linux-kernel - 回复： Re: [PATCH linux-next] net/dccp/timer.c: use 'u64' instead of 's64' to avoid compiler's warning

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Message-ID: <263613432.57393.1400803091663.JavaMail.root@bj-mail03.pku.edu.cn>
Date:	Fri, 23 May 2014 07:58:11 +0800 (CST)
From:	管雪涛 <gxt@....edu.cn>
To:	David Miller <davem@...emloft.net>
Cc:	gang chen 5i5j <gang.chen.5i5j@...il.com>, gerrit@....abdn.ac.uk,
	gxt@...c.pku.edu.cn, dccp@...r.kernel.org, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: 回复： Re: [PATCH linux-next] net/dccp/timer.c: use 'u64' instead of 's64' to avoid compiler's warning


----- David Miller <davem@...emloft.net> 写道：
> From: Chen Gang <gang.chen.5i5j@...il.com>
> Date: Wed, 21 May 2014 08:19:34 +0800
> 
> > 'dccp_timestamp_seed' is initialized once by ktime_get_real() in
> > dccp_timestamping_init(). It is always less than ktime_get_real()
> > in dccp_timestamp().
> > 
> > Then, ktime_us_delta() in dccp_timestamp() will always return positive
> > number. So can use manual type cast to let compiler and do_div() know
> > about it to avoid warning.
> > 
> > The related warning (with allmodconfig under unicore32):
> > 
> >     CC [M]  net/dccp/timer.o
> >   net/dccp/timer.c: In function ‘dccp_timestamp’:
> >   net/dccp/timer.c:285: warning: comparison of distinct pointer types lacks a cast
> > 
> > 
> > Signed-off-by: Chen Gang <gang.chen.5i5j@...il.com>
> 
> Applied to net-next, thanks.
> 
> But that type check in include/asm-generic/div64.h is bogus, it should
> be checking sizeof(X) == 8 rather than the type thing, it just wants to
> make sure that the value is 64-bit regardless of it's signedness.
> 
> The arch local implementations do not do this, and that's why very few
> other people notice this warning.

Arch-dependent codes implement it with unsigned long long type.
And, every warning should not be ignored.
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