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({                                                                      \
  51        unsigned long __ptr;                                            \
  52        __asm__ ("" : "=r"(__ptr) : "0"(ptr));                          \
  53        (typeof(ptr)) (__ptr + (off));                                  \
  54})
  55
  56/* Make the optimizer believe the variable can be manipulated arbitrarily. */
  57#define OPTIMIZER_HIDE_VAR(var)                                         \
  58        __asm__ ("" : "=r" (var) : "0" (var))
  59
  60#ifdef __CHECKER__
  61#define __must_be_array(a)      0
  62#else
  63/* &a[0] degrades to a pointer: a different type from an array */
  64#define __must_be_array(a)      BUILD_BUG_ON_ZERO(__same_type((a), &(a)[0]))
  65#endif
  66
  67/*
  68 * Force always-inline if the user requests it so via the .config,
  69 * or if gcc is too old:
  70 */
  71#if !defined(CONFIG_ARCH_SUPPORTS_OPTIMIZED_INLINING) ||                \
  72    !defined(CONFIG_OPTIMIZE_INLINING) || (__GNUC__ < 4)
  73#define inline          inline          __attribute__((always_inline)) notrace
  74#define __inline__      __inline__      __attribute__((always_inline)) notrace
  75#define __inline        __inline        __attribute__((always_inline)) notrace
  76#else
  77/* A lot of inline functions can cause havoc with function tracing */
  78#define inline          inline          notrace
  79#define __inline__      __inline__      notrace
  80#define __inline        __inline        notrace
  81#endif
  82
  83#define __always_inline inline __attribute__((always_inline))
  84#define  noinline       __attribute__((noinline))
  85
  86#define __deprecated    __attribute__((deprecated))
  87#define __packed        __attribute__((packed))
  88#define __weak          __attribute__((weak))
  89#define __alias(symbol) __attribute__((alias(#symbol)))
  90
  91/*
  92 * it doesn't make sense on ARM (currently the only user of __naked)
  93 * to trace naked functions because then mcount is called without
  94 * stack and frame pointer being set up and there is no chance to
  95 * restore the lr register to the value before mcount was called.
  96 *
  97 * The asm() bodies of naked functions often depend on standard calling
  98 * conventions, therefore they must be noinline and noclone.
  99 *
 100 * GCC 4.[56] currently fail to enforce this, so we must do so ourselves.
 101 * See GCC PR44290.
 102 */
 103#define __naked         __attribute__((naked)) noinline __noclone notrace
 104
 105#define __noreturn      __attribute__((noreturn))
 106
 107/*
 108 * From the GCC manual:
 109 *
 110 * Many functions have no effects except the return value and their
 111 * return value depends only on the parameters and/or global
 112 * variables.  Such a function can be subject to common subexpression
 113 * elimination and loop optimization just as an arithmetic operator
 114 * would be.
 115 * [...]
 116 */
 117#define __pure                  __attribute__((pure))
 118#define __aligned(x)            __attribute__((aligned(x)))
 119#define __printf(a, b)          __attribute__((format(printf, a, b)))
 120#define __scanf(a, b)           __attribute__((format(scanf, a, b)))
 121#define __attribute_const__     __attribute__((__const__))
 122#define __maybe_unused          __attribute__((unused))
 123#define __always_unused         __attribute__((unused))
 124
 125/* gcc version specific checks */
 126
 127#if GCC_VERSION < 30200
 128# error Sorry, your compiler is too old - please upgrade it.
 129#endif
 130
 131#if GCC_VERSION < 30300
 132# define __used                 __attribute__((__unused__))
 133#else
 134# define __used                 __attribute__((__used__))
 135#endif
 136
 137#ifdef CONFIG_GCOV_KERNEL
 138# if GCC_VERSION < 30400
 139#   error "GCOV profiling support for gcc versions below 3.4 not included"
 140# endif /* __GNUC_MINOR__ */
 141#endif /* CONFIG_GCOV_KERNEL */
 142
 143#if GCC_VERSION >= 30400
 144#define __must_check            __attribute__((warn_unused_result))
 145#endif
 146
 147#if GCC_VERSION >= 40000
 148
 149/* GCC 4.1.[01] miscompiles __weak */
 150#ifdef __KERNEL__
 151# if GCC_VERSION >= 40100 &&  GCC_VERSION <= 40101
 152#  error Your version of gcc miscompiles the __weak directive
 153# endif
 154#endif
 155
 156#define __used                  __attribute__((__used__))
 157#define __compiler_offsetof(a, b)                                       \
 158        __builtin_offsetof(a, b)
 159
 160#if GCC_VERSION >= 40100 && GCC_VERSION < 40600
 161# define __compiletime_object_size(obj) __builtin_object_size(obj, 0)
 162#endif
 163
 164#if GCC_VERSION >= 40300
 165/* Mark functions as cold. gcc will assume any path leading to a call
 166 * to them will be unlikely.  This means a lot of manual unlikely()s
 167 * are unnecessary now for any paths leading to the usual suspects
 168 * like BUG(), printk(), panic() etc. [but let's keep them for now for
 169 * older compilers]
 170 *
 171 * Early snapshots of gcc 4.3 don't support this and we can't detect this
 172 * in the preprocessor, but we can live with this because they're unreleased.
 173 * Maketime probing would be overkill here.
 174 *
 175 * gcc also has a __attribute__((__hot__)) to move hot functions into
 176 * a special section, but I don't see any sense in this right now in
 177 * the kernel context
 178 */
 179#define __cold                  __attribute__((__cold__))
 180
 181#define __UNIQUE_ID(prefix) __PASTE(__PASTE(__UNIQUE_ID_, prefix), __COUNTER__)
 182
 183#ifndef __CHECKER__
 184# define __compiletime_warning(message) __attribute__((warning(message)))
 185# define __compiletime_error(message) __attribute__((error(message)))
 186#endif /* __CHECKER__ */
 187#endif /* GCC_VERSION >= 40300 */
 188
 189#if GCC_VERSION >= 40500
 190/*
 191 * Mark a position in code as unreachable.  This can be used to
 192 * suppress control flow warnings after asm blocks that transfer
 193 * control elsewhere.
 194 *
 195 * Early snapshots of gcc 4.5 don't support this and we can't detect
 196 * this in the preprocessor, but we can live with this because they're
 197 * unreleased.  Really, we need to have autoconf for the kernel.
 198 */
 199#define unreachable() __builtin_unreachable()
 200
 201/* Mark a function definition as prohibited from being cloned. */
 202#define __noclone       __attribute__((__noclone__))
 203
 204#endif /* GCC_VERSION >= 40500 */
 205
 206#if GCC_VERSION >= 40600
 207/*
 208 * Tell the optimizer that something else uses this function or variable.
 209 */
 210#define __visible       __attribute__((externally_visible))
 211#endif
 212
 213/*
 214 * GCC 'asm goto' miscompiles certain code sequences:
 215 *
 216 *   http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58670
 217 *
 218 * Work it around via a compiler barrier quirk suggested by Jakub Jelinek.
 219 *
 220 * (asm goto is automatically volatile - the naming reflects this.)
 221 */
 222#define asm_volatile_goto(x...) do { asm goto(x); asm (""); } while (0)
 223
 224#ifdef CONFIG_ARCH_USE_BUILTIN_BSWAP
 225#if GCC_VERSION >= 40400
 226#define __HAVE_BUILTIN_BSWAP32__
 227#define __HAVE_BUILTIN_BSWAP64__
 228#endif
 229#if GCC_VERSION >= 40800 || (defined(__powerpc__) && GCC_VERSION >= 40600)
 230#define __HAVE_BUILTIN_BSWAP16__
 231#endif
 232#endif /* CONFIG_ARCH_USE_BUILTIN_BSWAP */
 233
 234#if GCC_VERSION >= 50000
 235#define KASAN_ABI_VERSION 4
 236#elif GCC_VERSION >= 40902
 237#define KASAN_ABI_VERSION 3
 238#endif
 239
 240#if GCC_VERSION >= 40902
 241/*
 242 * Tell the compiler that address safety instrumentation (KASAN)
 243 * should not be applied to that function.
 244 * Conflicts with inlining: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67368
 245 */
 246#define __no_sanitize_address __attribute__((no_sanitize_address))
 247#endif
 248
 249#endif  /* gcc version >= 40000 specific checks */
 250
 251#if !defined(__noclone)
 252#define __noclone       /* not needed */
 253#endif
 254
 255#if !defined(__no_sanitize_address)
 256#define __no_sanitize_address
 257#endif
 258
 259/*
 260 * A trick to suppress uninitialized variable warning without generating any
 261 * code
 262 */
 263#define uninitialized_var(x) x = x
 264