linux-kernel - Re: defconfig fails if CROSS_COMPILE is set while cross-gcc is not avaialble

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Message-ID: <CAK7LNAR0ghuhDXUqJ=nX0dtbtoOvFff9Eeu-hHWLkTONG09GAQ@mail.gmail.com>
Date:   Wed, 12 Sep 2018 21:53:19 +0900
From:   Masahiro Yamada <yamada.masahiro@...ionext.com>
To:     Alexey Brodkin <Alexey.Brodkin@...opsys.com>
Cc:     "keescook@...omium.org" <keescook@...omium.org>,
        "linux-kbuild@...r.kernel.org" <linux-kbuild@...r.kernel.org>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-snps-arc@...ts.infradead.org" 
        <linux-snps-arc@...ts.infradead.org>
Subject: Re: defconfig fails if CROSS_COMPILE is set while cross-gcc is not avaialble

Hi Alexey.

2018-09-12 21:08 GMT+09:00 Alexey Brodkin <Alexey.Brodkin@...opsys.com>:
> Hello Masahiro-san,
>
> Starting from kernel v4.17 it is no longer possible to install kernel headers
> for ARC architecture if there's no cross-toolchain in PATH.


Really?

I can do 'make ARCH=arc headers_install'
with the latest Linus' tree.

I see the following warnings, but possible to install kernel headers.

./scripts/gcc-version.sh: line 26: arc-linux-gcc: command not found
./scripts/gcc-version.sh: line 27: arc-linux-gcc: command not found


If ARC compiler is not found in PATH,
those warnings are displayed with v4.16 or older as well.

I do not see much difference in the behavior.


I am trying to fix even those warnings
by eliminating unneeded compiler invocation.  It is WIP.



> Note installation of headers is just one of use-cases when we might not
> have cross-tools available but still want to run "make xxx_defconfig".
> I.e. the problem is "make xxx_defconfig" with no cross-toolchain.
>
> That's what I see:
> ----------------------------->8--------------------------
> ./scripts/gcc-version.sh: line 26: arc-linux-gcc: command not found
> ./scripts/gcc-version.sh: line 27: arc-linux-gcc: command not found
> ./scripts/gcc-version.sh: line 26: arc-linux-gcc: command not found
> ./scripts/gcc-version.sh: line 27: arc-linux-gcc: command not found
> make: arc-linux-gcc: Command not found
> /bin/sh: arc-linux-gcc: command not found
> /bin/sh: arc-linux-gcc: command not found
> *** Default configuration is based on 'nsim_700_defconfig'
> ./scripts/gcc-version.sh: line 26: arc-linux-gcc: command not found
> ./scripts/gcc-version.sh: line 27: arc-linux-gcc: command not found
> ./scripts/gcc-version.sh: line 29: arc-linux-gcc: command not found
> ./scripts/gcc-version.sh: line 26: arc-linux-gcc: command not found
> ./scripts/gcc-version.sh: line 27: arc-linux-gcc: command not found
> ./scripts/gcc-version.sh: line 29: arc-linux-gcc: command not found
> init/Kconfig:17: syntax error
> init/Kconfig:16: invalid option
> ./scripts/clang-version.sh: line 15: arc-linux-gcc: command not found
> ./scripts/gcc-plugin.sh: line 11: arc-linux-gcc: command not found
> make[1]: *** [scripts/kconfig/Makefile:91: defconfig] Error 1
> make: *** [Makefile:531: defconfig] Error 2
> ----------------------------->8--------------------------
>
> That doesn't happen for ARM and other arches simply because for ARC
> we define CROSS_COMPILE if it is not set by user, see:
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arc/Makefile#n9

I do not think it is a good practice
to forcibly set CROSS_COMPILE that users may not have.

arch/m68k/Makefile uses cc-cross-prefix helper
to set the first found compiler.


> Still if CROSS_COMPILE is set before execution of "make defconfig"
> then the same problem happens for others.
>
> I was able to find a series of commits which cause this problem,
> here they are:
> ----------------------------->8--------------------------
> 59f53855babf - gcc-plugins: test plugin support in Kconfig and clean up Makefile
> 469cb7376c06 - kconfig: add CC_IS_CLANG and CLANG_VERSION
> a4353898980c - kconfig: add CC_IS_GCC and GCC_VERSION
> ----------------------------->8--------------------------
>
> What happen is "$(CC)" is passed as an argument and in its turn CC is
> "$(CROSS_COMPILE)gcc", see:
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Makefile#n385
>
>
> So if I substitute "CC" with "HOSTCC" in a couple of places (see below)
> the problem goes away. But I'm not really sure if what I do is correct.
> I.e. when we're interested in CC for target and when only host CC is of
> our interest.

I think the log of commit 316d55d55f49eca44
is a good source to know the background of this change.

Now Kconfig requires the target compiler.
So, it does not make sense to
do defconfig with non-existing compiler.



> Would be interesting to know your opinion here.

I'd recommend to not hard-code CROSS_COMPILE.



Thanks.

-- 
Best Regards
Masahiro Yamada