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/staging/static-keys.rst
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()", \
87 #ifdef CONFIG_JUMP_LABEL
90 * To make anonymous unions work with old compilers, the static
91 * initialization of them requires brackets. This creates a dependency
92 * on the order of the struct with the initializers. If any fields
93 * are added, STATIC_KEY_INIT_TRUE and STATIC_KEY_INIT_FALSE may need
96 * bit 0 => 1 if key is initially true
97 * 0 if initially false
98 * bit 1 => 1 if points to struct static_key_mod
99 * 0 if points to struct jump_entry
103 struct jump_entry *entries;
104 struct static_key_mod *next;
106 #endif /* CONFIG_JUMP_LABEL */
109 #endif /* __ASSEMBLY__ */
111 #ifdef CONFIG_JUMP_LABEL
112 #include <asm/jump_label.h>
115 #ifdef CONFIG_HAVE_ARCH_JUMP_LABEL_RELATIVE
120 long key; // key may be far away from the core kernel under KASLR
123 static inline unsigned long jump_entry_code(const struct jump_entry *entry)
125 return (unsigned long)&entry->code + entry->code;
128 static inline unsigned long jump_entry_target(const struct jump_entry *entry)
130 return (unsigned long)&entry->target + entry->target;
133 static inline struct static_key *jump_entry_key(const struct jump_entry *entry)
135 long offset = entry->key & ~3L;
137 return (struct static_key *)((unsigned long)&entry->key + offset);
142 static inline unsigned long jump_entry_code(const struct jump_entry *entry)
147 static inline unsigned long jump_entry_target(const struct jump_entry *entry)
149 return entry->target;
152 static inline struct static_key *jump_entry_key(const struct jump_entry *entry)
154 return (struct static_key *)((unsigned long)entry->key & ~3UL);
159 static inline bool jump_entry_is_branch(const struct jump_entry *entry)
161 return (unsigned long)entry->key & 1UL;
164 static inline bool jump_entry_is_init(const struct jump_entry *entry)
166 return (unsigned long)entry->key & 2UL;
169 static inline void jump_entry_set_init(struct jump_entry *entry, bool set)
177 static inline int jump_entry_size(struct jump_entry *entry)
179 #ifdef JUMP_LABEL_NOP_SIZE
180 return JUMP_LABEL_NOP_SIZE;
182 return arch_jump_entry_size(entry);
191 enum jump_label_type {
198 #ifdef CONFIG_JUMP_LABEL
200 #define JUMP_TYPE_FALSE 0UL
201 #define JUMP_TYPE_TRUE 1UL
202 #define JUMP_TYPE_LINKED 2UL
203 #define JUMP_TYPE_MASK 3UL
205 static __always_inline bool static_key_false(struct static_key *key)
207 return arch_static_branch(key, false);
210 static __always_inline bool static_key_true(struct static_key *key)
212 return !arch_static_branch(key, true);
215 extern struct jump_entry __start___jump_table[];
216 extern struct jump_entry __stop___jump_table[];
218 extern void jump_label_init(void);
219 extern void jump_label_lock(void);
220 extern void jump_label_unlock(void);
221 extern void arch_jump_label_transform(struct jump_entry *entry,
222 enum jump_label_type type);
223 extern void arch_jump_label_transform_static(struct jump_entry *entry,
224 enum jump_label_type type);
225 extern bool arch_jump_label_transform_queue(struct jump_entry *entry,
226 enum jump_label_type type);
227 extern void arch_jump_label_transform_apply(void);
228 extern int jump_label_text_reserved(void *start, void *end);
229 extern void static_key_slow_inc(struct static_key *key);
230 extern void static_key_slow_dec(struct static_key *key);
231 extern void static_key_slow_inc_cpuslocked(struct static_key *key);
232 extern void static_key_slow_dec_cpuslocked(struct static_key *key);
233 extern void jump_label_apply_nops(struct module *mod);
234 extern int static_key_count(struct static_key *key);
235 extern void static_key_enable(struct static_key *key);
236 extern void static_key_disable(struct static_key *key);
237 extern void static_key_enable_cpuslocked(struct static_key *key);
238 extern void static_key_disable_cpuslocked(struct static_key *key);
241 * We should be using ATOMIC_INIT() for initializing .enabled, but
242 * the inclusion of atomic.h is problematic for inclusion of jump_label.h
243 * in 'low-level' headers. Thus, we are initializing .enabled with a
244 * raw value, but have added a BUILD_BUG_ON() to catch any issues in
245 * jump_label_init() see: kernel/jump_label.c.
247 #define STATIC_KEY_INIT_TRUE \
248 { .enabled = { 1 }, \
249 { .type = JUMP_TYPE_TRUE } }
250 #define STATIC_KEY_INIT_FALSE \
251 { .enabled = { 0 }, \
252 { .type = JUMP_TYPE_FALSE } }
254 #else /* !CONFIG_JUMP_LABEL */
256 #include <linux/atomic.h>
257 #include <linux/bug.h>
259 static inline int static_key_count(struct static_key *key)
261 return atomic_read(&key->enabled);
264 static __always_inline void jump_label_init(void)
266 static_key_initialized = true;
269 static __always_inline bool static_key_false(struct static_key *key)
271 if (unlikely_notrace(static_key_count(key) > 0))
276 static __always_inline bool static_key_true(struct static_key *key)
278 if (likely_notrace(static_key_count(key) > 0))
283 static inline void static_key_slow_inc(struct static_key *key)
285 STATIC_KEY_CHECK_USE(key);
286 atomic_inc(&key->enabled);
289 static inline void static_key_slow_dec(struct static_key *key)
291 STATIC_KEY_CHECK_USE(key);
292 atomic_dec(&key->enabled);
295 #define static_key_slow_inc_cpuslocked(key) static_key_slow_inc(key)
296 #define static_key_slow_dec_cpuslocked(key) static_key_slow_dec(key)
298 static inline int jump_label_text_reserved(void *start, void *end)
303 static inline void jump_label_lock(void) {}
304 static inline void jump_label_unlock(void) {}
306 static inline int jump_label_apply_nops(struct module *mod)
311 static inline void static_key_enable(struct static_key *key)
313 STATIC_KEY_CHECK_USE(key);
315 if (atomic_read(&key->enabled) != 0) {
316 WARN_ON_ONCE(atomic_read(&key->enabled) != 1);
319 atomic_set(&key->enabled, 1);
322 static inline void static_key_disable(struct static_key *key)
324 STATIC_KEY_CHECK_USE(key);
326 if (atomic_read(&key->enabled) != 1) {
327 WARN_ON_ONCE(atomic_read(&key->enabled) != 0);
330 atomic_set(&key->enabled, 0);
333 #define static_key_enable_cpuslocked(k) static_key_enable((k))
334 #define static_key_disable_cpuslocked(k) static_key_disable((k))
336 #define STATIC_KEY_INIT_TRUE { .enabled = ATOMIC_INIT(1) }
337 #define STATIC_KEY_INIT_FALSE { .enabled = ATOMIC_INIT(0) }
339 #endif /* CONFIG_JUMP_LABEL */
341 #define STATIC_KEY_INIT STATIC_KEY_INIT_FALSE
342 #define jump_label_enabled static_key_enabled
344 /* -------------------------------------------------------------------------- */
347 * Two type wrappers around static_key, such that we can use compile time
348 * type differentiation to emit the right code.
350 * All the below code is macros in order to play type games.
353 struct static_key_true {
354 struct static_key key;
357 struct static_key_false {
358 struct static_key key;
361 #define STATIC_KEY_TRUE_INIT (struct static_key_true) { .key = STATIC_KEY_INIT_TRUE, }
362 #define STATIC_KEY_FALSE_INIT (struct static_key_false){ .key = STATIC_KEY_INIT_FALSE, }
364 #define DEFINE_STATIC_KEY_TRUE(name) \
365 struct static_key_true name = STATIC_KEY_TRUE_INIT
367 #define DEFINE_STATIC_KEY_TRUE_RO(name) \
368 struct static_key_true name __ro_after_init = STATIC_KEY_TRUE_INIT
370 #define DECLARE_STATIC_KEY_TRUE(name) \
371 extern struct static_key_true name
373 #define DEFINE_STATIC_KEY_FALSE(name) \
374 struct static_key_false name = STATIC_KEY_FALSE_INIT
376 #define DEFINE_STATIC_KEY_FALSE_RO(name) \
377 struct static_key_false name __ro_after_init = STATIC_KEY_FALSE_INIT
379 #define DECLARE_STATIC_KEY_FALSE(name) \
380 extern struct static_key_false name
382 #define DEFINE_STATIC_KEY_ARRAY_TRUE(name, count) \
383 struct static_key_true name[count] = { \
384 [0 ... (count) - 1] = STATIC_KEY_TRUE_INIT, \
387 #define DEFINE_STATIC_KEY_ARRAY_FALSE(name, count) \
388 struct static_key_false name[count] = { \
389 [0 ... (count) - 1] = STATIC_KEY_FALSE_INIT, \
392 #define _DEFINE_STATIC_KEY_1(name) DEFINE_STATIC_KEY_TRUE(name)
393 #define _DEFINE_STATIC_KEY_0(name) DEFINE_STATIC_KEY_FALSE(name)
394 #define DEFINE_STATIC_KEY_MAYBE(cfg, name) \
395 __PASTE(_DEFINE_STATIC_KEY_, IS_ENABLED(cfg))(name)
397 #define _DEFINE_STATIC_KEY_RO_1(name) DEFINE_STATIC_KEY_TRUE_RO(name)
398 #define _DEFINE_STATIC_KEY_RO_0(name) DEFINE_STATIC_KEY_FALSE_RO(name)
399 #define DEFINE_STATIC_KEY_MAYBE_RO(cfg, name) \
400 __PASTE(_DEFINE_STATIC_KEY_RO_, IS_ENABLED(cfg))(name)
402 #define _DECLARE_STATIC_KEY_1(name) DECLARE_STATIC_KEY_TRUE(name)
403 #define _DECLARE_STATIC_KEY_0(name) DECLARE_STATIC_KEY_FALSE(name)
404 #define DECLARE_STATIC_KEY_MAYBE(cfg, name) \
405 __PASTE(_DECLARE_STATIC_KEY_, IS_ENABLED(cfg))(name)
407 extern bool ____wrong_branch_error(void);
409 #define static_key_enabled(x) \
411 if (!__builtin_types_compatible_p(typeof(*x), struct static_key) && \
412 !__builtin_types_compatible_p(typeof(*x), struct static_key_true) &&\
413 !__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \
414 ____wrong_branch_error(); \
415 static_key_count((struct static_key *)x) > 0; \
418 #ifdef CONFIG_JUMP_LABEL
421 * Combine the right initial value (type) with the right branch order
422 * to generate the desired result.
425 * type\branch| likely (1) | unlikely (0)
426 * -----------+-----------------------+------------------
428 * true (1) | ... | ...
430 * | <br-stmts> | 1: ...
436 * -----------+-----------------------+------------------
438 * false (0) | ... | ...
440 * | <br-stmts> | 1: ...
446 * -----------+-----------------------+------------------
448 * The initial value is encoded in the LSB of static_key::entries,
449 * type: 0 = false, 1 = true.
451 * The branch type is encoded in the LSB of jump_entry::key,
452 * branch: 0 = unlikely, 1 = likely.
454 * This gives the following logic table:
456 * enabled type branch instuction
457 * -----------------------------+-----------
468 * Which gives the following functions:
470 * dynamic: instruction = enabled ^ branch
471 * static: instruction = type ^ branch
473 * See jump_label_type() / jump_label_init_type().
476 #define static_branch_likely(x) \
479 if (__builtin_types_compatible_p(typeof(*x), struct static_key_true)) \
480 branch = !arch_static_branch(&(x)->key, true); \
481 else if (__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \
482 branch = !arch_static_branch_jump(&(x)->key, true); \
484 branch = ____wrong_branch_error(); \
485 likely_notrace(branch); \
488 #define static_branch_unlikely(x) \
491 if (__builtin_types_compatible_p(typeof(*x), struct static_key_true)) \
492 branch = arch_static_branch_jump(&(x)->key, false); \
493 else if (__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \
494 branch = arch_static_branch(&(x)->key, false); \
496 branch = ____wrong_branch_error(); \
497 unlikely_notrace(branch); \
500 #else /* !CONFIG_JUMP_LABEL */
502 #define static_branch_likely(x) likely_notrace(static_key_enabled(&(x)->key))
503 #define static_branch_unlikely(x) unlikely_notrace(static_key_enabled(&(x)->key))
505 #endif /* CONFIG_JUMP_LABEL */
507 #define static_branch_maybe(config, x) \
508 (IS_ENABLED(config) ? static_branch_likely(x) \
509 : static_branch_unlikely(x))
512 * Advanced usage; refcount, branch is enabled when: count != 0
515 #define static_branch_inc(x) static_key_slow_inc(&(x)->key)
516 #define static_branch_dec(x) static_key_slow_dec(&(x)->key)
517 #define static_branch_inc_cpuslocked(x) static_key_slow_inc_cpuslocked(&(x)->key)
518 #define static_branch_dec_cpuslocked(x) static_key_slow_dec_cpuslocked(&(x)->key)
521 * Normal usage; boolean enable/disable.
524 #define static_branch_enable(x) static_key_enable(&(x)->key)
525 #define static_branch_disable(x) static_key_disable(&(x)->key)
526 #define static_branch_enable_cpuslocked(x) static_key_enable_cpuslocked(&(x)->key)
527 #define static_branch_disable_cpuslocked(x) static_key_disable_cpuslocked(&(x)->key)
529 #endif /* __ASSEMBLY__ */
531 #endif /* _LINUX_JUMP_LABEL_H */