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Subject: Re: [RFC][PATCH 0/5] Fixes for abs() usage on 64bit values
From: Linus Torvalds <torvalds@linux-foundation.org>
To: Ingo Molnar <mingo@kernel.org>
Cc: John Stultz <john.stultz@linaro.org>, Tejun Heo <tj@kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        "Steven Rostedt (Red Hat)" <rostedt@goodmis.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>,
        Michal Nazarewicz <mina86@mina86.com>,
        Prarit Bhargava <prarit@redhat.com>,
        Richard Cochran <richardcochran@gmail.com>,
        Thomas Gleixner <tglx@linutronix.de>, "Theodore Ts'o" <tytso@mit.edu>,
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        Dave Chinner <dchinner@redhat.com>,
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On Mon, Sep 14, 2015 at 10:20 PM, Ingo Molnar <mingo@kernel.org> wrote:
>
> Linus, any preferences?

I like the "auto-expand to 64-bit when necessary", but yes, that thing
needs to continue to use a signed type. Using __builtin_choose_expr()
would seem to be the right thing to do (not Andrew's version that
makes the return type be s64 unconditionally).

Just a quick grep shows that we currently use "abs()" on unsigned long
and we expect it to be a signed comparison with zero, so the "simple"
typeof that John suggested definitely will not work.

            Linus