1 /* SPDX-License-Identifier: GPL-2.0 */
2 #ifndef _LINUX_JUMP_LABEL_H
3 #define _LINUX_JUMP_LABEL_H
8 * Copyright (C) 2009-2012 Jason Baron <jbaron@redhat.com>
9 * Copyright (C) 2011-2012 Red Hat, Inc., Peter Zijlstra
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:
16 * struct static_key false = STATIC_KEY_INIT_FALSE;
17 * struct static_key true = STATIC_KEY_INIT_TRUE;
21 * The updated API replacements are:
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()
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.
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.
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'.
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.
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.
68 * Lacking toolchain and or architecture support, static keys fall back to a
69 * simple conditional branch.
71 * Additional babbling in: Documentation/static-keys.txt
76 #include <linux/types.h>
77 #include <linux/compiler.h>
79 extern bool static_key_initialized;
81 #define STATIC_KEY_CHECK_USE(key) WARN(!static_key_initialized, \
82 "%s(): static key '%pS' used before call to jump_label_init()", \
85 #ifdef CONFIG_JUMP_LABEL
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
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
104 struct jump_entry *entries;
105 struct static_key_mod *next;
113 #endif /* CONFIG_JUMP_LABEL */
114 #endif /* __ASSEMBLY__ */
116 #ifdef CONFIG_JUMP_LABEL
117 #include <asm/jump_label.h>
120 #ifdef CONFIG_HAVE_ARCH_JUMP_LABEL_RELATIVE
125 long key; // key may be far away from the core kernel under KASLR
128 static inline unsigned long jump_entry_code(const struct jump_entry *entry)
130 return (unsigned long)&entry->code + entry->code;
133 static inline unsigned long jump_entry_target(const struct jump_entry *entry)
135 return (unsigned long)&entry->target + entry->target;
138 static inline struct static_key *jump_entry_key(const struct jump_entry *entry)
140 long offset = entry->key & ~3L;
142 return (struct static_key *)((unsigned long)&entry->key + offset);
147 static inline unsigned long jump_entry_code(const struct jump_entry *entry)
152 static inline unsigned long jump_entry_target(const struct jump_entry *entry)
154 return entry->target;
157 static inline struct static_key *jump_entry_key(const struct jump_entry *entry)
159 return (struct static_key *)((unsigned long)entry->key & ~3UL);
164 static inline bool jump_entry_is_branch(const struct jump_entry *entry)
166 return (unsigned long)entry->key & 1UL;
169 static inline bool jump_entry_is_init(const struct jump_entry *entry)
171 return (unsigned long)entry->key & 2UL;
174 static inline void jump_entry_set_init(struct jump_entry *entry)
184 enum jump_label_type {
191 #ifdef CONFIG_JUMP_LABEL
193 #define JUMP_TYPE_FALSE 0UL
194 #define JUMP_TYPE_TRUE 1UL
195 #define JUMP_TYPE_LINKED 2UL
196 #define JUMP_TYPE_MASK 3UL
198 static __always_inline bool static_key_false(struct static_key *key)
200 return arch_static_branch(key, false);
203 static __always_inline bool static_key_true(struct static_key *key)
205 return !arch_static_branch(key, true);
208 extern struct jump_entry __start___jump_table[];
209 extern struct jump_entry __stop___jump_table[];
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 int jump_label_text_reserved(void *start, void *end);
219 extern void static_key_slow_inc(struct static_key *key);
220 extern void static_key_slow_dec(struct static_key *key);
221 extern void static_key_slow_inc_cpuslocked(struct static_key *key);
222 extern void static_key_slow_dec_cpuslocked(struct static_key *key);
223 extern void jump_label_apply_nops(struct module *mod);
224 extern int static_key_count(struct static_key *key);
225 extern void static_key_enable(struct static_key *key);
226 extern void static_key_disable(struct static_key *key);
227 extern void static_key_enable_cpuslocked(struct static_key *key);
228 extern void static_key_disable_cpuslocked(struct static_key *key);
231 * We should be using ATOMIC_INIT() for initializing .enabled, but
232 * the inclusion of atomic.h is problematic for inclusion of jump_label.h
233 * in 'low-level' headers. Thus, we are initializing .enabled with a
234 * raw value, but have added a BUILD_BUG_ON() to catch any issues in
235 * jump_label_init() see: kernel/jump_label.c.
237 #define STATIC_KEY_INIT_TRUE \
238 { .enabled = { 1 }, \
239 { .entries = (void *)JUMP_TYPE_TRUE } }
240 #define STATIC_KEY_INIT_FALSE \
241 { .enabled = { 0 }, \
242 { .entries = (void *)JUMP_TYPE_FALSE } }
244 #else /* !CONFIG_JUMP_LABEL */
246 #include <linux/atomic.h>
247 #include <linux/bug.h>
249 static inline int static_key_count(struct static_key *key)
251 return atomic_read(&key->enabled);
254 static __always_inline void jump_label_init(void)
256 static_key_initialized = true;
259 static __always_inline bool static_key_false(struct static_key *key)
261 if (unlikely(static_key_count(key) > 0))
266 static __always_inline bool static_key_true(struct static_key *key)
268 if (likely(static_key_count(key) > 0))
273 static inline void static_key_slow_inc(struct static_key *key)
275 STATIC_KEY_CHECK_USE(key);
276 atomic_inc(&key->enabled);
279 static inline void static_key_slow_dec(struct static_key *key)
281 STATIC_KEY_CHECK_USE(key);
282 atomic_dec(&key->enabled);
285 #define static_key_slow_inc_cpuslocked(key) static_key_slow_inc(key)
286 #define static_key_slow_dec_cpuslocked(key) static_key_slow_dec(key)
288 static inline int jump_label_text_reserved(void *start, void *end)
293 static inline void jump_label_lock(void) {}
294 static inline void jump_label_unlock(void) {}
296 static inline int jump_label_apply_nops(struct module *mod)
301 static inline void static_key_enable(struct static_key *key)
303 STATIC_KEY_CHECK_USE(key);
305 if (atomic_read(&key->enabled) != 0) {
306 WARN_ON_ONCE(atomic_read(&key->enabled) != 1);
309 atomic_set(&key->enabled, 1);
312 static inline void static_key_disable(struct static_key *key)
314 STATIC_KEY_CHECK_USE(key);
316 if (atomic_read(&key->enabled) != 1) {
317 WARN_ON_ONCE(atomic_read(&key->enabled) != 0);
320 atomic_set(&key->enabled, 0);
323 #define static_key_enable_cpuslocked(k) static_key_enable((k))
324 #define static_key_disable_cpuslocked(k) static_key_disable((k))
326 #define STATIC_KEY_INIT_TRUE { .enabled = ATOMIC_INIT(1) }
327 #define STATIC_KEY_INIT_FALSE { .enabled = ATOMIC_INIT(0) }
329 #endif /* CONFIG_JUMP_LABEL */
331 #define STATIC_KEY_INIT STATIC_KEY_INIT_FALSE
332 #define jump_label_enabled static_key_enabled
334 /* -------------------------------------------------------------------------- */
337 * Two type wrappers around static_key, such that we can use compile time
338 * type differentiation to emit the right code.
340 * All the below code is macros in order to play type games.
343 struct static_key_true {
344 struct static_key key;
347 struct static_key_false {
348 struct static_key key;
351 #define STATIC_KEY_TRUE_INIT (struct static_key_true) { .key = STATIC_KEY_INIT_TRUE, }
352 #define STATIC_KEY_FALSE_INIT (struct static_key_false){ .key = STATIC_KEY_INIT_FALSE, }
354 #define DEFINE_STATIC_KEY_TRUE(name) \
355 struct static_key_true name = STATIC_KEY_TRUE_INIT
357 #define DEFINE_STATIC_KEY_TRUE_RO(name) \
358 struct static_key_true name __ro_after_init = STATIC_KEY_TRUE_INIT
360 #define DECLARE_STATIC_KEY_TRUE(name) \
361 extern struct static_key_true name
363 #define DEFINE_STATIC_KEY_FALSE(name) \
364 struct static_key_false name = STATIC_KEY_FALSE_INIT
366 #define DEFINE_STATIC_KEY_FALSE_RO(name) \
367 struct static_key_false name __ro_after_init = STATIC_KEY_FALSE_INIT
369 #define DECLARE_STATIC_KEY_FALSE(name) \
370 extern struct static_key_false name
372 #define DEFINE_STATIC_KEY_ARRAY_TRUE(name, count) \
373 struct static_key_true name[count] = { \
374 [0 ... (count) - 1] = STATIC_KEY_TRUE_INIT, \
377 #define DEFINE_STATIC_KEY_ARRAY_FALSE(name, count) \
378 struct static_key_false name[count] = { \
379 [0 ... (count) - 1] = STATIC_KEY_FALSE_INIT, \
382 extern bool ____wrong_branch_error(void);
384 #define static_key_enabled(x) \
386 if (!__builtin_types_compatible_p(typeof(*x), struct static_key) && \
387 !__builtin_types_compatible_p(typeof(*x), struct static_key_true) &&\
388 !__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \
389 ____wrong_branch_error(); \
390 static_key_count((struct static_key *)x) > 0; \
393 #ifdef CONFIG_JUMP_LABEL
396 * Combine the right initial value (type) with the right branch order
397 * to generate the desired result.
400 * type\branch| likely (1) | unlikely (0)
401 * -----------+-----------------------+------------------
403 * true (1) | ... | ...
405 * | <br-stmts> | 1: ...
411 * -----------+-----------------------+------------------
413 * false (0) | ... | ...
415 * | <br-stmts> | 1: ...
421 * -----------+-----------------------+------------------
423 * The initial value is encoded in the LSB of static_key::entries,
424 * type: 0 = false, 1 = true.
426 * The branch type is encoded in the LSB of jump_entry::key,
427 * branch: 0 = unlikely, 1 = likely.
429 * This gives the following logic table:
431 * enabled type branch instuction
432 * -----------------------------+-----------
443 * Which gives the following functions:
445 * dynamic: instruction = enabled ^ branch
446 * static: instruction = type ^ branch
448 * See jump_label_type() / jump_label_init_type().
451 #define static_branch_likely(x) \
454 if (__builtin_types_compatible_p(typeof(*x), struct static_key_true)) \
455 branch = !arch_static_branch(&(x)->key, true); \
456 else if (__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \
457 branch = !arch_static_branch_jump(&(x)->key, true); \
459 branch = ____wrong_branch_error(); \
463 #define static_branch_unlikely(x) \
466 if (__builtin_types_compatible_p(typeof(*x), struct static_key_true)) \
467 branch = arch_static_branch_jump(&(x)->key, false); \
468 else if (__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \
469 branch = arch_static_branch(&(x)->key, false); \
471 branch = ____wrong_branch_error(); \
475 #else /* !CONFIG_JUMP_LABEL */
477 #define static_branch_likely(x) likely(static_key_enabled(&(x)->key))
478 #define static_branch_unlikely(x) unlikely(static_key_enabled(&(x)->key))
480 #endif /* CONFIG_JUMP_LABEL */
483 * Advanced usage; refcount, branch is enabled when: count != 0
486 #define static_branch_inc(x) static_key_slow_inc(&(x)->key)
487 #define static_branch_dec(x) static_key_slow_dec(&(x)->key)
488 #define static_branch_inc_cpuslocked(x) static_key_slow_inc_cpuslocked(&(x)->key)
489 #define static_branch_dec_cpuslocked(x) static_key_slow_dec_cpuslocked(&(x)->key)
492 * Normal usage; boolean enable/disable.
495 #define static_branch_enable(x) static_key_enable(&(x)->key)
496 #define static_branch_disable(x) static_key_disable(&(x)->key)
497 #define static_branch_enable_cpuslocked(x) static_key_enable_cpuslocked(&(x)->key)
498 #define static_branch_disable_cpuslocked(x) static_key_disable_cpuslocked(&(x)->key)
500 #endif /* __ASSEMBLY__ */
502 #endif /* _LINUX_JUMP_LABEL_H */