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From:   Arnd Bergmann <arnd@arndb.de>
Date:   Mon, 3 May 2021 11:57:30 +0200
Message-ID: <CAK8P3a19QJ_5tbbEq2f9=XKjVYUZcAy8QMvoM=8SNEdCnvmwyQ@mail.gmail.com>
Subject: Re: [PATCH] Raise the minimum GCC version to 5.2
To:     Segher Boessenkool <segher@kernel.crashing.org>
Cc:     Joe Perches <joe@perches.com>,
        Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>,
        Masahiro Yamada <masahiroy@kernel.org>,
        Albert Ou <aou@eecs.berkeley.edu>,
        Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Jonathan Corbet <corbet@lwn.net>,
        Linux Doc Mailing List <linux-doc@vger.kernel.org>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Miguel Ojeda <ojeda@kernel.org>,
        Paul Mackerras <paulus@samba.org>,
        linux-riscv <linux-riscv@lists.infradead.org>,
        linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
        Will Deacon <will@kernel.org>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>
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On Mon, May 3, 2021 at 2:44 AM Segher Boessenkool
<segher@kernel.crashing.org> wrote:
>
> On Sun, May 02, 2021 at 02:23:01PM -0700, Joe Perches wrote:
> > On Sun, 2021-05-02 at 15:32 -0500, Segher Boessenkool wrote:
> > > On Sun, May 02, 2021 at 01:00:28PM -0700, Joe Perches wrote:
> > []
> > > > Perhaps 8 might be best as that has a __diag warning control mechanism.
> > >
> > > I have no idea what you mean?
> >
> > ? read the last bit of compiler-gcc.h
>
> Ah, you mean
> #pragma GCC diagnostic
> (which has existed since GCC 4.2).  Does anything in this __diag stuff
> require GCC 8?  Other than that this is hardcoded here :-)

The '8' was just a kernel thing, we made it configurable to have version
specific warnings, and I have a header file that adds these macros
for all supported compilers, but the version that is in mainline only does
it for gcc-8 or later.

Early compilers only supported "#pragma GCC diagnostic", but I think
even gcc-4.6 supported the _Pragma() syntax that lets you do it inside
of a macro.

It's something we should improve with plumbing on top, e.g. I want
a macro that lets you locally turn off both -Woverride-init on gcc
and -Winitializer-overrides on clang. It's not a reason to mandate
a newer compiler though.

        Arnd