include/linux/compiler.h

   1 /* SPDX-License-Identifier: GPL-2.0 */
   2 #ifndef __LINUX_COMPILER_H
   3 #define __LINUX_COMPILER_H
   4
   5 #include <linux/compiler_types.h>
   6
   7 #ifndef __ASSEMBLY__
   8
   9 #ifdef __KERNEL__
  10
  11 /*
  12  * Note: DISABLE_BRANCH_PROFILING can be used by special lowlevel code
  13  * to disable branch tracing on a per file basis.
  14  */
  15 #if defined(CONFIG_TRACE_BRANCH_PROFILING) \
  16     && !defined(DISABLE_BRANCH_PROFILING) && !defined(__CHECKER__)
  17 void ftrace_likely_update(struct ftrace_likely_data *f, int val,
  18                           int expect, int is_constant);
  19
  20 #define likely_notrace(x)       __builtin_expect(!!(x), 1)
  21 #define unlikely_notrace(x)     __builtin_expect(!!(x), 0)
  22
  23 #define __branch_check__(x, expect, is_constant) ({                     \
  24                         long ______r;                                   \
  25                         static struct ftrace_likely_data                \
  26                                 __aligned(4)                            \
  27                                 __section(_ftrace_annotated_branch)     \
  28                                 ______f = {                             \
  29                                 .data.func = __func__,                  \
  30                                 .data.file = __FILE__,                  \
  31                                 .data.line = __LINE__,                  \
  32                         };                                              \
  33                         ______r = __builtin_expect(!!(x), expect);      \
  34                         ftrace_likely_update(&______f, ______r,         \
  35                                              expect, is_constant);      \
  36                         ______r;                                        \
  37                 })
  38
  39 /*
  40  * Using __builtin_constant_p(x) to ignore cases where the return
  41  * value is always the same.  This idea is taken from a similar patch
  42  * written by Daniel Walker.
  43  */
  44 # ifndef likely
  45 #  define likely(x)     (__branch_check__(x, 1, __builtin_constant_p(x)))
  46 # endif
  47 # ifndef unlikely
  48 #  define unlikely(x)   (__branch_check__(x, 0, __builtin_constant_p(x)))
  49 # endif
  50
  51 #ifdef CONFIG_PROFILE_ALL_BRANCHES
  52 /*
  53  * "Define 'is'", Bill Clinton
  54  * "Define 'if'", Steven Rostedt
  55  */
  56 #define if(cond, ...) if ( __trace_if_var( !!(cond , ## __VA_ARGS__) ) )
  57
  58 #define __trace_if_var(cond) (__builtin_constant_p(cond) ? (cond) : __trace_if_value(cond))
  59
  60 #define __trace_if_value(cond) ({                       \
  61         static struct ftrace_branch_data                \
  62                 __aligned(4)                            \
  63                 __section(_ftrace_branch)               \
  64                 __if_trace = {                          \
  65                         .func = __func__,               \
  66                         .file = __FILE__,               \
  67                         .line = __LINE__,               \
  68                 };                                      \
  69         (cond) ?                                        \
  70                 (__if_trace.miss_hit[1]++,1) :          \
  71                 (__if_trace.miss_hit[0]++,0);           \
  72 })
  73
  74 #endif /* CONFIG_PROFILE_ALL_BRANCHES */
  75
  76 #else
  77 # define likely(x)      __builtin_expect(!!(x), 1)
  78 # define unlikely(x)    __builtin_expect(!!(x), 0)
  79 #endif
  80
  81 /* Optimization barrier */
  82 #ifndef barrier
  83 # define barrier() __memory_barrier()
  84 #endif
  85
  86 #ifndef barrier_data
  87 # define barrier_data(ptr) barrier()
  88 #endif
  89
  90 /* workaround for GCC PR82365 if needed */
  91 #ifndef barrier_before_unreachable
  92 # define barrier_before_unreachable() do { } while (0)
  93 #endif
  94
  95 /* Unreachable code */
  96 #ifdef CONFIG_STACK_VALIDATION
  97 /*
  98  * These macros help objtool understand GCC code flow for unreachable code.
  99  * The __COUNTER__ based labels are a hack to make each instance of the macros
 100  * unique, to convince GCC not to merge duplicate inline asm statements.
 101  */
 102 #define annotate_reachable() ({                                         \
 103         asm volatile("%c0:\n\t"                                         \
 104                      ".pushsection .discard.reachable\n\t"              \
 105                      ".long %c0b - .\n\t"                               \
 106                      ".popsection\n\t" : : "i" (__COUNTER__));          \
 107 })
 108 #define annotate_unreachable() ({                                       \
 109         asm volatile("%c0:\n\t"                                         \
 110                      ".pushsection .discard.unreachable\n\t"            \
 111                      ".long %c0b - .\n\t"                               \
 112                      ".popsection\n\t" : : "i" (__COUNTER__));          \
 113 })
 114 #define ASM_UNREACHABLE                                                 \
 115         "999:\n\t"                                                      \
 116         ".pushsection .discard.unreachable\n\t"                         \
 117         ".long 999b - .\n\t"                                            \
 118         ".popsection\n\t"
 119
 120 /* Annotate a C jump table to allow objtool to follow the code flow */
 121 #define __annotate_jump_table __section(.rodata..c_jump_table)
 122
 123 #ifdef CONFIG_DEBUG_ENTRY
 124 /* Begin/end of an instrumentation safe region */
 125 #define instrumentation_begin() ({                                      \
 126         asm volatile("%c0:\n\t"                                         \
 127                      ".pushsection .discard.instr_begin\n\t"            \
 128                      ".long %c0b - .\n\t"                               \
 129                      ".popsection\n\t" : : "i" (__COUNTER__));          \
 130 })
 131
 132 /*
 133  * Because instrumentation_{begin,end}() can nest, objtool validation considers
 134  * _begin() a +1 and _end() a -1 and computes a sum over the instructions.
 135  * When the value is greater than 0, we consider instrumentation allowed.
 136  *
 137  * There is a problem with code like:
 138  *
 139  * noinstr void foo()
 140  * {
 141  *      instrumentation_begin();
 142  *      ...
 143  *      if (cond) {
 144  *              instrumentation_begin();
 145  *              ...
 146  *              instrumentation_end();
 147  *      }
 148  *      bar();
 149  *      instrumentation_end();
 150  * }
 151  *
 152  * If instrumentation_end() would be an empty label, like all the other
 153  * annotations, the inner _end(), which is at the end of a conditional block,
 154  * would land on the instruction after the block.
 155  *
 156  * If we then consider the sum of the !cond path, we'll see that the call to
 157  * bar() is with a 0-value, even though, we meant it to happen with a positive
 158  * value.
 159  *
 160  * To avoid this, have _end() be a NOP instruction, this ensures it will be
 161  * part of the condition block and does not escape.
 162  */
 163 #define instrumentation_end() ({                                        \
 164         asm volatile("%c0: nop\n\t"                                     \
 165                      ".pushsection .discard.instr_end\n\t"              \
 166                      ".long %c0b - .\n\t"                               \
 167                      ".popsection\n\t" : : "i" (__COUNTER__));          \
 168 })
 169 #endif /* CONFIG_DEBUG_ENTRY */
 170
 171 #else
 172 #define annotate_reachable()
 173 #define annotate_unreachable()
 174 #define __annotate_jump_table
 175 #endif
 176
 177 #ifndef instrumentation_begin
 178 #define instrumentation_begin()         do { } while(0)
 179 #define instrumentation_end()           do { } while(0)
 180 #endif
 181
 182 #ifndef ASM_UNREACHABLE
 183 # define ASM_UNREACHABLE
 184 #endif
 185 #ifndef unreachable
 186 # define unreachable() do {             \
 187         annotate_unreachable();         \
 188         __builtin_unreachable();        \
 189 } while (0)
 190 #endif
 191
 192 /*
 193  * KENTRY - kernel entry point
 194  * This can be used to annotate symbols (functions or data) that are used
 195  * without their linker symbol being referenced explicitly. For example,
 196  * interrupt vector handlers, or functions in the kernel image that are found
 197  * programatically.
 198  *
 199  * Not required for symbols exported with EXPORT_SYMBOL, or initcalls. Those
 200  * are handled in their own way (with KEEP() in linker scripts).
 201  *
 202  * KENTRY can be avoided if the symbols in question are marked as KEEP() in the
 203  * linker script. For example an architecture could KEEP() its entire
 204  * boot/exception vector code rather than annotate each function and data.
 205  */
 206 #ifndef KENTRY
 207 # define KENTRY(sym)                                            \
 208         extern typeof(sym) sym;                                 \
 209         static const unsigned long __kentry_##sym               \
 210         __used                                                  \
 211         __section("___kentry" "+" #sym )                        \
 212         = (unsigned long)&sym;
 213 #endif
 214
 215 #ifndef RELOC_HIDE
 216 # define RELOC_HIDE(ptr, off)                                   \
 217   ({ unsigned long __ptr;                                       \
 218      __ptr = (unsigned long) (ptr);                             \
 219     (typeof(ptr)) (__ptr + (off)); })
 220 #endif
 221
 222 #ifndef OPTIMIZER_HIDE_VAR
 223 /* Make the optimizer believe the variable can be manipulated arbitrarily. */
 224 #define OPTIMIZER_HIDE_VAR(var)                                         \
 225         __asm__ ("" : "=r" (var) : "0" (var))
 226 #endif
 227
 228 /* Not-quite-unique ID. */
 229 #ifndef __UNIQUE_ID
 230 # define __UNIQUE_ID(prefix) __PASTE(__PASTE(__UNIQUE_ID_, prefix), __LINE__)
 231 #endif
 232
 233 /*
 234  * Prevent the compiler from merging or refetching reads or writes. The
 235  * compiler is also forbidden from reordering successive instances of
 236  * READ_ONCE and WRITE_ONCE, but only when the compiler is aware of some
 237  * particular ordering. One way to make the compiler aware of ordering is to
 238  * put the two invocations of READ_ONCE or WRITE_ONCE in different C
 239  * statements.
 240  *
 241  * These two macros will also work on aggregate data types like structs or
 242  * unions.
 243  *
 244  * Their two major use cases are: (1) Mediating communication between
 245  * process-level code and irq/NMI handlers, all running on the same CPU,
 246  * and (2) Ensuring that the compiler does not fold, spindle, or otherwise
 247  * mutilate accesses that either do not require ordering or that interact
 248  * with an explicit memory barrier or atomic instruction that provides the
 249  * required ordering.
 250  */
 251 #include <asm/barrier.h>
 252 #include <linux/kasan-checks.h>
 253
 254 /*
 255  * Use __READ_ONCE() instead of READ_ONCE() if you do not require any
 256  * atomicity or dependency ordering guarantees. Note that this may result
 257  * in tears!
 258  */
 259 #define __READ_ONCE(x)  (*(const volatile __unqual_scalar_typeof(x) *)&(x))
 260
 261 #define __READ_ONCE_SCALAR(x)                                           \
 262 ({                                                                      \
 263         __unqual_scalar_typeof(x) __x = __READ_ONCE(x);                 \
 264         smp_read_barrier_depends();                                     \
 265         (typeof(x))__x;                                                 \
 266 })
 267
 268 #define READ_ONCE(x)                                                    \
 269 ({                                                                      \
 270         compiletime_assert_rwonce_type(x);                              \
 271         __READ_ONCE_SCALAR(x);                                          \
 272 })
 273
 274 #define __WRITE_ONCE(x, val)                            \
 275 do {                                                    \
 276         *(volatile typeof(x) *)&(x) = (val);            \
 277 } while (0)
 278
 279 #define WRITE_ONCE(x, val)                              \
 280 do {                                                    \
 281         compiletime_assert_rwonce_type(x);              \
 282         __WRITE_ONCE(x, val);                           \
 283 } while (0)
 284
 285 #ifdef CONFIG_KASAN
 286 /*
 287  * We can't declare function 'inline' because __no_sanitize_address conflicts
 288  * with inlining. Attempt to inline it may cause a build failure.
 289  *     https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67368
 290  * '__maybe_unused' allows us to avoid defined-but-not-used warnings.
 291  */
 292 # define __no_kasan_or_inline __no_sanitize_address notrace __maybe_unused
 293 #else
 294 # define __no_kasan_or_inline __always_inline
 295 #endif
 296
 297 static __no_kasan_or_inline
 298 unsigned long __read_once_word_nocheck(const void *addr)
 299 {
 300         return __READ_ONCE(*(unsigned long *)addr);
 301 }
 302
 303 /*
 304  * Use READ_ONCE_NOCHECK() instead of READ_ONCE() if you need to load a
 305  * word from memory atomically but without telling KASAN. This is usually
 306  * used by unwinding code when walking the stack of a running process.
 307  */
 308 #define READ_ONCE_NOCHECK(x)                                            \
 309 ({                                                                      \
 310         unsigned long __x;                                              \
 311         compiletime_assert(sizeof(x) == sizeof(__x),                    \
 312                 "Unsupported access size for READ_ONCE_NOCHECK().");    \
 313         __x = __read_once_word_nocheck(&(x));                           \
 314         smp_read_barrier_depends();                                     \
 315         (typeof(x))__x;                                                 \
 316 })
 317
 318 static __no_kasan_or_inline
 319 unsigned long read_word_at_a_time(const void *addr)
 320 {
 321         kasan_check_read(addr, 1);
 322         return *(unsigned long *)addr;
 323 }
 324
 325 #endif /* __KERNEL__ */
 326
 327 /*
 328  * Force the compiler to emit 'sym' as a symbol, so that we can reference
 329  * it from inline assembler. Necessary in case 'sym' could be inlined
 330  * otherwise, or eliminated entirely due to lack of references that are
 331  * visible to the compiler.
 332  */
 333 #define __ADDRESSABLE(sym) \
 334         static void * __section(.discard.addressable) __used \
 335                 __PASTE(__addressable_##sym, __LINE__) = (void *)&sym;
 336
 337 /**
 338  * offset_to_ptr - convert a relative memory offset to an absolute pointer
 339  * @off:        the address of the 32-bit offset value
 340  */
 341 static inline void *offset_to_ptr(const int *off)
 342 {
 343         return (void *)((unsigned long)off + *off);
 344 }
 345
 346 #endif /* __ASSEMBLY__ */
 347
 348 /* Compile time object size, -1 for unknown */
 349 #ifndef __compiletime_object_size
 350 # define __compiletime_object_size(obj) -1
 351 #endif
 352 #ifndef __compiletime_warning
 353 # define __compiletime_warning(message)
 354 #endif
 355 #ifndef __compiletime_error
 356 # define __compiletime_error(message)
 357 #endif
 358
 359 #ifdef __OPTIMIZE__
 360 # define __compiletime_assert(condition, msg, prefix, suffix)           \
 361         do {                                                            \
 362                 extern void prefix ## suffix(void) __compiletime_error(msg); \
 363                 if (!(condition))                                       \
 364                         prefix ## suffix();                             \
 365         } while (0)
 366 #else
 367 # define __compiletime_assert(condition, msg, prefix, suffix) do { } while (0)
 368 #endif
 369
 370 #define _compiletime_assert(condition, msg, prefix, suffix) \
 371         __compiletime_assert(condition, msg, prefix, suffix)
 372
 373 /**
 374  * compiletime_assert - break build and emit msg if condition is false
 375  * @condition: a compile-time constant condition to check
 376  * @msg:       a message to emit if condition is false
 377  *
 378  * In tradition of POSIX assert, this macro will break the build if the
 379  * supplied condition is *false*, emitting the supplied error message if the
 380  * compiler has support to do so.
 381  */
 382 #define compiletime_assert(condition, msg) \
 383         _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
 384
 385 #define compiletime_assert_atomic_type(t)                               \
 386         compiletime_assert(__native_word(t),                            \
 387                 "Need native word sized stores/loads for atomicity.")
 388
 389 /*
 390  * Yes, this permits 64-bit accesses on 32-bit architectures. These will
 391  * actually be atomic in some cases (namely Armv7 + LPAE), but for others we
 392  * rely on the access being split into 2x32-bit accesses for a 32-bit quantity
 393  * (e.g. a virtual address) and a strong prevailing wind.
 394  */
 395 #define compiletime_assert_rwonce_type(t)                                       \
 396         compiletime_assert(__native_word(t) || sizeof(t) == sizeof(long long),  \
 397                 "Unsupported access size for {READ,WRITE}_ONCE().")
 398
 399 /* &a[0] degrades to a pointer: a different type from an array */
 400 #define __must_be_array(a)      BUILD_BUG_ON_ZERO(__same_type((a), &(a)[0]))
 401
 402 /*
 403  * This is needed in functions which generate the stack canary, see
 404  * arch/x86/kernel/smpboot.c::start_secondary() for an example.
 405  */
 406 #define prevent_tail_call_optimization()        mb()
 407
 408 #endif /* __LINUX_COMPILER_H */