~ [ source navigation ] ~ [ diff markup ] ~ [ identifier search ] ~

TOMOYO Linux Cross Reference
Linux/include/linux/jump_label.h

Version: ~ [ linux-5.16-rc3 ] ~ [ linux-5.15.5 ] ~ [ linux-5.14.21 ] ~ [ linux-5.13.19 ] ~ [ linux-5.12.19 ] ~ [ linux-5.11.22 ] ~ [ linux-5.10.82 ] ~ [ linux-5.9.16 ] ~ [ linux-5.8.18 ] ~ [ linux-5.7.19 ] ~ [ linux-5.6.19 ] ~ [ linux-5.5.19 ] ~ [ linux-5.4.162 ] ~ [ linux-5.3.18 ] ~ [ linux-5.2.21 ] ~ [ linux-5.1.21 ] ~ [ linux-5.0.21 ] ~ [ linux-4.20.17 ] ~ [ linux-4.19.218 ] ~ [ linux-4.18.20 ] ~ [ linux-4.17.19 ] ~ [ linux-4.16.18 ] ~ [ linux-4.15.18 ] ~ [ linux-4.14.256 ] ~ [ linux-4.13.16 ] ~ [ linux-4.12.14 ] ~ [ linux-4.11.12 ] ~ [ linux-4.10.17 ] ~ [ linux-4.9.291 ] ~ [ linux-4.8.17 ] ~ [ linux-4.7.10 ] ~ [ linux-4.6.7 ] ~ [ linux-4.5.7 ] ~ [ linux-4.4.293 ] ~ [ linux-4.3.6 ] ~ [ linux-4.2.8 ] ~ [ linux-4.1.52 ] ~ [ linux-4.0.9 ] ~ [ linux-3.18.140 ] ~ [ linux-3.16.85 ] ~ [ linux-3.14.79 ] ~ [ linux-3.12.74 ] ~ [ linux-3.10.108 ] ~ [ linux-2.6.32.71 ] ~ [ linux-2.6.0 ] ~ [ linux-2.4.37.11 ] ~ [ unix-v6-master ] ~ [ ccs-tools-1.8.5 ] ~ [ policy-sample ] ~
Architecture: ~ [ i386 ] ~ [ alpha ] ~ [ m68k ] ~ [ mips ] ~ [ ppc ] ~ [ sparc ] ~ [ sparc64 ] ~

  1 /* SPDX-License-Identifier: GPL-2.0 */
  2 #ifndef _LINUX_JUMP_LABEL_H
  3 #define _LINUX_JUMP_LABEL_H
  4 
  5 /*
  6  * Jump label support
  7  *
  8  * Copyright (C) 2009-2012 Jason Baron <jbaron@redhat.com>
  9  * Copyright (C) 2011-2012 Red Hat, Inc., Peter Zijlstra
 10  *
 11  * DEPRECATED API:
 12  *
 13  * The use of 'struct static_key' directly, is now DEPRECATED. In addition
 14  * static_key_{true,false}() is also DEPRECATED. IE DO NOT use the following:
 15  *
 16  * struct static_key false = STATIC_KEY_INIT_FALSE;
 17  * struct static_key true = STATIC_KEY_INIT_TRUE;
 18  * static_key_true()
 19  * static_key_false()
 20  *
 21  * The updated API replacements are:
 22  *
 23  * DEFINE_STATIC_KEY_TRUE(key);
 24  * DEFINE_STATIC_KEY_FALSE(key);
 25  * DEFINE_STATIC_KEY_ARRAY_TRUE(keys, count);
 26  * DEFINE_STATIC_KEY_ARRAY_FALSE(keys, count);
 27  * static_branch_likely()
 28  * static_branch_unlikely()
 29  *
 30  * Jump labels provide an interface to generate dynamic branches using
 31  * self-modifying code. Assuming toolchain and architecture support, if we
 32  * define a "key" that is initially false via "DEFINE_STATIC_KEY_FALSE(key)",
 33  * an "if (static_branch_unlikely(&key))" statement is an unconditional branch
 34  * (which defaults to false - and the true block is placed out of line).
 35  * Similarly, we can define an initially true key via
 36  * "DEFINE_STATIC_KEY_TRUE(key)", and use it in the same
 37  * "if (static_branch_unlikely(&key))", in which case we will generate an
 38  * unconditional branch to the out-of-line true branch. Keys that are
 39  * initially true or false can be using in both static_branch_unlikely()
 40  * and static_branch_likely() statements.
 41  *
 42  * At runtime we can change the branch target by setting the key
 43  * to true via a call to static_branch_enable(), or false using
 44  * static_branch_disable(). If the direction of the branch is switched by
 45  * these calls then we run-time modify the branch target via a
 46  * no-op -> jump or jump -> no-op conversion. For example, for an
 47  * initially false key that is used in an "if (static_branch_unlikely(&key))"
 48  * statement, setting the key to true requires us to patch in a jump
 49  * to the out-of-line of true branch.
 50  *
 51  * In addition to static_branch_{enable,disable}, we can also reference count
 52  * the key or branch direction via static_branch_{inc,dec}. Thus,
 53  * static_branch_inc() can be thought of as a 'make more true' and
 54  * static_branch_dec() as a 'make more false'.
 55  *
 56  * Since this relies on modifying code, the branch modifying functions
 57  * must be considered absolute slow paths (machine wide synchronization etc.).
 58  * OTOH, since the affected branches are unconditional, their runtime overhead
 59  * will be absolutely minimal, esp. in the default (off) case where the total
 60  * effect is a single NOP of appropriate size. The on case will patch in a jump
 61  * to the out-of-line block.
 62  *
 63  * When the control is directly exposed to userspace, it is prudent to delay the
 64  * decrement to avoid high frequency code modifications which can (and do)
 65  * cause significant performance degradation. Struct static_key_deferred and
 66  * static_key_slow_dec_deferred() provide for this.
 67  *
 68  * Lacking toolchain and or architecture support, static keys fall back to a
 69  * simple conditional branch.
 70  *
 71  * Additional babbling in: Documentation/static-keys.txt
 72  */
 73 
 74 #ifndef __ASSEMBLY__
 75 
 76 #include <linux/types.h>
 77 #include <linux/compiler.h>
 78 
 79 extern bool static_key_initialized;
 80 
 81 #define STATIC_KEY_CHECK_USE(key) WARN(!static_key_initialized,               \
 82                                     "%s(): static key '%pS' used before call to jump_label_init()", \
 83                                     __func__, (key))
 84 
 85 #ifdef CONFIG_JUMP_LABEL
 86 
 87 struct static_key {
 88         atomic_t enabled;
 89 /*
 90  * Note:
 91  *   To make anonymous unions work with old compilers, the static
 92  *   initialization of them requires brackets. This creates a dependency
 93  *   on the order of the struct with the initializers. If any fields
 94  *   are added, STATIC_KEY_INIT_TRUE and STATIC_KEY_INIT_FALSE may need
 95  *   to be modified.
 96  *
 97  * bit 0 => 1 if key is initially true
 98  *          0 if initially false
 99  * bit 1 => 1 if points to struct static_key_mod
100  *          0 if points to struct jump_entry
101  */
102         union {
103                 unsigned long type;
104                 struct jump_entry *entries;
105                 struct static_key_mod *next;
106         };
107 };
108 
109 #else
110 struct static_key {
111         atomic_t enabled;
112 };
113 #endif  /* CONFIG_JUMP_LABEL */
114 #endif /* __ASSEMBLY__ */
115 
116 #ifdef CONFIG_JUMP_LABEL
117 #include <asm/jump_label.h>
118 
119 #ifndef __ASSEMBLY__
120 #ifdef CONFIG_HAVE_ARCH_JUMP_LABEL_RELATIVE
121 
122 struct jump_entry {
123         s32 code;
124         s32 target;
125         long key;       // key may be far away from the core kernel under KASLR
126 };
127 
128 static inline unsigned long jump_entry_code(const struct jump_entry *entry)
129 {
130         return (unsigned long)&entry->code + entry->code;
131 }
132 
133 static inline unsigned long jump_entry_target(const struct jump_entry *entry)
134 {
135         return (unsigned long)&entry->target + entry->target;
136 }
137 
138 static inline struct static_key *jump_entry_key(const struct jump_entry *entry)
139 {
140         long offset = entry->key & ~3L;
141 
142         return (struct static_key *)((unsigned long)&entry->key + offset);
143 }
144 
145 #else
146 
147 static inline unsigned long jump_entry_code(const struct jump_entry *entry)
148 {
149         return entry->code;
150 }
151 
152 static inline unsigned long jump_entry_target(const struct jump_entry *entry)
153 {
154         return entry->target;
155 }
156 
157 static inline struct static_key *jump_entry_key(const struct jump_entry *entry)
158 {
159         return (struct static_key *)((unsigned long)entry->key & ~3UL);
160 }
161 
162 #endif
163 
164 static inline bool jump_entry_is_branch(const struct jump_entry *entry)
165 {
166         return (unsigned long)entry->key & 1UL;
167 }
168 
169 static inline bool jump_entry_is_init(const struct jump_entry *entry)
170 {
171         return (unsigned long)entry->key & 2UL;
172 }
173 
174 static inline void jump_entry_set_init(struct jump_entry *entry)
175 {
176         entry->key |= 2;
177 }
178 
179 #endif
180 #endif
181 
182 #ifndef __ASSEMBLY__
183 
184 enum jump_label_type {
185         JUMP_LABEL_NOP = 0,
186         JUMP_LABEL_JMP,
187 };
188 
189 struct module;
190 
191 #ifdef CONFIG_JUMP_LABEL
192 
193 #define JUMP_TYPE_FALSE         0UL
194 #define JUMP_TYPE_TRUE          1UL
195 #define JUMP_TYPE_LINKED        2UL
196 #define JUMP_TYPE_MASK          3UL
197 
198 static __always_inline bool static_key_false(struct static_key *key)
199 {
200         return arch_static_branch(key, false);
201 }
202 
203 static __always_inline bool static_key_true(struct static_key *key)
204 {
205         return !arch_static_branch(key, true);
206 }
207 
208 extern struct jump_entry __start___jump_table[];
209 extern struct jump_entry __stop___jump_table[];
210 
211 extern void jump_label_init(void);
212 extern void jump_label_lock(void);
213 extern void jump_label_unlock(void);
214 extern void arch_jump_label_transform(struct jump_entry *entry,
215                                       enum jump_label_type type);
216 extern void arch_jump_label_transform_static(struct jump_entry *entry,
217                                              enum jump_label_type type);
218 extern bool arch_jump_label_transform_queue(struct jump_entry *entry,
219                                             enum jump_label_type type);
220 extern void arch_jump_label_transform_apply(void);
221 extern int jump_label_text_reserved(void *start, void *end);
222 extern void static_key_slow_inc(struct static_key *key);
223 extern void static_key_slow_dec(struct static_key *key);
224 extern void static_key_slow_inc_cpuslocked(struct static_key *key);
225 extern void static_key_slow_dec_cpuslocked(struct static_key *key);
226 extern void jump_label_apply_nops(struct module *mod);
227 extern int static_key_count(struct static_key *key);
228 extern void static_key_enable(struct static_key *key);
229 extern void static_key_disable(struct static_key *key);
230 extern void static_key_enable_cpuslocked(struct static_key *key);
231 extern void static_key_disable_cpuslocked(struct static_key *key);
232 
233 /*
234  * We should be using ATOMIC_INIT() for initializing .enabled, but
235  * the inclusion of atomic.h is problematic for inclusion of jump_label.h
236  * in 'low-level' headers. Thus, we are initializing .enabled with a
237  * raw value, but have added a BUILD_BUG_ON() to catch any issues in
238  * jump_label_init() see: kernel/jump_label.c.
239  */
240 #define STATIC_KEY_INIT_TRUE                                    \
241         { .enabled = { 1 },                                     \
242           { .entries = (void *)JUMP_TYPE_TRUE } }
243 #define STATIC_KEY_INIT_FALSE                                   \
244         { .enabled = { 0 },                                     \
245           { .entries = (void *)JUMP_TYPE_FALSE } }
246 
247 #else  /* !CONFIG_JUMP_LABEL */
248 
249 #include <linux/atomic.h>
250 #include <linux/bug.h>
251 
252 static inline int static_key_count(struct static_key *key)
253 {
254         return atomic_read(&key->enabled);
255 }
256 
257 static __always_inline void jump_label_init(void)
258 {
259         static_key_initialized = true;
260 }
261 
262 static __always_inline bool static_key_false(struct static_key *key)
263 {
264         if (unlikely(static_key_count(key) > 0))
265                 return true;
266         return false;
267 }
268 
269 static __always_inline bool static_key_true(struct static_key *key)
270 {
271         if (likely(static_key_count(key) > 0))
272                 return true;
273         return false;
274 }
275 
276 static inline void static_key_slow_inc(struct static_key *key)
277 {
278         STATIC_KEY_CHECK_USE(key);
279         atomic_inc(&key->enabled);
280 }
281 
282 static inline void static_key_slow_dec(struct static_key *key)
283 {
284         STATIC_KEY_CHECK_USE(key);
285         atomic_dec(&key->enabled);
286 }
287 
288 #define static_key_slow_inc_cpuslocked(key) static_key_slow_inc(key)
289 #define static_key_slow_dec_cpuslocked(key) static_key_slow_dec(key)
290 
291 static inline int jump_label_text_reserved(void *start, void *end)
292 {
293         return 0;
294 }
295 
296 static inline void jump_label_lock(void) {}
297 static inline void jump_label_unlock(void) {}
298 
299 static inline int jump_label_apply_nops(struct module *mod)
300 {
301         return 0;
302 }
303 
304 static inline void static_key_enable(struct static_key *key)
305 {
306         STATIC_KEY_CHECK_USE(key);
307 
308         if (atomic_read(&key->enabled) != 0) {
309                 WARN_ON_ONCE(atomic_read(&key->enabled) != 1);
310                 return;
311         }
312         atomic_set(&key->enabled, 1);
313 }
314 
315 static inline void static_key_disable(struct static_key *key)
316 {
317         STATIC_KEY_CHECK_USE(key);
318 
319         if (atomic_read(&key->enabled) != 1) {
320                 WARN_ON_ONCE(atomic_read(&key->enabled) != 0);
321                 return;
322         }
323         atomic_set(&key->enabled, 0);
324 }
325 
326 #define static_key_enable_cpuslocked(k)         static_key_enable((k))
327 #define static_key_disable_cpuslocked(k)        static_key_disable((k))
328 
329 #define STATIC_KEY_INIT_TRUE    { .enabled = ATOMIC_INIT(1) }
330 #define STATIC_KEY_INIT_FALSE   { .enabled = ATOMIC_INIT(0) }
331 
332 #endif  /* CONFIG_JUMP_LABEL */
333 
334 #define STATIC_KEY_INIT STATIC_KEY_INIT_FALSE
335 #define jump_label_enabled static_key_enabled
336 
337 /* -------------------------------------------------------------------------- */
338 
339 /*
340  * Two type wrappers around static_key, such that we can use compile time
341  * type differentiation to emit the right code.
342  *
343  * All the below code is macros in order to play type games.
344  */
345 
346 struct static_key_true {
347         struct static_key key;
348 };
349 
350 struct static_key_false {
351         struct static_key key;
352 };
353 
354 #define STATIC_KEY_TRUE_INIT  (struct static_key_true) { .key = STATIC_KEY_INIT_TRUE,  }
355 #define STATIC_KEY_FALSE_INIT (struct static_key_false){ .key = STATIC_KEY_INIT_FALSE, }
356 
357 #define DEFINE_STATIC_KEY_TRUE(name)    \
358         struct static_key_true name = STATIC_KEY_TRUE_INIT
359 
360 #define DEFINE_STATIC_KEY_TRUE_RO(name) \
361         struct static_key_true name __ro_after_init = STATIC_KEY_TRUE_INIT
362 
363 #define DECLARE_STATIC_KEY_TRUE(name)   \
364         extern struct static_key_true name
365 
366 #define DEFINE_STATIC_KEY_FALSE(name)   \
367         struct static_key_false name = STATIC_KEY_FALSE_INIT
368 
369 #define DEFINE_STATIC_KEY_FALSE_RO(name)        \
370         struct static_key_false name __ro_after_init = STATIC_KEY_FALSE_INIT
371 
372 #define DECLARE_STATIC_KEY_FALSE(name)  \
373         extern struct static_key_false name
374 
375 #define DEFINE_STATIC_KEY_ARRAY_TRUE(name, count)               \
376         struct static_key_true name[count] = {                  \
377                 [0 ... (count) - 1] = STATIC_KEY_TRUE_INIT,     \
378         }
379 
380 #define DEFINE_STATIC_KEY_ARRAY_FALSE(name, count)              \
381         struct static_key_false name[count] = {                 \
382                 [0 ... (count) - 1] = STATIC_KEY_FALSE_INIT,    \
383         }
384 
385 extern bool ____wrong_branch_error(void);
386 
387 #define static_key_enabled(x)                                                   \
388 ({                                                                              \
389         if (!__builtin_types_compatible_p(typeof(*x), struct static_key) &&     \
390             !__builtin_types_compatible_p(typeof(*x), struct static_key_true) &&\
391             !__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \
392                 ____wrong_branch_error();                                       \
393         static_key_count((struct static_key *)x) > 0;                           \
394 })
395 
396 #ifdef CONFIG_JUMP_LABEL
397 
398 /*
399  * Combine the right initial value (type) with the right branch order
400  * to generate the desired result.
401  *
402  *
403  * type\branch| likely (1)            | unlikely (0)
404  * -----------+-----------------------+------------------
405  *            |                       |
406  *  true (1)  |    ...                |    ...
407  *            |    NOP                |    JMP L
408  *            |    <br-stmts>         | 1: ...
409  *            | L: ...                |
410  *            |                       |
411  *            |                       | L: <br-stmts>
412  *            |                       |    jmp 1b
413  *            |                       |
414  * -----------+-----------------------+------------------
415  *            |                       |
416  *  false (0) |    ...                |    ...
417  *            |    JMP L              |    NOP
418  *            |    <br-stmts>         | 1: ...
419  *            | L: ...                |
420  *            |                       |
421  *            |                       | L: <br-stmts>
422  *            |                       |    jmp 1b
423  *            |                       |
424  * -----------+-----------------------+------------------
425  *
426  * The initial value is encoded in the LSB of static_key::entries,
427  * type: 0 = false, 1 = true.
428  *
429  * The branch type is encoded in the LSB of jump_entry::key,
430  * branch: 0 = unlikely, 1 = likely.
431  *
432  * This gives the following logic table:
433  *
434  *      enabled type    branch    instuction
435  * -----------------------------+-----------
436  *      0       0       0       | NOP
437  *      0       0       1       | JMP
438  *      0       1       0       | NOP
439  *      0       1       1       | JMP
440  *
441  *      1       0       0       | JMP
442  *      1       0       1       | NOP
443  *      1       1       0       | JMP
444  *      1       1       1       | NOP
445  *
446  * Which gives the following functions:
447  *
448  *   dynamic: instruction = enabled ^ branch
449  *   static:  instruction = type ^ branch
450  *
451  * See jump_label_type() / jump_label_init_type().
452  */
453 
454 #define static_branch_likely(x)                                                 \
455 ({                                                                              \
456         bool branch;                                                            \
457         if (__builtin_types_compatible_p(typeof(*x), struct static_key_true))   \
458                 branch = !arch_static_branch(&(x)->key, true);                  \
459         else if (__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \
460                 branch = !arch_static_branch_jump(&(x)->key, true);             \
461         else                                                                    \
462                 branch = ____wrong_branch_error();                              \
463         likely(branch);                                                         \
464 })
465 
466 #define static_branch_unlikely(x)                                               \
467 ({                                                                              \
468         bool branch;                                                            \
469         if (__builtin_types_compatible_p(typeof(*x), struct static_key_true))   \
470                 branch = arch_static_branch_jump(&(x)->key, false);             \
471         else if (__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \
472                 branch = arch_static_branch(&(x)->key, false);                  \
473         else                                                                    \
474                 branch = ____wrong_branch_error();                              \
475         unlikely(branch);                                                       \
476 })
477 
478 #else /* !CONFIG_JUMP_LABEL */
479 
480 #define static_branch_likely(x)         likely(static_key_enabled(&(x)->key))
481 #define static_branch_unlikely(x)       unlikely(static_key_enabled(&(x)->key))
482 
483 #endif /* CONFIG_JUMP_LABEL */
484 
485 /*
486  * Advanced usage; refcount, branch is enabled when: count != 0
487  */
488 
489 #define static_branch_inc(x)            static_key_slow_inc(&(x)->key)
490 #define static_branch_dec(x)            static_key_slow_dec(&(x)->key)
491 #define static_branch_inc_cpuslocked(x) static_key_slow_inc_cpuslocked(&(x)->key)
492 #define static_branch_dec_cpuslocked(x) static_key_slow_dec_cpuslocked(&(x)->key)
493 
494 /*
495  * Normal usage; boolean enable/disable.
496  */
497 
498 #define static_branch_enable(x)                 static_key_enable(&(x)->key)
499 #define static_branch_disable(x)                static_key_disable(&(x)->key)
500 #define static_branch_enable_cpuslocked(x)      static_key_enable_cpuslocked(&(x)->key)
501 #define static_branch_disable_cpuslocked(x)     static_key_disable_cpuslocked(&(x)->key)
502 
503 #endif /* __ASSEMBLY__ */
504 
505 #endif  /* _LINUX_JUMP_LABEL_H */
506 

~ [ source navigation ] ~ [ diff markup ] ~ [ identifier search ] ~

kernel.org | git.kernel.org | LWN.net | Project Home | Wiki (Japanese) | Wiki (English) | SVN repository | Mail admin

Linux® is a registered trademark of Linus Torvalds in the United States and other countries.
TOMOYO® is a registered trademark of NTT DATA CORPORATION.

osdn.jp