diff options
Diffstat (limited to 'include/linux/compiler.h')
| -rw-r--r-- | include/linux/compiler.h | 22 |
1 files changed, 22 insertions, 0 deletions
diff --git a/include/linux/compiler.h b/include/linux/compiler.h index efd43df3a99a..b087de2f3e94 100644 --- a/include/linux/compiler.h +++ b/include/linux/compiler.h @@ -308,6 +308,28 @@ static inline void *offset_to_ptr(const int *off) #define statically_true(x) (__builtin_constant_p(x) && (x)) /* + * 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) + +/* * This is needed in functions which generate the stack canary, see * arch/x86/kernel/smpboot.c::start_secondary() for an example. */ |