LXR linux/include/linux/compiler-gcc.h

   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/* Optimization barrier */
  13
  14/* The "volatile" is due to gcc bugs */
  15#define barrier() __asm__ __volatile__("": : :"memory")
  16/*
  17 * This version is i.e. to prevent dead stores elimination on @ptr
  18 * where gcc and llvm may behave differently when otherwise using
  19 * normal barrier(): while gcc behavior gets along with a normal
  20 * barrier(), llvm needs an explicit input variable to be assumed
  21 * clobbered. The issue is as follows: while the inline asm might
  22 * access any memory it wants, the compiler could have fit all of
  23 * @ptr into memory registers instead, and since @ptr never escaped
  24 * from that, it proofed that the inline asm wasn't touching any of
  25 * it. This version works well with both compilers, i.e. we're telling
  26 * the compiler that the inline asm absolutely may see the contents
  27 * of @ptr. See also: https://llvm.org/bugs/show_bug.cgi?id=15495
  28 */
  29#define barrier_data(ptr) __asm__ __volatile__("": :"r"(ptr) :"memory")
  30
  31/*
  32 * This macro obfuscates arithmetic on a variable address so that gcc
  33 * shouldn't recognize the original var, and make assumptions about it.
  34 *
  35 * This is needed because the C standard makes it undefined to do
  36 * pointer arithmetic on "objects" outside their boundaries and the
  37 * gcc optimizers assume this is the case. In particular they
  38 * assume such arithmetic does not wrap.
  39 *
  40 * A miscompilation has been observed because of this on PPC.
  41 * To work around it we hide the relationship of the pointer and the object
  42 * using this macro.
  43 *
  44 * Versions of the ppc64 compiler before 4.1 had a bug where use of
  45 * RELOC_HIDE could trash r30. The bug can be worked around by changing
  46 * the inline assembly constraint from =g to =r, in this particular
  47 * case either is valid.
  48 */
  49#define RELOC_HIDE(ptr, off)                                    \
  50  ({ unsigned long __ptr;                                       \
  51    __asm__ ("" : "=r"(__ptr) : "0"(ptr));              \
  52    (typeof(ptr)) (__ptr + (off)); })
  53
  54/* Make the optimizer believe the variable can be manipulated arbitrarily. */
  55#define OPTIMIZER_HIDE_VAR(var) __asm__ ("" : "=r" (var) : "0" (var))
  56
  57#ifdef __CHECKER__
  58#define __must_be_array(arr) 0
  59#else
  60/* &a[0] degrades to a pointer: a different type from an array */
  61#define __must_be_array(a) BUILD_BUG_ON_ZERO(__same_type((a), &(a)[0]))
  62#endif
  63
  64/*
  65 * Force always-inline if the user requests it so via the .config,
  66 * or if gcc is too old:
  67 */
  68#if !defined(CONFIG_ARCH_SUPPORTS_OPTIMIZED_INLINING) || \
  69    !defined(CONFIG_OPTIMIZE_INLINING) || (__GNUC__ < 4)
  70# define inline         inline          __attribute__((always_inline)) notrace
  71# define __inline__     __inline__      __attribute__((always_inline)) notrace
  72# define __inline       __inline        __attribute__((always_inline)) notrace
  73#else
  74/* A lot of inline functions can cause havoc with function tracing */
  75# define inline         inline          notrace
  76# define __inline__     __inline__      notrace
  77# define __inline       __inline        notrace
  78#endif
  79
  80#define __deprecated                    __attribute__((deprecated))
  81#define __packed                        __attribute__((packed))
  82#define __weak                          __attribute__((weak))
  83#define __alias(symbol)         __attribute__((alias(#symbol)))
  84
  85/*
  86 * it doesn't make sense on ARM (currently the only user of __naked) to trace
  87 * naked functions because then mcount is called without stack and frame pointer
  88 * being set up and there is no chance to restore the lr register to the value
  89 * before mcount was called.
  90 *
  91 * The asm() bodies of naked functions often depend on standard calling conventions,
  92 * therefore they must be noinline and noclone.  GCC 4.[56] currently fail to enforce
  93 * this, so we must do so ourselves.  See GCC PR44290.
  94 */
  95#define __naked                         __attribute__((naked)) noinline __noclone notrace
  96
  97#define __noreturn                      __attribute__((noreturn))
  98
  99/*
 100 * From the GCC manual:
 101 *
 102 * Many functions have no effects except the return value and their
 103 * return value depends only on the parameters and/or global
 104 * variables.  Such a function can be subject to common subexpression
 105 * elimination and loop optimization just as an arithmetic operator
 106 * would be.
 107 * [...]
 108 */
 109#define __pure                          __attribute__((pure))
 110#define __aligned(x)                    __attribute__((aligned(x)))
 111#define __printf(a, b)                  __attribute__((format(printf, a, b)))
 112#define __scanf(a, b)                   __attribute__((format(scanf, a, b)))
 113#define  noinline                       __attribute__((noinline))
 114#define __attribute_const__             __attribute__((__const__))
 115#define __maybe_unused                  __attribute__((unused))
 116#define __always_unused                 __attribute__((unused))
 117
 118#define __gcc_header(x) #x
 119#define _gcc_header(x) __gcc_header(linux/compiler-gcc##x.h)
 120#define gcc_header(x) _gcc_header(x)
 121#include gcc_header(__GNUC__)
 122
 123#if !defined(__noclone)
 124#define __noclone       /* not needed */
 125#endif
 126
 127/*
 128 * A trick to suppress uninitialized variable warning without generating any
 129 * code
 130 */
 131#define uninitialized_var(x) x = x
 132
 133#define __always_inline         inline __attribute__((always_inline))
 134