`--target` argument breaks with LLVM style triples

[mati865]

Consider this demonstration (tested inside ubuntu:22.04 container from Rust build system, not that it should matter):

$ touch a.c

$ /usr/local/bin/aarch64-w64-mingw32-gcc a.c -###  2>&1 | tail -1
 "/usr/local/bin/ld.lld" "-m" "arm64pe" "-Bdynamic" "-o" "a.exe" "/usr/local/aarch64-w64-mingw32/lib/crt2.o" "/usr/local/aarch64-w64-mingw32/lib/crtbegin.o" "-L/usr/local/aarch64-w64-mingw32/lib" "-L/usr/local/aarch64-w64-mingw32/mingw/lib" "-L/usr/local/lib/clang/20/lib/windows" "/tmp/a-253b57.o" "-lmingw32" "/usr/local/lib/clang/20/lib/windows/libclang_rt.builtins-aarch64.a" "-lunwind" "-lmoldname" "-lmingwex" "-lmsvcrt" "-ladvapi32" "-lshell32" "-luser32" "-lkernel32" "-lmingw32" "/usr/local/lib/clang/20/lib/windows/libclang_rt.builtins-aarch64.a" "-lunwind" "-lmoldname" "-lmingwex" "-lmsvcrt" "-lkernel32" "/usr/local/aarch64-w64-mingw32/lib/crtend.o"

$ /usr/local/bin/aarch64-w64-mingw32-gcc a.c -### --target=aarch64-w64-mingw32 2>&1 | tail -1
 "/usr/local/bin/ld.lld" "-m" "arm64pe" "-Bdynamic" "-o" "a.exe" "/usr/local/aarch64-w64-mingw32/lib/crt2.o" "/usr/local/aarch64-w64-mingw32/lib/crtbegin.o" "-L/usr/local/aarch64-w64-mingw32/lib" "-L/usr/local/aarch64-w64-mingw32/mingw/lib" "-L/usr/local/lib/clang/20/lib/windows" "/tmp/a-ce15a9.o" "-lmingw32" "/usr/local/lib/clang/20/lib/windows/libclang_rt.builtins-aarch64.a" "-lunwind" "-lmoldname" "-lmingwex" "-lmsvcrt" "-ladvapi32" "-lshell32" "-luser32" "-lkernel32" "-lmingw32" "/usr/local/lib/clang/20/lib/windows/libclang_rt.builtins-aarch64.a" "-lunwind" "-lmoldname" "-lmingwex" "-lmsvcrt" "-lkernel32" "/usr/local/aarch64-w64-mingw32/lib/crtend.o"

$ /usr/local/bin/aarch64-w64-mingw32-gcc a.c -### --target=aarch64-pc-windows-gnu 2>&1 | tail -1
 "/usr/bin/ld" "-m" "arm64pe" "-Bdynamic" "-o" "a.exe" "/usr/local/aarch64-w64-mingw32/lib/crt2.o" "/usr/local/aarch64-w64-mingw32/lib/crtbegin.o" "-L/usr/local/aarch64-w64-mingw32/lib" "-L/usr/local/aarch64-w64-mingw32/mingw/lib" "-L/usr/local/lib/clang/20/lib/windows" "/tmp/a-2a1238.o" "-lmingw32" "-lgcc" "-lgcc_eh" "-lmoldname" "-lmingwex" "-lmsvcrt" "-ladvapi32" "-lshell32" "-luser32" "-lkernel32" "-lmingw32" "-lgcc" "-lgcc_eh" "-lmoldname" "-lmingwex" "-lmsvcrt" "-lkernel32" "/usr/local/aarch64-w64-mingw32/lib/crtend.o"

--target=aarch64-pc-windows-gnu made Clang fallback to the host linker, the same happens for x86_64.

llvm-mingw version: llvm-mingw-20250417-ucrt-ubuntu-22.04-x86_64.tar.xz

[mstorsjo]

This is because llvm-mingw uses Clang config files now, rather than setting most arguments in the wrapper frontend. A target like aarch64-w64-mingw32 or aarch64-w64-windows-gnu ends up loading the aarch64-w64-windows-gnu.cfg config file, which loads mingw32-common.cfg which sets -fuse-ld=lld, but one with the vendor field set to pc won't find any aarch64-pc-windows-gnu.cfg config file.

I guess this would be fairly straightforward to fix by just duplicating the config files with both pc and w64 vendor fields in the triples.

[mati865]

Ah, makes sense.
I thought about normalising the tripe inside wrapper but using symlinks/copies indeed seems easier.

[mstorsjo]

Yeah - the point of moving most logic from the wrapper to config files, is that it should be equivalent to do aarch64-w64-mingw32-clang or clang -target aarch64-w64-mingw32, or similar. But this has the downside that even if you do invoke the wrapper script/executable, you can miss the config file if the target is overridden.