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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, ...) __trace_if( (cond , ## __VA_ARGS__) )
 57 #define __trace_if(cond) \
 58         if (__builtin_constant_p(!!(cond)) ? !!(cond) :                 \
 59         ({                                                              \
 60                 int ______r;                                            \
 61                 static struct ftrace_branch_data                        \
 62                         __aligned(4)                                    \
 63                         __section("_ftrace_branch")                     \
 64                         ______f = {                                     \
 65                                 .func = __func__,                       \
 66                                 .file = __FILE__,                       \
 67                                 .line = __LINE__,                       \
 68                         };                                              \
 69                 ______r = !!(cond);                                     \
 70                 ______f.miss_hit[______r]++;                                    \
 71                 ______r;                                                \
 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 #endif
 79 
 80 /* Optimization barrier */
 81 #ifndef barrier
 82 # define barrier() __memory_barrier()
 83 #endif
 84 
 85 #ifndef barrier_data
 86 # define barrier_data(ptr) barrier()
 87 #endif
 88 
 89 /* workaround for GCC PR82365 if needed */
 90 #ifndef barrier_before_unreachable
 91 # define barrier_before_unreachable() do { } while (0)
 92 #endif
 93 
 94 /* Unreachable code */
 95 #ifdef CONFIG_STACK_VALIDATION
 96 /*
 97  * These macros help objtool understand GCC code flow for unreachable code.
 98  * The __COUNTER__ based labels are a hack to make each instance of the macros
 99  * unique, to convince GCC not to merge duplicate inline asm statements.
100  */
101 #define annotate_reachable() ({                                         \
102         asm volatile("%c0:\n\t"                                         \
103                      ".pushsection .discard.reachable\n\t"              \
104                      ".long %c0b - .\n\t"                               \
105                      ".popsection\n\t" : : "i" (__COUNTER__));          \
106 })
107 #define annotate_unreachable() ({                                       \
108         asm volatile("%c0:\n\t"                                         \
109                      ".pushsection .discard.unreachable\n\t"            \
110                      ".long %c0b - .\n\t"                               \
111                      ".popsection\n\t" : : "i" (__COUNTER__));          \
112 })
113 #define ASM_UNREACHABLE                                                 \
114         "999:\n\t"                                                      \
115         ".pushsection .discard.unreachable\n\t"                         \
116         ".long 999b - .\n\t"                                            \
117         ".popsection\n\t"
118 #else
119 #define annotate_reachable()
120 #define annotate_unreachable()
121 #endif
122 
123 #ifndef ASM_UNREACHABLE
124 # define ASM_UNREACHABLE
125 #endif
126 #ifndef unreachable
127 # define unreachable() do {             \
128         annotate_unreachable();         \
129         __builtin_unreachable();        \
130 } while (0)
131 #endif
132 
133 /*
134  * KENTRY - kernel entry point
135  * This can be used to annotate symbols (functions or data) that are used
136  * without their linker symbol being referenced explicitly. For example,
137  * interrupt vector handlers, or functions in the kernel image that are found
138  * programatically.
139  *
140  * Not required for symbols exported with EXPORT_SYMBOL, or initcalls. Those
141  * are handled in their own way (with KEEP() in linker scripts).
142  *
143  * KENTRY can be avoided if the symbols in question are marked as KEEP() in the
144  * linker script. For example an architecture could KEEP() its entire
145  * boot/exception vector code rather than annotate each function and data.
146  */
147 #ifndef KENTRY
148 # define KENTRY(sym)                                            \
149         extern typeof(sym) sym;                                 \
150         static const unsigned long __kentry_##sym               \
151         __used                                                  \
152         __section("___kentry" "+" #sym )                        \
153         = (unsigned long)&sym;
154 #endif
155 
156 #ifndef RELOC_HIDE
157 # define RELOC_HIDE(ptr, off)                                   \
158   ({ unsigned long __ptr;                                       \
159      __ptr = (unsigned long) (ptr);                             \
160     (typeof(ptr)) (__ptr + (off)); })
161 #endif
162 
163 #ifndef OPTIMIZER_HIDE_VAR
164 /* Make the optimizer believe the variable can be manipulated arbitrarily. */
165 #define OPTIMIZER_HIDE_VAR(var)                                         \
166         __asm__ ("" : "=r" (var) : "" (var))
167 #endif
168 
169 /* Not-quite-unique ID. */
170 #ifndef __UNIQUE_ID
171 # define __UNIQUE_ID(prefix) __PASTE(__PASTE(__UNIQUE_ID_, prefix), __LINE__)
172 #endif
173 
174 #include <uapi/linux/types.h>
175 
176 #define __READ_ONCE_SIZE                                                \
177 ({                                                                      \
178         switch (size) {                                                 \
179         case 1: *(__u8 *)res = *(volatile __u8 *)p; break;              \
180         case 2: *(__u16 *)res = *(volatile __u16 *)p; break;            \
181         case 4: *(__u32 *)res = *(volatile __u32 *)p; break;            \
182         case 8: *(__u64 *)res = *(volatile __u64 *)p; break;            \
183         default:                                                        \
184                 barrier();                                              \
185                 __builtin_memcpy((void *)res, (const void *)p, size);   \
186                 barrier();                                              \
187         }                                                               \
188 })
189 
190 static __always_inline
191 void __read_once_size(const volatile void *p, void *res, int size)
192 {
193         __READ_ONCE_SIZE;
194 }
195 
196 #ifdef CONFIG_KASAN
197 /*
198  * We can't declare function 'inline' because __no_sanitize_address confilcts
199  * with inlining. Attempt to inline it may cause a build failure.
200  *      https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67368
201  * '__maybe_unused' allows us to avoid defined-but-not-used warnings.
202  */
203 # define __no_kasan_or_inline __no_sanitize_address notrace __maybe_unused
204 #else
205 # define __no_kasan_or_inline __always_inline
206 #endif
207 
208 static __no_kasan_or_inline
209 void __read_once_size_nocheck(const volatile void *p, void *res, int size)
210 {
211         __READ_ONCE_SIZE;
212 }
213 
214 static __always_inline void __write_once_size(volatile void *p, void *res, int size)
215 {
216         switch (size) {
217         case 1: *(volatile __u8 *)p = *(__u8 *)res; break;
218         case 2: *(volatile __u16 *)p = *(__u16 *)res; break;
219         case 4: *(volatile __u32 *)p = *(__u32 *)res; break;
220         case 8: *(volatile __u64 *)p = *(__u64 *)res; break;
221         default:
222                 barrier();
223                 __builtin_memcpy((void *)p, (const void *)res, size);
224                 barrier();
225         }
226 }
227 
228 /*
229  * Prevent the compiler from merging or refetching reads or writes. The
230  * compiler is also forbidden from reordering successive instances of
231  * READ_ONCE and WRITE_ONCE, but only when the compiler is aware of some
232  * particular ordering. One way to make the compiler aware of ordering is to
233  * put the two invocations of READ_ONCE or WRITE_ONCE in different C
234  * statements.
235  *
236  * These two macros will also work on aggregate data types like structs or
237  * unions. If the size of the accessed data type exceeds the word size of
238  * the machine (e.g., 32 bits or 64 bits) READ_ONCE() and WRITE_ONCE() will
239  * fall back to memcpy(). There's at least two memcpy()s: one for the
240  * __builtin_memcpy() and then one for the macro doing the copy of variable
241  * - '__u' allocated on the stack.
242  *
243  * Their two major use cases are: (1) Mediating communication between
244  * process-level code and irq/NMI handlers, all running on the same CPU,
245  * and (2) Ensuring that the compiler does not fold, spindle, or otherwise
246  * mutilate accesses that either do not require ordering or that interact
247  * with an explicit memory barrier or atomic instruction that provides the
248  * required ordering.
249  */
250 #include <asm/barrier.h>
251 #include <linux/kasan-checks.h>
252 
253 #define __READ_ONCE(x, check)                                           \
254 ({                                                                      \
255         union { typeof(x) __val; char __c[1]; } __u;                    \
256         if (check)                                                      \
257                 __read_once_size(&(x), __u.__c, sizeof(x));             \
258         else                                                            \
259                 __read_once_size_nocheck(&(x), __u.__c, sizeof(x));     \
260         smp_read_barrier_depends(); /* Enforce dependency ordering from x */ \
261         __u.__val;                                                      \
262 })
263 #define READ_ONCE(x) __READ_ONCE(x, 1)
264 
265 /*
266  * Use READ_ONCE_NOCHECK() instead of READ_ONCE() if you need
267  * to hide memory access from KASAN.
268  */
269 #define READ_ONCE_NOCHECK(x) __READ_ONCE(x, 0)
270 
271 static __no_kasan_or_inline
272 unsigned long read_word_at_a_time(const void *addr)
273 {
274         kasan_check_read(addr, 1);
275         return *(unsigned long *)addr;
276 }
277 
278 #define WRITE_ONCE(x, val) \
279 ({                                                      \
280         union { typeof(x) __val; char __c[1]; } __u =   \
281                 { .__val = (__force typeof(x)) (val) }; \
282         __write_once_size(&(x), __u.__c, sizeof(x));    \
283         __u.__val;                                      \
284 })
285 
286 #endif /* __KERNEL__ */
287 
288 /*
289  * Force the compiler to emit 'sym' as a symbol, so that we can reference
290  * it from inline assembler. Necessary in case 'sym' could be inlined
291  * otherwise, or eliminated entirely due to lack of references that are
292  * visible to the compiler.
293  */
294 #define __ADDRESSABLE(sym) \
295         static void * __section(".discard.addressable") __used \
296                 __PASTE(__addressable_##sym, __LINE__) = (void *)&sym;
297 
298 /**
299  * offset_to_ptr - convert a relative memory offset to an absolute pointer
300  * @off:        the address of the 32-bit offset value
301  */
302 static inline void *offset_to_ptr(const int *off)
303 {
304         return (void *)((unsigned long)off + *off);
305 }
306 
307 #endif /* __ASSEMBLY__ */
308 
309 /* Compile time object size, -1 for unknown */
310 #ifndef __compiletime_object_size
311 # define __compiletime_object_size(obj) -1
312 #endif
313 #ifndef __compiletime_warning
314 # define __compiletime_warning(message)
315 #endif
316 #ifndef __compiletime_error
317 # define __compiletime_error(message)
318 #endif
319 
320 #ifdef __OPTIMIZE__
321 # define __compiletime_assert(condition, msg, prefix, suffix)           \
322         do {                                                            \
323                 extern void prefix ## suffix(void) __compiletime_error(msg); \
324                 if (!(condition))                                       \
325                         prefix ## suffix();                             \
326         } while (0)
327 #else
328 # define __compiletime_assert(condition, msg, prefix, suffix) do { } while (0)
329 #endif
330 
331 #define _compiletime_assert(condition, msg, prefix, suffix) \
332         __compiletime_assert(condition, msg, prefix, suffix)
333 
334 /**
335  * compiletime_assert - break build and emit msg if condition is false
336  * @condition: a compile-time constant condition to check
337  * @msg:       a message to emit if condition is false
338  *
339  * In tradition of POSIX assert, this macro will break the build if the
340  * supplied condition is *false*, emitting the supplied error message if the
341  * compiler has support to do so.
342  */
343 #define compiletime_assert(condition, msg) \
344         _compiletime_assert(condition, msg, __compiletime_assert_, __LINE__)
345 
346 #define compiletime_assert_atomic_type(t)                               \
347         compiletime_assert(__native_word(t),                            \
348                 "Need native word sized stores/loads for atomicity.")
349 
350 /* &a[0] degrades to a pointer: a different type from an array */
351 #define __must_be_array(a)      BUILD_BUG_ON_ZERO(__same_type((a), &(a)[0]))
352 
353 #endif /* __LINUX_COMPILER_H */
354 

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