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

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Message-Id: <20140522.153313.958087444510569794.davem@davemloft.net>
Date:	Thu, 22 May 2014 15:33:13 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	gang.chen.5i5j@...il.com
Cc:	gerrit@....abdn.ac.uk, gxt@...c.pku.edu.cn, dccp@...r.kernel.org,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH linux-next] net/dccp/timer.c: use 'u64' instead of
 's64' to avoid compiler's warning

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.