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
   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 /* &a[0] degrades to a pointer: a different type from an array */
  38 #define __must_be_array(a) BUILD_BUG_ON_ZERO(__same_type((a), &(a)[0]))
  39
  40 /*
  41  * Force always-inline if the user requests it so via the .config,
  42  * or if gcc is too old:
  43  */
  44 #if !defined(CONFIG_ARCH_SUPPORTS_OPTIMIZED_INLINING) || \
  45     !defined(CONFIG_OPTIMIZE_INLINING) || (__GNUC__ < 4)
  46 # define inline         inline          __attribute__((always_inline))
  47 # define __inline__     __inline__      __attribute__((always_inline))
  48 # define __inline       __inline        __attribute__((always_inline))
  49 #endif
  50
  51 #define __deprecated                    __attribute__((deprecated))
  52 #define __packed                        __attribute__((packed))
  53 #define __weak                          __attribute__((weak))
  54
  55 /*
  56  * it doesn't make sense on ARM (currently the only user of __naked) to trace
  57  * naked functions because then mcount is called without stack and frame pointer
  58  * being set up and there is no chance to restore the lr register to the value
  59  * before mcount was called.
  60  *
  61  * The asm() bodies of naked functions often depend on standard calling conventions,
  62  * therefore they must be noinline and noclone.  GCC 4.[56] currently fail to enforce
  63  * this, so we must do so ourselves.  See GCC PR44290.
  64  */
  65 #define __naked                         __attribute__((naked)) noinline __noclone notrace
  66
  67 #define __noreturn                      __attribute__((noreturn))
  68
  69 /*
  70  * From the GCC manual:
  71  *
  72  * Many functions have no effects except the return value and their
  73  * return value depends only on the parameters and/or global
  74  * variables.  Such a function can be subject to common subexpression
  75  * elimination and loop optimization just as an arithmetic operator
  76  * would be.
  77  * [...]
  78  */
  79 #define __pure                          __attribute__((pure))
  80 #define __aligned(x)                    __attribute__((aligned(x)))
  81 #define __printf(a,b)                   __attribute__((format(printf,a,b)))
  82 #define  noinline                       __attribute__((noinline))
  83 #define __attribute_const__             __attribute__((__const__))
  84 #define __maybe_unused                  __attribute__((unused))
  85 #define __always_unused                 __attribute__((unused))
  86
  87 #define __gcc_header(x) #x
  88 #define _gcc_header(x) __gcc_header(linux/compiler-gcc##x.h)
  89 #define gcc_header(x) _gcc_header(x)
  90 #include gcc_header(__GNUC__)
  91
  92 #if !defined(__noclone)
  93 #define __noclone       /* not needed */
  94 #endif
  95
  96 /*
  97  * A trick to suppress uninitialized variable warning without generating any
  98  * code
  99  */
 100 #define uninitialized_var(x) x = x
 101
 102 #define __always_inline         inline __attribute__((always_inline))