Subject: Re: [PATCH 7/8] percpu: add __percpu sparse annotations to hw_breakpoint

From: Tejun Heo <[email-masked]>
Date: Tue, 26 Jan 2010 11:16:42 +0900

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