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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Fri, 15 Jan 2021 15:24:07 -0800
Message-ID: <CAHk-=whrJ_3iTz+Wz2cSufxnw2+g39P=YsTGaE6M24Qg4=Ef5Q@mail.gmail.com>
Subject: Re: [PATCH] compiler.h: Raise minimum version of GCC to 5.1 for arm64
To:     Joe Perches <joe@perches.com>
Cc:     Ard Biesheuvel <ardb@kernel.org>,
        Russell King - ARM Linux admin <linux@armlinux.org.uk>,
        Florian Weimer <fweimer@redhat.com>,
        Arnd Bergmann <arnd@kernel.org>,
        "Cc: Android Kernel" <kernel-team@android.com>,
        "Theodore Ts'o" <tytso@mit.edu>,
        Peter Zijlstra <peterz@infradead.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Masahiro Yamada <masahiroy@kernel.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Will Deacon <will@kernel.org>,
        linux-arm-kernel <linux-arm-kernel@lists.infradead.org>
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On Thu, Jan 14, 2021 at 4:30 PM Joe Perches <joe@perches.com> wrote:
>
> KASAN v5 instead of all the old versions
> gcc 7.1 supports fallthrough.

Considering that most people won't even enable KASAN, I think that's
not a huge reason to then force people to potentially upgrade their
compilers.

That said, I do think that it might be good to just try to standardize
on the KASAN v5 code - but that could easily be done by simply making
KASAN depend as a feature on having a newer compiler version.

So the KASAN option itself could just have something like

       depends on !CC_IS_GCC || GCC_VERSION >= 70000

in it, which would allow us to just say "only v5 need apply".

As to "fallthrough", I think it's more than enough that lots of people
build with compilers that support it, and then any warnings they see
will be fixed. No need to force upgrades - it doesn't buy kernel
developers anything.

          Linus