[runtimes] [openmp] `-nostdlib++` added to `CMAKE_REQUIRED_FLAGS` breaks hwloc detection for OMPT

[mgorny]

To reproduce:

$ cmake -G Ninja -DLLVM_ENABLE_RUNTIMES=openmp -DLIBOMP_USE_HWLOC=ON ${path_to_llvm_project}/runtimes
[…]
-- Looking for hwloc.h
-- Looking for hwloc.h - not found
-- Looking for hwloc_topology_init in /usr/lib64/libhwloc.so
-- Looking for hwloc_topology_init in /usr/lib64/libhwloc.so - not found
-- LIBOMP: Could not find hwloc
CMake Error at /home/mgorny/git/llvm-project/openmp/runtime/cmake/LibompUtils.cmake:26 (message):
  LIBOMP: Hwloc requested but not available
Call Stack (most recent call first):
  /home/mgorny/git/llvm-project/openmp/runtime/CMakeLists.txt:387 (libomp_error_say)


-- Configuring incomplete, errors occurred!

CMakeFiles/CMakeConfigureLog.yaml hints at the problem:

  -
    kind: "try_compile-v1"
    backtrace:
      - "/usr/share/cmake/Modules/CheckIncludeFile.cmake:90 (try_compile)"
      - "/home/mgorny/git/llvm-project/openmp/runtime/cmake/config-ix.cmake:351 (check_include_file)"
      - "/home/mgorny/git/llvm-project/openmp/runtime/CMakeLists.txt:276 (include)"
    checks:
      - "Looking for hwloc.h"
    directories:
      source: "/home/mgorny/git/llvm-project/build/CMakeFiles/CMakeScratch/TryCompile-EEYwvY"
      binary: "/home/mgorny/git/llvm-project/build/CMakeFiles/CMakeScratch/TryCompile-EEYwvY"
    cmakeVariables:
      CMAKE_C_FLAGS: " -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wno-missing-field-initializers -Wno-comment -fdiagnostics-color -Wall -Wcast-qual -Wimplicit-fallthrough -Wsign-compare -Wno-extra -Wno-pedantic -Wno-maybe-uninitialized -fno-semantic-interposition -fdata-sections"
      CMAKE_C_FLAGS_DEBUG: "-g"
      CMAKE_EXE_LINKER_FLAGS: ""
      CMAKE_MODULE_PATH: "/home/mgorny/git/llvm-project/openmp/runtime/cmake;/home/mgorny/git/llvm-project/openmp/cmake;/home/mgorny/git/llvm-project/openmp/../cmake/Modules;/home/mgorny/git/llvm-project/runtimes/cmake;/home/mgorny/git/llvm-project/runtimes/cmake/modules;/home/mgorny/git/llvm-project/runtimes/../cmake;/home/mgorny/git/llvm-project/runtimes/../cmake/Modules;/home/mgorny/git/llvm-project/runtimes/../llvm/cmake;/home/mgorny/git/llvm-project/runtimes/../llvm/cmake/modules"
    buildResult:
      variable: "LIBOMP_HAVE_HWLOC_H"
      cached: true
      stdout: |
        Change Dir: '/home/mgorny/git/llvm-project/build/CMakeFiles/CMakeScratch/TryCompile-EEYwvY'
        
        Run Build Command(s): /usr/bin/ninja -v cmTC_5eb96
        [1/2] /usr/bin/cc   -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wno-missing-field-initializers -Wno-comment -fdiagnostics-color -Wall -Wcast-qual -Wimplicit-fallthrough -Wsign-compare -Wno-extra -Wno-pedantic -Wno-maybe-uninitialized -fno-semantic-interposition -fdata-sections  -nostdlib++ -nostdinc++ -o CMakeFiles/cmTC_5eb96.dir/CheckIncludeFile.c.o -c /home/mgorny/git/llvm-project/build/CMakeFiles/CMakeScratch/TryCompile-EEYwvY/CheckIncludeFile.c
        FAILED: CMakeFiles/cmTC_5eb96.dir/CheckIncludeFile.c.o 
        /usr/bin/cc   -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wno-missing-field-initializers -Wno-comment -fdiagnostics-color -Wall -Wcast-qual -Wimplicit-fallthrough -Wsign-compare -Wno-extra -Wno-pedantic -Wno-maybe-uninitialized -fno-semantic-interposition -fdata-sections  -nostdlib++ -nostdinc++ -o CMakeFiles/cmTC_5eb96.dir/CheckIncludeFile.c.o -c /home/mgorny/git/llvm-project/build/CMakeFiles/CMakeScratch/TryCompile-EEYwvY/CheckIncludeFile.c
        cc: error: unrecognized command-line option ‘-nostdlib++’
        ninja: build stopped: subcommand failed.
        
      exitCode: 1

i.e. the nostdlib++ flags gets appended to both C and C++ compiler flags, effectively breaking all compilations done in C mode.

CC @mstorsjo as the one who added the logic

[llvmbot]

@llvm/issue-subscribers-openmp

Author: Michał Górny (mgorny)

To reproduce:

$ cmake -G Ninja -DLLVM_ENABLE_RUNTIMES=openmp -DLIBOMP_USE_HWLOC=ON ${path_to_llvm_project}/runtimes
[…]
-- Looking for hwloc.h
-- Looking for hwloc.h - not found
-- Looking for hwloc_topology_init in /usr/lib64/libhwloc.so
-- Looking for hwloc_topology_init in /usr/lib64/libhwloc.so - not found
-- LIBOMP: Could not find hwloc
CMake Error at /home/mgorny/git/llvm-project/openmp/runtime/cmake/LibompUtils.cmake:26 (message):
  LIBOMP: Hwloc requested but not available
Call Stack (most recent call first):
  /home/mgorny/git/llvm-project/openmp/runtime/CMakeLists.txt:387 (libomp_error_say)


-- Configuring incomplete, errors occurred!

CMakeFiles/CMakeConfigureLog.yaml hints at the problem:

  -
    kind: "try_compile-v1"
    backtrace:
      - "/usr/share/cmake/Modules/CheckIncludeFile.cmake:90 (try_compile)"
      - "/home/mgorny/git/llvm-project/openmp/runtime/cmake/config-ix.cmake:351 (check_include_file)"
      - "/home/mgorny/git/llvm-project/openmp/runtime/CMakeLists.txt:276 (include)"
    checks:
      - "Looking for hwloc.h"
    directories:
      source: "/home/mgorny/git/llvm-project/build/CMakeFiles/CMakeScratch/TryCompile-EEYwvY"
      binary: "/home/mgorny/git/llvm-project/build/CMakeFiles/CMakeScratch/TryCompile-EEYwvY"
    cmakeVariables:
      CMAKE_C_FLAGS: " -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wno-missing-field-initializers -Wno-comment -fdiagnostics-color -Wall -Wcast-qual -Wimplicit-fallthrough -Wsign-compare -Wno-extra -Wno-pedantic -Wno-maybe-uninitialized -fno-semantic-interposition -fdata-sections"
      CMAKE_C_FLAGS_DEBUG: "-g"
      CMAKE_EXE_LINKER_FLAGS: ""
      CMAKE_MODULE_PATH: "/home/mgorny/git/llvm-project/openmp/runtime/cmake;/home/mgorny/git/llvm-project/openmp/cmake;/home/mgorny/git/llvm-project/openmp/../cmake/Modules;/home/mgorny/git/llvm-project/runtimes/cmake;/home/mgorny/git/llvm-project/runtimes/cmake/modules;/home/mgorny/git/llvm-project/runtimes/../cmake;/home/mgorny/git/llvm-project/runtimes/../cmake/Modules;/home/mgorny/git/llvm-project/runtimes/../llvm/cmake;/home/mgorny/git/llvm-project/runtimes/../llvm/cmake/modules"
    buildResult:
      variable: "LIBOMP_HAVE_HWLOC_H"
      cached: true
      stdout: |
        Change Dir: '/home/mgorny/git/llvm-project/build/CMakeFiles/CMakeScratch/TryCompile-EEYwvY'
        
        Run Build Command(s): /usr/bin/ninja -v cmTC_5eb96
        [1/2] /usr/bin/cc   -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wno-missing-field-initializers -Wno-comment -fdiagnostics-color -Wall -Wcast-qual -Wimplicit-fallthrough -Wsign-compare -Wno-extra -Wno-pedantic -Wno-maybe-uninitialized -fno-semantic-interposition -fdata-sections  -nostdlib++ -nostdinc++ -o CMakeFiles/cmTC_5eb96.dir/CheckIncludeFile.c.o -c /home/mgorny/git/llvm-project/build/CMakeFiles/CMakeScratch/TryCompile-EEYwvY/CheckIncludeFile.c
        FAILED: CMakeFiles/cmTC_5eb96.dir/CheckIncludeFile.c.o 
        /usr/bin/cc   -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wno-missing-field-initializers -Wno-comment -fdiagnostics-color -Wall -Wcast-qual -Wimplicit-fallthrough -Wsign-compare -Wno-extra -Wno-pedantic -Wno-maybe-uninitialized -fno-semantic-interposition -fdata-sections  -nostdlib++ -nostdinc++ -o CMakeFiles/cmTC_5eb96.dir/CheckIncludeFile.c.o -c /home/mgorny/git/llvm-project/build/CMakeFiles/CMakeScratch/TryCompile-EEYwvY/CheckIncludeFile.c
        cc: error: unrecognized command-line option ‘-nostdlib++’
        ninja: build stopped: subcommand failed.
        
      exitCode: 1

i.e. the nostdlib++ flags gets appended to both C and C++ compiler flags, effectively breaking all compilations done in C mode.

CC @mstorsjo as the one who added the logic

[Chrismarsh]

I am seeing this when trying to compile llvm 17.0.6. The error is slightly different in that the flag is accepted, however, there are missing symbols.

    kind: "try_compile-v1"
    backtrace:
      - "/gpfs/tp/gwf/gwf_cmt/cmarsh/spack/install/linux-rhel9-skylake_avx512/gcc-12.3.1/cmake-3.29.6-q6iwwch2crujenzcug42iuvx32hi2mz5/share/cmake-3.29/Modules/CheckLibraryExists.cmake:69 (try_compile)"
      - "/gpfs/tp/gwf/gwf_cmt/cmarsh/spack/stage/spack-stage-llvm-17.0.6-siym653rezmksycrvlez7jah5tk72os3/spack-src/openmp/runtime/cmake/config-ix.cmake:349 (check_library_exists)"
      - "/gpfs/tp/gwf/gwf_cmt/cmarsh/spack/stage/spack-stage-llvm-17.0.6-siym653rezmksycrvlez7jah5tk72os3/spack-src/openmp/runtime/CMakeLists.txt:245 (include)"
    checks:
      - "Looking for hwloc_topology_init in /globalhome/cbm038/HPC/project/spack/install/linux-rhel9-skylake_avx512/gcc-12.3.1/hwloc-2.9.3-rpi4timtsf6t32tbrgvhkxcwfqxnywhv/lib/libhwloc.so"
    directories:
      source: "/gpfs/tp/gwf/gwf_cmt/cmarsh/spack/stage/spack-stage-llvm-17.0.6-siym653rezmksycrvlez7jah5tk72os3/spack-build-siym653/runtimes/runtimes-bins/CMakeFiles/CMakeScratch/TryCompile-XydOOq"
      binary: "/gpfs/tp/gwf/gwf_cmt/cmarsh/spack/stage/spack-stage-llvm-17.0.6-siym653rezmksycrvlez7jah5tk72os3/spack-build-siym653/runtimes/runtimes-bins/CMakeFiles/CMakeScratch/TryCompile-XydOOq"
    cmakeVariables:
      CMAKE_CXX_COMPILER_CLANG_SCAN_DEPS: "CMAKE_CXX_COMPILER_CLANG_SCAN_DEPS-NOTFOUND"
      CMAKE_CXX_COMPILER_TARGET: "x86_64-unknown-linux-gnu"
      CMAKE_C_COMPILER_TARGET: "x86_64-unknown-linux-gnu"
      CMAKE_C_FLAGS: "--gcc-install-dir=/cvmfs/soft.computecanada.ca/gentoo/2023/x86-64-v3/usr/lib/gcc/x86_64-pc-linux-gnu/12 -fPIC -fno-semantic-interposition -Werror=date-time -Werror=unguarded-availability-new -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wmissing-field-initializers -Wimplicit-fallthrough -Wcovered-switch-default -Wstring-conversion -Wmisleading-indentation -Wctad-maybe-unsupported -fdiagnostics-color -ffunction-sections -fdata-sections -Wall -Wcast-qual -Wformat-pedantic -Wimplicit-fallthrough -Wsign-compare -Wno-enum-constexpr-conversion -Wno-extra -Wno-pedantic"
      CMAKE_C_FLAGS_DEBUG: "-g"
      CMAKE_EXE_LINKER_FLAGS: ""
      CMAKE_MODULE_PATH: "/gpfs/tp/gwf/gwf_cmt/cmarsh/spack/stage/spack-stage-llvm-17.0.6-siym653rezmksycrvlez7jah5tk72os3/spack-src/openmp/runtime/cmake;/gpfs/tp/gwf/gwf_cmt/cmarsh/spack/stage/spack-stage-llvm-17.0.6-siym653rezmksycrvlez7jah5tk72os3/spack-src/openmp/cmake;/gpfs/tp/gwf/gwf_cmt/cmarsh/spack/stage/spack-stage-llvm-17.0.6-siym653rezmksycrvlez7jah5tk72os3/spack-src/openmp/../cmake/Modules;/gpfs/tp/gwf/gwf_cmt/cmarsh/spack/stage/spack-stage-llvm-17.0.6-siym653rezmksycrvlez7jah5tk72os3/spack-src/runtimes/cmake;/gpfs/tp/gwf/gwf_cmt/cmarsh/spack/stage/spack-stage-llvm-17.0.6-siym653rezmksycrvlez7jah5tk72os3/spack-src/runtimes/cmake/modules;/gpfs/tp/gwf/gwf_cmt/cmarsh/spack/stage/spack-stage-llvm-17.0.6-siym653rezmksycrvlez7jah5tk72os3/spack-src/runtimes/../cmake;/gpfs/tp/gwf/gwf_cmt/cmarsh/spack/stage/spack-stage-llvm-17.0.6-siym653rezmksycrvlez7jah5tk72os3/spack-src/runtimes/../cmake/Modules;/gpfs/tp/gwf/gwf_cmt/cmarsh/spack/stage/spack-stage-llvm-17.0.6-siym653rezmksycrvlez7jah5tk72os3/spack-src/runtimes/../llvm/cmake;/gpfs/tp/gwf/gwf_cmt/cmarsh/spack/stage/spack-stage-llvm-17.0.6-siym653rezmksycrvlez7jah5tk72os3/spack-src/runtimes/../llvm/cmake/modules;/gpfs/tp/gwf/gwf_cmt/cmarsh/spack/stage/spack-stage-llvm-17.0.6-siym653rezmksycrvlez7jah5tk72os3/spack-build-siym653/lib/cmake/llvm;/gpfs/tp/gwf/gwf_cmt/cmarsh/spack/stage/spack-stage-llvm-17.0.6-siym653rezmksycrvlez7jah5tk72os3/spack-build-siym653/lib/cmake/llvm"
    buildResult:
      variable: "LIBOMP_HAVE_LIBHWLOC"
      cached: true
      stdout: |
        Change Dir: '/gpfs/tp/gwf/gwf_cmt/cmarsh/spack/stage/spack-stage-llvm-17.0.6-siym653rezmksycrvlez7jah5tk72os3/spack-build-siym653/runtimes/runtimes-bins/CMakeFiles/CMakeScratch/TryCompile-XydOOq'
        
        Run Build Command(s): /globalhome/cbm038/HPC/project/spack/install/linux-rhel9-skylake_avx512/gcc-12.3.1/ninja-1.12.0-x2csjlvyad6s7gnfoa5ubpncbt3cu3dg/bin/ninja-build -v cmTC_48e41
        [1/2] /gpfs/tp/gwf/gwf_cmt/cmarsh/spack/stage/spack-stage-llvm-17.0.6-siym653rezmksycrvlez7jah5tk72os3/spack-build-siym653/bin/clang --target=x86_64-unknown-linux-gnu   --gcc-install-dir=/cvmfs/soft.computecanada.ca/gentoo/2023/x86-64-v3/usr/lib/gcc/x86_64-pc-linux-gnu/12 -fPIC -fno-semantic-interposition -Werror=date-time -Werror=unguarded-availability-new -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wmissing-field-initializers -Wimplicit-fallthrough -Wcovered-switch-default -Wstring-conversion -Wmisleading-indentation -Wctad-maybe-unsupported -fdiagnostics-color -ffunction-sections -fdata-sections -Wall -Wcast-qual -Wformat-pedantic -Wimplicit-fallthrough -Wsign-compare -Wno-enum-constexpr-conversion -Wno-extra -Wno-pedantic -DCHECK_FUNCTION_EXISTS=hwloc_topology_init  --start-no-unused-arguments --unwindlib=none --end-no-unused-arguments -nostdlib++ -nostdinc++ -MD -MT CMakeFiles/cmTC_48e41.dir/CheckFunctionExists.c.o -MF CMakeFiles/cmTC_48e41.dir/CheckFunctionExists.c.o.d -o CMakeFiles/cmTC_48e41.dir/CheckFunctionExists.c.o -c /gpfs/tp/gwf/gwf_cmt/cmarsh/spack/stage/spack-stage-llvm-17.0.6-siym653rezmksycrvlez7jah5tk72os3/spack-build-siym653/runtimes/runtimes-bins/CMakeFiles/CMakeScratch/TryCompile-XydOOq/CheckFunctionExists.c
        [2/2] : && /gpfs/tp/gwf/gwf_cmt/cmarsh/spack/stage/spack-stage-llvm-17.0.6-siym653rezmksycrvlez7jah5tk72os3/spack-build-siym653/bin/clang --target=x86_64-unknown-linux-gnu --gcc-install-dir=/cvmfs/soft.computecanada.ca/gentoo/2023/x86-64-v3/usr/lib/gcc/x86_64-pc-linux-gnu/12 -fPIC -fno-semantic-interposition -Werror=date-time -Werror=unguarded-availability-new -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wmissing-field-initializers -Wimplicit-fallthrough -Wcovered-switch-default -Wstring-conversion -Wmisleading-indentation -Wctad-maybe-unsupported -fdiagnostics-color -ffunction-sections -fdata-sections -Wall -Wcast-qual -Wformat-pedantic -Wimplicit-fallthrough -Wsign-compare -Wno-enum-constexpr-conversion -Wno-extra -Wno-pedantic -DCHECK_FUNCTION_EXISTS=hwloc_topology_init  --start-no-unused-arguments --unwindlib=none --end-no-unused-arguments -nostdlib++ -nostdinc++  CMakeFiles/cmTC_48e41.dir/CheckFunctionExists.c.o -o cmTC_48e41 -L/globalhome/cbm038/HPC/project/spack/install/linux-rhel9-skylake_avx512/gcc-12.3.1/hwloc-2.9.3-rpi4timtsf6t32tbrgvhkxcwfqxnywhv/lib -Wl,-rpath,/globalhome/cbm038/HPC/project/spack/install/linux-rhel9-skylake_avx512/gcc-12.3.1/hwloc-2.9.3-rpi4timtsf6t32tbrgvhkxcwfqxnywhv/lib  /globalhome/cbm038/HPC/project/spack/install/linux-rhel9-skylake_avx512/gcc-12.3.1/hwloc-2.9.3-rpi4timtsf6t32tbrgvhkxcwfqxnywhv/lib/libhwloc.so && :
        FAILED: cmTC_48e41 
        : && /gpfs/tp/gwf/gwf_cmt/cmarsh/spack/stage/spack-stage-llvm-17.0.6-siym653rezmksycrvlez7jah5tk72os3/spack-build-siym653/bin/clang --target=x86_64-unknown-linux-gnu --gcc-install-dir=/cvmfs/soft.computecanada.ca/gentoo/2023/x86-64-v3/usr/lib/gcc/x86_64-pc-linux-gnu/12 -fPIC -fno-semantic-interposition -Werror=date-time -Werror=unguarded-availability-new -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wmissing-field-initializers -Wimplicit-fallthrough -Wcovered-switch-default -Wstring-conversion -Wmisleading-indentation -Wctad-maybe-unsupported -fdiagnostics-color -ffunction-sections -fdata-sections -Wall -Wcast-qual -Wformat-pedantic -Wimplicit-fallthrough -Wsign-compare -Wno-enum-constexpr-conversion -Wno-extra -Wno-pedantic -DCHECK_FUNCTION_EXISTS=hwloc_topology_init  --start-no-unused-arguments --unwindlib=none --end-no-unused-arguments -nostdlib++ -nostdinc++  CMakeFiles/cmTC_48e41.dir/CheckFunctionExists.c.o -o cmTC_48e41 -L/globalhome/cbm038/HPC/project/spack/install/linux-rhel9-skylake_avx512/gcc-12.3.1/hwloc-2.9.3-rpi4timtsf6t32tbrgvhkxcwfqxnywhv/lib -Wl,-rpath,/globalhome/cbm038/HPC/project/spack/install/linux-rhel9-skylake_avx512/gcc-12.3.1/hwloc-2.9.3-rpi4timtsf6t32tbrgvhkxcwfqxnywhv/lib  /globalhome/cbm038/HPC/project/spack/install/linux-rhel9-skylake_avx512/gcc-12.3.1/hwloc-2.9.3-rpi4timtsf6t32tbrgvhkxcwfqxnywhv/lib/libhwloc.so && :
        /cvmfs/soft.computecanada.ca/gentoo/2023/x86-64-v3/usr/x86_64-pc-linux-gnu/binutils-bin/2.41/ld: /cvmfs/soft.computecanada.ca/gentoo/2023/x86-64-v3/usr/lib/gcc/x86_64-pc-linux-gnu/12/libgcc_s.so.1: undefined reference to `_dl_find_object@GLIBC_2.35'
        /cvmfs/soft.computecanada.ca/gentoo/2023/x86-64-v3/usr/x86_64-pc-linux-gnu/binutils-bin/2.41/ld: /cvmfs/soft.computecanada.ca/gentoo/2023/x86-64-v3/usr/lib/gcc/x86_64-pc-linux-gnu/12/libstdc++.so.6: undefined reference to `arc4random@GLIBC_2.36'
        clang: error: linker command failed with exit code 1 (use -v to see invocation)
        ninja: build stopped: subcommand failed.
        
      exitCode: 1
...

[mstorsjo]

Sorry, I somehow missed the initial notification on this back in April... I'd like to CC in @petrhosek as well, who also has worked a lot on this aspect.

So I presume the source of these flags is in https://github.com/llvm/llvm-project/blob/llvmorg-19-init/runtimes/CMakeLists.txt#L138-L149. They're quite essential for any probing in C++ mode.

Offhand, I don't have any good idea about how to try to fix this issue. Does @petrhosek have any ideas?

[h-vetinari]

I've run into this with libcxx 18.1.8 on linux, where dl gets misdetected:

-- Looking for dladdr in dl
-- Looking for dladdr in dl - not found
-- Looking for pthread_once in pthread
-- Looking for pthread_once in pthread - not found

and then compilation fails on missing symbols for dladdr. Looking under the hood of that detection failure, it's likewise due to -nostdlib++:

    kind: "try_compile-v1"
    backtrace:
      - "$BUILD_PREFIX/share/cmake-3.30/Modules/CheckLibraryExists.cmake:69 (try_compile)"
      - "$SRC_DIR/libcxxabi/cmake/config-ix.cmake:109 (check_library_exists)"
      - "$SRC_DIR/libcxxabi/CMakeLists.txt:249 (include)"
    checks:
      - "Looking for dladdr in dl"
    directories:
      source: "$SRC_DIR/build/CMakeFiles/CMakeScratch/TryCompile-dRIlTz"
      binary: "$SRC_DIR/build/CMakeFiles/CMakeScratch/TryCompile-dRIlTz"
    cmakeVariables:
      CMAKE_C_FLAGS: "-march=nocona -mtune=haswell -ftree-vectorize -fPIC -fstack-protector-strong -fno-plt -O2 -ffunction-sections -pipe -isystem $PREFIX/include -fdebug-prefix-map=$SRC_DIR=/usr/local/src/conda/libcxx_and_libcxxabi-18.1.8 -fdebug-prefix-map=$PREFIX=/usr/local/src/conda-prefix -I$PREFIX/include -I$BUILD_PREFIX/include -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wno-missing-field-initializers -Wno-comment -fdiagnostics-color"
      CMAKE_C_FLAGS_DEBUG: "-g"
      CMAKE_EXE_LINKER_FLAGS: "-Wl,-O2 -Wl,--sort-common -Wl,--as-needed -Wl,-z,relro -Wl,-z,now -Wl,--disable-new-dtags -Wl,--gc-sections -Wl,--allow-shlib-undefined -Wl,-rpath,$PREFIX/lib -Wl,-rpath-link,$PREFIX/lib -L$PREFIX/lib -L$PREFIX/lib -Wl,-rpath,$PREFIX/lib -L$BUILD_PREFIX/lib -Wl,-rpath,$BUILD_PREFIX/lib"
      CMAKE_MODULE_PATH: "$SRC_DIR/libcxxabi/cmake;$SRC_DIR/libcxxabi/cmake/Modules;$SRC_DIR/libcxxabi/cmake;$SRC_DIR/libcxxabi/cmake/Modules;$SRC_DIR/libcxxabi/../runtimes/cmake/Modules;$SRC_DIR/libcxxabi/../cmake;$SRC_DIR/libcxxabi/../cmake/Modules;$SRC_DIR/runtimes/cmake;$SRC_DIR/runtimes/cmake/modules;$SRC_DIR/runtimes/../cmake;$SRC_DIR/runtimes/../cmake/Modules;$SRC_DIR/runtimes/../llvm/cmake;$SRC_DIR/runtimes/../llvm/cmake/modules"
    buildResult:
      variable: "LIBCXXABI_HAS_DL_LIB"
      cached: true
      stdout: |
        Change Dir: '$SRC_DIR/build/CMakeFiles/CMakeScratch/TryCompile-dRIlTz'
        
        Run Build Command(s): $BUILD_PREFIX/bin/ninja -v cmTC_c57b3
        [1/2] $BUILD_PREFIX/bin/x86_64-conda-linux-gnu-cc   -march=nocona -mtune=haswell -ftree-vectorize -fPIC -fstack-protector-strong -fno-plt -O2 -ffunction-sections -pipe -isystem $PREFIX/include -fdebug-prefix-map=$SRC_DIR=/usr/local/src/conda/libcxx_and_libcxxabi-18.1.8 -fdebug-prefix-map=$PREFIX=/usr/local/src/conda-prefix -I$PREFIX/include -I$BUILD_PREFIX/include -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wno-missing-field-initializers -Wno-comment -fdiagnostics-color -DCHECK_FUNCTION_EXISTS=dladdr  -nostdlib++ -nostdinc++ -nostdlib++ -o CMakeFiles/cmTC_c57b3.dir/CheckFunctionExists.c.o -c $SRC_DIR/build/CMakeFiles/CMakeScratch/TryCompile-dRIlTz/CheckFunctionExists.c
        FAILED: CMakeFiles/cmTC_c57b3.dir/CheckFunctionExists.c.o 
        $BUILD_PREFIX/bin/x86_64-conda-linux-gnu-cc   -march=nocona -mtune=haswell -ftree-vectorize -fPIC -fstack-protector-strong -fno-plt -O2 -ffunction-sections -pipe -isystem $PREFIX/include -fdebug-prefix-map=$SRC_DIR=/usr/local/src/conda/libcxx_and_libcxxabi-18.1.8 -fdebug-prefix-map=$PREFIX=/usr/local/src/conda-prefix -I$PREFIX/include -I$BUILD_PREFIX/include -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wno-missing-field-initializers -Wno-comment -fdiagnostics-color -DCHECK_FUNCTION_EXISTS=dladdr  -nostdlib++ -nostdinc++ -nostdlib++ -o CMakeFiles/cmTC_c57b3.dir/CheckFunctionExists.c.o -c $SRC_DIR/build/CMakeFiles/CMakeScratch/TryCompile-dRIlTz/CheckFunctionExists.c
        x86_64-conda-linux-gnu-cc: error: unrecognized command-line option '-nostdlib++'
        x86_64-conda-linux-gnu-cc: error: unrecognized command-line option '-nostdlib++'
        ninja: build stopped: subcommand failed.
        
      exitCode: 1

[Chrismarsh]

Is there any progress on this or anything else that can be contributed to help?

[mstorsjo]

I'm trying to wrap my head around why this isn't an issue in more cases than it does currently.

With clang, passing -nostdlib++ while linking with the C mode compiler, isn't an issue.

GCC supports -nostdlib++ since GCC 13, but even there, doing e.g. gcc -nostdlib++ foo.c seems to run fine (tested on Ubuntu 24.04 just now).

The cases where this is an issue - what are the respective C and C++ compilers that are involved in the cmake configurations, where the C++ compiler apparently supports the option, but the C compiler doesn't?

[mgorny]

$ gcc -nostdlib++ foo.c
gcc: error: unrecognized command-line option ‘-nostdlib++’
$ gcc --version
gcc (Gentoo 14.2.1_p20240817 p4) 14.2.1 20240817
Copyright (C) 2024 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

[mstorsjo]

$ gcc -nostdlib++ foo.c
gcc: error: unrecognized command-line option ‘-nostdlib++’
$ gcc --version
gcc (Gentoo 14.2.1_p20240817 p4) 14.2.1 20240817
Copyright (C) 2024 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

That’s odd, I see the same behavior as before, with gcc (Ubuntu 14.2.0-4ubuntu1) 14.2.0:

$ gcc -nostdlib++ test.c
$ gcc --version
gcc (Ubuntu 14.2.0-4ubuntu1) 14.2.0
Copyright (C) 2024 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

I wonder which one has downstream patches that affects this behavior…