linux-kernel - Re: [PATCH] vsyscall: use __iter_div_u64

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Message-ID: <CAKwvOdkubvsRCnJKCaesB=PF=DgXfsBzwzR8kyE9NzWPU8Gehg@mail.gmail.com>
Date:   Thu, 11 Jul 2019 10:14:10 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Vincenzo Frascino <vincenzo.frascino@....com>,
        Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-arch <linux-arch@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linux-mips@...r.kernel.org,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Russell King <linux@...linux.org.uk>,
        Ralf Baechle <ralf@...ux-mips.org>,
        Paul Burton <paul.burton@...s.com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Mark Salyzyn <salyzyn@...roid.com>,
        Peter Collingbourne <pcc@...gle.com>,
        Shuah Khan <shuah@...nel.org>,
        Dmitry Safonov <0x7f454c46@...il.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Huw Davies <huw@...eweavers.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>
Subject: Re: [PATCH] vsyscall: use __iter_div_u64_rem()

On Thu, Jul 11, 2019 at 5:28 AM Arnd Bergmann <arnd@...db.de> wrote:
> clang does not like an inline assembly with a "=q" contraint for
> a 64-bit output:

Seems like starting in GCC 7, GCC may not like it either:
https://godbolt.org/z/UyBUfh
it simply warns then proceeds with code gen.  Another difference may
come from when GCC vs Clang perform dead code elimination (DCE) vs
semantic analysis.

-- 
Thanks,
~Nick Desaulniers