Xen devel - May 2005 - [patch] double incrementing l2tab

For PAE, l2e_get_phys() will look something like this:

  #define l2e_get_phys(_x)          ((((u64)(_x).l2_hi & 0x0f) << 32) 
|\
                                      ((u64)(_x).l2_lo & PAGE_MASK)) 

Thus l2e_get_phys(++foo) is not safe, as the increment will be evaluated
multiple times and at undefined times.

sRp

-- 
Scott Parish
Signed-off-by: srparish@us.ibm.com


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On 12 May 2005, at 22:06, Scott Parish wrote:
> For PAE, l2e_get_phys() will look something like this:
>
>   #define l2e_get_phys(_x)          ((((u64)(_x).l2_hi & 0x0f) <<
32)
> |\
>                                       ((u64)(_x).l2_lo & PAGE_MASK))
>
> Thus l2e_get_phys(++foo) is not safe, as the increment will be 
> evaluated
> multiple times and at undefined times.
This leaves the macro to bite you in future. Either make l2e_get_phys() 
a static inline function, or do something like:

#define l2e_get_phys(_x) ({ \
     u64 __x = (_x); \
     <your macro here but _x -> __x>; \
})

  -- Keir


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