linux-kernel - Re: [PATCH] kbuild, LLVMLinux: Add -Werror to cc-option to support clang

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Date:   Mon, 3 Apr 2017 06:46:02 +0900
From:   Masahiro Yamada <yamada.masahiro@...ionext.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Mark Charlebois <charlebm@...il.com>,
        Behan Webster <behanw@...verseincode.com>,
        Michal Marek <mmarek@...e.com>,
        Nicolas Pitre <nicolas.pitre@...aro.org>,
        Kees Cook <keescook@...omium.org>,
        Emese Revfy <re.emese@...il.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] kbuild, LLVMLinux: Add -Werror to cc-option to support clang

Hi Arnd,

2017-04-01 5:38 GMT+09:00 Arnd Bergmann <arnd@...db.de>:
> From: Mark Charlebois <charlebm@...il.com>
>
> Clang will warn about unknown warnings but will not return false
> unless -Werror is set. GCC will return false if an unknown
> warning is passed.
>
> Adding -Werror make both compiler behave the same.
>
> [arnd: it turns out we need the same patch for testing whether -ffunction-sections
>        works right with gcc. I've build tested extensively with this patch
>        applied, so let's just merge this one now.]
>
> Signed-off-by: Mark Charlebois <charlebm@...il.com>
> Signed-off-by: Behan Webster <behanw@...verseincode.com>
> Reviewed-by: Jan-Simon Möller <dl9pf@....de>
> Signed-off-by: Arnd Bergmann <arnd@...db.de>

Thank you for forwarding this patch.

The code diff looks good to me,
but I'd like to be sure about git-log before applying it.

As far as I tested, the statement
"Clang will warn about unknown warnings but will not
return false unless -Werror is set." does not seem true
on recent versions.

[1] When I use version 3.3

masahiro@...ver:~$ clang --version
clang version 3.3 (tags/RELEASE_33/final)
Target: x86_64-unknown-linux-gnu
Thread model: posix
masahiro@...ver:~$ clang  -foobar -c -x c /dev/null
clang: warning: argument unused during compilation: '-foobar'
masahiro@...ver:~$ echo $?
0

[2] When I use version 3.4

masahiro@...ver:~$ clang --version
clang version 3.4 (tags/RELEASE_34/final)
Target: x86_64-unknown-linux-gnu
Thread model: posix
masahiro@...ver:~$ clang  -foobar -c -x c /dev/null
clang: error: unknown argument: '-foobar'
masahiro@...ver:~$ echo $?
1

I agree we can apply this patch anyway
even if the original motivation is not true anymore.

Can you check it out,
and add a little more comments if you agree?

-- 
Best Regards
Masahiro Yamada