source: GPL/trunk/include/linux/compiler.h

#ifndef __LINUX_COMPILER_H
#define __LINUX_COMPILER_H

#ifdef __CHECKER__
# define __user         __attribute__((noderef, address_space(1)))
# define __kernel       /* default address space */
# define __safe         __attribute__((safe))
#else
# define __user
# define __kernel
# define __safe
# define __nocast
# define __iomem
# define __deprecated           /* unimplemented */
#endif

#define __GNUC__  3

#define __counted_by(member)
#define __free(x)

/* Indirect macros required for expanded argument pasting, eg. __LINE__. */
#define ___PASTE(a,b) a##b
#define __PASTE(a,b) ___PASTE(a,b)

#define __UNIQUE_ID(prefix) __PASTE(__PASTE(__UNIQUE_ID_, prefix), __COUNTER__)

#ifndef __ASSEMBLY__
#if __GNUC__ > 3
# include <linux/compiler-gcc+.h>       /* catch-all for GCC 4, 5, etc. */
#elif __GNUC__ == 3
# include <linux/compiler-gcc3.h>
#elif __GNUC__ == 2
# include <linux/compiler-gcc2.h>
#else
# error Sorry, your compiler is too old/not recognized.
#endif

/* Intel compiler defines __GNUC__. So we will overwrite implementations
 * coming from above header files here
 */
#ifdef __INTEL_COMPILER
# include <linux/compiler-intel.h>
#endif

/*
 * Generic compiler-dependent macros required for kernel
 * build go below this comment. Actual compiler/compiler version
 * specific implementations come from the above header files
 */

#define likely(x)       __builtin_expect(!!(x), 1)
#define unlikely(x)     __builtin_expect(!!(x), 0)


#ifndef RELOC_HIDE
# define RELOC_HIDE(ptr, off)                                   \
  ({ unsigned long __ptr;                                       \
     __ptr = (unsigned long) (ptr);                             \
    (typeof(ptr)) (__ptr + (off)); })
#endif

#endif /* __KERNEL__ */

/*
 * Allow us to mark functions as 'deprecated' and have gcc emit a nice
 * warning for each use, in hopes of speeding the functions removal.
 * Usage is:
 *              int __deprecated foo(void)
 */
#ifndef __deprecated
# define __deprecated           /* unimplemented */
#endif

/*
 * Allow us to avoid 'defined but not used' warnings on functions and data,
 * as well as force them to be emitted to the assembly file.
 *
 * As of gcc 3.3, static functions that are not marked with attribute((used))
 * may be elided from the assembly file.  As of gcc 3.3, static data not so
 * marked will not be elided, but this may change in a future gcc version.
 *
 * In prior versions of gcc, such functions and data would be emitted, but
 * would be warned about except with attribute((unused)).
 */
#ifndef __attribute_used__
# define __attribute_used__     /* unimplemented */
#endif

/*
 * From the GCC manual:
 *
 * Many functions have no effects except the return value and their
 * return value depends only on the parameters and/or global
 * variables.  Such a function can be subject to common subexpression
 * elimination and loop optimization just as an arithmetic operator
 * would be.
 * [...]
 */
#ifndef __attribute_pure__
# define __attribute_pure__     /* unimplemented */
#endif

/*
 * From the GCC manual:
 *
 * Many functions do not examine any values except their arguments,
 * and have no effects except the return value.  Basically this is
 * just slightly more strict class than the `pure' attribute above,
 * since function is not allowed to read global memory.
 *
 * Note that a function that has pointer arguments and examines the
 * data pointed to must _not_ be declared `const'.  Likewise, a
 * function that calls a non-`const' function usually must not be
 * `const'.  It does not make sense for a `const' function to return
 * `void'.
 */
#ifndef __attribute_const__
# define __attribute_const__    /* unimplemented */
#endif

#ifndef noinline
#define noinline
#endif
#define WARN(condition, format,...) { }

#define __must_check
#define __maybe_unused
#define __acquires(x)
#define __releases(x)
#define BUG() do {} while (1)
#define READ_ONCE(x) x
#define WRITE_ONCE(x, val) x=(val)
#define __force
#define __always_unused
#define fallthrough                    do {} while (0)  /* fallthrough */
#define __builtin_return_address(a)     0
#define __builtin_expect(x, expected_value) (x)

#endif /* __LINUX_COMPILER_H */