`CROSS_COMPILE` variable not set

[infn-ke]

The llvm toolchain does not set the cmake CROSS_COMPILE variable. This leads to issues with Zephyr build recipes, e.g. the puncover target in zephyr depends on this variable. The variable is being set by gnu gcc here zephyr-sdk-1.0.1/cmake/zephyr/gnu/generic.cmake, but it is not set by llvm counter-part zephyr-sdk-1.0.1/cmake/zephyr/llvm/generic.cmake.

[infn-ke]

@keith-packard any ideas on how to handle CROSS_COMPILE variable for llvm?

[stephanosio]

CROSS_COMPILE variable is for the "cross compile" toolchain, which is a generic GNU toolchain.

It does not make sense for the LLVM toolchain to set this variable.

[infn-ke]

Tricky thing to get zephyr repo clang compatible. The cmake recipe that expected CROSS_COMPILE is this one for puncover

https://github.com/zephyrproject-rtos/zephyr/blob/main/cmake/reports/CMakeLists.txt#L131

puncover makes objdump etc. so it tries set gcc-tools-base to CROSS_COMPILE which gets empty now. On the other hand I'm not sure puncover works with the objdump output from llvm.

[infn-ke]

I learned that gentoo distro solves this with a clang/gcc compatibility symlink in its ebuild

$ qfile /usr/lib/llvm/21/bin/x86_64-pc-linux-gnu-clang
llvm-core/clang: /usr/lib/llvm/21/bin/x86_64-pc-linux-gnu-clang
$ ls -l /usr/lib/llvm/21/bin/x86_64-pc-linux-gnu-clang
lrwxrwxrwx 1 root root 28 Apr 24 12:39 /usr/lib/llvm/21/bin/x86_64-pc-linux-gnu-clang -> x86_64-pc-linux-gnu-clang-21*
$ ls -l /usr/lib/llvm/21/bin/x86_64-pc-linux-gnu-clang-21 
lrwxrwxrwx 1 root root 8 Apr 24 12:39 /usr/lib/llvm/21/bin/x86_64-pc-linux-gnu-clang-21 -> clang-21*

Maybe something for zephyr-sdk to consider?