54 lines
1.7 KiB
CMake
54 lines
1.7 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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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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# -latomic, 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<uint8_t> n8 (0); // riscv64
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std::atomic<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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return 0;
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}")
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check_cxx_source_compiles("${atomic_code}" ATOMICS_LOCK_FREE_INSTRUCTIONS)
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if (ATOMICS_LOCK_FREE_INSTRUCTIONS)
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set(ATOMICS_FOUND TRUE)
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set(ATOMICS_LIBRARIES)
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else()
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set(CMAKE_REQUIRED_LIBRARIES "-latomic")
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check_cxx_source_compiles("${atomic_code}" ATOMICS_IN_LIBRARY)
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set(CMAKE_REQUIRED_LIBRARIES)
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if (ATOMICS_IN_LIBRARY)
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set(ATOMICS_LIBRARY atomic)
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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})
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unset(ATOMICS_LIBRARY)
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else()
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if (Atomics_FIND_REQUIRED)
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message(FATAL_ERROR "Neither lock free instructions nor -latomic found.")
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endif()
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endif()
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endif()
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unset(atomic_code)
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