source: bootcd/isolinux/syslinux-6.03/com32/include/klibc/compiler.h

/*
 * klibc/compiler.h
 *
 * Various compiler features
 */

#ifndef _KLIBC_COMPILER_H
#define _KLIBC_COMPILER_H

#define __user

/* Specific calling conventions */
/* __cdecl is used when we want varadic and non-varadic functions to have
   the same binary calling convention. */
#ifdef __i386__
# ifdef __GNUC__
#  define __cdecl __attribute__((cdecl,regparm(0)))
# else
  /* Most other C compilers have __cdecl as a keyword */
# endif
#else
# define __cdecl                /* Meaningless on non-i386 */
#endif

/* How to declare a function that *must* be inlined */
#ifdef __GNUC__
# if __GNUC_MAJOR__ >= 3
#  define __must_inline static __inline__ __attribute__((always_inline))
# else
#  define __must_inline extern __inline__
# endif
#else
# define __must_inline inline   /* Just hope this works... */
#endif

/* How to declare a function that does not return */
#ifdef __GNUC__
# define __noreturn void __attribute__((noreturn))
#else
# define __noreturn void
#endif

/* "const" function:

     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'.
*/
#ifdef __GNUC__
# define __constfunc __attribute__((const))
#else
# define __constfunc
#endif
#undef __attribute_const__
#define __attribute_const__ __constfunc

/* "pure" function:

     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.  These functions should be declared with the attribute
     `pure'.
*/
#ifdef __GNUC__
# define __purefunc __attribute__((pure))
#else
# define __purefunc
#endif
#undef __attribute_pure__
#define __attribute_pure__ __purefunc

/* Format attribute */
#ifdef __GNUC__
# define __formatfunc(t,f,a) __attribute__((format(t,f,a)))
#else
# define __formatfunc(t,f,a)
#endif

/* malloc() function (returns unaliased pointer) */
#if defined(__GNUC__) && (__GNUC_MAJOR__ >= 3)
# define __mallocfunc __attribute__((malloc))
#else
# define __mallocfunc
#endif

/* likely/unlikely */
#if defined(__GNUC__) && (__GNUC_MAJOR__ > 2 || (__GNUC_MAJOR__ == 2 && __GNUC_MINOR__ >= 95))
# define __likely(x)   __builtin_expect(!!(x), 1)
# define __unlikely(x) __builtin_expect(!!(x), 0)
#else
# define __likely(x)   (!!(x))
# define __unlikely(x) (!!(x))
#endif

/* Possibly unused function */
#ifdef __GNUC__
# define __unusedfunc   __attribute__((unused))
#else
# define __unusedfunc
#endif

/* Declare a variable or data structure as unused. */
#ifdef __GNUC__
# define __unused       __attribute__((unused))
#else
# define __unused
#endif

/* Used symbol */
#define __used                          __attribute__((used))

/* Constructors and destructors */
#define __constructor   __attribute__((constructor))
#define __destructor    __attribute__((destructor))

/* Packed structures */
#define __packed        __attribute__((packed))

/* Weak symbols */
#define __weak          __attribute__((weak))

/* Alignment */
#define __aligned(x)    __attribute__((aligned(x)))
#define __alignas(x)    __attribute__((aligned(__alignof__(x))))

/* Handling of common (affect constructors/destructors) */
#define __common        __attribute__((common))
#define __nocommon      __attribute__((nocommon))

/* Weak symbols */
#define __weak                  __attribute__((weak))

#define __export                __attribute__((visibility("default")))

#endif