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# define likely_notrace(x)      likely(x)
  80# define unlikely_notrace(x)    unlikely(x)
  81#endif
  82
  83/* Optimization barrier */
  84#ifndef barrier
  85/* The "volatile" is due to gcc bugs */
  86# define barrier() __asm__ __volatile__("": : :"memory")
  87#endif
  88
  89#ifndef barrier_data
  90/*
  91 * This version is i.e. to prevent dead stores elimination on @ptr
  92 * where gcc and llvm may behave differently when otherwise using
  93 * normal barrier(): while gcc behavior gets along with a normal
  94 * barrier(), llvm needs an explicit input variable to be assumed
  95 * clobbered. The issue is as follows: while the inline asm might
  96 * access any memory it wants, the compiler could have fit all of
  97 * @ptr into memory registers instead, and since @ptr never escaped
  98 * from that, it proved that the inline asm wasn't touching any of
  99 * it. This version works well with both compilers, i.e. we're telling
 100 * the compiler that the inline asm absolutely may see the contents
 101 * of @ptr. See also: https://llvm.org/bugs/show_bug.cgi?id=15495
 102 */
 103# define barrier_data(ptr) __asm__ __volatile__("": :"r"(ptr) :"memory")
 104#endif
 105
 106/* workaround for GCC PR82365 if needed */
 107#ifndef barrier_before_unreachable
 108# define barrier_before_unreachable() do { } while (0)
 109#endif
 110
 111/* Unreachable code */
 112#ifdef CONFIG_STACK_VALIDATION
 113/*
 114 * These macros help objtool understand GCC code flow for unreachable code.
 115 * The __COUNTER__ based labels are a hack to make each instance of the macros
 116 * unique, to convince GCC not to merge duplicate inline asm statements.
 117 */
 118#define annotate_reachable() ({                                         \
 119        asm volatile("%c0:\n\t"                                         \
 120                     ".pushsection .discard.reachable\n\t"              \
 121                     ".long %c0b - .\n\t"                               \
 122                     ".popsection\n\t" : : "i" (__COUNTER__));          \
 123})
 124#define annotate_unreachable() ({                                       \
 125        asm volatile("%c0:\n\t"                                         \
 126                     ".pushsection .discard.unreachable\n\t"            \
 127                     ".long %c0b - .\n\t"                               \
 128                     ".popsection\n\t" : : "i" (__COUNTER__));          \
 129})
 130#define ASM_UNREACHABLE                                                 \
 131        "999:\n\t"                                                      \
 132        ".pushsection .discard.unreachable\n\t"                         \
 133        ".long 999b - .\n\t"                                            \
 134        ".popsection\n\t"
 135
 136/* Annotate a C jump table to allow objtool to follow the code flow */
 137#define __annotate_jump_table __section(".rodata..c_jump_table")
 138
 139#else
 140#define annotate_reachable()
 141#define annotate_unreachable()
 142#define __annotate_jump_table
 143#endif
 144
 145#ifndef ASM_UNREACHABLE
 146# define ASM_UNREACHABLE
 147#endif
 148#ifndef unreachable
 149# define unreachable() do {             \
 150        annotate_unreachable();         \
 151        __builtin_unreachable();        \
 152} while (0)
 153#endif
 154
 155/*
 156 * KENTRY - kernel entry point
 157 * This can be used to annotate symbols (functions or data) that are used
 158 * without their linker symbol being referenced explicitly. For example,
 159 * interrupt vector handlers, or functions in the kernel image that are found
 160 * programatically.
 161 *
 162 * Not required for symbols exported with EXPORT_SYMBOL, or initcalls. Those
 163 * are handled in their own way (with KEEP() in linker scripts).
 164 *
 165 * KENTRY can be avoided if the symbols in question are marked as KEEP() in the
 166 * linker script. For example an architecture could KEEP() its entire
 167 * boot/exception vector code rather than annotate each function and data.
 168 */
 169#ifndef KENTRY
 170# define KENTRY(sym)                                            \
 171        extern typeof(sym) sym;                                 \
 172        static const unsigned long __kentry_##sym               \
 173        __used                                                  \
 174        __attribute__((__section__("___kentry+" #sym)))         \
 175        = (unsigned long)&sym;
 176#endif
 177
 178#ifndef RELOC_HIDE
 179# define RELOC_HIDE(ptr, off)                                   \
 180  ({ unsigned long __ptr;                                       \
 181     __ptr = (unsigned long) (ptr);                             \
 182    (typeof(ptr)) (__ptr + (off)); })
 183#endif
 184
 185#ifndef OPTIMIZER_HIDE_VAR
 186/* Make the optimizer believe the variable can be manipulated arbitrarily. */
 187#define OPTIMIZER_HIDE_VAR(var)                                         \
 188        __asm__ ("" : "=r" (var) : "0" (var))
 189#endif
 190
 191/* Not-quite-unique ID. */
 192#ifndef __UNIQUE_ID
 193# define __UNIQUE_ID(prefix) __PASTE(__PASTE(__UNIQUE_ID_, prefix), __LINE__)
 194#endif
 195
 196/**
 197 * data_race - mark an expression as containing intentional data races
 198 *
 199 * This data_race() macro is useful for situations in which data races
 200 * should be forgiven.  One example is diagnostic code that accesses
 201 * shared variables but is not a part of the core synchronization design.
 202 *
 203 * This macro *does not* affect normal code generation, but is a hint
 204 * to tooling that data races here are to be ignored.
 205 */
 206#define data_race(expr)                                                 \
 207({                                                                      \
 208        __unqual_scalar_typeof(({ expr; })) __v = ({                    \
 209                __kcsan_disable_current();                              \
 210                expr;                                                   \
 211        });                                                             \
 212        __kcsan_enable_current();                                       \
 213        __v;                                                            \
 214})
 215
 216#endif /* __KERNEL__ */
 217
 218/*
 219 * Force the compiler to emit 'sym' as a symbol, so that we can reference
 220 * it from inline assembler. Necessary in case 'sym' could be inlined
 221 * otherwise, or eliminated entirely due to lack of references that are
 222 * visible to the compiler.
 223 */
 224#define __ADDRESSABLE(sym) \
 225        static void * __section(".discard.addressable") __used \
 226                __UNIQUE_ID(__PASTE(__addressable_,sym)) = (void *)&sym;
 227
 228/**
 229 * offset_to_ptr - convert a relative memory offset to an absolute pointer
 230 * @off:        the address of the 32-bit offset value
 231 */
 232static inline void *offset_to_ptr(const int *off)
 233{
 234        return (void *)((unsigned long)off + *off);
 235}
 236
 237#endif /* __ASSEMBLY__ */
 238
 239/* &a[0] degrades to a pointer: a different type from an array */
 240#define __must_be_array(a)      BUILD_BUG_ON_ZERO(__same_type((a), &(a)[0]))
 241
 242/*
 243 * This is needed in functions which generate the stack canary, see
 244 * arch/x86/kernel/smpboot.c::start_secondary() for an example.
 245 */
 246#define prevent_tail_call_optimization()        mb()
 247
 248#include <asm/rwonce.h>
 249
 250#endif /* __LINUX_COMPILER_H */
 251