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Date: Mon, 14 Sep 2015 21:49:36 -0400
From: Tejun Heo <tj@kernel.org>
To: John Stultz <john.stultz@linaro.org>
Cc: LKML <linux-kernel@vger.kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Ingo Molnar <mingo@kernel.org>,
        "Steven Rostedt (Red Hat)" <rostedt@goodmis.org>,
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        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>,
        Andreas Dilger <adilger.kernel@dilger.ca>,
        Dave Chinner <dchinner@redhat.com>, Joe Perches <joe@perches.com>
Subject: Re: [RFC][PATCH 0/5] Fixes for abs() usage on 64bit values
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Hello,

On Mon, Sep 14, 2015 at 06:05:19PM -0700, John Stultz wrote:
> As noted in include/linux/kernel.h:
>  "abs() should not be used for 64-bit types (s64, u64, long long)
>  - use abs64() for those."
> 
> Unfortunately, there are quite a number of places where abs()
> was used w/ 64bit values in the kernel, and the results are
> then silently capped to 32-bit values on 32-bit systems.

I don't get it.  Why can't we just do the following?

#define abs(x)									\
({										\
	 typeof(x) __x = (x);							\
	 __x < 0 ? -__x : __x;							\
})

The current macros are kinda broken because they'd end up converting
u32 or u64 values which are over the max values of signed counterparts
to their complements.

Thanks.

-- 
tejun