linux-kernel - Re: [PATCH-ugly] kmemtrace: casting a gfp_t requires _

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Date:	Sat, 8 Nov 2008 00:50:16 +0200
From:	Eduard - Gabriel Munteanu <eduard.munteanu@...ux360.ro>
To:	Alexey Dobriyan <adobriyan@...il.com>
Cc:	Harvey Harrison <harvey.harrison@...il.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH-ugly] kmemtrace: casting a gfp_t requires __force

On Fri, Nov 07, 2008 at 10:20:29PM +0300, Alexey Dobriyan wrote:
> On Fri, Nov 07, 2008 at 10:58:41AM -0800, Harvey Harrison wrote:
> > --- a/include/linux/kmemtrace.h
> > +++ b/include/linux/kmemtrace.h
> > @@ -34,7 +34,7 @@ static inline void kmemtrace_mark_alloc_node(enum kmemtrace_type_id type_id,
> >  		   "bytes_req %lu bytes_alloc %lu gfp_flags %lu node %d",
> >  		   type_id, call_site, (unsigned long) ptr,
> >  		   (unsigned long) bytes_req, (unsigned long) bytes_alloc,
> > -		   (unsigned long) gfp_flags, node);
> > +		   (__force unsigned long)gfp_flags, node);
> 
> gfp_t is "unsigned int" actually. These casts are bogus.
> 
> Subject: How do I printk <type> correctly?
> 
> If variable is of Type	use	printk format specifier.
> ---------------------------------------------------------
> 		int			%d or %x
> 		unsigned int		%u or %x
> 		long			%ld ot %lx
> 		unsigned long		%lu or %lx
> 		long long		%lld or %llx
> 		unsigned long long	%llu or %llx
> 		size_t			%zu or %zx
> 		ssize_t			%zd or %zx
> 
> Raw pointer value SHOULD be printed with %p.
> 
> u64 SHOULD be printed with %llu/%llx, (unsigned long long):
> 
> 	printk("%llu", (unsigned long long)u64_var);
> 
> s64 SHOULD be printed with %lld/%llx, (long long):
> 
> 	printk("%lld", (long long)s64_var);
> 
> If type is dependent on config option (sector_t), use format specifier
> of biggest type and explicitly cast to it.
> 
> Reminder: sizeof() result is of type size_t.
> 
> Thank you for your cooperation.

Hi,

Actually, "%zu" was the first thing that crossed my mind too. But we
don't want to carry such types into the probe callbacks. It's a lot
easier to see which u* an unsigned long fits into than it is for
size_t. So we take care of this inside a wrapper; the sooner, the better.

Also take into account that debugging code usually casts pointers to
unsigned long. This can easily be seen by looking at _RET_IP_ definition
or SLAB code. I think there's a very good reason to do so, since it adds
opacity to something that's not supposed to be used as a pointer.


	Cheers,
	Eduard

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