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Linux/include/linux/compiler.h

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  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) : "" (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 */
269 

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