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 void 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 *)(uintptr_t)&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  */
 220 static 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  * Details:
 236  * - sizeof() return an integer constant expression, and does not evaluate
 237  *   the value of its operand; it only examines the type of its operand.
 238  * - The results of comparing two integer constant expressions is also
 239  *   an integer constant expression.
 240  * - The first literal "8" isn't important. It could be any literal value.
 241  * - The second literal "8" is to avoid warnings about unaligned pointers;
 242  *   this could otherwise just be "1".
 243  * - (long)(x) is used to avoid warnings about 64-bit types on 32-bit
 244  *   architectures.
 245  * - The C Standard defines "null pointer constant", "(void *)0", as
 246  *   distinct from other void pointers.
 247  * - If (x) is an integer constant expression, then the "* 0l" resolves
 248  *   it into an integer constant expression of value 0. Since it is cast to
 249  *   "void *", this makes the second operand a null pointer constant.
 250  * - If (x) is not an integer constant expression, then the second operand
 251  *   resolves to a void pointer (but not a null pointer constant: the value
 252  *   is not an integer constant 0).
 253  * - The conditional operator's third operand, "(int *)8", is an object
 254  *   pointer (to type "int").
 255  * - The behavior (including the return type) of the conditional operator
 256  *   ("operand1 ? operand2 : operand3") depends on the kind of expressions
 257  *   given for the second and third operands. This is the central mechanism
 258  *   of the macro:
 259  *   - When one operand is a null pointer constant (i.e. when x is an integer
 260  *     constant expression) and the other is an object pointer (i.e. our
 261  *     third operand), the conditional operator returns the type of the
 262  *     object pointer operand (i.e. "int *). Here, within the sizeof(), we
 263  *     would then get:
 264  *       sizeof(*((int *)(...))  == sizeof(int)  == 4
 265  *   - When one operand is a void pointer (i.e. when x is not an integer
 266  *     constant expression) and the other is an object pointer (i.e. our
 267  *     third operand), the conditional operator returns a "void *" type.
 268  *     Here, within the sizeof(), we would then get:
 269  *       sizeof(*((void *)(...)) == sizeof(void) == 1
 270  * - The equality comparison to "sizeof(int)" therefore depends on (x):
 271  *     sizeof(int) == sizeof(int)     (x) was a constant expression
 272  *     sizeof(int) != sizeof(void)    (x) was not a constant expression
 273  */
 274 #define __is_constexpr(x) \
 275         (sizeof(int) == sizeof(*(8 ? ((void *)((long)(x) * 0l)) : (int *)8)))
 276
 277 /*
 278  * Whether 'type' is a signed type or an unsigned type. Supports scalar types,
 279  * bool and also pointer types.
 280  */
 281 #define is_signed_type(type) (((type)(-1)) < (__force type)1)
 282 #define is_unsigned_type(type) (!is_signed_type(type))
 283
 284 /*
 285  * This is needed in functions which generate the stack canary, see
 286  * arch/x86/kernel/smpboot.c::start_secondary() for an example.
 287  */
 288 #define prevent_tail_call_optimization()        mb()
 289
 290 #include <asm/rwonce.h>
 291
 292 #endif /* __LINUX_COMPILER_H */