60 lines
1.8 KiB
CMake
60 lines
1.8 KiB
CMake
# Original issue:
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# * https://gitlab.kitware.com/cmake/cmake/-/issues/23021#note_1098733
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#
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# For reference:
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# * https://gcc.gnu.org/wiki/Atomic/GCCMM
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#
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# riscv64 specific:
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# * https://lists.debian.org/debian-riscv/2022/01/msg00009.html
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#
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# ATOMICS_FOUND - system has C++ atomics
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# ATOMICS_LIBRARIES - libraries needed to use C++ atomics
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if (ATOMICS_FOUND)
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return()
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endif()
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include(CheckCXXSourceCompiles)
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# RISC-V only has 32-bit and 64-bit atomic instructions. GCC is supposed
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# to convert smaller atomics to those larger ones via masking and
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# shifting like LLVM, but it’s a known bug that it does not. This means
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# anything that wants to use atomics on 1-byte or 2-byte types needs
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# to link atomic library, but not 4-byte or 8-byte (though it does no harm).
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set(ATOMIC_CODE
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"
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#include <atomic>
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#include <cstdint>
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std::atomic<std::uint8_t> n8(0); // riscv64
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std::atomic<std::uint64_t> n64(0); // armel, mipsel, powerpc
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int main() {
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++n8;
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++n64;
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}")
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set(ATOMICS_LIBS " " "-latomic")
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foreach (ATOMICS_LIBRARY ${ATOMICS_LIBS})
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unset(ATOMICS_FOUND CACHE)
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set(CMAKE_REQUIRED_LIBRARIES "${ATOMICS_LIBRARY}")
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check_cxx_source_compiles("${ATOMIC_CODE}" ATOMICS_FOUND)
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unset(CMAKE_REQUIRED_LIBRARIES)
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if (ATOMICS_FOUND)
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if (NOT ATOMICS_LIBRARY STREQUAL " ")
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include(FindPackageHandleStandardArgs)
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find_package_handle_standard_args(Atomics DEFAULT_MSG ATOMICS_LIBRARY)
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set(ATOMICS_LIBRARIES "${ATOMICS_LIBRARY}" CACHE STRING "Atomic library" FORCE)
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else()
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set(ATOMICS_LIBRARIES "" CACHE STRING "Atomic operations library" FORCE)
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endif()
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break()
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endif()
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endforeach()
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if (Atomics_FIND_REQUIRED AND NOT ATOMICS_FOUND)
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message(FATAL_ERROR "Atomic operations library isn't found.")
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endif()
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unset(ATOMICS_LIBRARY)
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unset(ATOMICS_LIBS)
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unset(ATOMIC_CODE)
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