linux-kernel - Re: kbuild: check the minimum compiler version in Kconfig

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Date:   Wed, 16 Nov 2022 16:24:44 -0700
From:   Nathan Chancellor <nathan@...nel.org>
To:     Florian Fainelli <f.fainelli@...il.com>
Cc:     Nick Desaulniers <ndesaulniers@...gle.com>,
        Masahiro Yamada <masahiroy@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Paul Gortmaker <paul.gortmaker@...driver.com>,
        Nathan Chancellor <natechancellor@...il.com>, ojeda@...nel.org,
        sedat.dilek@...il.com, clang-built-linux <llvm@...ts.linux.dev>,
        Manoj Gupta <manojgupta@...gle.com>
Subject: Re: kbuild: check the minimum compiler version in Kconfig

On Wed, Nov 16, 2022 at 03:16:32PM -0800, Florian Fainelli wrote:
> On 11/16/22 15:11, Nick Desaulniers wrote:
> > On Wed, Nov 16, 2022 at 3:10 PM Nick Desaulniers
> > <ndesaulniers@...gle.com> wrote:
> > > 
> > > On Wed, Nov 16, 2022 at 2:56 PM Florian Fainelli <f.fainelli@...il.com> wrote:
> > > > 
> > > > On 11/16/22 14:48, Nick Desaulniers wrote:
> > > > > On Wed, Nov 16, 2022 at 1:48 PM Florian Fainelli <f.fainelli@...il.com> wrote:
> > > > > > 
> > > > > > Hi Masahiro, Nick,
> > > > > > 
> > > > > > The compiler version check performed with
> > > > > > aec6c60a01d3a3170242d6a99372a388e1136dc6 ("kbuild: check the minimum
> > > > > > compiler version in Kconfig") can be defeated and prevent running the
> > > > > > *config targets if specifying LLVM=1 on the command line, in that way:
> > > > > > 
> > > > > > BR_BINARIES_DIR=/local/users/fainelli/buildroot-llvm/output/arm64/images
> > > > > > LLVM=1 LLVM_IAS=1 PKG_CONFIG_PATH="" /usr/bin/make -j49 -C
> > > > > > /local/users/fainelli/buildroot-llvm/output/arm64/build/linux-custom
> > > > > > HOSTCC="/usr/bin/gcc"
> > > > > > HOSTCC="/local/users/fainelli/buildroot-llvm/output/arm64/host/bin/ccache
> > > > > > /usr/bin/gcc -O2
> > > > > > -I/local/users/fainelli/buildroot-llvm/output/arm64/host/include
> > > > > > -DNDEBUG -L/local/users/fainelli/buildroot-llvm/output/arm64/host/lib
> > > > > > -Wl,-rpath,/local/users/fainelli/buildroot-llvm/output/arm64/host/lib"
> > > > > > ARCH=arm64
> > > > > > INSTALL_MOD_PATH=/local/users/fainelli/buildroot-llvm/output/arm64/target
> > > > > > CROSS_COMPILE="/local/users/fainelli/buildroot-llvm/output/arm64/host/bin/aarch64-linux-"
> > > > > > WERROR=0
> > > > > > DEPMOD=/local/users/fainelli/buildroot-llvm/output/arm64/host/sbin/depmod
> > > > > > INSTALL_MOD_STRIP=1 HOSTCC="/usr/bin/gcc" menuconfig
> > > > > >      UPD     scripts/kconfig/mconf-cfg
> > > > > >      HOSTCC  scripts/kconfig/mconf.o
> > > > > >      HOSTCC  scripts/kconfig/lxdialog/checklist.o
> > > > > >      HOSTCC  scripts/kconfig/lxdialog/inputbox.o
> > > > > >      HOSTCC  scripts/kconfig/lxdialog/menubox.o
> > > > > >      HOSTCC  scripts/kconfig/lxdialog/textbox.o
> > > > > >      HOSTCC  scripts/kconfig/lxdialog/util.o
> > > > > >      HOSTCC  scripts/kconfig/lxdialog/yesno.o
> > > > > >      HOSTLD  scripts/kconfig/mconf
> > > > > > ***
> > > > > > *** Compiler is too old.
> > > > > > ***   Your Clang version:    10.0.0
> > > > > > ***   Minimum Clang version: 10.0.1
> > > > > > ***
> > > > > > scripts/Kconfig.include:44: Sorry, this compiler is not supported.
> > > > > > 
> > > > > > Here, the compiler check is actually checking the host compiler clang
> > > > > > version installed on my Ubuntu 20.04 system, as opposed to the cross
> > > > > > compiler clang version that is being used.
> > > > > 
> > > > > LLVM=1 will use `clang` as found by your $PATH.  Where did you express
> > > > > to make what the "cross compiler clang version" is? (And why do you
> > > > > set HOSTCC three times)
> > > > 
> > > > We are setting CROSS_COMPILE to express the cross compiler clang prefix
> > > > to use.
> > > 
> > > Can you try setting CLANG_PREFIX rather than CROSS_COMPILE (to the same value)?
> > > 
> > > CLANG_PREFIX=/local/users/fainelli/buildroot-llvm/output/arm64/host/bin/aarch64-linux-
> > 
> > sorry, I meant LLVM_PREFIX
> 
> Same results unfortunately.

What kernel version is this?

If you are not using PATH to control which binaries are being used, you
can use

    $ make LLVM=.../

to use .../clang, .../ld.lld, etc (the trailing slash is critical for
this), which will behave similar to CROSS_COMPILE for GCC. When building
with LLVM, CROSS_COMPILE only controls the target triple and it is
unnecessary when using all LLVM tools. That LLVM behavior is relatively
new, see commit e9c281928c24 ("kbuild: Make $(LLVM) more flexible").

Cheers,
Nathan