reproduce (this is a W=1 build):
        git clone https://github.com/intel/lkp-tests.git ~/lkp-tests
        # install riscv cross compiling tool for clang build
        # apt-get install binutils-riscv64-linux-gnu
        # https://git.kernel.org/pub/scm/linux/kernel/git/namhyung/linux-perf.git/commit/?id=ebf6eaa62ac38d0ae392387881d348aaee2694e1
        git remote add namhyung-perf https://git.kernel.org/pub/scm/linux/kernel/git/namhyung/linux-perf.git
        git fetch --no-tags namhyung-perf bpf/slab-iter-v2
        git checkout ebf6eaa62ac38d0ae392387881d348aaee2694e1
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang-20 ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=riscv olddefconfig
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang-20 ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=riscv SHELL=/bin/bash kernel/bpf/