unsupported option '-mwindows' for target 'x86_64-pc-windows-msvc'

[jakirkham]

Am seeing the following error when building with Clang 17.0.2 on Windows using MSVC 14.3. AFAICT this is a similar issue as occurred with MinGW ( #64464 ), but this is with MSVC. More background in the OP of PR ( #67891 ) (though that doesn't fix the MSVC target issue)

clang.exe -DHAVE_CONFIG_H -I. -I../../include/private/autogen -I../../include/hwloc/autogen  -I"/d/bld/libhwloc_1696580296225/work"/include -I"/d/bld/libhwloc_1696580296225/work"/include -I../../utils/hwloc  -DLSTOPO_HAVE_GRAPHICS -ID:/bld/libhwloc_1696580296225/_h_env/Library/include -O2 -D_CRT_SECURE_NO_WARNINGS -D_MT -D_DLL -nostdlib -Xclang --dependent-lib=msvcrt -fuse-ld=lld -Dputenv=_putenv -Dmktemp=_mktemp -Dopen=_open -Dunlink=_unlink -Dclose=_close -Dstrdup=_strdup  -mwindows -ID:/bld/libhwloc_1696580296225/_h_env/Library/include -O2 -D_CRT_SECURE_NO_WARNINGS -D_MT -D_DLL -nostdlib -Xclang --dependent-lib=msvcrt -fuse-ld=lld -c -o lstopo_win-lstopo.o `test -f 'lstopo.c' || echo './'`lstopo.c
clang: error: unsupported option '-mwindows' for target 'x86_64-pc-windows-msvc'

[mstorsjo]

In MSVC mode, the -mwindows flag has never had any effect, and you have probably been getting a warning like clang-16: warning: argument unused during compilation: '-mwindows' [-Wunused-command-line-argument] in older versions.

In conda-forge/libhwloc-feedstock#69 (comment) I see this comment:

However, the problem could be on the libhwloc side, as -mwindows may be a flag that does not make sense for the msvc toolchain of clang, and just by chance this was working on clang <= 16 .

That's exactly the case.

[jakirkham]

Gotcha. Thanks for your help! 🙏

Will follow up with hwloc then

[jakirkham]

Raised hwloc issue: open-mpi/hwloc#631

[bgoglin]

(hwloc upstream developer)
GCC -mwindows means "It specifies that a GUI application is to be generated by instructing the linker to set the PE header subsystem type appropriately. "
Is there any way to do that with Clang?

[mstorsjo]

GCC -mwindows means "It specifies that a GUI application is to be generated by instructing the linker to set the PE header subsystem type appropriately. " Is there any way to do that with Clang?

With Clang in MinGW mode, you can still use -mwindows in that exact same way.

With MSVC, and Clang acting in MSVC mode, you don't normally pass any such flag. It is possible to pass it to the linker (in MSVC mode, most build systems invoke link.exe or lld-link directly without using the compiler driver inbetween) by setting a suitable subsystem parameter, but in most cases, you don't need to, afaik. If no subsystem is specified, it is inferred from the symbols of the linked object files: https://github.com/llvm/llvm-project/blob/llvmorg-17.0.3/lld/COFF/Driver.cpp#L761-L784

[bgoglin]

Hmm, thanks, that's a bit too complicated for my basic knowledge of all these ways to build on windows. I was going to remove -mwindows if building for "x86_64-pc-windows-msvc", but our configure actually see "x86_64-pc-mingw64" instead. It also sees that the compiler is Clang with _MSC_VER defined. Is that a good way to detect this case?

[mstorsjo]

I was going to remove -mwindows if building for "x86_64-pc-windows-msvc", but our configure actually see "x86_64-pc-mingw64" instead.

I'm not sure what your build environment is - but it seems to be made up from a number of not entirely matched components. You might have some mingw tools somewhere, but the Clang executable you have defaults to MSVC mode.

Primarily, Clang in MSVC mode would be used via the clang-cl interface, which is compatible with the argument style of MSVC's cl.exe. However one can also use Clang in MSVC mode with the GCC-like interface, but that's occasionally confusing.

It also sees that the compiler is Clang with _MSC_VER defined. Is that a good way to detect this case?

Yes, if _MSC_VER is defined, then Clang is operating in MSVC mode.

[llvmbot]

@llvm/issue-subscribers-clang-driver

Author: None (jakirkham)

Am seeing the following error when building with Clang 17.0.2 on Windows using MSVC 14.3. AFAICT this is a similar issue as occurred with MinGW ( https://github.com//issues/64464 ), but this is with MSVC. More background in the OP of PR ( https://github.com//pull/67891 ) (though that doesn't fix the MSVC target issue)

clang.exe -DHAVE_CONFIG_H -I. -I../../include/private/autogen -I../../include/hwloc/autogen  -I"/d/bld/libhwloc_1696580296225/work"/include -I"/d/bld/libhwloc_1696580296225/work"/include -I../../utils/hwloc  -DLSTOPO_HAVE_GRAPHICS -ID:/bld/libhwloc_1696580296225/_h_env/Library/include -O2 -D_CRT_SECURE_NO_WARNINGS -D_MT -D_DLL -nostdlib -Xclang --dependent-lib=msvcrt -fuse-ld=lld -Dputenv=_putenv -Dmktemp=_mktemp -Dopen=_open -Dunlink=_unlink -Dclose=_close -Dstrdup=_strdup  -mwindows -ID:/bld/libhwloc_1696580296225/_h_env/Library/include -O2 -D_CRT_SECURE_NO_WARNINGS -D_MT -D_DLL -nostdlib -Xclang --dependent-lib=msvcrt -fuse-ld=lld -c -o lstopo_win-lstopo.o `test -f 'lstopo.c' || echo './'`lstopo.c
clang: error: unsupported option '-mwindows' for target 'x86_64-pc-windows-msvc'