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  The __KERNEL__ macro is defined because there is programs (like libraries) than include kernel code and there is many things that you don't want them to include. So most modules will want the__KERNEL__ macro to be enabled. When you compile your kernel, __KERNEL__ is defined on the command line. User-space programs need access to the kernel headers, but some of the info in kernel headers ...       GCC阅读全文

在看linux内核代码的时候，经常会看到likely(x)和unlikely(x)宏的使用。那这两个宏有什么作用呢？ 这两个宏在内核中的定义如下： # define likely(x) __builtin_expect(!!(x), 1) # define unlikely(x) __builtin_expect(!!(x), 0) 可见这里使用了gcc的内建函数__builtin_expect()。 __builtin_expect (long exp, long c)函数： 该函数用来引导gcc进行条件分支预测。在一条指令执行时，由于流水线的作用，CPU可以同时完成下...       GCC阅读全文