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, ...) 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
 196static __always_inline
 197void __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
 214static __no_kasan_or_inline
 215void __read_once_size_nocheck(const volatile void *p, void *res, int size)
 216{
 217        __READ_ONCE_SIZE;
 218}
 219
 220static __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
 277static __no_kasan_or_inline
 278unsigned 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 */
 308static 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_, __LINE__)
 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#endif /* __LINUX_COMPILER_H */
 360