_1'
  /usr/lib/gcc/riscv64-unknown-linux-gnu/9.1.0/../../../../riscv64-unknown-linux-gnu/bin/ld: tools/dsymutil/CMakeFiles/dsymutil.dir/dsymutil.cpp.o: in function `.L2508':
  dsymutil.cpp:(.text.startup.main+0x1b2a): undefined reference to `__atomic_fetch_and_1'
  collect2: error: ld returned 1 exit status

libcxx has the following in CMakeLists.txt:

  if (LIBCXX_HAVE_CXX_ATOMICS_WITH_LIB)
    target_link_libraries(${target} PRIVATE atomic)
  endif()

but LLVM's CMakeLists.txt does not contain anything like that.

I think we have potentially 3 separate bugs:

1. In LLVM, the check for libatomic has false positives in RISC-V (which the patch is addressing).
2. In LLVM, the result of the libatomic check is not being used to add '-latomic' to LDFLAGS.
3. libcxx libatomic check is likely to exhibit false positive in RISC-V.


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D68964/new/

https://reviews.llvm.org/D68964