include/linux/build_bug.h

   1 /* SPDX-License-Identifier: GPL-2.0 */
   2 #ifndef _LINUX_BUILD_BUG_H
   3 #define _LINUX_BUILD_BUG_H
   4
   5 #include <linux/compiler.h>
   6
   7 #ifdef __CHECKER__
   8 #define __BUILD_BUG_ON_NOT_POWER_OF_2(n) (0)
   9 #define BUILD_BUG_ON_NOT_POWER_OF_2(n) (0)
  10 #define BUILD_BUG_ON_ZERO(e) (0)
  11 #define BUILD_BUG_ON_INVALID(e) (0)
  12 #define BUILD_BUG_ON_MSG(cond, msg) (0)
  13 #define BUILD_BUG_ON(condition) (0)
  14 #define BUILD_BUG() (0)
  15 #else /* __CHECKER__ */
  16
  17 /* Force a compilation error if a constant expression is not a power of 2 */
  18 #define __BUILD_BUG_ON_NOT_POWER_OF_2(n)        \
  19         BUILD_BUG_ON(((n) & ((n) - 1)) != 0)
  20 #define BUILD_BUG_ON_NOT_POWER_OF_2(n)                  \
  21         BUILD_BUG_ON((n) == 0 || (((n) & ((n) - 1)) != 0))
  22
  23 /*
  24  * Force a compilation error if condition is true, but also produce a
  25  * result (of value 0 and type size_t), so the expression can be used
  26  * e.g. in a structure initializer (or where-ever else comma expressions
  27  * aren't permitted).
  28  */
  29 #define BUILD_BUG_ON_ZERO(e) (sizeof(struct { int:(-!!(e)); }))
  30
  31 /*
  32  * BUILD_BUG_ON_INVALID() permits the compiler to check the validity of the
  33  * expression but avoids the generation of any code, even if that expression
  34  * has side-effects.
  35  */
  36 #define BUILD_BUG_ON_INVALID(e) ((void)(sizeof((__force long)(e))))
  37
  38 /**
  39  * BUILD_BUG_ON_MSG - break compile if a condition is true & emit supplied
  40  *                    error message.
  41  * @condition: the condition which the compiler should know is false.
  42  *
  43  * See BUILD_BUG_ON for description.
  44  */
  45 #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
  46
  47 /**
  48  * BUILD_BUG_ON - break compile if a condition is true.
  49  * @condition: the condition which the compiler should know is false.
  50  *
  51  * If you have some code which relies on certain constants being equal, or
  52  * some other compile-time-evaluated condition, you should use BUILD_BUG_ON to
  53  * detect if someone changes it.
  54  *
  55  * The implementation uses gcc's reluctance to create a negative array, but gcc
  56  * (as of 4.4) only emits that error for obvious cases (e.g. not arguments to
  57  * inline functions).  Luckily, in 4.3 they added the "error" function
  58  * attribute just for this type of case.  Thus, we use a negative sized array
  59  * (should always create an error on gcc versions older than 4.4) and then call
  60  * an undefined function with the error attribute (should always create an
  61  * error on gcc 4.3 and later).  If for some reason, neither creates a
  62  * compile-time error, we'll still have a link-time error, which is harder to
  63  * track down.
  64  */
  65 #ifndef __OPTIMIZE__
  66 #define BUILD_BUG_ON(condition) ((void)sizeof(char[1 - 2*!!(condition)]))
  67 #else
  68 #define BUILD_BUG_ON(condition) \
  69         BUILD_BUG_ON_MSG(condition, "BUILD_BUG_ON failed: " #condition)
  70 #endif
  71
  72 /**
  73  * BUILD_BUG - break compile if used.
  74  *
  75  * If you have some code that you expect the compiler to eliminate at
  76  * build time, you should use BUILD_BUG to detect if it is
  77  * unexpectedly used.
  78  */
  79 #define BUILD_BUG() BUILD_BUG_ON_MSG(1, "BUILD_BUG failed")
  80
  81 #endif  /* __CHECKER__ */
  82
  83 #endif  /* _LINUX_BUILD_BUG_H */