diff options
Diffstat (limited to 'tools/include/linux/compiler.h')
| -rw-r--r-- | tools/include/linux/compiler.h | 30 |
1 files changed, 30 insertions, 0 deletions
diff --git a/tools/include/linux/compiler.h b/tools/include/linux/compiler.h index 9c05a59f0184..33411ca0cc90 100644 --- a/tools/include/linux/compiler.h +++ b/tools/include/linux/compiler.h @@ -81,6 +81,28 @@ #define __is_constexpr(x) \ (sizeof(int) == sizeof(*(8 ? ((void *)((long)(x) * 0l)) : (int *)8))) +/* + * Similar to statically_true() but produces a constant expression + * + * To be used in conjunction with macros, such as BUILD_BUG_ON_ZERO(), + * which require their input to be a constant expression and for which + * statically_true() would otherwise fail. + * + * This is a trade-off: const_true() requires all its operands to be + * compile time constants. Else, it would always returns false even on + * the most trivial cases like: + * + * true || non_const_var + * + * On the opposite, statically_true() is able to fold more complex + * tautologies and will return true on expressions such as: + * + * !(non_const_var * 8 % 4) + * + * For the general case, statically_true() is better. + */ +#define const_true(x) __builtin_choose_expr(__is_constexpr(x), x, false) + #ifdef __ANDROID__ /* * FIXME: Big hammer to get rid of tons of: @@ -222,6 +244,14 @@ static __always_inline void __write_once_size(volatile void *p, void *res, int s __asm__ ("" : "=r" (var) : "0" (var)) #endif +#ifndef __BUILD_BUG_ON_ZERO_MSG +#if defined(__clang__) +#define __BUILD_BUG_ON_ZERO_MSG(e, msg, ...) ((int)(sizeof(struct { int:(-!!(e)); }))) +#else +#define __BUILD_BUG_ON_ZERO_MSG(e, msg, ...) ((int)sizeof(struct {_Static_assert(!(e), msg);})) +#endif +#endif + #endif /* __ASSEMBLY__ */ #endif /* _TOOLS_LINUX_COMPILER_H */ |