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 */
  15void ftrace_likely_update(struct ftrace_likely_data *f, int val,
  16                          int expect, int is_constant);
  17#if defined(CONFIG_TRACE_BRANCH_PROFILING) \
  18    && !defined(DISABLE_BRANCH_PROFILING) && !defined(__CHECKER__)
  19#define likely_notrace(x)       __builtin_expect(!!(x), 1)
  20#define unlikely_notrace(x)     __builtin_expect(!!(x), 0)
  21
  22#define __branch_check__(x, expect, is_constant) ({                     \
  23                        long ______r;                                   \
  24                        static struct ftrace_likely_data                \
  25                                __aligned(4)                            \
  26                                __section("_ftrace_annotated_branch")   \
  27                                ______f = {                             \
  28                                .data.func = __func__,                  \
  29                                .data.file = __FILE__,                  \
  30                                .data.line = __LINE__,                  \
  31                        };                                              \
  32                        ______r = __builtin_expect(!!(x), expect);      \
  33                        ftrace_likely_update(&______f, ______r,         \
  34                                             expect, is_constant);      \
  35                        ______r;                                        \
  36                })
  37
  38/*
  39 * Using __builtin_constant_p(x) to ignore cases where the return
  40 * value is always the same.  This idea is taken from a similar patch
  41 * written by Daniel Walker.
  42 */
  43# ifndef likely
  44#  define likely(x)     (__branch_check__(x, 1, __builtin_constant_p(x)))
  45# endif
  46# ifndef unlikely
  47#  define unlikely(x)   (__branch_check__(x, 0, __builtin_constant_p(x)))
  48# endif
  49
  50#ifdef CONFIG_PROFILE_ALL_BRANCHES
  51/*
  52 * "Define 'is'", Bill Clinton
  53 * "Define 'if'", Steven Rostedt
  54 */
  55#define if(cond, ...) if ( __trace_if_var( !!(cond , ## __VA_ARGS__) ) )
  56
  57#define __trace_if_var(cond) (__builtin_constant_p(cond) ? (cond) : __trace_if_value(cond))
  58
  59#define __trace_if_value(cond) ({                       \
  60        static struct ftrace_branch_data                \
  61                __aligned(4)                            \
  62                __section("_ftrace_branch")             \
  63                __if_trace = {                          \
  64                        .func = __func__,               \
  65                        .file = __FILE__,               \
  66                        .line = __LINE__,               \
  67                };                                      \
  68        (cond) ?                                        \
  69                (__if_trace.miss_hit[1]++,1) :          \
  70                (__if_trace.miss_hit[0]++,0);           \
  71})
  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# define likely_notrace(x)      likely(x)
  79# define unlikely_notrace(x)    unlikely(x)
  80#endif
  81
  82/* Optimization barrier */
  83#ifndef barrier
  84/* The "volatile" is due to gcc bugs */
  85# define barrier() __asm__ __volatile__("": : :"memory")
  86#endif
  87
  88#ifndef barrier_data
  89/*
  90 * This version is i.e. to prevent dead stores elimination on @ptr
  91 * where gcc and llvm may behave differently when otherwise using
  92 * normal barrier(): while gcc behavior gets along with a normal
  93 * barrier(), llvm needs an explicit input variable to be assumed
  94 * clobbered. The issue is as follows: while the inline asm might
  95 * access any memory it wants, the compiler could have fit all of
  96 * @ptr into memory registers instead, and since @ptr never escaped
  97 * from that, it proved that the inline asm wasn't touching any of
  98 * it. This version works well with both compilers, i.e. we're telling
  99 * the compiler that the inline asm absolutely may see the contents
 100 * of @ptr. See also: https://llvm.org/bugs/show_bug.cgi?id=15495
 101 */
 102# define barrier_data(ptr) __asm__ __volatile__("": :"r"(ptr) :"memory")
 103#endif
 104
 105/* workaround for GCC PR82365 if needed */
 106#ifndef barrier_before_unreachable
 107# define barrier_before_unreachable() do { } while (0)
 108#endif
 109
 110/* Unreachable code */
 111#ifdef CONFIG_OBJTOOL
 112/*
 113 * These macros help objtool understand GCC code flow for unreachable code.
 114 * The __COUNTER__ based labels are a hack to make each instance of the macros
 115 * unique, to convince GCC not to merge duplicate inline asm statements.
 116 */
 117#define __stringify_label(n) #n
 118
 119#define __annotate_unreachable(c) ({                                    \
 120        asm volatile(__stringify_label(c) ":\n\t"                       \
 121                     ".pushsection .discard.unreachable\n\t"            \
 122                     ".long " __stringify_label(c) "b - .\n\t"          \
 123                     ".popsection\n\t" : : "i" (c));                    \
 124})
 125#define annotate_unreachable() __annotate_unreachable(__COUNTER__)
 126
 127/* Annotate a C jump table to allow objtool to follow the code flow */
 128#define __annotate_jump_table __section(".rodata..c_jump_table")
 129
 130#else /* !CONFIG_OBJTOOL */
 131#define annotate_unreachable()
 132#define __annotate_jump_table
 133#endif /* CONFIG_OBJTOOL */
 134
 135#ifndef unreachable
 136# define unreachable() do {             \
 137        annotate_unreachable();         \
 138        __builtin_unreachable();        \
 139} while (0)
 140#endif
 141
 142/*
 143 * KENTRY - kernel entry point
 144 * This can be used to annotate symbols (functions or data) that are used
 145 * without their linker symbol being referenced explicitly. For example,
 146 * interrupt vector handlers, or functions in the kernel image that are found
 147 * programatically.
 148 *
 149 * Not required for symbols exported with EXPORT_SYMBOL, or initcalls. Those
 150 * are handled in their own way (with KEEP() in linker scripts).
 151 *
 152 * KENTRY can be avoided if the symbols in question are marked as KEEP() in the
 153 * linker script. For example an architecture could KEEP() its entire
 154 * boot/exception vector code rather than annotate each function and data.
 155 */
 156#ifndef KENTRY
 157# define KENTRY(sym)                                            \
 158        extern typeof(sym) sym;                                 \
 159        static const unsigned long __kentry_##sym               \
 160        __used                                                  \
 161        __attribute__((__section__("___kentry+" #sym)))         \
 162        = (unsigned long)&sym;
 163#endif
 164
 165#ifndef RELOC_HIDE
 166# define RELOC_HIDE(ptr, off)                                   \
 167  ({ unsigned long __ptr;                                       \
 168     __ptr = (unsigned long) (ptr);                             \
 169    (typeof(ptr)) (__ptr + (off)); })
 170#endif
 171
 172#define absolute_pointer(val)   RELOC_HIDE((void *)(val), 0)
 173
 174#ifndef OPTIMIZER_HIDE_VAR
 175/* Make the optimizer believe the variable can be manipulated arbitrarily. */
 176#define OPTIMIZER_HIDE_VAR(var)                                         \
 177        __asm__ ("" : "=r" (var) : "0" (var))
 178#endif
 179
 180#define __UNIQUE_ID(prefix) __PASTE(__PASTE(__UNIQUE_ID_, prefix), __COUNTER__)
 181
 182/**
 183 * data_race - mark an expression as containing intentional data races
 184 *
 185 * This data_race() macro is useful for situations in which data races
 186 * should be forgiven.  One example is diagnostic code that accesses
 187 * shared variables but is not a part of the core synchronization design.
 188 *
 189 * This macro *does not* affect normal code generation, but is a hint
 190 * to tooling that data races here are to be ignored.
 191 */
 192#define data_race(expr)                                                 \
 193({                                                                      \
 194        __unqual_scalar_typeof(({ expr; })) __v = ({                    \
 195                __kcsan_disable_current();                              \
 196                expr;                                                   \
 197        });                                                             \
 198        __kcsan_enable_current();                                       \
 199        __v;                                                            \
 200})
 201
 202#endif /* __KERNEL__ */
 203
 204/*
 205 * Force the compiler to emit 'sym' as a symbol, so that we can reference
 206 * it from inline assembler. Necessary in case 'sym' could be inlined
 207 * otherwise, or eliminated entirely due to lack of references that are
 208 * visible to the compiler.
 209 */
 210#define ___ADDRESSABLE(sym, __attrs) \
 211        static void * __used __attrs \
 212                __UNIQUE_ID(__PASTE(__addressable_,sym)) = (void *)&sym;
 213#define __ADDRESSABLE(sym) \
 214        ___ADDRESSABLE(sym, __section(".discard.addressable"))
 215
 216/**
 217 * offset_to_ptr - convert a relative memory offset to an absolute pointer
 218 * @off:        the address of the 32-bit offset value
 219 */
 220static inline void *offset_to_ptr(const int *off)
 221{
 222        return (void *)((unsigned long)off + *off);
 223}
 224
 225#endif /* __ASSEMBLY__ */
 226
 227/* &a[0] degrades to a pointer: a different type from an array */
 228#define __must_be_array(a)      BUILD_BUG_ON_ZERO(__same_type((a), &(a)[0]))
 229
 230/*
 231 * This returns a constant expression while determining if an argument is
 232 * a constant expression, most importantly without evaluating the argument.
 233 * Glory to Martin Uecker <Martin.Uecker@med.uni-goettingen.de>
 234 */
 235#define __is_constexpr(x) \
 236        (sizeof(int) == sizeof(*(8 ? ((void *)((long)(x) * 0l)) : (int *)8)))
 237
 238/*
 239 * Whether 'type' is a signed type or an unsigned type. Supports scalar types,
 240 * bool and also pointer types.
 241 */
 242#define is_signed_type(type) (((type)(-1)) < (__force type)1)
 243#define is_unsigned_type(type) (!is_signed_type(type))
 244
 245/*
 246 * This is needed in functions which generate the stack canary, see
 247 * arch/x86/kernel/smpboot.c::start_secondary() for an example.
 248 */
 249#define prevent_tail_call_optimization()        mb()
 250
 251#include <asm/rwonce.h>
 252
 253#endif /* __LINUX_COMPILER_H */
 254