include/linux/bug.h

   1 #ifndef _LINUX_BUG_H
   2 #define _LINUX_BUG_H
   3
   4 #include <linux/compiler.h>
   5
   6 #ifdef __CHECKER__
   7 #define BUILD_BUG_ON_NOT_POWER_OF_2(n) (0)
   8 #define BUILD_BUG_ON_ZERO(e) (0)
   9 #define BUILD_BUG_ON_NULL(e) ((void*)0)
  10 #define BUILD_BUG_ON_INVALID(e) (0)
  11 #define BUILD_BUG_ON(condition) (0)
  12 #define BUILD_BUG() (0)
  13 #else /* __CHECKER__ */
  14
  15 /* Force a compilation error if a constant expression is not a power of 2 */
  16 #define BUILD_BUG_ON_NOT_POWER_OF_2(n)                  \
  17         BUILD_BUG_ON((n) == 0 || (((n) & ((n) - 1)) != 0))
  18
  19 /* Force a compilation error if condition is true, but also produce a
  20    result (of value 0 and type size_t), so the expression can be used
  21    e.g. in a structure initializer (or where-ever else comma expressions
  22    aren't permitted). */
  23 #define BUILD_BUG_ON_ZERO(e) (sizeof(struct { int:-!!(e); }))
  24 #define BUILD_BUG_ON_NULL(e) ((void *)sizeof(struct { int:-!!(e); }))
  25
  26 /*
  27  * BUILD_BUG_ON_INVALID() permits the compiler to check the validity of the
  28  * expression but avoids the generation of any code, even if that expression
  29  * has side-effects.
  30  */
  31 #define BUILD_BUG_ON_INVALID(e) ((void)(sizeof((__force long)(e))))
  32
  33 /**
  34  * BUILD_BUG_ON - break compile if a condition is true.
  35  * @condition: the condition which the compiler should know is false.
  36  *
  37  * If you have some code which relies on certain constants being equal, or
  38  * some other compile-time-evaluated condition, you should use BUILD_BUG_ON to
  39  * detect if someone changes it.
  40  *
  41  * The implementation uses gcc's reluctance to create a negative array, but gcc
  42  * (as of 4.4) only emits that error for obvious cases (e.g. not arguments to
  43  * inline functions).  Luckily, in 4.3 they added the "error" function
  44  * attribute just for this type of case.  Thus, we use a negative sized array
  45  * (should always create an error on gcc versions older than 4.4) and then call
  46  * an undefined function with the error attribute (should always create an
  47  * error on gcc 4.3 and later).  If for some reason, neither creates a
  48  * compile-time error, we'll still have a link-time error, which is harder to
  49  * track down.
  50  */
  51 #define BUILD_BUG_ON(condition) ((void)sizeof(char[1 - 2*!!(condition)]))
  52
  53 #endif  /* __CHECKER__ */
  54
  55 #endif  /* _LINUX_BUG_H */