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__)
  17 void 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 __stringify_label(n) #n
 119
 120 #define __annotate_reachable(c) ({                                      \
 121         asm volatile(__stringify_label(c) ":\n\t"                       \
 122                      ".pushsection .discard.reachable\n\t"              \
 123                      ".long " __stringify_label(c) "b - .\n\t"          \
 124                      ".popsection\n\t");                                \
 125 })
 126 #define annotate_reachable() __annotate_reachable(__COUNTER__)
 127
 128 #define __annotate_unreachable(c) ({                                    \
 129         asm volatile(__stringify_label(c) ":\n\t"                       \
 130                      ".pushsection .discard.unreachable\n\t"            \
 131                      ".long " __stringify_label(c) "b - .\n\t"          \
 132                      ".popsection\n\t");                                \
 133 })
 134 #define annotate_unreachable() __annotate_unreachable(__COUNTER__)
 135
 136 #define ASM_UNREACHABLE                                                 \
 137         "999:\n\t"                                                      \
 138         ".pushsection .discard.unreachable\n\t"                         \
 139         ".long 999b - .\n\t"                                            \
 140         ".popsection\n\t"
 141
 142 /* Annotate a C jump table to allow objtool to follow the code flow */
 143 #define __annotate_jump_table __section(".rodata..c_jump_table")
 144
 145 #else
 146 #define annotate_reachable()
 147 #define annotate_unreachable()
 148 #define __annotate_jump_table
 149 #endif
 150
 151 #ifndef ASM_UNREACHABLE
 152 # define ASM_UNREACHABLE
 153 #endif
 154 #ifndef unreachable
 155 # define unreachable() do {             \
 156         annotate_unreachable();         \
 157         __builtin_unreachable();        \
 158 } while (0)
 159 #endif
 160
 161 /*
 162  * KENTRY - kernel entry point
 163  * This can be used to annotate symbols (functions or data) that are used
 164  * without their linker symbol being referenced explicitly. For example,
 165  * interrupt vector handlers, or functions in the kernel image that are found
 166  * programatically.
 167  *
 168  * Not required for symbols exported with EXPORT_SYMBOL, or initcalls. Those
 169  * are handled in their own way (with KEEP() in linker scripts).
 170  *
 171  * KENTRY can be avoided if the symbols in question are marked as KEEP() in the
 172  * linker script. For example an architecture could KEEP() its entire
 173  * boot/exception vector code rather than annotate each function and data.
 174  */
 175 #ifndef KENTRY
 176 # define KENTRY(sym)                                            \
 177         extern typeof(sym) sym;                                 \
 178         static const unsigned long __kentry_##sym               \
 179         __used                                                  \
 180         __attribute__((__section__("___kentry+" #sym)))         \
 181         = (unsigned long)&sym;
 182 #endif
 183
 184 #ifndef RELOC_HIDE
 185 # define RELOC_HIDE(ptr, off)                                   \
 186   ({ unsigned long __ptr;                                       \
 187      __ptr = (unsigned long) (ptr);                             \
 188     (typeof(ptr)) (__ptr + (off)); })
 189 #endif
 190
 191 #define absolute_pointer(val)   RELOC_HIDE((void *)(val), 0)
 192
 193 #ifndef OPTIMIZER_HIDE_VAR
 194 /* Make the optimizer believe the variable can be manipulated arbitrarily. */
 195 #define OPTIMIZER_HIDE_VAR(var)                                         \
 196         __asm__ ("" : "=r" (var) : "0" (var))
 197 #endif
 198
 199 /* Not-quite-unique ID. */
 200 #ifndef __UNIQUE_ID
 201 # define __UNIQUE_ID(prefix) __PASTE(__PASTE(__UNIQUE_ID_, prefix), __LINE__)
 202 #endif
 203
 204 /**
 205  * data_race - mark an expression as containing intentional data races
 206  *
 207  * This data_race() macro is useful for situations in which data races
 208  * should be forgiven.  One example is diagnostic code that accesses
 209  * shared variables but is not a part of the core synchronization design.
 210  *
 211  * This macro *does not* affect normal code generation, but is a hint
 212  * to tooling that data races here are to be ignored.
 213  */
 214 #define data_race(expr)                                                 \
 215 ({                                                                      \
 216         __unqual_scalar_typeof(({ expr; })) __v = ({                    \
 217                 __kcsan_disable_current();                              \
 218                 expr;                                                   \
 219         });                                                             \
 220         __kcsan_enable_current();                                       \
 221         __v;                                                            \
 222 })
 223
 224 /*
 225  * With CONFIG_CFI_CLANG, the compiler replaces function addresses in
 226  * instrumented C code with jump table addresses. Architectures that
 227  * support CFI can define this macro to return the actual function address
 228  * when needed.
 229  */
 230 #ifndef function_nocfi
 231 #define function_nocfi(x) (x)
 232 #endif
 233
 234 #endif /* __KERNEL__ */
 235
 236 /*
 237  * Force the compiler to emit 'sym' as a symbol, so that we can reference
 238  * it from inline assembler. Necessary in case 'sym' could be inlined
 239  * otherwise, or eliminated entirely due to lack of references that are
 240  * visible to the compiler.
 241  */
 242 #define __ADDRESSABLE(sym) \
 243         static void * __section(".discard.addressable") __used \
 244                 __UNIQUE_ID(__PASTE(__addressable_,sym)) = (void *)&sym;
 245
 246 /**
 247  * offset_to_ptr - convert a relative memory offset to an absolute pointer
 248  * @off:        the address of the 32-bit offset value
 249  */
 250 static inline void *offset_to_ptr(const int *off)
 251 {
 252         return (void *)((unsigned long)off + *off);
 253 }
 254
 255 #endif /* __ASSEMBLY__ */
 256
 257 /* &a[0] degrades to a pointer: a different type from an array */
 258 #define __must_be_array(a)      BUILD_BUG_ON_ZERO(__same_type((a), &(a)[0]))
 259
 260 /*
 261  * This is needed in functions which generate the stack canary, see
 262  * arch/x86/kernel/smpboot.c::start_secondary() for an example.
 263  */
 264 #define prevent_tail_call_optimization()        mb()
 265
 266 #include <asm/rwonce.h>
 267
 268 #endif /* __LINUX_COMPILER_H */