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                                __attribute__((__aligned__(4)))         \
  27                                __attribute__((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                        __attribute__((__aligned__(4)))                 \
  63                        __attribute__((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 { annotate_reachable(); do { } while (1); } while (0)
 128#endif
 129
 130/*
 131 * KENTRY - kernel entry point
 132 * This can be used to annotate symbols (functions or data) that are used
 133 * without their linker symbol being referenced explicitly. For example,
 134 * interrupt vector handlers, or functions in the kernel image that are found
 135 * programatically.
 136 *
 137 * Not required for symbols exported with EXPORT_SYMBOL, or initcalls. Those
 138 * are handled in their own way (with KEEP() in linker scripts).
 139 *
 140 * KENTRY can be avoided if the symbols in question are marked as KEEP() in the
 141 * linker script. For example an architecture could KEEP() its entire
 142 * boot/exception vector code rather than annotate each function and data.
 143 */
 144#ifndef KENTRY
 145# define KENTRY(sym)                                            \
 146        extern typeof(sym) sym;                                 \
 147        static const unsigned long __kentry_##sym               \
 148        __used                                                  \
 149        __attribute__((section("___kentry" "+" #sym ), used))   \
 150        = (unsigned long)&sym;
 151#endif
 152
 153#ifndef RELOC_HIDE
 154# define RELOC_HIDE(ptr, off)                                   \
 155  ({ unsigned long __ptr;                                       \
 156     __ptr = (unsigned long) (ptr);                             \
 157    (typeof(ptr)) (__ptr + (off)); })
 158#endif
 159
 160#ifndef OPTIMIZER_HIDE_VAR
 161#define OPTIMIZER_HIDE_VAR(var) barrier()
 162#endif
 163
 164/* Not-quite-unique ID. */
 165#ifndef __UNIQUE_ID
 166# define __UNIQUE_ID(prefix) __PASTE(__PASTE(__UNIQUE_ID_, prefix), __LINE__)
 167#endif
 168
 169#include <uapi/linux/types.h>
 170
 171#define __READ_ONCE_SIZE                                                \
 172({                                                                      \
 173        switch (size) {                                                 \
 174        case 1: *(__u8 *)res = *(volatile __u8 *)p; break;              \
 175        case 2: *(__u16 *)res = *(volatile __u16 *)p; break;            \
 176        case 4: *(__u32 *)res = *(volatile __u32 *)p; break;            \
 177        case 8: *(__u64 *)res = *(volatile __u64 *)p; break;            \
 178        default:                                                        \
 179                barrier();                                              \
 180                __builtin_memcpy((void *)res, (const void *)p, size);   \
 181                barrier();                                              \
 182        }                                                               \
 183})
 184
 185static __always_inline
 186void __read_once_size(const volatile void *p, void *res, int size)
 187{
 188        __READ_ONCE_SIZE;
 189}
 190
 191#ifdef CONFIG_KASAN
 192/*
 193 * We can't declare function 'inline' because __no_sanitize_address confilcts
 194 * with inlining. Attempt to inline it may cause a build failure.
 195 *      https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67368
 196 * '__maybe_unused' allows us to avoid defined-but-not-used warnings.
 197 */
 198# define __no_kasan_or_inline __no_sanitize_address __maybe_unused
 199#else
 200# define __no_kasan_or_inline __always_inline
 201#endif
 202
 203static __no_kasan_or_inline
 204void __read_once_size_nocheck(const volatile void *p, void *res, int size)
 205{
 206        __READ_ONCE_SIZE;
 207}
 208
 209static __always_inline void __write_once_size(volatile void *p, void *res, int size)
 210{
 211        switch (size) {
 212        case 1: *(volatile __u8 *)p = *(__u8 *)res; break;
 213        case 2: *(volatile __u16 *)p = *(__u16 *)res; break;
 214        case 4: *(volatile __u32 *)p = *(__u32 *)res; break;
 215        case 8: *(volatile __u64 *)p = *(__u64 *)res; break;
 216        default:
 217                barrier();
 218                __builtin_memcpy((void *)p, (const void *)res, size);
 219                barrier();
 220        }
 221}
 222
 223/*
 224 * Prevent the compiler from merging or refetching reads or writes. The
 225 * compiler is also forbidden from reordering successive instances of
 226 * READ_ONCE and WRITE_ONCE, but only when the compiler is aware of some
 227 * particular ordering. One way to make the compiler aware of ordering is to
 228 * put the two invocations of READ_ONCE or WRITE_ONCE in different C
 229 * statements.
 230 *
 231 * These two macros will also work on aggregate data types like structs or
 232 * unions. If the size of the accessed data type exceeds the word size of
 233 * the machine (e.g., 32 bits or 64 bits) READ_ONCE() and WRITE_ONCE() will
 234 * fall back to memcpy(). There's at least two memcpy()s: one for the
 235 * __builtin_memcpy() and then one for the macro doing the copy of variable
 236 * - '__u' allocated on the stack.
 237 *
 238 * Their two major use cases are: (1) Mediating communication between
 239 * process-level code and irq/NMI handlers, all running on the same CPU,
 240 * and (2) Ensuring that the compiler does not fold, spindle, or otherwise
 241 * mutilate accesses that either do not require ordering or that interact
 242 * with an explicit memory barrier or atomic instruction that provides the
 243 * required ordering.
 244 */
 245#include <asm/barrier.h>
 246#include <linux/kasan-checks.h>
 247
 248#define __READ_ONCE(x, check)                                           \
 249({                                                                      \
 250        union { typeof(x) __val; char __c[1]; } __u;                    \
 251        if (check)                                                      \
 252                __read_once_size(&(x), __u.__c, sizeof(x));             \
 253        else                                                            \
 254                __read_once_size_nocheck(&(x), __u.__c, sizeof(x));     \
 255        smp_read_barrier_depends(); /* Enforce dependency ordering from x */ \
 256        __u.__val;                                                      \
 257})
 258#define READ_ONCE(x) __READ_ONCE(x, 1)
 259
 260/*
 261 * Use READ_ONCE_NOCHECK() instead of READ_ONCE() if you need
 262 * to hide memory access from KASAN.
 263 */
 264#define READ_ONCE_NOCHECK(x) __READ_ONCE(x, 0)
 265
 266static __no_kasan_or_inline
 267unsigned long read_word_at_a_time(const void *addr)
 268{
 269        kasan_check_read(addr, 1);
 270        return *(unsigned long *)addr;
 271}
 272
 273#define WRITE_ONCE(x, val) \
 274({                                                      \
 275        union { typeof(x) __val; char __c[1]; } __u =   \
 276                { .__val = (__force typeof(x)) (val) }; \
 277        __write_once_size(&(x), __u.__c, sizeof(x));    \
 278        __u.__val;                                      \
 279})
 280
 281#endif /* __KERNEL__ */
 282
 283/*
 284 * Force the compiler to emit 'sym' as a symbol, so that we can reference
 285 * it from inline assembler. Necessary in case 'sym' could be inlined
 286 * otherwise, or eliminated entirely due to lack of references that are
 287 * visible to the compiler.
 288 */
 289#define __ADDRESSABLE(sym) \
 290        static void * __attribute__((section(".discard.addressable"), used)) \
 291                __PASTE(__addressable_##sym, __LINE__) = (void *)&sym;
 292
 293/**
 294 * offset_to_ptr - convert a relative memory offset to an absolute pointer
 295 * @off:        the address of the 32-bit offset value
 296 */
 297static inline void *offset_to_ptr(const int *off)
 298{
 299        return (void *)((unsigned long)off + *off);
 300}
 301
 302#endif /* __ASSEMBLY__ */
 303
 304#ifndef __optimize
 305# define __optimize(level)
 306#endif
 307
 308/* Compile time object size, -1 for unknown */
 309#ifndef __compiletime_object_size
 310# define __compiletime_object_size(obj) -1
 311#endif
 312#ifndef __compiletime_warning
 313# define __compiletime_warning(message)
 314#endif
 315#ifndef __compiletime_error
 316# define __compiletime_error(message)
 317/*
 318 * Sparse complains of variable sized arrays due to the temporary variable in
 319 * __compiletime_assert. Unfortunately we can't just expand it out to make
 320 * sparse see a constant array size without breaking compiletime_assert on old
 321 * versions of GCC (e.g. 4.2.4), so hide the array from sparse altogether.
 322 */
 323# ifndef __CHECKER__
 324#  define __compiletime_error_fallback(condition) \
 325        do { ((void)sizeof(char[1 - 2 * condition])); } while (0)
 326# endif
 327#endif
 328#ifndef __compiletime_error_fallback
 329# define __compiletime_error_fallback(condition) do { } while (0)
 330#endif
 331
 332#ifdef __OPTIMIZE__
 333# define __compiletime_assert(condition, msg, prefix, suffix)           \
 334        do {                                                            \
 335                int __cond = !(condition);                              \
 336                extern void prefix ## suffix(void) __compiletime_error(msg); \
 337                if (__cond)                                             \
 338                        prefix ## suffix();                             \
 339                __compiletime_error_fallback(__cond);                   \
 340        } while (0)
 341#else
 342# define __compiletime_assert(condition, msg, prefix, suffix) do { } while (0)
 343#endif
 344
 345#define _compiletime_assert(condition, msg, prefix, suffix) \
 346        __compiletime_assert(condition, msg, prefix, suffix)
 347
 348/**
 349 * compiletime_assert - break build and emit msg if condition is false
 350 * @condition: a compile-time constant condition to check
 351 * @msg:       a message to emit if condition is false
 352 *
 353 * In tradition of POSIX assert, this macro will break the build if the
 354 * supplied condition is *false*, emitting the supplied error message if the
 355 * compiler has support to do so.
 356 */
 357#define compiletime_assert(condition, msg) \
 358        _compiletime_assert(condition, msg, __compiletime_assert_, __LINE__)
 359
 360#define compiletime_assert_atomic_type(t)                               \
 361        compiletime_assert(__native_word(t),                            \
 362                "Need native word sized stores/loads for atomicity.")
 363
 364#endif /* __LINUX_COMPILER_H */
 365