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TOMOYO Linux Cross Reference
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                         int ______r;                                    \
 25                         static struct ftrace_likely_data                \
 26                                 __attribute__((__aligned__(4)))         \
 27                                 __attribute__((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                         __attribute__((__aligned__(4)))                 \
 63                         __attribute__((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 /* Unreachable code */
 90 #ifdef CONFIG_STACK_VALIDATION
 91 /*
 92  * These macros help objtool understand GCC code flow for unreachable code.
 93  * The __COUNTER__ based labels are a hack to make each instance of the macros
 94  * unique, to convince GCC not to merge duplicate inline asm statements.
 95  */
 96 #define annotate_reachable() ({                                         \
 97         asm volatile("%c0:\n\t"                                         \
 98                      ".pushsection .discard.reachable\n\t"              \
 99                      ".long %c0b - .\n\t"                               \
100                      ".popsection\n\t" : : "i" (__COUNTER__));          \
101 })
102 #define annotate_unreachable() ({                                       \
103         asm volatile("%c0:\n\t"                                         \
104                      ".pushsection .discard.unreachable\n\t"            \
105                      ".long %c0b - .\n\t"                               \
106                      ".popsection\n\t" : : "i" (__COUNTER__));          \
107 })
108 #define ASM_UNREACHABLE                                                 \
109         "999:\n\t"                                                      \
110         ".pushsection .discard.unreachable\n\t"                         \
111         ".long 999b - .\n\t"                                            \
112         ".popsection\n\t"
113 #else
114 #define annotate_reachable()
115 #define annotate_unreachable()
116 #endif
117 
118 #ifndef ASM_UNREACHABLE
119 # define ASM_UNREACHABLE
120 #endif
121 #ifndef unreachable
122 # define unreachable() do { annotate_reachable(); do { } while (1); } while (0)
123 #endif
124 
125 /*
126  * KENTRY - kernel entry point
127  * This can be used to annotate symbols (functions or data) that are used
128  * without their linker symbol being referenced explicitly. For example,
129  * interrupt vector handlers, or functions in the kernel image that are found
130  * programatically.
131  *
132  * Not required for symbols exported with EXPORT_SYMBOL, or initcalls. Those
133  * are handled in their own way (with KEEP() in linker scripts).
134  *
135  * KENTRY can be avoided if the symbols in question are marked as KEEP() in the
136  * linker script. For example an architecture could KEEP() its entire
137  * boot/exception vector code rather than annotate each function and data.
138  */
139 #ifndef KENTRY
140 # define KENTRY(sym)                                            \
141         extern typeof(sym) sym;                                 \
142         static const unsigned long __kentry_##sym               \
143         __used                                                  \
144         __attribute__((section("___kentry" "+" #sym ), used))   \
145         = (unsigned long)&sym;
146 #endif
147 
148 #ifndef RELOC_HIDE
149 # define RELOC_HIDE(ptr, off)                                   \
150   ({ unsigned long __ptr;                                       \
151      __ptr = (unsigned long) (ptr);                             \
152     (typeof(ptr)) (__ptr + (off)); })
153 #endif
154 
155 #ifndef OPTIMIZER_HIDE_VAR
156 #define OPTIMIZER_HIDE_VAR(var) barrier()
157 #endif
158 
159 /* Not-quite-unique ID. */
160 #ifndef __UNIQUE_ID
161 # define __UNIQUE_ID(prefix) __PASTE(__PASTE(__UNIQUE_ID_, prefix), __LINE__)
162 #endif
163 
164 #include <uapi/linux/types.h>
165 
166 #define __READ_ONCE_SIZE                                                \
167 ({                                                                      \
168         switch (size) {                                                 \
169         case 1: *(__u8 *)res = *(volatile __u8 *)p; break;              \
170         case 2: *(__u16 *)res = *(volatile __u16 *)p; break;            \
171         case 4: *(__u32 *)res = *(volatile __u32 *)p; break;            \
172         case 8: *(__u64 *)res = *(volatile __u64 *)p; break;            \
173         default:                                                        \
174                 barrier();                                              \
175                 __builtin_memcpy((void *)res, (const void *)p, size);   \
176                 barrier();                                              \
177         }                                                               \
178 })
179 
180 static __always_inline
181 void __read_once_size(const volatile void *p, void *res, int size)
182 {
183         __READ_ONCE_SIZE;
184 }
185 
186 #ifdef CONFIG_KASAN
187 /*
188  * This function is not 'inline' because __no_sanitize_address confilcts
189  * with inlining. Attempt to inline it may cause a build failure.
190  *      https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67368
191  * '__maybe_unused' allows us to avoid defined-but-not-used warnings.
192  */
193 static __no_sanitize_address __maybe_unused
194 void __read_once_size_nocheck(const volatile void *p, void *res, int size)
195 {
196         __READ_ONCE_SIZE;
197 }
198 #else
199 static __always_inline
200 void __read_once_size_nocheck(const volatile void *p, void *res, int size)
201 {
202         __READ_ONCE_SIZE;
203 }
204 #endif
205 
206 static __always_inline void __write_once_size(volatile void *p, void *res, int size)
207 {
208         switch (size) {
209         case 1: *(volatile __u8 *)p = *(__u8 *)res; break;
210         case 2: *(volatile __u16 *)p = *(__u16 *)res; break;
211         case 4: *(volatile __u32 *)p = *(__u32 *)res; break;
212         case 8: *(volatile __u64 *)p = *(__u64 *)res; break;
213         default:
214                 barrier();
215                 __builtin_memcpy((void *)p, (const void *)res, size);
216                 barrier();
217         }
218 }
219 
220 /*
221  * Prevent the compiler from merging or refetching reads or writes. The
222  * compiler is also forbidden from reordering successive instances of
223  * READ_ONCE and WRITE_ONCE, but only when the compiler is aware of some
224  * particular ordering. One way to make the compiler aware of ordering is to
225  * put the two invocations of READ_ONCE or WRITE_ONCE in different C
226  * statements.
227  *
228  * These two macros will also work on aggregate data types like structs or
229  * unions. If the size of the accessed data type exceeds the word size of
230  * the machine (e.g., 32 bits or 64 bits) READ_ONCE() and WRITE_ONCE() will
231  * fall back to memcpy(). There's at least two memcpy()s: one for the
232  * __builtin_memcpy() and then one for the macro doing the copy of variable
233  * - '__u' allocated on the stack.
234  *
235  * Their two major use cases are: (1) Mediating communication between
236  * process-level code and irq/NMI handlers, all running on the same CPU,
237  * and (2) Ensuring that the compiler does not fold, spindle, or otherwise
238  * mutilate accesses that either do not require ordering or that interact
239  * with an explicit memory barrier or atomic instruction that provides the
240  * required ordering.
241  */
242 #include <asm/barrier.h>
243 
244 #define __READ_ONCE(x, check)                                           \
245 ({                                                                      \
246         union { typeof(x) __val; char __c[1]; } __u;                    \
247         if (check)                                                      \
248                 __read_once_size(&(x), __u.__c, sizeof(x));             \
249         else                                                            \
250                 __read_once_size_nocheck(&(x), __u.__c, sizeof(x));     \
251         smp_read_barrier_depends(); /* Enforce dependency ordering from x */ \
252         __u.__val;                                                      \
253 })
254 #define READ_ONCE(x) __READ_ONCE(x, 1)
255 
256 /*
257  * Use READ_ONCE_NOCHECK() instead of READ_ONCE() if you need
258  * to hide memory access from KASAN.
259  */
260 #define READ_ONCE_NOCHECK(x) __READ_ONCE(x, 0)
261 
262 #define WRITE_ONCE(x, val) \
263 ({                                                      \
264         union { typeof(x) __val; char __c[1]; } __u =   \
265                 { .__val = (__force typeof(x)) (val) }; \
266         __write_once_size(&(x), __u.__c, sizeof(x));    \
267         __u.__val;                                      \
268 })
269 
270 #endif /* __KERNEL__ */
271 
272 #endif /* __ASSEMBLY__ */
273 
274 #ifndef __optimize
275 # define __optimize(level)
276 #endif
277 
278 /* Compile time object size, -1 for unknown */
279 #ifndef __compiletime_object_size
280 # define __compiletime_object_size(obj) -1
281 #endif
282 #ifndef __compiletime_warning
283 # define __compiletime_warning(message)
284 #endif
285 #ifndef __compiletime_error
286 # define __compiletime_error(message)
287 /*
288  * Sparse complains of variable sized arrays due to the temporary variable in
289  * __compiletime_assert. Unfortunately we can't just expand it out to make
290  * sparse see a constant array size without breaking compiletime_assert on old
291  * versions of GCC (e.g. 4.2.4), so hide the array from sparse altogether.
292  */
293 # ifndef __CHECKER__
294 #  define __compiletime_error_fallback(condition) \
295         do { ((void)sizeof(char[1 - 2 * condition])); } while (0)
296 # endif
297 #endif
298 #ifndef __compiletime_error_fallback
299 # define __compiletime_error_fallback(condition) do { } while (0)
300 #endif
301 
302 #ifdef __OPTIMIZE__
303 # define __compiletime_assert(condition, msg, prefix, suffix)           \
304         do {                                                            \
305                 bool __cond = !(condition);                             \
306                 extern void prefix ## suffix(void) __compiletime_error(msg); \
307                 if (__cond)                                             \
308                         prefix ## suffix();                             \
309                 __compiletime_error_fallback(__cond);                   \
310         } while (0)
311 #else
312 # define __compiletime_assert(condition, msg, prefix, suffix) do { } while (0)
313 #endif
314 
315 #define _compiletime_assert(condition, msg, prefix, suffix) \
316         __compiletime_assert(condition, msg, prefix, suffix)
317 
318 /**
319  * compiletime_assert - break build and emit msg if condition is false
320  * @condition: a compile-time constant condition to check
321  * @msg:       a message to emit if condition is false
322  *
323  * In tradition of POSIX assert, this macro will break the build if the
324  * supplied condition is *false*, emitting the supplied error message if the
325  * compiler has support to do so.
326  */
327 #define compiletime_assert(condition, msg) \
328         _compiletime_assert(condition, msg, __compiletime_assert_, __LINE__)
329 
330 #define compiletime_assert_atomic_type(t)                               \
331         compiletime_assert(__native_word(t),                            \
332                 "Need native word sized stores/loads for atomicity.")
333 
334 #endif /* __LINUX_COMPILER_H */
335 

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