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#define GCC_VERSION (__GNUC__ * 10000 \
   9                   + __GNUC_MINOR__ * 100 \
  10                   + __GNUC_PATCHLEVEL__)
  11
  12
  13/* Optimization barrier */
  14/* The "volatile" is due to gcc bugs */
  15#define barrier() __asm__ __volatile__("": : :"memory")
  16
  17/*
  18 * This macro obfuscates arithmetic on a variable address so that gcc
  19 * shouldn't recognize the original var, and make assumptions about it.
  20 *
  21 * This is needed because the C standard makes it undefined to do
  22 * pointer arithmetic on "objects" outside their boundaries and the
  23 * gcc optimizers assume this is the case. In particular they
  24 * assume such arithmetic does not wrap.
  25 *
  26 * A miscompilation has been observed because of this on PPC.
  27 * To work around it we hide the relationship of the pointer and the object
  28 * using this macro.
  29 *
  30 * Versions of the ppc64 compiler before 4.1 had a bug where use of
  31 * RELOC_HIDE could trash r30. The bug can be worked around by changing
  32 * the inline assembly constraint from =g to =r, in this particular
  33 * case either is valid.
  34 */
  35#define RELOC_HIDE(ptr, off)                                    \
  36  ({ unsigned long __ptr;                                       \
  37    __asm__ ("" : "=r"(__ptr) : "0"(ptr));              \
  38    (typeof(ptr)) (__ptr + (off)); })
  39
  40#ifdef __CHECKER__
  41#define __must_be_array(arr) 0
  42#else
  43/* &a[0] degrades to a pointer: a different type from an array */
  44#define __must_be_array(a) BUILD_BUG_ON_ZERO(__same_type((a), &(a)[0]))
  45#endif
  46
  47/*
  48 * Force always-inline if the user requests it so via the .config,
  49 * or if gcc is too old:
  50 */
  51#if !defined(CONFIG_ARCH_SUPPORTS_OPTIMIZED_INLINING) || \
  52    !defined(CONFIG_OPTIMIZE_INLINING) || (__GNUC__ < 4)
  53# define inline         inline          __attribute__((always_inline)) notrace
  54# define __inline__     __inline__      __attribute__((always_inline)) notrace
  55# define __inline       __inline        __attribute__((always_inline)) notrace
  56#else
  57/* A lot of inline functions can cause havoc with function tracing */
  58# define inline         inline          notrace
  59# define __inline__     __inline__      notrace
  60# define __inline       __inline        notrace
  61#endif
  62
  63#define __deprecated                    __attribute__((deprecated))
  64#define __packed                        __attribute__((packed))
  65#define __weak                          __attribute__((weak))
  66
  67/*
  68 * it doesn't make sense on ARM (currently the only user of __naked) to trace
  69 * naked functions because then mcount is called without stack and frame pointer
  70 * being set up and there is no chance to restore the lr register to the value
  71 * before mcount was called.
  72 *
  73 * The asm() bodies of naked functions often depend on standard calling conventions,
  74 * therefore they must be noinline and noclone.  GCC 4.[56] currently fail to enforce
  75 * this, so we must do so ourselves.  See GCC PR44290.
  76 */
  77#define __naked                         __attribute__((naked)) noinline __noclone notrace
  78
  79#define __noreturn                      __attribute__((noreturn))
  80
  81/*
  82 * From the GCC manual:
  83 *
  84 * Many functions have no effects except the return value and their
  85 * return value depends only on the parameters and/or global
  86 * variables.  Such a function can be subject to common subexpression
  87 * elimination and loop optimization just as an arithmetic operator
  88 * would be.
  89 * [...]
  90 */
  91#define __pure                          __attribute__((pure))
  92#define __aligned(x)                    __attribute__((aligned(x)))
  93#define __printf(a, b)                  __attribute__((format(printf, a, b)))
  94#define __scanf(a, b)                   __attribute__((format(scanf, a, b)))
  95#define  noinline                       __attribute__((noinline))
  96#define __attribute_const__             __attribute__((__const__))
  97#define __maybe_unused                  __attribute__((unused))
  98#define __always_unused                 __attribute__((unused))
  99
 100#define __gcc_header(x) #x
 101#define _gcc_header(x) __gcc_header(linux/compiler-gcc##x.h)
 102#define gcc_header(x) _gcc_header(x)
 103#include gcc_header(__GNUC__)
 104
 105#if !defined(__noclone)
 106#define __noclone       /* not needed */
 107#endif
 108
 109/*
 110 * A trick to suppress uninitialized variable warning without generating any
 111 * code
 112 */
 113#define uninitialized_var(x) x = x
 114
 115#define __always_inline         inline __attribute__((always_inline))
 116
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