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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>,
	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>,
	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
Date: Mon, 14 Sep 2015 21:49:36 -0400	[thread overview]
Message-ID: <20150915014936.GA25658@htj.duckdns.org> (raw)
In-Reply-To: <1442279124-7309-1-git-send-email-john.stultz@linaro.org>

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

  parent reply	other threads:[~2015-09-15  1:49 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-09-15  1:05 John Stultz
2015-09-15  1:05 ` [RFC][PATCH 1/5] clocksource: Fix abs() usage w/ " John Stultz
2015-10-02 20:57   ` [tip:timers/urgent] " tip-bot for John Stultz
2015-09-15  1:05 ` [RFC][PATCH 2/5] time: Fix abs() usage with 64-bit values John Stultz
2015-09-15  1:05 ` [RFC][PATCH 3/5] ext4: Fix abs() usage in ext4_mb_check_group_pa John Stultz
2015-09-15  1:05 ` [RFC][PATCH 4/5] percpu: Fix abs() usage in percpu_counter_compare() John Stultz
2015-09-15  1:05 ` [RFC][PATCH 5/5] abs(): Provide build error on passing 64bit value to abs() John Stultz
2015-09-15  5:22   ` Ingo Molnar
2015-09-15 23:52     ` Linus Torvalds
2015-09-16 12:57       ` [PATCH] kernel.h: make abs() work with 64-bit types Michal Nazarewicz
2015-09-18  3:12         ` John Stultz
2015-09-15  1:49 ` Tejun Heo [this message]
2015-09-15  3:27   ` [RFC][PATCH 0/5] Fixes for abs() usage on 64bit values John Stultz
2015-09-15  3:46     ` Tejun Heo
2015-09-15 12:09       ` Jeff Epler
2015-09-15 21:21       ` Andrew Morton
2015-09-15 22:54         ` Michal Nazarewicz
2015-09-15  5:20     ` Ingo Molnar
2015-09-15 23:43       ` Linus Torvalds

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