linux-kernel - Re: [RFC][PATCH 0/5] Fixes for abs() usage on 64bit values

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Message-ID: <CA+55aFxmAD69W9sT9Lvmdqt0xVbkCj4q0d7z82f3+SxUM8UPqw@mail.gmail.com>
Date:	Tue, 15 Sep 2015 16:43:15 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	John Stultz <john.stultz@...aro.org>, Tejun Heo <tj@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Steven Rostedt (Red Hat)" <rostedt@...dmis.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Michal Nazarewicz <mina86@...a86.com>,
	Prarit Bhargava <prarit@...hat.com>,
	Richard Cochran <richardcochran@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"Theodore Ts'o" <tytso@....edu>,
	Andreas Dilger <adilger.kernel@...ger.ca>,
	Dave Chinner <dchinner@...hat.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [RFC][PATCH 0/5] Fixes for abs() usage on 64bit values

On Mon, Sep 14, 2015 at 10:20 PM, Ingo Molnar <mingo@...nel.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
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