linux-kernel - Re: [PATCH 7/8] percpu: add __percpu sparse annotations to hw

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Message-ID: <4B5E508A.1030305@kernel.org>
Date:	Tue, 26 Jan 2010 11:16:42 +0900
From:	Tejun Heo <tj@...nel.org>
To:	Al Viro <viro@...IV.linux.org.uk>
CC:	"H. Peter Anvin" <hpa@...or.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	linux-kernel@...r.kernel.org, axboe@...nel.dk,
	rusty@...tcorp.com.au, akpm@...ux-foundation.org,
	ebiederm@...ssion.com, tytso@....edu, Trond.Myklebust@...app.com,
	aelder@....com, hch@...radead.org, davem@...emloft.net,
	netdev@...r.kernel.org, x86@...nel.org, mingo@...hat.com,
	dan.j.williams@...el.com, borislav.petkov@....com,
	ying.huang@...el.com, lenb@...nel.org, neilb@...e.de,
	cl@...ux-foundation.org
Subject: Re: [PATCH 7/8] percpu: add __percpu sparse annotations to	hw_breakpoint

On 01/26/2010 11:04 AM, Al Viro wrote:
> On Tue, Jan 26, 2010 at 11:06:10AM +0900, Tejun Heo wrote:
>> Hello,
>>
>> On 01/26/2010 10:02 AM, H. Peter Anvin wrote:
>>> A cast (using __typeof__) combined with an address space override?
>>
>> That still puts the address specification at the wrong level.  The
>> problem is that the __typeof__ would be an array type which itself
>> doesn't have address space set but its members are in address space 3.
>> So, you need to get *inside* the array type def to change that.  :-(
> 
> Could you post the actual definitions in one piece?  Would be easier to
> discuss what's going on...

Here it is.

# define RELOC_HIDE(ptr, off)					\
  ({ unsigned long __ptr;					\
     __ptr = (unsigned long) (ptr);				\
    (typeof(ptr)) (__ptr + (off)); })

#define __verify_pcpu_ptr(ptr)	do {					\
	const void __percpu *__vpp_verify = (typeof(ptr))NULL;		\
	(void)__vpp_verify;						\
} while (0)

/* Weird cast keeps both GCC and sparse happy. */
#define SHIFT_PERCPU_PTR(__p, __offset)	({				\
	__verify_pcpu_ptr((__p));					\
	RELOC_HIDE((typeof(*(__p)) __kernel __force *)(__p), (__offset)); \
})

#define per_cpu(var, cpu) \
	(*SHIFT_PERCPU_PTR(&(var), per_cpu_offset(cpu)))

Thanks.

-- 
tejun
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