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
        # clang-21 might not be officially released. Try a lower version if installation fails.
        # https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=fda1dd3c54ef3c4200c2e77634a91610da973950
        git remote add linus https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
        git fetch --no-tags linus master
        git checkout fda1dd3c54ef3c4200c2e77634a91610da973950
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang-21 ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=riscv olddefconfig
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang-21 ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=riscv SHELL=/bin/bash drivers/firmware/efi/libstub/ drivers/gpu/drm/ drivers/input/joystick/ drivers/net/wireless/ath/ath11k/ drivers/net/wireless/realtek/rtlwifi/rtl8188ee/ drivers/net/wireless/realtek/rtlwifi/rtl8723be/ drivers/net/wireless/realtek/rtw88/ drivers/scsi/mpt3sas/ fs/btrfs/ fs/hfsplus/ kernel/trace/ lib/crypto/