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 #else
 124 #define annotate_reachable()
 125 #define annotate_unreachable()
 126 #define __annotate_jump_table
 127 #endif
 128
 129 #ifndef ASM_UNREACHABLE
 130 # define ASM_UNREACHABLE
 131 #endif
 132 #ifndef unreachable
 133 # define unreachable() do {             \
 134         annotate_unreachable();         \
 135         __builtin_unreachable();        \
 136 } while (0)
 137 #endif
 138
 139 /*
 140  * KENTRY - kernel entry point
 141  * This can be used to annotate symbols (functions or data) that are used
 142  * without their linker symbol being referenced explicitly. For example,
 143  * interrupt vector handlers, or functions in the kernel image that are found
 144  * programatically.
 145  *
 146  * Not required for symbols exported with EXPORT_SYMBOL, or initcalls. Those
 147  * are handled in their own way (with KEEP() in linker scripts).
 148  *
 149  * KENTRY can be avoided if the symbols in question are marked as KEEP() in the
 150  * linker script. For example an architecture could KEEP() its entire
 151  * boot/exception vector code rather than annotate each function and data.
 152  */
 153 #ifndef KENTRY
 154 # define KENTRY(sym)                                            \
 155         extern typeof(sym) sym;                                 \
 156         static const unsigned long __kentry_##sym               \
 157         __used                                                  \
 158         __section("___kentry" "+" #sym )                        \
 159         = (unsigned long)&sym;
 160 #endif
 161
 162 #ifndef RELOC_HIDE
 163 # define RELOC_HIDE(ptr, off)                                   \
 164   ({ unsigned long __ptr;                                       \
 165      __ptr = (unsigned long) (ptr);                             \
 166     (typeof(ptr)) (__ptr + (off)); })
 167 #endif
 168
 169 #ifndef OPTIMIZER_HIDE_VAR
 170 /* Make the optimizer believe the variable can be manipulated arbitrarily. */
 171 #define OPTIMIZER_HIDE_VAR(var)                                         \
 172         __asm__ ("" : "=r" (var) : "0" (var))
 173 #endif
 174
 175 /* Not-quite-unique ID. */
 176 #ifndef __UNIQUE_ID
 177 # define __UNIQUE_ID(prefix) __PASTE(__PASTE(__UNIQUE_ID_, prefix), __LINE__)
 178 #endif
 179
 180 #include <uapi/linux/types.h>
 181
 182 #define __READ_ONCE_SIZE                                                \
 183 ({                                                                      \
 184         switch (size) {                                                 \
 185         case 1: *(__u8 *)res = *(volatile __u8 *)p; break;              \
 186         case 2: *(__u16 *)res = *(volatile __u16 *)p; break;            \
 187         case 4: *(__u32 *)res = *(volatile __u32 *)p; break;            \
 188         case 8: *(__u64 *)res = *(volatile __u64 *)p; break;            \
 189         default:                                                        \
 190                 barrier();                                              \
 191                 __builtin_memcpy((void *)res, (const void *)p, size);   \
 192                 barrier();                                              \
 193         }                                                               \
 194 })
 195
 196 static __always_inline
 197 void __read_once_size(const volatile void *p, void *res, int size)
 198 {
 199         __READ_ONCE_SIZE;
 200 }
 201
 202 #ifdef CONFIG_KASAN
 203 /*
 204  * We can't declare function 'inline' because __no_sanitize_address confilcts
 205  * with inlining. Attempt to inline it may cause a build failure.
 206  *      https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67368
 207  * '__maybe_unused' allows us to avoid defined-but-not-used warnings.
 208  */
 209 # define __no_kasan_or_inline __no_sanitize_address notrace __maybe_unused
 210 #else
 211 # define __no_kasan_or_inline __always_inline
 212 #endif
 213
 214 static __no_kasan_or_inline
 215 void __read_once_size_nocheck(const volatile void *p, void *res, int size)
 216 {
 217         __READ_ONCE_SIZE;
 218 }
 219
 220 static __always_inline void __write_once_size(volatile void *p, void *res, int size)
 221 {
 222         switch (size) {
 223         case 1: *(volatile __u8 *)p = *(__u8 *)res; break;
 224         case 2: *(volatile __u16 *)p = *(__u16 *)res; break;
 225         case 4: *(volatile __u32 *)p = *(__u32 *)res; break;
 226         case 8: *(volatile __u64 *)p = *(__u64 *)res; break;
 227         default:
 228                 barrier();
 229                 __builtin_memcpy((void *)p, (const void *)res, size);
 230                 barrier();
 231         }
 232 }
 233
 234 /*
 235  * Prevent the compiler from merging or refetching reads or writes. The
 236  * compiler is also forbidden from reordering successive instances of
 237  * READ_ONCE and WRITE_ONCE, but only when the compiler is aware of some
 238  * particular ordering. One way to make the compiler aware of ordering is to
 239  * put the two invocations of READ_ONCE or WRITE_ONCE in different C
 240  * statements.
 241  *
 242  * These two macros will also work on aggregate data types like structs or
 243  * unions. If the size of the accessed data type exceeds the word size of
 244  * the machine (e.g., 32 bits or 64 bits) READ_ONCE() and WRITE_ONCE() will
 245  * fall back to memcpy(). There's at least two memcpy()s: one for the
 246  * __builtin_memcpy() and then one for the macro doing the copy of variable
 247  * - '__u' allocated on the stack.
 248  *
 249  * Their two major use cases are: (1) Mediating communication between
 250  * process-level code and irq/NMI handlers, all running on the same CPU,
 251  * and (2) Ensuring that the compiler does not fold, spindle, or otherwise
 252  * mutilate accesses that either do not require ordering or that interact
 253  * with an explicit memory barrier or atomic instruction that provides the
 254  * required ordering.
 255  */
 256 #include <asm/barrier.h>
 257 #include <linux/kasan-checks.h>
 258
 259 #define __READ_ONCE(x, check)                                           \
 260 ({                                                                      \
 261         union { typeof(x) __val; char __c[1]; } __u;                    \
 262         if (check)                                                      \
 263                 __read_once_size(&(x), __u.__c, sizeof(x));             \
 264         else                                                            \
 265                 __read_once_size_nocheck(&(x), __u.__c, sizeof(x));     \
 266         smp_read_barrier_depends(); /* Enforce dependency ordering from x */ \
 267         __u.__val;                                                      \
 268 })
 269 #define READ_ONCE(x) __READ_ONCE(x, 1)
 270
 271 /*
 272  * Use READ_ONCE_NOCHECK() instead of READ_ONCE() if you need
 273  * to hide memory access from KASAN.
 274  */
 275 #define READ_ONCE_NOCHECK(x) __READ_ONCE(x, 0)
 276
 277 static __no_kasan_or_inline
 278 unsigned long read_word_at_a_time(const void *addr)
 279 {
 280         kasan_check_read(addr, 1);
 281         return *(unsigned long *)addr;
 282 }
 283
 284 #define WRITE_ONCE(x, val) \
 285 ({                                                      \
 286         union { typeof(x) __val; char __c[1]; } __u =   \
 287                 { .__val = (__force typeof(x)) (val) }; \
 288         __write_once_size(&(x), __u.__c, sizeof(x));    \
 289         __u.__val;                                      \
 290 })
 291
 292 #endif /* __KERNEL__ */
 293
 294 /*
 295  * Force the compiler to emit 'sym' as a symbol, so that we can reference
 296  * it from inline assembler. Necessary in case 'sym' could be inlined
 297  * otherwise, or eliminated entirely due to lack of references that are
 298  * visible to the compiler.
 299  */
 300 #define __ADDRESSABLE(sym) \
 301         static void * __section(.discard.addressable) __used \
 302                 __PASTE(__addressable_##sym, __LINE__) = (void *)&sym;
 303
 304 /**
 305  * offset_to_ptr - convert a relative memory offset to an absolute pointer
 306  * @off:        the address of the 32-bit offset value
 307  */
 308 static inline void *offset_to_ptr(const int *off)
 309 {
 310         return (void *)((unsigned long)off + *off);
 311 }
 312
 313 #endif /* __ASSEMBLY__ */
 314
 315 /* Compile time object size, -1 for unknown */
 316 #ifndef __compiletime_object_size
 317 # define __compiletime_object_size(obj) -1
 318 #endif
 319 #ifndef __compiletime_warning
 320 # define __compiletime_warning(message)
 321 #endif
 322 #ifndef __compiletime_error
 323 # define __compiletime_error(message)
 324 #endif
 325
 326 #ifdef __OPTIMIZE__
 327 # define __compiletime_assert(condition, msg, prefix, suffix)           \
 328         do {                                                            \
 329                 extern void prefix ## suffix(void) __compiletime_error(msg); \
 330                 if (!(condition))                                       \
 331                         prefix ## suffix();                             \
 332         } while (0)
 333 #else
 334 # define __compiletime_assert(condition, msg, prefix, suffix) do { } while (0)
 335 #endif
 336
 337 #define _compiletime_assert(condition, msg, prefix, suffix) \
 338         __compiletime_assert(condition, msg, prefix, suffix)
 339
 340 /**
 341  * compiletime_assert - break build and emit msg if condition is false
 342  * @condition: a compile-time constant condition to check
 343  * @msg:       a message to emit if condition is false
 344  *
 345  * In tradition of POSIX assert, this macro will break the build if the
 346  * supplied condition is *false*, emitting the supplied error message if the
 347  * compiler has support to do so.
 348  */
 349 #define compiletime_assert(condition, msg) \
 350         _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
 351
 352 #define compiletime_assert_atomic_type(t)                               \
 353         compiletime_assert(__native_word(t),                            \
 354                 "Need native word sized stores/loads for atomicity.")
 355
 356 /* &a[0] degrades to a pointer: a different type from an array */
 357 #define __must_be_array(a)      BUILD_BUG_ON_ZERO(__same_type((a), &(a)[0]))
 358
 359 /*
 360  * This is needed in functions which generate the stack canary, see
 361  * arch/x86/kernel/smpboot.c::start_secondary() for an example.
 362  */
 363 #define prevent_tail_call_optimization()        mb()
 364
 365 #endif /* __LINUX_COMPILER_H */