LXR linux/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__)
  17void 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, ...) __trace_if( (cond , ## __VA_ARGS__) )
  57#define __trace_if(cond) \
  58        if (__builtin_constant_p(!!(cond)) ? !!(cond) :                 \
  59        ({                                                              \
  60                int ______r;                                            \
  61                static struct ftrace_branch_data                        \
  62                        __aligned(4)                                    \
  63                        __section("_ftrace_branch")                     \
  64                        ______f = {                                     \
  65                                .func = __func__,                       \
  66                                .file = __FILE__,                       \
  67                                .line = __LINE__,                       \
  68                        };                                              \
  69                ______r = !!(cond);                                     \
  70                ______f.miss_hit[______r]++;                                    \
  71                ______r;                                                \
  72        }))
  73#endif /* CONFIG_PROFILE_ALL_BRANCHES */
  74
  75#else
  76# define likely(x)      __builtin_expect(!!(x), 1)
  77# define unlikely(x)    __builtin_expect(!!(x), 0)
  78#endif
  79
  80/* Optimization barrier */
  81#ifndef barrier
  82# define barrier() __memory_barrier()
  83#endif
  84
  85#ifndef barrier_data
  86# define barrier_data(ptr) barrier()
  87#endif
  88
  89/* workaround for GCC PR82365 if needed */
  90#ifndef barrier_before_unreachable
  91# define barrier_before_unreachable() do { } while (0)
  92#endif
  93
  94/* Unreachable code */
  95#ifdef CONFIG_STACK_VALIDATION
  96/*
  97 * These macros help objtool understand GCC code flow for unreachable code.
  98 * The __COUNTER__ based labels are a hack to make each instance of the macros
  99 * unique, to convince GCC not to merge duplicate inline asm statements.
 100 */
 101#define annotate_reachable() ({                                         \
 102        asm volatile("%c0:\n\t"                                         \
 103                     ".pushsection .discard.reachable\n\t"              \
 104                     ".long %c0b - .\n\t"                               \
 105                     ".popsection\n\t" : : "i" (__COUNTER__));          \
 106})
 107#define annotate_unreachable() ({                                       \
 108        asm volatile("%c0:\n\t"                                         \
 109                     ".pushsection .discard.unreachable\n\t"            \
 110                     ".long %c0b - .\n\t"                               \
 111                     ".popsection\n\t" : : "i" (__COUNTER__));          \
 112})
 113#define ASM_UNREACHABLE                                                 \
 114        "999:\n\t"                                                      \
 115        ".pushsection .discard.unreachable\n\t"                         \
 116        ".long 999b - .\n\t"                                            \
 117        ".popsection\n\t"
 118#else
 119#define annotate_reachable()
 120#define annotate_unreachable()
 121#endif
 122
 123#ifndef ASM_UNREACHABLE
 124# define ASM_UNREACHABLE
 125#endif
 126#ifndef unreachable
 127# define unreachable() do {             \
 128        annotate_unreachable();         \
 129        __builtin_unreachable();        \
 130} while (0)
 131#endif
 132
 133/*
 134 * KENTRY - kernel entry point
 135 * This can be used to annotate symbols (functions or data) that are used
 136 * without their linker symbol being referenced explicitly. For example,
 137 * interrupt vector handlers, or functions in the kernel image that are found
 138 * programatically.
 139 *
 140 * Not required for symbols exported with EXPORT_SYMBOL, or initcalls. Those
 141 * are handled in their own way (with KEEP() in linker scripts).
 142 *
 143 * KENTRY can be avoided if the symbols in question are marked as KEEP() in the
 144 * linker script. For example an architecture could KEEP() its entire
 145 * boot/exception vector code rather than annotate each function and data.
 146 */
 147#ifndef KENTRY
 148# define KENTRY(sym)                                            \
 149        extern typeof(sym) sym;                                 \
 150        static const unsigned long __kentry_##sym               \
 151        __used                                                  \
 152        __section("___kentry" "+" #sym )                        \
 153        = (unsigned long)&sym;
 154#endif
 155
 156#ifndef RELOC_HIDE
 157# define RELOC_HIDE(ptr, off)                                   \
 158  ({ unsigned long __ptr;                                       \
 159     __ptr = (unsigned long) (ptr);                             \
 160    (typeof(ptr)) (__ptr + (off)); })
 161#endif
 162
 163#ifndef OPTIMIZER_HIDE_VAR
 164/* Make the optimizer believe the variable can be manipulated arbitrarily. */
 165#define OPTIMIZER_HIDE_VAR(var)                                         \
 166        __asm__ ("" : "=r" (var) : "0" (var))
 167#endif
 168
 169/* Not-quite-unique ID. */
 170#ifndef __UNIQUE_ID
 171# define __UNIQUE_ID(prefix) __PASTE(__PASTE(__UNIQUE_ID_, prefix), __LINE__)
 172#endif
 173
 174#include <uapi/linux/types.h>
 175
 176#define __READ_ONCE_SIZE                                                \
 177({                                                                      \
 178        switch (size) {                                                 \
 179        case 1: *(__u8 *)res = *(volatile __u8 *)p; break;              \
 180        case 2: *(__u16 *)res = *(volatile __u16 *)p; break;            \
 181        case 4: *(__u32 *)res = *(volatile __u32 *)p; break;            \
 182        case 8: *(__u64 *)res = *(volatile __u64 *)p; break;            \
 183        default:                                                        \
 184                barrier();                                              \
 185                __builtin_memcpy((void *)res, (const void *)p, size);   \
 186                barrier();                                              \
 187        }                                                               \
 188})
 189
 190static __always_inline
 191void __read_once_size(const volatile void *p, void *res, int size)
 192{
 193        __READ_ONCE_SIZE;
 194}
 195
 196#ifdef CONFIG_KASAN
 197/*
 198 * We can't declare function 'inline' because __no_sanitize_address confilcts
 199 * with inlining. Attempt to inline it may cause a build failure.
 200 *      https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67368
 201 * '__maybe_unused' allows us to avoid defined-but-not-used warnings.
 202 */
 203# define __no_kasan_or_inline __no_sanitize_address notrace __maybe_unused
 204#else
 205# define __no_kasan_or_inline __always_inline
 206#endif
 207
 208static __no_kasan_or_inline
 209void __read_once_size_nocheck(const volatile void *p, void *res, int size)
 210{
 211        __READ_ONCE_SIZE;
 212}
 213
 214static __always_inline void __write_once_size(volatile void *p, void *res, int size)
 215{
 216        switch (size) {
 217        case 1: *(volatile __u8 *)p = *(__u8 *)res; break;
 218        case 2: *(volatile __u16 *)p = *(__u16 *)res; break;
 219        case 4: *(volatile __u32 *)p = *(__u32 *)res; break;
 220        case 8: *(volatile __u64 *)p = *(__u64 *)res; break;
 221        default:
 222                barrier();
 223                __builtin_memcpy((void *)p, (const void *)res, size);
 224                barrier();
 225        }
 226}
 227
 228/*
 229 * Prevent the compiler from merging or refetching reads or writes. The
 230 * compiler is also forbidden from reordering successive instances of
 231 * READ_ONCE and WRITE_ONCE, but only when the compiler is aware of some
 232 * particular ordering. One way to make the compiler aware of ordering is to
 233 * put the two invocations of READ_ONCE or WRITE_ONCE in different C
 234 * statements.
 235 *
 236 * These two macros will also work on aggregate data types like structs or
 237 * unions. If the size of the accessed data type exceeds the word size of
 238 * the machine (e.g., 32 bits or 64 bits) READ_ONCE() and WRITE_ONCE() will
 239 * fall back to memcpy(). There's at least two memcpy()s: one for the
 240 * __builtin_memcpy() and then one for the macro doing the copy of variable
 241 * - '__u' allocated on the stack.
 242 *
 243 * Their two major use cases are: (1) Mediating communication between
 244 * process-level code and irq/NMI handlers, all running on the same CPU,
 245 * and (2) Ensuring that the compiler does not fold, spindle, or otherwise
 246 * mutilate accesses that either do not require ordering or that interact
 247 * with an explicit memory barrier or atomic instruction that provides the
 248 * required ordering.
 249 */
 250#include <asm/barrier.h>
 251#include <linux/kasan-checks.h>
 252
 253#define __READ_ONCE(x, check)                                           \
 254({                                                                      \
 255        union { typeof(x) __val; char __c[1]; } __u;                    \
 256        if (check)                                                      \
 257                __read_once_size(&(x), __u.__c, sizeof(x));             \
 258        else                                                            \
 259                __read_once_size_nocheck(&(x), __u.__c, sizeof(x));     \
 260        smp_read_barrier_depends(); /* Enforce dependency ordering from x */ \
 261        __u.__val;                                                      \
 262})
 263#define READ_ONCE(x) __READ_ONCE(x, 1)
 264
 265/*
 266 * Use READ_ONCE_NOCHECK() instead of READ_ONCE() if you need
 267 * to hide memory access from KASAN.
 268 */
 269#define READ_ONCE_NOCHECK(x) __READ_ONCE(x, 0)
 270
 271static __no_kasan_or_inline
 272unsigned long read_word_at_a_time(const void *addr)
 273{
 274        kasan_check_read(addr, 1);
 275        return *(unsigned long *)addr;
 276}
 277
 278#define WRITE_ONCE(x, val) \
 279({                                                      \
 280        union { typeof(x) __val; char __c[1]; } __u =   \
 281                { .__val = (__force typeof(x)) (val) }; \
 282        __write_once_size(&(x), __u.__c, sizeof(x));    \
 283        __u.__val;                                      \
 284})
 285
 286#endif /* __KERNEL__ */
 287
 288/*
 289 * Force the compiler to emit 'sym' as a symbol, so that we can reference
 290 * it from inline assembler. Necessary in case 'sym' could be inlined
 291 * otherwise, or eliminated entirely due to lack of references that are
 292 * visible to the compiler.
 293 */
 294#define __ADDRESSABLE(sym) \
 295        static void * __section(".discard.addressable") __used \
 296                __PASTE(__addressable_##sym, __LINE__) = (void *)&sym;
 297
 298/**
 299 * offset_to_ptr - convert a relative memory offset to an absolute pointer
 300 * @off:        the address of the 32-bit offset value
 301 */
 302static inline void *offset_to_ptr(const int *off)
 303{
 304        return (void *)((unsigned long)off + *off);
 305}
 306
 307#endif /* __ASSEMBLY__ */
 308
 309/* Compile time object size, -1 for unknown */
 310#ifndef __compiletime_object_size
 311# define __compiletime_object_size(obj) -1
 312#endif
 313#ifndef __compiletime_warning
 314# define __compiletime_warning(message)
 315#endif
 316#ifndef __compiletime_error
 317# define __compiletime_error(message)
 318#endif
 319
 320#ifdef __OPTIMIZE__
 321# define __compiletime_assert(condition, msg, prefix, suffix)           \
 322        do {                                                            \
 323                extern void prefix ## suffix(void) __compiletime_error(msg); \
 324                if (!(condition))                                       \
 325                        prefix ## suffix();                             \
 326        } while (0)
 327#else
 328# define __compiletime_assert(condition, msg, prefix, suffix) do { } while (0)
 329#endif
 330
 331#define _compiletime_assert(condition, msg, prefix, suffix) \
 332        __compiletime_assert(condition, msg, prefix, suffix)
 333
 334/**
 335 * compiletime_assert - break build and emit msg if condition is false
 336 * @condition: a compile-time constant condition to check
 337 * @msg:       a message to emit if condition is false
 338 *
 339 * In tradition of POSIX assert, this macro will break the build if the
 340 * supplied condition is *false*, emitting the supplied error message if the
 341 * compiler has support to do so.
 342 */
 343#define compiletime_assert(condition, msg) \
 344        _compiletime_assert(condition, msg, __compiletime_assert_, __LINE__)
 345
 346#define compiletime_assert_atomic_type(t)                               \
 347        compiletime_assert(__native_word(t),                            \
 348                "Need native word sized stores/loads for atomicity.")
 349
 350/* &a[0] degrades to a pointer: a different type from an array */
 351#define __must_be_array(a)      BUILD_BUG_ON_ZERO(__same_type((a), &(a)[0]))
 352
 353#endif /* __LINUX_COMPILER_H */
 354