linux-kernel - RE: Warning with asm-generic/div64.h

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Date:	Tue, 29 Mar 2011 19:41:56 +0800
From:	"Guan Xuetao" <gxt@...c.pku.edu.cn>
To:	"'Arnd Bergmann'" <arnd@...db.de>
Cc:	<linux-kernel@...r.kernel.org>, <linux-arch@...r.kernel.org>,
	"'Len Brown'" <len.brown@...el.com>,
	"'Pavel Machek'" <pavel@....cz>,
	"'Rafael J. Wysocki'" <rjw@...k.pl>,
	<linux-pm@...ts.linux-foundation.org>
Subject: RE: Warning with asm-generic/div64.h



> -----Original Message-----
> From: Arnd Bergmann [mailto:arnd@...db.de]
> Sent: Friday, March 25, 2011 9:40 PM
> To: Guan Xuetao
> Cc: linux-kernel@...r.kernel.org; linux-arch@...r.kernel.org
> Subject: Re: Warning with asm-generic/div64.h
> 
> On Friday 25 March 2011, Guan Xuetao wrote:
> > Following warning is generated when using <asm-generic/div64.h>
> >
> > kernel/power/hibernate.c: In function 'swsusp_show_speed':
> > kernel/power/hibernate.c:227: warning: comparison of distinct pointer types lacks a cast
> >
> > After expanding the do_div() macro, the problem line is:
> >
> >         (void)(((typeof((n)) *)0) == ((uint64_t *)0));
> >
> > while the type of n is s64.
> >
> > I am puzzled with the usage of the problem line.
> >
> > And how to correct it?
> 
> The purpose of this line is to generate a warning when the input is the
> wrong type, as the comment says:
>  /* The unnecessary pointer compare is there
>   * to check for type safety (n must be 64bit)
Yes, it works. And, I think type s64 should be ok also.

> 
> The macro doesn't work for signed input or for 32 bit input. I'd suggest
> fixing the caller to use an unsigned type.

Then,
Cc: Len Brown <len.brown@...el.com> (supporter:SUSPEND TO RAM)
Cc: Pavel Machek <pavel@....cz> (supporter:SUSPEND TO RAM)
Cc: "Rafael J. Wysocki" <rjw@...k.pl> (supporter:SUSPEND TO RAM)
Cc: linux-pm@...ts.linux-foundation.org (open list:SUSPEND TO RAM)

> 
> 	Arnd
Thanks, and sorry for replying late.

Guan Xuetao

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