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 #define __malloc                __attribute__((__malloc__))
 146 #endif
 147
 148 #if GCC_VERSION >= 40000
 149
 150 /* GCC 4.1.[01] miscompiles __weak */
 151 #ifdef __KERNEL__
 152 # if GCC_VERSION >= 40100 &&  GCC_VERSION <= 40101
 153 #  error Your version of gcc miscompiles the __weak directive
 154 # endif
 155 #endif
 156
 157 #define __used                  __attribute__((__used__))
 158 #define __compiler_offsetof(a, b)                                       \
 159         __builtin_offsetof(a, b)
 160
 161 #if GCC_VERSION >= 40100
 162 # define __compiletime_object_size(obj) __builtin_object_size(obj, 0)
 163 #endif
 164
 165 #if GCC_VERSION >= 40300
 166 /* Mark functions as cold. gcc will assume any path leading to a call
 167  * to them will be unlikely.  This means a lot of manual unlikely()s
 168  * are unnecessary now for any paths leading to the usual suspects
 169  * like BUG(), printk(), panic() etc. [but let's keep them for now for
 170  * older compilers]
 171  *
 172  * Early snapshots of gcc 4.3 don't support this and we can't detect this
 173  * in the preprocessor, but we can live with this because they're unreleased.
 174  * Maketime probing would be overkill here.
 175  *
 176  * gcc also has a __attribute__((__hot__)) to move hot functions into
 177  * a special section, but I don't see any sense in this right now in
 178  * the kernel context
 179  */
 180 #define __cold                  __attribute__((__cold__))
 181
 182 #define __UNIQUE_ID(prefix) __PASTE(__PASTE(__UNIQUE_ID_, prefix), __COUNTER__)
 183
 184 #ifndef __CHECKER__
 185 # define __compiletime_warning(message) __attribute__((warning(message)))
 186 # define __compiletime_error(message) __attribute__((error(message)))
 187 #endif /* __CHECKER__ */
 188 #endif /* GCC_VERSION >= 40300 */
 189
 190 #if GCC_VERSION >= 40500
 191
 192 #ifndef __CHECKER__
 193 #ifdef LATENT_ENTROPY_PLUGIN
 194 #define __latent_entropy __attribute__((latent_entropy))
 195 #endif
 196 #endif
 197
 198 /*
 199  * Mark a position in code as unreachable.  This can be used to
 200  * suppress control flow warnings after asm blocks that transfer
 201  * control elsewhere.
 202  *
 203  * Early snapshots of gcc 4.5 don't support this and we can't detect
 204  * this in the preprocessor, but we can live with this because they're
 205  * unreleased.  Really, we need to have autoconf for the kernel.
 206  */
 207 #define unreachable() __builtin_unreachable()
 208
 209 /* Mark a function definition as prohibited from being cloned. */
 210 #define __noclone       __attribute__((__noclone__, __optimize__("no-tracer")))
 211
 212 #endif /* GCC_VERSION >= 40500 */
 213
 214 #if GCC_VERSION >= 40600
 215 /*
 216  * When used with Link Time Optimization, gcc can optimize away C functions or
 217  * variables which are referenced only from assembly code.  __visible tells the
 218  * optimizer that something else uses this function or variable, thus preventing
 219  * this.
 220  */
 221 #define __visible       __attribute__((externally_visible))
 222 #endif
 223
 224
 225 #if GCC_VERSION >= 40900 && !defined(__CHECKER__)
 226 /*
 227  * __assume_aligned(n, k): Tell the optimizer that the returned
 228  * pointer can be assumed to be k modulo n. The second argument is
 229  * optional (default 0), so we use a variadic macro to make the
 230  * shorthand.
 231  *
 232  * Beware: Do not apply this to functions which may return
 233  * ERR_PTRs. Also, it is probably unwise to apply it to functions
 234  * returning extra information in the low bits (but in that case the
 235  * compiler should see some alignment anyway, when the return value is
 236  * massaged by 'flags = ptr & 3; ptr &= ~3;').
 237  */
 238 #define __assume_aligned(a, ...) __attribute__((__assume_aligned__(a, ## __VA_ARGS__)))
 239 #endif
 240
 241 /*
 242  * GCC 'asm goto' miscompiles certain code sequences:
 243  *
 244  *   http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58670
 245  *
 246  * Work it around via a compiler barrier quirk suggested by Jakub Jelinek.
 247  *
 248  * (asm goto is automatically volatile - the naming reflects this.)
 249  */
 250 #define asm_volatile_goto(x...) do { asm goto(x); asm (""); } while (0)
 251
 252 /*
 253  * sparse (__CHECKER__) pretends to be gcc, but can't do constant
 254  * folding in __builtin_bswap*() (yet), so don't set these for it.
 255  */
 256 #if defined(CONFIG_ARCH_USE_BUILTIN_BSWAP) && !defined(__CHECKER__)
 257 #if GCC_VERSION >= 40400
 258 #define __HAVE_BUILTIN_BSWAP32__
 259 #define __HAVE_BUILTIN_BSWAP64__
 260 #endif
 261 #if GCC_VERSION >= 40800
 262 #define __HAVE_BUILTIN_BSWAP16__
 263 #endif
 264 #endif /* CONFIG_ARCH_USE_BUILTIN_BSWAP && !__CHECKER__ */
 265
 266 #if GCC_VERSION >= 50000
 267 #define KASAN_ABI_VERSION 4
 268 #elif GCC_VERSION >= 40902
 269 #define KASAN_ABI_VERSION 3
 270 #endif
 271
 272 #if GCC_VERSION >= 40902
 273 /*
 274  * Tell the compiler that address safety instrumentation (KASAN)
 275  * should not be applied to that function.
 276  * Conflicts with inlining: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67368
 277  */
 278 #define __no_sanitize_address __attribute__((no_sanitize_address))
 279 #endif
 280
 281 #endif  /* gcc version >= 40000 specific checks */
 282
 283 #if !defined(__noclone)
 284 #define __noclone       /* not needed */
 285 #endif
 286
 287 #if !defined(__no_sanitize_address)
 288 #define __no_sanitize_address
 289 #endif
 290
 291 /*
 292  * A trick to suppress uninitialized variable warning without generating any
 293  * code
 294  */
 295 #define uninitialized_var(x) x = x