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