kernel-ark/include/linux/compiler-gcc4.h

#ifndef __LINUX_COMPILER_H
#error "Please don't include <linux/compiler-gcc4.h> directly, include <linux/compiler.h> instead."
#endif

/* These definitions are for GCC v4.x.  */
#include <linux/compiler-gcc.h>

#define __used			__attribute__((__used__))
#define __must_check 		__attribute__((warn_unused_result))
#define __compiler_offsetof(a,b) __builtin_offsetof(a,b)
#define __always_inline		inline __attribute__((always_inline))

/*
 * A trick to suppress uninitialized variable warning without generating any
 * code
 */
#define uninitialized_var(x) x = x

#if !(__GNUC__ == 4 && __GNUC_MINOR__ < 3)
/* Mark functions as cold. gcc will assume any path leading to a call
   to them will be unlikely.  This means a lot of manual unlikely()s
   are unnecessary now for any paths leading to the usual suspects
   like BUG(), printk(), panic() etc. [but let's keep them for now for
   older compilers]

   Early snapshots of gcc 4.3 don't support this and we can't detect this
   in the preprocessor, but we can live with this because they're unreleased.
   Maketime probing would be overkill here.

   gcc also has a __attribute__((__hot__)) to move hot functions into
   a special section, but I don't see any sense in this right now in
   the kernel context */
#define __cold			__attribute__((__cold__))

#endif