Specifying linker by path is broken!

Usage
,
1

According to the documentation the following should be possible:

cmake -B build \
        -DCMAKE_C_COMPILER=/llvm-project/llvm/build/projects/bin/clang \
        -DCMAKE_CXX_COMPILER=/llvm-project/llvm/build/projects/bin/clang++ \
        -DCMAKE_LINKER_TYPE=LLD \
        -DCMAKE_CXX_USING_LINKER_LLD=/llvm-project/llvm/build/projects/bin/lld \
        -DCMAKE_CXX_USING_LINKER_MODE=TOOL

But this results in linking to be performed via the clang++ frontend instead of the specified lld. Why is this documented if it plainly does not work at all? Or am I misunderstanding the docs?

2

You effectively misunderstood how linker specification works.

It is possible to specify an alternate tool only on environments relying already directly on the linker tool for the link step: this is mainly the Windows platform with the MSVC compiler (or alternate compilers simulating this compiler). For other environments, the link step is done using the compiler as driver: this behavior cannot be changed.

Maybe some clarification is needed about these variables.

3

It’s not impossible to change this behavior, is it? There is CMAKE_CXX_LINK_* which lets you replace the compiler as a driver, I thought this was a new way to do just that but looking at the docs again they don’t actually imply that. And I don’t quite understand the purpose of CMAKE_*_USING_LINKER_MODE in that case since this seems to be “predetermined” by the compiler in use (i.e. TOOL for MSVS and FLAG for Clang/GCC).

4

It is not possible to change the behavior of how the link step is done (compiler as driver or linker).

And, effectively, the CMAKE_*_USING_LINKER_MODE variable is a bit curious but was there by the lack of the correct information. Now, CMake provides this information through the CMAKE_<LANG>_LINK_MODE variable, so this variable will be suppressed in some CMake future release.

5

Okay, that makes sense then, thank you