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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Wed, 13 Jan 2021 14:08:09 -0800
Message-ID: <CAHk-=wjqGRXUp6KOdx-eHYEotGvY=a5tSY1mF-BkAcX2YAuBYw@mail.gmail.com>
Subject: Re: [PATCH] compiler.h: Raise minimum version of GCC to 5.1 for arm64
To:     Russell King - ARM Linux admin <linux@armlinux.org.uk>
Cc:     Masahiro Yamada <masahiroy@kernel.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
        Will Deacon <will@kernel.org>, Arnd Bergmann <arnd@kernel.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        "Theodore Ts'o" <tytso@mit.edu>,
        "Cc: Android Kernel" <kernel-team@android.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Florian Weimer <fweimer@redhat.com>
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On Wed, Jan 13, 2021 at 1:44 PM Russell King - ARM Linux admin
<linux@armlinux.org.uk> wrote:
>
> So, maybe the Sparc issue was just a similar but different bug in gcc
> 4.9.x.

Good catch. And I know this bug has happened independently on
different architectures several times (I remember this on x86-64 as
well), so I started looking around.

And in fact, 4.9 was buggy on x86-64 too:

    https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61904

And yeah, _that_ gcc bug wasn't actually x86-64 specific, but
apparently a generic instruction scheduling bug.

So it's an independent bug, but I do have to admit that the arguments
against 4.9 are piling up (even if that particular fix apparently got
fixed in the gcc branches and apparently backported to distro
compilers too).

         Linus