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[cmake] Skip mold with gcc < 12.1 #4036

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Merged
merged 3 commits into from
Apr 11, 2025
Merged

[cmake] Skip mold with gcc < 12.1 #4036

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4e165aa
[cmake] Skip `mold` with `gcc` < 12.1
ricab Apr 10, 2025
9d94ea7
[cmake] Explicitly set the linker
ricab Apr 10, 2025
e106b64
[cmake/configure-linker] use fallback method for < GCC 12.1
xmkg Apr 10, 2025
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23 changes: 19 additions & 4 deletions src/cmake/configure-linker.cmake
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Original file line number Diff line number Diff line change
Expand Up @@ -24,20 +24,35 @@ function(configure_linker)
set (LLD_LINKER_NAMES lld-link)
else()
set(LLD_LINKER_NAMES ld.lld ld64.lld)
set(MOLD_LINKER_NAMES mold sold)
set(MOLD_LINKER_NAMES /usr/libexec/mold/ld /usr/local/libexec/mold/ld mold sold)
find_program(MOLD_LINKER NAMES ${MOLD_LINKER_NAMES})
endif()

find_program(LLD_LINKER NAMES ${LLD_LINKER_NAMES})

if(MOLD_LINKER)
message(STATUS "configure_linker: `mold` found in environment, will use it as default.")
message(STATUS "configure_linker: `mold` (${MOLD_LINKER}) found in environment, will use it as default.")
set(CMAKE_LINKER_TYPE MOLD PARENT_SCOPE)
if(MOLD_LINKER MATCHES "libexec")
string(REPLACE "/ld" "" MOLD_LINKER_PATH ${MOLD_LINKER})
#
# The reason why we're setting this variables is that GCC < 12.1 does not
# support the "-fuse-ld=mold" parameter, which causes CMake configure to fail
# when configured with mold + < GCC 12.1 combo. There's a detailed discussion
# about this in CMake issue board: https://gitlab.kitware.com/cmake/cmake/-/issues/25748#note_1494202
# The gist of itis that CMake maintainers decided to not to cover this edge case
# so we have to intervene.
#
# CMake will override this with "-fuse-ld=mold" for clang and GCC >= 12.1
#
set(CMAKE_C_USING_LINKER_MOLD "-B${MOLD_LINKER_PATH}" PARENT_SCOPE)
set(CMAKE_CXX_USING_LINKER_MOLD "-B${MOLD_LINKER_PATH}" PARENT_SCOPE)
endif()
elseif(LLD_LINKER)
message(STATUS "configure_linker: `lld` found in environment, will use it as default.")
message(STATUS "configure_linker: `lld` (${LLD_LINKER}) found in environment, will use it as default.")
set(CMAKE_LINKER_TYPE LLD PARENT_SCOPE)
else()
message(STATUS "configure_linker: neither `mold` or `lld` is present in the environment, will use the toolchain default.")
message(STATUS "configure_linker: could use neither `mold` nor `lld`; will use the toolchain default.")
endif()
else()
message(STATUS "configure_linker: will use the user specified linker: `${CMAKE_LINKER_TYPE}`")
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