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
  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 /* Make the optimizer believe the variable can be manipulated arbitrarily. */
  41 #define OPTIMIZER_HIDE_VAR(var) __asm__ ("" : "=r" (var) : "0" (var))
  42
  43 #ifdef __CHECKER__
  44 #define __must_be_array(arr) 0
  45 #else
  46 /* &a[0] degrades to a pointer: a different type from an array */
  47 #define __must_be_array(a) BUILD_BUG_ON_ZERO(__same_type((a), &(a)[0]))
  48 #endif
  49
  50 /*
  51  * Force always-inline if the user requests it so via the .config,
  52  * or if gcc is too old:
  53  */
  54 #if !defined(CONFIG_ARCH_SUPPORTS_OPTIMIZED_INLINING) || \
  55     !defined(CONFIG_OPTIMIZE_INLINING) || (__GNUC__ < 4)
  56 # define inline         inline          __attribute__((always_inline)) notrace
  57 # define __inline__     __inline__      __attribute__((always_inline)) notrace
  58 # define __inline       __inline        __attribute__((always_inline)) notrace
  59 #else
  60 /* A lot of inline functions can cause havoc with function tracing */
  61 # define inline         inline          notrace
  62 # define __inline__     __inline__      notrace
  63 # define __inline       __inline        notrace
  64 #endif
  65
  66 #define __deprecated                    __attribute__((deprecated))
  67 #define __packed                        __attribute__((packed))
  68 #define __weak                          __attribute__((weak))
  69
  70 /*
  71  * it doesn't make sense on ARM (currently the only user of __naked) to trace
  72  * naked functions because then mcount is called without stack and frame pointer
  73  * being set up and there is no chance to restore the lr register to the value
  74  * before mcount was called.
  75  *
  76  * The asm() bodies of naked functions often depend on standard calling conventions,
  77  * therefore they must be noinline and noclone.  GCC 4.[56] currently fail to enforce
  78  * this, so we must do so ourselves.  See GCC PR44290.
  79  */
  80 #define __naked                         __attribute__((naked)) noinline __noclone notrace
  81
  82 #define __noreturn                      __attribute__((noreturn))
  83
  84 /*
  85  * From the GCC manual:
  86  *
  87  * Many functions have no effects except the return value and their
  88  * return value depends only on the parameters and/or global
  89  * variables.  Such a function can be subject to common subexpression
  90  * elimination and loop optimization just as an arithmetic operator
  91  * would be.
  92  * [...]
  93  */
  94 #define __pure                          __attribute__((pure))
  95 #define __aligned(x)                    __attribute__((aligned(x)))
  96 #define __printf(a, b)                  __attribute__((format(printf, a, b)))
  97 #define __scanf(a, b)                   __attribute__((format(scanf, a, b)))
  98 #define  noinline                       __attribute__((noinline))
  99 #define __attribute_const__             __attribute__((__const__))
 100 #define __maybe_unused                  __attribute__((unused))
 101 #define __always_unused                 __attribute__((unused))
 102
 103 /* gcc version specific checks */
 104
 105 #if GCC_VERSION < 30200
 106 # error Sorry, your compiler is too old - please upgrade it.
 107 #endif
 108
 109 #if GCC_VERSION < 30300
 110 # define __used                 __attribute__((__unused__))
 111 #else
 112 # define __used                 __attribute__((__used__))
 113 #endif
 114
 115 #ifdef CONFIG_GCOV_KERNEL
 116 # if GCC_VERSION < 30400
 117 #   error "GCOV profiling support for gcc versions below 3.4 not included"
 118 # endif /* __GNUC_MINOR__ */
 119 #endif /* CONFIG_GCOV_KERNEL */
 120
 121 #if GCC_VERSION >= 30400
 122 #define __must_check            __attribute__((warn_unused_result))
 123 #endif
 124
 125 #if GCC_VERSION >= 40000
 126
 127 /* GCC 4.1.[01] miscompiles __weak */
 128 #ifdef __KERNEL__
 129 # if GCC_VERSION >= 40100 &&  GCC_VERSION <= 40101
 130 #  error Your version of gcc miscompiles the __weak directive
 131 # endif
 132 #endif
 133
 134 #define __used                  __attribute__((__used__))
 135 #define __compiler_offsetof(a, b)                                       \
 136         __builtin_offsetof(a, b)
 137
 138 #if GCC_VERSION >= 40100 && GCC_VERSION < 40600
 139 # define __compiletime_object_size(obj) __builtin_object_size(obj, 0)
 140 #endif
 141
 142 #if GCC_VERSION >= 40300
 143 /* Mark functions as cold. gcc will assume any path leading to a call
 144  * to them will be unlikely.  This means a lot of manual unlikely()s
 145  * are unnecessary now for any paths leading to the usual suspects
 146  * like BUG(), printk(), panic() etc. [but let's keep them for now for
 147  * older compilers]
 148  *
 149  * Early snapshots of gcc 4.3 don't support this and we can't detect this
 150  * in the preprocessor, but we can live with this because they're unreleased.
 151  * Maketime probing would be overkill here.
 152  *
 153  * gcc also has a __attribute__((__hot__)) to move hot functions into
 154  * a special section, but I don't see any sense in this right now in
 155  * the kernel context
 156  */
 157 #define __cold                  __attribute__((__cold__))
 158
 159 #define __UNIQUE_ID(prefix) __PASTE(__PASTE(__UNIQUE_ID_, prefix), __COUNTER__)
 160
 161 #ifndef __CHECKER__
 162 # define __compiletime_warning(message) __attribute__((warning(message)))
 163 # define __compiletime_error(message) __attribute__((error(message)))
 164 #endif /* __CHECKER__ */
 165 #endif /* GCC_VERSION >= 40300 */
 166
 167 #if GCC_VERSION >= 40500
 168 /*
 169  * Mark a position in code as unreachable.  This can be used to
 170  * suppress control flow warnings after asm blocks that transfer
 171  * control elsewhere.
 172  *
 173  * Early snapshots of gcc 4.5 don't support this and we can't detect
 174  * this in the preprocessor, but we can live with this because they're
 175  * unreleased.  Really, we need to have autoconf for the kernel.
 176  */
 177 #define unreachable() __builtin_unreachable()
 178
 179 /* Mark a function definition as prohibited from being cloned. */
 180 #define __noclone       __attribute__((__noclone__, __optimize__("no-tracer")))
 181
 182 #endif /* GCC_VERSION >= 40500 */
 183
 184 #if GCC_VERSION >= 40600
 185 /*
 186  * Tell the optimizer that something else uses this function or variable.
 187  */
 188 #define __visible       __attribute__((externally_visible))
 189 #endif
 190
 191 /*
 192  * GCC 'asm goto' miscompiles certain code sequences:
 193  *
 194  *   http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58670
 195  *
 196  * Work it around via a compiler barrier quirk suggested by Jakub Jelinek.
 197  *
 198  * (asm goto is automatically volatile - the naming reflects this.)
 199  */
 200 #define asm_volatile_goto(x...) do { asm goto(x); asm (""); } while (0)
 201
 202 #ifdef CONFIG_ARCH_USE_BUILTIN_BSWAP
 203 #if GCC_VERSION >= 40400
 204 #define __HAVE_BUILTIN_BSWAP32__
 205 #define __HAVE_BUILTIN_BSWAP64__
 206 #endif
 207 #if GCC_VERSION >= 40800 || (defined(__powerpc__) && GCC_VERSION >= 40600)
 208 #define __HAVE_BUILTIN_BSWAP16__
 209 #endif
 210 #endif /* CONFIG_ARCH_USE_BUILTIN_BSWAP */
 211
 212 #endif  /* gcc version >= 40000 specific checks */
 213
 214 #if !defined(__noclone)
 215 #define __noclone       /* not needed */
 216 #endif
 217
 218 /*
 219  * A trick to suppress uninitialized variable warning without generating any
 220  * code
 221  */
 222 #define uninitialized_var(x) x = x
 223
 224 #define __always_inline         inline __attribute__((always_inline))