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 proved 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  * GCC does not warn about unused static inline functions for
  71  * -Wunused-function.  This turns out to avoid the need for complex #ifdef
  72  * directives.  Suppress the warning in clang as well by using "unused"
  73  * function attribute, which is redundant but not harmful for gcc.
  74  */
  75 #if !defined(CONFIG_ARCH_SUPPORTS_OPTIMIZED_INLINING) ||                \
  76     !defined(CONFIG_OPTIMIZE_INLINING) || (__GNUC__ < 4)
  77 #define inline inline           __attribute__((always_inline,unused)) notrace
  78 #define __inline__ __inline__   __attribute__((always_inline,unused)) notrace
  79 #define __inline __inline       __attribute__((always_inline,unused)) notrace
  80 #else
  81 /* A lot of inline functions can cause havoc with function tracing */
  82 #define inline inline           __attribute__((unused)) notrace
  83 #define __inline__ __inline__   __attribute__((unused)) notrace
  84 #define __inline __inline       __attribute__((unused)) notrace
  85 #endif
  86
  87 #define __always_inline inline __attribute__((always_inline))
  88 #define  noinline       __attribute__((noinline))
  89
  90 #define __deprecated    __attribute__((deprecated))
  91 #define __packed        __attribute__((packed))
  92 #define __weak          __attribute__((weak))
  93 #define __alias(symbol) __attribute__((alias(#symbol)))
  94
  95 /*
  96  * it doesn't make sense on ARM (currently the only user of __naked)
  97  * to trace naked functions because then mcount is called without
  98  * stack and frame pointer being set up and there is no chance to
  99  * restore the lr register to the value before mcount was called.
 100  *
 101  * The asm() bodies of naked functions often depend on standard calling
 102  * conventions, therefore they must be noinline and noclone.
 103  *
 104  * GCC 4.[56] currently fail to enforce this, so we must do so ourselves.
 105  * See GCC PR44290.
 106  */
 107 #define __naked         __attribute__((naked)) noinline __noclone notrace
 108
 109 #define __noreturn      __attribute__((noreturn))
 110
 111 /*
 112  * From the GCC manual:
 113  *
 114  * Many functions have no effects except the return value and their
 115  * return value depends only on the parameters and/or global
 116  * variables.  Such a function can be subject to common subexpression
 117  * elimination and loop optimization just as an arithmetic operator
 118  * would be.
 119  * [...]
 120  */
 121 #define __pure                  __attribute__((pure))
 122 #define __aligned(x)            __attribute__((aligned(x)))
 123 #define __aligned_largest       __attribute__((aligned))
 124 #define __printf(a, b)          __attribute__((format(printf, a, b)))
 125 #define __scanf(a, b)           __attribute__((format(scanf, a, b)))
 126 #define __attribute_const__     __attribute__((__const__))
 127 #define __maybe_unused          __attribute__((unused))
 128 #define __always_unused         __attribute__((unused))
 129 #define __mode(x)               __attribute__((mode(x)))
 130
 131 /* gcc version specific checks */
 132
 133 #if GCC_VERSION < 30200
 134 # error Sorry, your compiler is too old - please upgrade it.
 135 #endif
 136
 137 #if GCC_VERSION < 30300
 138 # define __used                 __attribute__((__unused__))
 139 #else
 140 # define __used                 __attribute__((__used__))
 141 #endif
 142
 143 #ifdef CONFIG_GCOV_KERNEL
 144 # if GCC_VERSION < 30400
 145 #   error "GCOV profiling support for gcc versions below 3.4 not included"
 146 # endif /* __GNUC_MINOR__ */
 147 #endif /* CONFIG_GCOV_KERNEL */
 148
 149 #if GCC_VERSION >= 30400
 150 #define __must_check            __attribute__((warn_unused_result))
 151 #define __malloc                __attribute__((__malloc__))
 152 #endif
 153
 154 #if GCC_VERSION >= 40000
 155
 156 /* GCC 4.1.[01] miscompiles __weak */
 157 #ifdef __KERNEL__
 158 # if GCC_VERSION >= 40100 &&  GCC_VERSION <= 40101
 159 #  error Your version of gcc miscompiles the __weak directive
 160 # endif
 161 #endif
 162
 163 #define __used                  __attribute__((__used__))
 164 #define __compiler_offsetof(a, b)                                       \
 165         __builtin_offsetof(a, b)
 166
 167 #if GCC_VERSION >= 40100
 168 # define __compiletime_object_size(obj) __builtin_object_size(obj, 0)
 169 #endif
 170
 171 #if GCC_VERSION >= 40300
 172 /* Mark functions as cold. gcc will assume any path leading to a call
 173  * to them will be unlikely.  This means a lot of manual unlikely()s
 174  * are unnecessary now for any paths leading to the usual suspects
 175  * like BUG(), printk(), panic() etc. [but let's keep them for now for
 176  * older compilers]
 177  *
 178  * Early snapshots of gcc 4.3 don't support this and we can't detect this
 179  * in the preprocessor, but we can live with this because they're unreleased.
 180  * Maketime probing would be overkill here.
 181  *
 182  * gcc also has a __attribute__((__hot__)) to move hot functions into
 183  * a special section, but I don't see any sense in this right now in
 184  * the kernel context
 185  */
 186 #define __cold                  __attribute__((__cold__))
 187
 188 #define __UNIQUE_ID(prefix) __PASTE(__PASTE(__UNIQUE_ID_, prefix), __COUNTER__)
 189
 190 #ifndef __CHECKER__
 191 # define __compiletime_warning(message) __attribute__((warning(message)))
 192 # define __compiletime_error(message) __attribute__((error(message)))
 193 #endif /* __CHECKER__ */
 194 #endif /* GCC_VERSION >= 40300 */
 195
 196 #if GCC_VERSION >= 40500
 197
 198 #ifndef __CHECKER__
 199 #ifdef LATENT_ENTROPY_PLUGIN
 200 #define __latent_entropy __attribute__((latent_entropy))
 201 #endif
 202 #endif
 203
 204 #ifdef CONFIG_STACK_VALIDATION
 205 #define annotate_unreachable() ({                                       \
 206         asm("%c0:\t\n"                                                  \
 207             ".pushsection .discard.unreachable\t\n"                     \
 208             ".long %c0b - .\t\n"                                        \
 209             ".popsection\t\n" : : "i" (__LINE__));                      \
 210 })
 211 #else
 212 #define annotate_unreachable()
 213 #endif
 214
 215 /*
 216  * Mark a position in code as unreachable.  This can be used to
 217  * suppress control flow warnings after asm blocks that transfer
 218  * control elsewhere.
 219  *
 220  * Early snapshots of gcc 4.5 don't support this and we can't detect
 221  * this in the preprocessor, but we can live with this because they're
 222  * unreleased.  Really, we need to have autoconf for the kernel.
 223  */
 224 #define unreachable() \
 225         do { annotate_unreachable(); __builtin_unreachable(); } while (0)
 226
 227 /* Mark a function definition as prohibited from being cloned. */
 228 #define __noclone       __attribute__((__noclone__, __optimize__("no-tracer")))
 229
 230 #ifdef RANDSTRUCT_PLUGIN
 231 #define __randomize_layout __attribute__((randomize_layout))
 232 #define __no_randomize_layout __attribute__((no_randomize_layout))
 233 #endif
 234
 235 #endif /* GCC_VERSION >= 40500 */
 236
 237 #if GCC_VERSION >= 40600
 238
 239 /*
 240  * When used with Link Time Optimization, gcc can optimize away C functions or
 241  * variables which are referenced only from assembly code.  __visible tells the
 242  * optimizer that something else uses this function or variable, thus preventing
 243  * this.
 244  */
 245 #define __visible       __attribute__((externally_visible))
 246
 247 /*
 248  * RANDSTRUCT_PLUGIN wants to use an anonymous struct, but it is only
 249  * possible since GCC 4.6. To provide as much build testing coverage
 250  * as possible, this is used for all GCC 4.6+ builds, and not just on
 251  * RANDSTRUCT_PLUGIN builds.
 252  */
 253 #define randomized_struct_fields_start  struct {
 254 #define randomized_struct_fields_end    } __randomize_layout;
 255
 256 #endif /* GCC_VERSION >= 40600 */
 257
 258
 259 #if GCC_VERSION >= 40900 && !defined(__CHECKER__)
 260 /*
 261  * __assume_aligned(n, k): Tell the optimizer that the returned
 262  * pointer can be assumed to be k modulo n. The second argument is
 263  * optional (default 0), so we use a variadic macro to make the
 264  * shorthand.
 265  *
 266  * Beware: Do not apply this to functions which may return
 267  * ERR_PTRs. Also, it is probably unwise to apply it to functions
 268  * returning extra information in the low bits (but in that case the
 269  * compiler should see some alignment anyway, when the return value is
 270  * massaged by 'flags = ptr & 3; ptr &= ~3;').
 271  */
 272 #define __assume_aligned(a, ...) __attribute__((__assume_aligned__(a, ## __VA_ARGS__)))
 273 #endif
 274
 275 /*
 276  * GCC 'asm goto' miscompiles certain code sequences:
 277  *
 278  *   http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58670
 279  *
 280  * Work it around via a compiler barrier quirk suggested by Jakub Jelinek.
 281  *
 282  * (asm goto is automatically volatile - the naming reflects this.)
 283  */
 284 #define asm_volatile_goto(x...) do { asm goto(x); asm (""); } while (0)
 285
 286 /*
 287  * sparse (__CHECKER__) pretends to be gcc, but can't do constant
 288  * folding in __builtin_bswap*() (yet), so don't set these for it.
 289  */
 290 #if defined(CONFIG_ARCH_USE_BUILTIN_BSWAP) && !defined(__CHECKER__)
 291 #if GCC_VERSION >= 40400
 292 #define __HAVE_BUILTIN_BSWAP32__
 293 #define __HAVE_BUILTIN_BSWAP64__
 294 #endif
 295 #if GCC_VERSION >= 40800
 296 #define __HAVE_BUILTIN_BSWAP16__
 297 #endif
 298 #endif /* CONFIG_ARCH_USE_BUILTIN_BSWAP && !__CHECKER__ */
 299
 300 #if GCC_VERSION >= 70000
 301 #define KASAN_ABI_VERSION 5
 302 #elif GCC_VERSION >= 50000
 303 #define KASAN_ABI_VERSION 4
 304 #elif GCC_VERSION >= 40902
 305 #define KASAN_ABI_VERSION 3
 306 #endif
 307
 308 #if GCC_VERSION >= 40902
 309 /*
 310  * Tell the compiler that address safety instrumentation (KASAN)
 311  * should not be applied to that function.
 312  * Conflicts with inlining: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67368
 313  */
 314 #define __no_sanitize_address __attribute__((no_sanitize_address))
 315 #endif
 316
 317 #if GCC_VERSION >= 50100
 318 /*
 319  * Mark structures as requiring designated initializers.
 320  * https://gcc.gnu.org/onlinedocs/gcc/Designated-Inits.html
 321  */
 322 #define __designated_init __attribute__((designated_init))
 323 #endif
 324
 325 #endif  /* gcc version >= 40000 specific checks */
 326
 327 #if !defined(__noclone)
 328 #define __noclone       /* not needed */
 329 #endif
 330
 331 #if !defined(__no_sanitize_address)
 332 #define __no_sanitize_address
 333 #endif
 334
 335 /*
 336  * A trick to suppress uninitialized variable warning without generating any
 337  * code
 338  */
 339 #define uninitialized_var(x) x = x