gcc invoked even with passing CC=clang to make

[tstellar]

I'm trying to build the Fedora kernel with clang and the build system is still invoking gcc even when I pass CC=clang to make. The failing command is:

/usr/bin/make V=1 CC=clang 'HOSTCFLAGS=-O2 -fexceptions -g -grecord-gcc-switches -pipe -Wall -Werror=format-security -Wp,-D_FORTIFY_SOURCE=2 -Wp,-D_GLIBCXX_ASSERTIONS --config /usr/lib/rpm/redhat/redhat-hardened-clang.cfg -fstack-protector-strong -fcommon -m64 -mtune=generic -fasynchronous-unwind-tables -fstack-clash-protection -fcf-protection' 'HOSTLDFLAGS=-Wl,-z,relro -Wl,--as-needed -Wl,-z,now ' ARCH=x86_64 olddefconfig

gcc: error: unrecognized command-line option '--config'; did you mean '-mpconfig'?
make[1]: *** [scripts/Makefile.host:95: scripts/basic/fixdep] Error 1
make: *** [Makefile:539: scripts_basic] Error 2

The Fedora build scripts runs a lot of commands before this, so I've attached the full build.log.

[nathanchance]

CC is used for compiling the kernel, HOSTCC is used for compiling the host utilities like the kconfig tool, which is what is happening in this instance. Specify HOSTCC=clang in addition to CC=clang for the intended result. Additionally, LLVM=1 will do that automatically and use all of the LLVM utilities.

[nickdesaulniers]

Yes; you should either be doing:

$ make CC=clang HOSTCC=clang ...

or

$ make LLVM=1 ...

[dileks]

@tstellar
Details see [1].

make LLVM=1 has some benefits but I am not very happy with it.
make LLVM=1 points to clang, ld.lld, llvm-ar, llvm-nm means without version-suffix etc.

Cannot speak for Red Hat based distros, but Debian offers the opportunity to co-install several LLVM toolchain versions.
llvm-toolchain-XX is a meta-package whereof Debian packages like llvm-12, clang-12 and lld-12 (here: XX=12) are generated.
This means in your system's and user's path you will have clang-12 etc.
Of course you can install llvm, clang and lld metapages, but they differ in XX for Debian stable/testing/unstable/experimental and I suggest not to install them when you plan to use more than one llvm-toolchain-XX.
Example: clang meta-package in Debian/bullseye symlinks to clang-11.
@tstellar
How is your distribution organizing its LLVM packages for misc LLVM versions?

To fullfill and as a workaround I added to my linux-kernel build-script:

### GCC and LLVM version settings
GCC_MAJOR_VER="10"
LLVM_MAJOR_VER="12"

### LLVM toolchain path options
# Explicitly set PATH to simplify LLVM=1 handling (see LLVM tools options)
# Option-1: Use system's LLVM toolchain
# Option-2: Use selfmade LLVM toolchain (here: ThinLTO+PGO optimized via tc-build)
# Option-3: Set custom PATH in ~/.bashrc
##LLVM_TOOLCHAIN_PATH="/usr/lib/llvm-${LLVM_MAJOR_VER}/bin"
LLVM_TOOLCHAIN_PATH="/opt/llvm-toolchain/bin"
if [ -d ${LLVM_TOOLCHAIN_PATH} ]; then
   export PATH="${LLVM_TOOLCHAIN_PATH}:${PATH}"
fi

XXX: TODO: Distinguish install-path for misc selfmade llvm-toolchain-XX?

Each time I want to test something in bash with my selfmade LLVM toolchain v12.0.0-rc1 and make LLVM=1 I have to be very careful.
Mostly, I do a cut'n'paste from my build-script.

Currently, I switched to and use my selfmade LLVM toolchain v12.0.0-rc1 and will upgrade with each v12.0.0-rcX until v12.0.0 final.

Why a selfmade LLVM toolchain?

1. stage1-toolchain approx. 10% faster than Debian's equivalent
2. ThinLTO+PGO optimized multistage-toolchain saves here approx. 33% of build-time.

I would like to have an whatever option to pass a custom LLVM_VER_SUFFIX to make.

[1] https://www.kernel.org/doc/html/latest/kbuild/llvm.html#llvm-utilities
[2] https://sources.debian.org/search/llvm-toolchain-12/
[3] https://packages.debian.org/bullseye/clang

[tstellar]

@dileks In Fedora, we just ship one version of the clang/llvm toolchain. We do provide compatibility packages with older versions of the clang/llvm libraries, but without the executables, like clang, llc, etc.

[dileks]

@tstellar
Thanks for the info.
Sometimes it is good to focus on one release/thing.
Do One Thing And Do It Well. (Unix philosophy)

[nickdesaulniers]

@tstellar please reopen if you still observe GCC invoked when building via make LLVM=1, otherwise feel free to open new issues for different bugs.