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 #define __gcc_header(x) #x
 104 #define _gcc_header(x) __gcc_header(linux/compiler-gcc##x.h)
 105 #define gcc_header(x) _gcc_header(x)
 106 #include gcc_header(__GNUC__)
 107
 108 #if !defined(__noclone)
 109 #define __noclone       /* not needed */
 110 #endif
 111
 112 /*
 113  * A trick to suppress uninitialized variable warning without generating any
 114  * code
 115  */
 116 #define uninitialized_var(x) x = x
 117
 118 #define __always_inline         inline __attribute__((always_inline))