linux/include/linux/compiler-gcc.h
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   1#ifndef __LINUX_COMPILER_H
   2#error "Please don't include <linux/compiler-gcc.h> directly, include <linux/compiler.h> instead."
   3#endif
   4
   5/*
   6 * Common definitions for all gcc versions go here.
   7 */
   8
   9
  10/* Optimization barrier */
  11/* The "volatile" is due to gcc bugs */
  12#define barrier() __asm__ __volatile__("": : :"memory")
  13
  14/*
  15 * This macro obfuscates arithmetic on a variable address so that gcc
  16 * shouldn't recognize the original var, and make assumptions about it.
  17 *
  18 * This is needed because the C standard makes it undefined to do
  19 * pointer arithmetic on "objects" outside their boundaries and the
  20 * gcc optimizers assume this is the case. In particular they
  21 * assume such arithmetic does not wrap.
  22 *
  23 * A miscompilation has been observed because of this on PPC.
  24 * To work around it we hide the relationship of the pointer and the object
  25 * using this macro.
  26 *
  27 * Versions of the ppc64 compiler before 4.1 had a bug where use of
  28 * RELOC_HIDE could trash r30. The bug can be worked around by changing
  29 * the inline assembly constraint from =g to =r, in this particular
  30 * case either is valid.
  31 */
  32#define RELOC_HIDE(ptr, off)                                    \
  33  ({ unsigned long __ptr;                                       \
  34    __asm__ ("" : "=r"(__ptr) : "0"(ptr));              \
  35    (typeof(ptr)) (__ptr + (off)); })
  36
  37#ifdef __CHECKER__
  38#define __must_be_array(arr) 0
  39#else
  40/* &a[0] degrades to a pointer: a different type from an array */
  41#define __must_be_array(a) BUILD_BUG_ON_ZERO(__same_type((a), &(a)[0]))
  42#endif
  43
  44/*
  45 * Force always-inline if the user requests it so via the .config,
  46 * or if gcc is too old:
  47 */
  48#if !defined(CONFIG_ARCH_SUPPORTS_OPTIMIZED_INLINING) || \
  49    !defined(CONFIG_OPTIMIZE_INLINING) || (__GNUC__ < 4)
  50# define inline         inline          __attribute__((always_inline)) notrace
  51# define __inline__     __inline__      __attribute__((always_inline)) notrace
  52# define __inline       __inline        __attribute__((always_inline)) notrace
  53#else
  54/* A lot of inline functions can cause havoc with function tracing */
  55# define inline         inline          notrace
  56# define __inline__     __inline__      notrace
  57# define __inline       __inline        notrace
  58#endif
  59
  60#define __deprecated                    __attribute__((deprecated))
  61#define __packed                        __attribute__((packed))
  62#define __weak                          __attribute__((weak))
  63
  64/*
  65 * it doesn't make sense on ARM (currently the only user of __naked) to trace
  66 * naked functions because then mcount is called without stack and frame pointer
  67 * being set up and there is no chance to restore the lr register to the value
  68 * before mcount was called.
  69 *
  70 * The asm() bodies of naked functions often depend on standard calling conventions,
  71 * therefore they must be noinline and noclone.  GCC 4.[56] currently fail to enforce
  72 * this, so we must do so ourselves.  See GCC PR44290.
  73 */
  74#define __naked                         __attribute__((naked)) noinline __noclone notrace
  75
  76#define __noreturn                      __attribute__((noreturn))
  77
  78/*
  79 * From the GCC manual:
  80 *
  81 * Many functions have no effects except the return value and their
  82 * return value depends only on the parameters and/or global
  83 * variables.  Such a function can be subject to common subexpression
  84 * elimination and loop optimization just as an arithmetic operator
  85 * would be.
  86 * [...]
  87 */
  88#define __pure                          __attribute__((pure))
  89#define __aligned(x)                    __attribute__((aligned(x)))
  90#define __printf(a, b)                  __attribute__((format(printf, a, b)))
  91#define __scanf(a, b)                   __attribute__((format(scanf, a, b)))
  92#define  noinline                       __attribute__((noinline))
  93#define __attribute_const__             __attribute__((__const__))
  94#define __maybe_unused                  __attribute__((unused))
  95#define __always_unused                 __attribute__((unused))
  96
  97#define __gcc_header(x) #x
  98#define _gcc_header(x) __gcc_header(linux/compiler-gcc##x.h)
  99#define gcc_header(x) _gcc_header(x)
 100#include gcc_header(__GNUC__)
 101
 102#if !defined(__noclone)
 103#define __noclone       /* not needed */
 104#endif
 105
 106/*
 107 * A trick to suppress uninitialized variable warning without generating any
 108 * code
 109 */
 110#define uninitialized_var(x) x = x
 111
 112#define __always_inline         inline __attribute__((always_inline))
 113
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