allow sys-kernel/zenpower to use clang

[mrturcot]

Heyo, so I use clang to compile my kernel

❯ cat /proc/version
Linux version 6.1.1-gentoo-filthy (root@GentooRig) (clang version 15.0.6, LLD 15.0.6) #4 SMP PREEMPT_DYNAMIC Wed Dec 21 20:36:14 PST 2022

This module fails to build while im using a clang-kernel. I have added zenpower to my clang-env as defined in portage/env & portage/package.env. (my clang-env https://github.com/mrturcot/Gentoo-Stuff/blob/master/portage/env/compiler-clang) It still tries uses GCC to build.... Can we detect the toolchain used to build kernel and use the necessary compiler to build module?

Similar issue that was resolved I had with xone kernel module https://gitlab.com/src_prepare/src_prepare-overlay/-/issues/43

ISSUE

warning: the compiler differs from the one used to build the kernel
  The kernel was built by: clang version 15.0.6
  You are using:           gcc (Gentoo 11.3.1_p20221209 p3) 11.3.1 20221209

Build log

 root  on GentooRig /root took 1s
[ 03:21:46 PM ] ❯ emerge-oneshot zenpower::ROKO__

These are the packages that would be merged, in order:

Calculating dependencies... done!
[ebuild  N    ~] sys-kernel/zenpower-0.1.12::ROKO__  USE="-dist-kernel" 0 KiB

Total: 1 package (1 new), Size of downloads: 0 KiB

Would you like to merge these packages? [Yes/No] 

>>> Verifying ebuild manifests

>>> Emerging (1 of 1) sys-kernel/zenpower-0.1.12::ROKO__
 * zenpower-0.1.12.tar.gz BLAKE2B SHA512 size ;-) ...                                                                                                                  [ ok ]
 * Determining the location of the kernel source code
 * Found kernel source directory:
 *     /usr/src/linux
 * Found sources for kernel version:
 *     6.1.1-gentoo-filthy
 * Checking for suitable kernel configuration options ...                                                                                                              [ ok ]
>>> Unpacking source...
>>> Unpacking zenpower-0.1.12.tar.gz to /var/tmp/portage/sys-kernel/zenpower-0.1.12/work
>>> Source unpacked in /var/tmp/portage/sys-kernel/zenpower-0.1.12/work
>>> Preparing source in /var/tmp/portage/sys-kernel/zenpower-0.1.12/work/zenpower-0.1.12 ...
>>> Source prepared.
>>> Configuring source in /var/tmp/portage/sys-kernel/zenpower-0.1.12/work/zenpower-0.1.12 ...
>>> Source configured.
>>> Compiling source in /var/tmp/portage/sys-kernel/zenpower-0.1.12/work/zenpower-0.1.12 ...
ln: failed to create symbolic link 'Module.symvers': File exists
 * Preparing zenpower module
make -j12 HOSTCC=clang 'LDFLAGS=-m elf_x86_64' modules 
make[1]: Entering directory '/usr/src/linux-6.1.1-gentoo'
warning: the compiler differs from the one used to build the kernel
  The kernel was built by: clang version 15.0.6
  You are using:           x86_64-pc-linux-gnu-gcc (Gentoo 11.3.1_p20221209 p3) 11.3.1 20221209
  CC [M]  /var/tmp/portage/sys-kernel/zenpower-0.1.12/work/zenpower-0.1.12/zenpower.o
x86_64-pc-linux-gnu-gcc: error: unrecognized command-line option ‘-Qunused-arguments’
x86_64-pc-linux-gnu-gcc: error: unrecognized command-line option ‘-mretpoline-external-thunk’
x86_64-pc-linux-gnu-gcc: error: unrecognized command-line option ‘-ftrivial-auto-var-init=zero’
x86_64-pc-linux-gnu-gcc: error: unrecognized command-line option ‘-fsplit-lto-unit’
x86_64-pc-linux-gnu-gcc: error: unrecognized command-line option ‘-Wformat-invalid-specifier’
x86_64-pc-linux-gnu-gcc: error: unrecognized command-line option ‘-Wformat-insufficient-args’
make[2]: *** [scripts/Makefile.build:250: /var/tmp/portage/sys-kernel/zenpower-0.1.12/work/zenpower-0.1.12/zenpower.o] Error 1
make[1]: *** [Makefile:1992: /var/tmp/portage/sys-kernel/zenpower-0.1.12/work/zenpower-0.1.12] Error 2
make[1]: Leaving directory '/usr/src/linux-6.1.1-gentoo'
make: *** [Makefile:27: modules] Error 2
 * ERROR: sys-kernel/zenpower-0.1.12::ROKO__ failed (compile phase):
 *   emake failed
 * 
 * If you need support, post the output of `emerge --info '=sys-kernel/zenpower-0.1.12::ROKO__'`,
 * the complete build log and the output of `emerge -pqv '=sys-kernel/zenpower-0.1.12::ROKO__'`.
 * The complete build log is located at '/var/log/portage/sys-kernel:zenpower-0.1.12:20221223-232245.log'.
 * For convenience, a symlink to the build log is located at '/var/tmp/portage/sys-kernel/zenpower-0.1.12/temp/build.log'.
 * The ebuild environment file is located at '/var/tmp/portage/sys-kernel/zenpower-0.1.12/temp/environment'.
 * Working directory: '/var/tmp/portage/sys-kernel/zenpower-0.1.12/work/zenpower-0.1.12'
 * S: '/var/tmp/portage/sys-kernel/zenpower-0.1.12/work/zenpower-0.1.12'

>>> Failed to emerge sys-kernel/zenpower-0.1.12, Log file:

>>>  '/var/log/portage/sys-kernel:zenpower-0.1.12:20221223-232245.log'

 * Messages for package sys-kernel/zenpower-0.1.12:
 * Log file: /var/log/portage/sys-kernel:zenpower-0.1.12:20221223-232245.log

 * Package:    sys-kernel/zenpower-0.1.12:0
 * Repository: ROKO__
 * USE:        abi_x86_64 amd64 elibc_glibc kernel_linux userland_GNU
 * FEATURES:   network-sandbox preserve-libs sandbox userpriv usersandbox
 * Determining the location of the kernel source code
 * Found kernel source directory:
 *     /usr/src/linux
 * Found sources for kernel version:
 *     6.1.1-gentoo-filthy
 * Checking for suitable kernel configuration options ...
 * Preparing zenpower module
 * ERROR: sys-kernel/zenpower-0.1.12::ROKO__ failed (compile phase):
 *   emake failed
 * 
 * If you need support, post the output of `emerge --info '=sys-kernel/zenpower-0.1.12::ROKO__'`,
 * the complete build log and the output of `emerge -pqv '=sys-kernel/zenpower-0.1.12::ROKO__'`.
 * The complete build log is located at '/var/log/portage/sys-kernel:zenpower-0.1.12:20221223-232245.log'.
 * For convenience, a symlink to the build log is located at '/var/tmp/portage/sys-kernel/zenpower-0.1.12/temp/build.log'.
 * The ebuild environment file is located at '/var/tmp/portage/sys-kernel/zenpower-0.1.12/temp/environment'.
 * Working directory: '/var/tmp/portage/sys-kernel/zenpower-0.1.12/work/zenpower-0.1.12'
 * S: '/var/tmp/portage/sys-kernel/zenpower-0.1.12/work/zenpower-0.1.12'

Thank you