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
74 #if defined(CC_HAVE_ASM_GOTO) && defined(CONFIG_JUMP_LABEL)
75 # define HAVE_JUMP_LABEL
80 #include <linux/types.h>
81 #include <linux/compiler.h>
83 extern bool static_key_initialized
;
85 #define STATIC_KEY_CHECK_USE() WARN(!static_key_initialized, \
86 "%s used before call to jump_label_init", \
89 #ifdef HAVE_JUMP_LABEL
95 * To make anonymous unions work with old compilers, the static
96 * initialization of them requires brackets. This creates a dependency
97 * on the order of the struct with the initializers. If any fields
98 * are added, STATIC_KEY_INIT_TRUE and STATIC_KEY_INIT_FALSE may need
101 * bit 0 => 1 if key is initially true
102 * 0 if initially false
103 * bit 1 => 1 if points to struct static_key_mod
104 * 0 if points to struct jump_entry
108 struct jump_entry
*entries
;
109 struct static_key_mod
*next
;
117 #endif /* HAVE_JUMP_LABEL */
118 #endif /* __ASSEMBLY__ */
120 #ifdef HAVE_JUMP_LABEL
121 #include <asm/jump_label.h>
126 enum jump_label_type
{
133 #ifdef HAVE_JUMP_LABEL
135 #define JUMP_TYPE_FALSE 0UL
136 #define JUMP_TYPE_TRUE 1UL
137 #define JUMP_TYPE_LINKED 2UL
138 #define JUMP_TYPE_MASK 3UL
140 static __always_inline
bool static_key_false(struct static_key
*key
)
142 return arch_static_branch(key
, false);
145 static __always_inline
bool static_key_true(struct static_key
*key
)
147 return !arch_static_branch(key
, true);
150 extern struct jump_entry __start___jump_table
[];
151 extern struct jump_entry __stop___jump_table
[];
153 extern void jump_label_init(void);
154 extern void jump_label_lock(void);
155 extern void jump_label_unlock(void);
156 extern void arch_jump_label_transform(struct jump_entry
*entry
,
157 enum jump_label_type type
);
158 extern void arch_jump_label_transform_static(struct jump_entry
*entry
,
159 enum jump_label_type type
);
160 extern int jump_label_text_reserved(void *start
, void *end
);
161 extern void static_key_slow_inc(struct static_key
*key
);
162 extern void static_key_slow_dec(struct static_key
*key
);
163 extern void jump_label_apply_nops(struct module
*mod
);
164 extern int static_key_count(struct static_key
*key
);
165 extern void static_key_enable(struct static_key
*key
);
166 extern void static_key_disable(struct static_key
*key
);
167 extern void static_key_enable_cpuslocked(struct static_key
*key
);
168 extern void static_key_disable_cpuslocked(struct static_key
*key
);
171 * We should be using ATOMIC_INIT() for initializing .enabled, but
172 * the inclusion of atomic.h is problematic for inclusion of jump_label.h
173 * in 'low-level' headers. Thus, we are initializing .enabled with a
174 * raw value, but have added a BUILD_BUG_ON() to catch any issues in
175 * jump_label_init() see: kernel/jump_label.c.
177 #define STATIC_KEY_INIT_TRUE \
178 { .enabled = { 1 }, \
179 { .entries = (void *)JUMP_TYPE_TRUE } }
180 #define STATIC_KEY_INIT_FALSE \
181 { .enabled = { 0 }, \
182 { .entries = (void *)JUMP_TYPE_FALSE } }
184 #else /* !HAVE_JUMP_LABEL */
186 #include <linux/atomic.h>
187 #include <linux/bug.h>
189 static inline int static_key_count(struct static_key
*key
)
191 return atomic_read(&key
->enabled
);
194 static __always_inline
void jump_label_init(void)
196 static_key_initialized
= true;
199 static __always_inline
bool static_key_false(struct static_key
*key
)
201 if (unlikely(static_key_count(key
) > 0))
206 static __always_inline
bool static_key_true(struct static_key
*key
)
208 if (likely(static_key_count(key
) > 0))
213 static inline void static_key_slow_inc(struct static_key
*key
)
215 STATIC_KEY_CHECK_USE();
216 atomic_inc(&key
->enabled
);
219 static inline void static_key_slow_dec(struct static_key
*key
)
221 STATIC_KEY_CHECK_USE();
222 atomic_dec(&key
->enabled
);
225 static inline int jump_label_text_reserved(void *start
, void *end
)
230 static inline void jump_label_lock(void) {}
231 static inline void jump_label_unlock(void) {}
233 static inline int jump_label_apply_nops(struct module
*mod
)
238 static inline void static_key_enable(struct static_key
*key
)
240 STATIC_KEY_CHECK_USE();
242 if (atomic_read(&key
->enabled
) != 0) {
243 WARN_ON_ONCE(atomic_read(&key
->enabled
) != 1);
246 atomic_set(&key
->enabled
, 1);
249 static inline void static_key_disable(struct static_key
*key
)
251 STATIC_KEY_CHECK_USE();
253 if (atomic_read(&key
->enabled
) != 1) {
254 WARN_ON_ONCE(atomic_read(&key
->enabled
) != 0);
257 atomic_set(&key
->enabled
, 0);
260 #define static_key_enable_cpuslocked(k) static_key_enable((k))
261 #define static_key_disable_cpuslocked(k) static_key_disable((k))
263 #define STATIC_KEY_INIT_TRUE { .enabled = ATOMIC_INIT(1) }
264 #define STATIC_KEY_INIT_FALSE { .enabled = ATOMIC_INIT(0) }
266 #endif /* HAVE_JUMP_LABEL */
268 #define STATIC_KEY_INIT STATIC_KEY_INIT_FALSE
269 #define jump_label_enabled static_key_enabled
271 /* -------------------------------------------------------------------------- */
274 * Two type wrappers around static_key, such that we can use compile time
275 * type differentiation to emit the right code.
277 * All the below code is macros in order to play type games.
280 struct static_key_true
{
281 struct static_key key
;
284 struct static_key_false
{
285 struct static_key key
;
288 #define STATIC_KEY_TRUE_INIT (struct static_key_true) { .key = STATIC_KEY_INIT_TRUE, }
289 #define STATIC_KEY_FALSE_INIT (struct static_key_false){ .key = STATIC_KEY_INIT_FALSE, }
291 #define DEFINE_STATIC_KEY_TRUE(name) \
292 struct static_key_true name = STATIC_KEY_TRUE_INIT
294 #define DECLARE_STATIC_KEY_TRUE(name) \
295 extern struct static_key_true name
297 #define DEFINE_STATIC_KEY_FALSE(name) \
298 struct static_key_false name = STATIC_KEY_FALSE_INIT
300 #define DECLARE_STATIC_KEY_FALSE(name) \
301 extern struct static_key_false name
303 #define DEFINE_STATIC_KEY_ARRAY_TRUE(name, count) \
304 struct static_key_true name[count] = { \
305 [0 ... (count) - 1] = STATIC_KEY_TRUE_INIT, \
308 #define DEFINE_STATIC_KEY_ARRAY_FALSE(name, count) \
309 struct static_key_false name[count] = { \
310 [0 ... (count) - 1] = STATIC_KEY_FALSE_INIT, \
313 extern bool ____wrong_branch_error(void);
315 #define static_key_enabled(x) \
317 if (!__builtin_types_compatible_p(typeof(*x), struct static_key) && \
318 !__builtin_types_compatible_p(typeof(*x), struct static_key_true) &&\
319 !__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \
320 ____wrong_branch_error(); \
321 static_key_count((struct static_key *)x) > 0; \
324 #ifdef HAVE_JUMP_LABEL
327 * Combine the right initial value (type) with the right branch order
328 * to generate the desired result.
331 * type\branch| likely (1) | unlikely (0)
332 * -----------+-----------------------+------------------
334 * true (1) | ... | ...
336 * | <br-stmts> | 1: ...
342 * -----------+-----------------------+------------------
344 * false (0) | ... | ...
346 * | <br-stmts> | 1: ...
352 * -----------+-----------------------+------------------
354 * The initial value is encoded in the LSB of static_key::entries,
355 * type: 0 = false, 1 = true.
357 * The branch type is encoded in the LSB of jump_entry::key,
358 * branch: 0 = unlikely, 1 = likely.
360 * This gives the following logic table:
362 * enabled type branch instuction
363 * -----------------------------+-----------
374 * Which gives the following functions:
376 * dynamic: instruction = enabled ^ branch
377 * static: instruction = type ^ branch
379 * See jump_label_type() / jump_label_init_type().
382 #define static_branch_likely(x) \
385 if (__builtin_types_compatible_p(typeof(*x), struct static_key_true)) \
386 branch = !arch_static_branch(&(x)->key, true); \
387 else if (__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \
388 branch = !arch_static_branch_jump(&(x)->key, true); \
390 branch = ____wrong_branch_error(); \
394 #define static_branch_unlikely(x) \
397 if (__builtin_types_compatible_p(typeof(*x), struct static_key_true)) \
398 branch = arch_static_branch_jump(&(x)->key, false); \
399 else if (__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \
400 branch = arch_static_branch(&(x)->key, false); \
402 branch = ____wrong_branch_error(); \
406 #else /* !HAVE_JUMP_LABEL */
408 #define static_branch_likely(x) likely(static_key_enabled(&(x)->key))
409 #define static_branch_unlikely(x) unlikely(static_key_enabled(&(x)->key))
411 #endif /* HAVE_JUMP_LABEL */
414 * Advanced usage; refcount, branch is enabled when: count != 0
417 #define static_branch_inc(x) static_key_slow_inc(&(x)->key)
418 #define static_branch_dec(x) static_key_slow_dec(&(x)->key)
421 * Normal usage; boolean enable/disable.
424 #define static_branch_enable(x) static_key_enable(&(x)->key)
425 #define static_branch_disable(x) static_key_disable(&(x)->key)
426 #define static_branch_enable_cpuslocked(x) static_key_enable_cpuslocked(&(x)->key)
427 #define static_branch_disable_cpuslocked(x) static_key_disable_cpuslocked(&(x)->key)
429 #endif /* __ASSEMBLY__ */
431 #endif /* _LINUX_JUMP_LABEL_H */