Re: definition of mfn_x() macro..

[Gianluca Guida <gianluca.guida@eu.citrix.com>]

Hi,

Sandesh wrote:
>   can you please tell me where the definition of mfn_x is?? I see it is
> being used at many places but not able to find its definition in xen
> source. 

It's a type safety feature for debug compilation. As you can see in 
xen/include/asm-x86/mm.h:

/* With this defined, we do some ugly things to force the compiler to 
 

  * give us type safety between mfns and gfns and other integers. 
 

  * TYPE_SAFE(int foo) defines a foo_t, and _foo() and foo_x() functions 
 

  * that translate beween int and foo_t. 
 

  * 
 

  * It does have some performance cost because the types now have 
 

  * a different storage attribute, so may not want it on all the time. */

#ifndef NDEBUG
#define TYPE_SAFETY 1
#endif

#ifdef TYPE_SAFETY
#define TYPE_SAFE(_type,_name)                                  \
typedef struct { _type _name; } _name##_t;                      \
static inline _name##_t _##_name(_type n) { return (_name##_t) { n }; } \
static inline _type _name##_x(_name##_t n) { return n._name; }
#else
#define TYPE_SAFE(_type,_name)                                          \
typedef _type _name##_t;                                                \
static inline _name##_t _##_name(_type n) { return n; }                 \
static inline _type _name##_x(_name##_t n) { return n; }
#endif

TYPE_SAFE(unsigned long,mfn);