include/linux/compiler-gcc.h

   1 /* SPDX-License-Identifier: GPL-2.0 */
   2 #ifndef __LINUX_COMPILER_H
   3 #error "Please don't include <linux/compiler-gcc.h> directly, include <linux/compiler.h> instead."
   4 #endif
   5
   6 /*
   7  * Common definitions for all gcc versions go here.
   8  */
   9 #define GCC_VERSION (__GNUC__ * 10000           \
  10                      + __GNUC_MINOR__ * 100     \
  11                      + __GNUC_PATCHLEVEL__)
  12
  13 /* Optimization barrier */
  14
  15 /* The "volatile" is due to gcc bugs */
  16 #define barrier() __asm__ __volatile__("": : :"memory")
  17 /*
  18  * This version is i.e. to prevent dead stores elimination on @ptr
  19  * where gcc and llvm may behave differently when otherwise using
  20  * normal barrier(): while gcc behavior gets along with a normal
  21  * barrier(), llvm needs an explicit input variable to be assumed
  22  * clobbered. The issue is as follows: while the inline asm might
  23  * access any memory it wants, the compiler could have fit all of
  24  * @ptr into memory registers instead, and since @ptr never escaped
  25  * from that, it proved that the inline asm wasn't touching any of
  26  * it. This version works well with both compilers, i.e. we're telling
  27  * the compiler that the inline asm absolutely may see the contents
  28  * of @ptr. See also: https://llvm.org/bugs/show_bug.cgi?id=15495
  29  */
  30 #define barrier_data(ptr) __asm__ __volatile__("": :"r"(ptr) :"memory")
  31
  32 /*
  33  * This macro obfuscates arithmetic on a variable address so that gcc
  34  * shouldn't recognize the original var, and make assumptions about it.
  35  *
  36  * This is needed because the C standard makes it undefined to do
  37  * pointer arithmetic on "objects" outside their boundaries and the
  38  * gcc optimizers assume this is the case. In particular they
  39  * assume such arithmetic does not wrap.
  40  *
  41  * A miscompilation has been observed because of this on PPC.
  42  * To work around it we hide the relationship of the pointer and the object
  43  * using this macro.
  44  *
  45  * Versions of the ppc64 compiler before 4.1 had a bug where use of
  46  * RELOC_HIDE could trash r30. The bug can be worked around by changing
  47  * the inline assembly constraint from =g to =r, in this particular
  48  * case either is valid.
  49  */
  50 #define RELOC_HIDE(ptr, off)                                            \
  51 ({                                                                      \
  52         unsigned long __ptr;                                            \
  53         __asm__ ("" : "=r"(__ptr) : "0"(ptr));                          \
  54         (typeof(ptr)) (__ptr + (off));                                  \
  55 })
  56
  57 /* Make the optimizer believe the variable can be manipulated arbitrarily. */
  58 #define OPTIMIZER_HIDE_VAR(var)                                         \
  59         __asm__ ("" : "=r" (var) : "0" (var))
  60
  61 #ifdef __CHECKER__
  62 #define __must_be_array(a)      0
  63 #else
  64 /* &a[0] degrades to a pointer: a different type from an array */
  65 #define __must_be_array(a)      BUILD_BUG_ON_ZERO(__same_type((a), &(a)[0]))
  66 #endif
  67
  68 /*
  69  * Force always-inline if the user requests it so via the .config,
  70  * or if gcc is too old.
  71  * GCC does not warn about unused static inline functions for
  72  * -Wunused-function.  This turns out to avoid the need for complex #ifdef
  73  * directives.  Suppress the warning in clang as well by using "unused"
  74  * function attribute, which is redundant but not harmful for gcc.
  75  */
  76 #if !defined(CONFIG_ARCH_SUPPORTS_OPTIMIZED_INLINING) ||                \
  77     !defined(CONFIG_OPTIMIZE_INLINING) || (__GNUC__ < 4)
  78 #define inline inline           __attribute__((always_inline,unused)) notrace
  79 #define __inline__ __inline__   __attribute__((always_inline,unused)) notrace
  80 #define __inline __inline       __attribute__((always_inline,unused)) notrace
  81 #else
  82 /* A lot of inline functions can cause havoc with function tracing */
  83 #define inline inline           __attribute__((unused)) notrace
  84 #define __inline__ __inline__   __attribute__((unused)) notrace
  85 #define __inline __inline       __attribute__((unused)) notrace
  86 #endif
  87
  88 #define __always_inline inline __attribute__((always_inline))
  89 #define  noinline       __attribute__((noinline))
  90
  91 #define __deprecated    __attribute__((deprecated))
  92 #define __packed        __attribute__((packed))
  93 #define __weak          __attribute__((weak))
  94 #define __alias(symbol) __attribute__((alias(#symbol)))
  95
  96 /*
  97  * it doesn't make sense on ARM (currently the only user of __naked)
  98  * to trace naked functions because then mcount is called without
  99  * stack and frame pointer being set up and there is no chance to
 100  * restore the lr register to the value before mcount was called.
 101  *
 102  * The asm() bodies of naked functions often depend on standard calling
 103  * conventions, therefore they must be noinline and noclone.
 104  *
 105  * GCC 4.[56] currently fail to enforce this, so we must do so ourselves.
 106  * See GCC PR44290.
 107  */
 108 #define __naked         __attribute__((naked)) noinline __noclone notrace
 109
 110 #define __noreturn      __attribute__((noreturn))
 111
 112 /*
 113  * From the GCC manual:
 114  *
 115  * Many functions have no effects except the return value and their
 116  * return value depends only on the parameters and/or global
 117  * variables.  Such a function can be subject to common subexpression
 118  * elimination and loop optimization just as an arithmetic operator
 119  * would be.
 120  * [...]
 121  */
 122 #define __pure                  __attribute__((pure))
 123 #define __aligned(x)            __attribute__((aligned(x)))
 124 #define __aligned_largest       __attribute__((aligned))
 125 #define __printf(a, b)          __attribute__((format(printf, a, b)))
 126 #define __scanf(a, b)           __attribute__((format(scanf, a, b)))
 127 #define __attribute_const__     __attribute__((__const__))
 128 #define __maybe_unused          __attribute__((unused))
 129 #define __always_unused         __attribute__((unused))
 130 #define __mode(x)               __attribute__((mode(x)))
 131
 132 /* gcc version specific checks */
 133
 134 #if GCC_VERSION < 30200
 135 # error Sorry, your compiler is too old - please upgrade it.
 136 #endif
 137
 138 #if GCC_VERSION < 30300
 139 # define __used                 __attribute__((__unused__))
 140 #else
 141 # define __used                 __attribute__((__used__))
 142 #endif
 143
 144 #ifdef CONFIG_GCOV_KERNEL
 145 # if GCC_VERSION < 30400
 146 #   error "GCOV profiling support for gcc versions below 3.4 not included"
 147 # endif /* __GNUC_MINOR__ */
 148 #endif /* CONFIG_GCOV_KERNEL */
 149
 150 #if GCC_VERSION >= 30400
 151 #define __must_check            __attribute__((warn_unused_result))
 152 #define __malloc                __attribute__((__malloc__))
 153 #endif
 154
 155 #if GCC_VERSION >= 40000
 156
 157 /* GCC 4.1.[01] miscompiles __weak */
 158 #ifdef __KERNEL__
 159 # if GCC_VERSION >= 40100 &&  GCC_VERSION <= 40101
 160 #  error Your version of gcc miscompiles the __weak directive
 161 # endif
 162 #endif
 163
 164 #define __used                  __attribute__((__used__))
 165 #define __compiler_offsetof(a, b)                                       \
 166         __builtin_offsetof(a, b)
 167
 168 #if GCC_VERSION >= 40100
 169 # define __compiletime_object_size(obj) __builtin_object_size(obj, 0)
 170
 171 #define __nostackprotector      __attribute__((__optimize__("no-stack-protector")))
 172 #endif
 173
 174 #if GCC_VERSION >= 40300
 175 /* Mark functions as cold. gcc will assume any path leading to a call
 176  * to them will be unlikely.  This means a lot of manual unlikely()s
 177  * are unnecessary now for any paths leading to the usual suspects
 178  * like BUG(), printk(), panic() etc. [but let's keep them for now for
 179  * older compilers]
 180  *
 181  * Early snapshots of gcc 4.3 don't support this and we can't detect this
 182  * in the preprocessor, but we can live with this because they're unreleased.
 183  * Maketime probing would be overkill here.
 184  *
 185  * gcc also has a __attribute__((__hot__)) to move hot functions into
 186  * a special section, but I don't see any sense in this right now in
 187  * the kernel context
 188  */
 189 #define __cold                  __attribute__((__cold__))
 190
 191 #define __UNIQUE_ID(prefix) __PASTE(__PASTE(__UNIQUE_ID_, prefix), __COUNTER__)
 192
 193 #ifndef __CHECKER__
 194 # define __compiletime_warning(message) __attribute__((warning(message)))
 195 # define __compiletime_error(message) __attribute__((error(message)))
 196 #endif /* __CHECKER__ */
 197 #endif /* GCC_VERSION >= 40300 */
 198
 199 #if GCC_VERSION >= 40500
 200
 201 #ifndef __CHECKER__
 202 #ifdef LATENT_ENTROPY_PLUGIN
 203 #define __latent_entropy __attribute__((latent_entropy))
 204 #endif
 205 #endif
 206
 207 /*
 208  * Mark a position in code as unreachable.  This can be used to
 209  * suppress control flow warnings after asm blocks that transfer
 210  * control elsewhere.
 211  *
 212  * Early snapshots of gcc 4.5 don't support this and we can't detect
 213  * this in the preprocessor, but we can live with this because they're
 214  * unreleased.  Really, we need to have autoconf for the kernel.
 215  */
 216 #define unreachable() \
 217         do { annotate_unreachable(); __builtin_unreachable(); } while (0)
 218
 219 /* Mark a function definition as prohibited from being cloned. */
 220 #define __noclone       __attribute__((__noclone__, __optimize__("no-tracer")))
 221
 222 #ifdef RANDSTRUCT_PLUGIN
 223 #define __randomize_layout __attribute__((randomize_layout))
 224 #define __no_randomize_layout __attribute__((no_randomize_layout))
 225 #endif
 226
 227 #endif /* GCC_VERSION >= 40500 */
 228
 229 #if GCC_VERSION >= 40600
 230
 231 /*
 232  * When used with Link Time Optimization, gcc can optimize away C functions or
 233  * variables which are referenced only from assembly code.  __visible tells the
 234  * optimizer that something else uses this function or variable, thus preventing
 235  * this.
 236  */
 237 #define __visible       __attribute__((externally_visible))
 238
 239 /*
 240  * RANDSTRUCT_PLUGIN wants to use an anonymous struct, but it is only
 241  * possible since GCC 4.6. To provide as much build testing coverage
 242  * as possible, this is used for all GCC 4.6+ builds, and not just on
 243  * RANDSTRUCT_PLUGIN builds.
 244  */
 245 #define randomized_struct_fields_start  struct {
 246 #define randomized_struct_fields_end    } __randomize_layout;
 247
 248 #endif /* GCC_VERSION >= 40600 */
 249
 250
 251 #if GCC_VERSION >= 40900 && !defined(__CHECKER__)
 252 /*
 253  * __assume_aligned(n, k): Tell the optimizer that the returned
 254  * pointer can be assumed to be k modulo n. The second argument is
 255  * optional (default 0), so we use a variadic macro to make the
 256  * shorthand.
 257  *
 258  * Beware: Do not apply this to functions which may return
 259  * ERR_PTRs. Also, it is probably unwise to apply it to functions
 260  * returning extra information in the low bits (but in that case the
 261  * compiler should see some alignment anyway, when the return value is
 262  * massaged by 'flags = ptr & 3; ptr &= ~3;').
 263  */
 264 #define __assume_aligned(a, ...) __attribute__((__assume_aligned__(a, ## __VA_ARGS__)))
 265 #endif
 266
 267 /*
 268  * GCC 'asm goto' miscompiles certain code sequences:
 269  *
 270  *   http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58670
 271  *
 272  * Work it around via a compiler barrier quirk suggested by Jakub Jelinek.
 273  *
 274  * (asm goto is automatically volatile - the naming reflects this.)
 275  */
 276 #define asm_volatile_goto(x...) do { asm goto(x); asm (""); } while (0)
 277
 278 /*
 279  * sparse (__CHECKER__) pretends to be gcc, but can't do constant
 280  * folding in __builtin_bswap*() (yet), so don't set these for it.
 281  */
 282 #if defined(CONFIG_ARCH_USE_BUILTIN_BSWAP) && !defined(__CHECKER__)
 283 #if GCC_VERSION >= 40400
 284 #define __HAVE_BUILTIN_BSWAP32__
 285 #define __HAVE_BUILTIN_BSWAP64__
 286 #endif
 287 #if GCC_VERSION >= 40800
 288 #define __HAVE_BUILTIN_BSWAP16__
 289 #endif
 290 #endif /* CONFIG_ARCH_USE_BUILTIN_BSWAP && !__CHECKER__ */
 291
 292 #if GCC_VERSION >= 70000
 293 #define KASAN_ABI_VERSION 5
 294 #elif GCC_VERSION >= 50000
 295 #define KASAN_ABI_VERSION 4
 296 #elif GCC_VERSION >= 40902
 297 #define KASAN_ABI_VERSION 3
 298 #endif
 299
 300 #if GCC_VERSION >= 40902
 301 /*
 302  * Tell the compiler that address safety instrumentation (KASAN)
 303  * should not be applied to that function.
 304  * Conflicts with inlining: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67368
 305  */
 306 #define __no_sanitize_address __attribute__((no_sanitize_address))
 307 #endif
 308
 309 #if GCC_VERSION >= 50100
 310 /*
 311  * Mark structures as requiring designated initializers.
 312  * https://gcc.gnu.org/onlinedocs/gcc/Designated-Inits.html
 313  */
 314 #define __designated_init __attribute__((designated_init))
 315 #endif
 316
 317 #endif  /* gcc version >= 40000 specific checks */
 318
 319 #if !defined(__noclone)
 320 #define __noclone       /* not needed */
 321 #endif
 322
 323 #if !defined(__no_sanitize_address)
 324 #define __no_sanitize_address
 325 #endif
 326
 327 /*
 328  * A trick to suppress uninitialized variable warning without generating any
 329  * code
 330  */
 331 #define uninitialized_var(x) x = x