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505 lines
15 KiB
505 lines
15 KiB
/* SPDX-License-Identifier: GPL-2.0 */ |
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#ifndef _LINUX_JUMP_LABEL_H |
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#define _LINUX_JUMP_LABEL_H |
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/* |
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* Jump label support |
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* |
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* Copyright (C) 2009-2012 Jason Baron <[email protected]> |
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* Copyright (C) 2011-2012 Red Hat, Inc., Peter Zijlstra |
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* |
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* DEPRECATED API: |
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* |
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* The use of 'struct static_key' directly, is now DEPRECATED. In addition |
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* static_key_{true,false}() is also DEPRECATED. IE DO NOT use the following: |
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* |
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* struct static_key false = STATIC_KEY_INIT_FALSE; |
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* struct static_key true = STATIC_KEY_INIT_TRUE; |
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* static_key_true() |
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* static_key_false() |
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* |
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* The updated API replacements are: |
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* |
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* DEFINE_STATIC_KEY_TRUE(key); |
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* DEFINE_STATIC_KEY_FALSE(key); |
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* DEFINE_STATIC_KEY_ARRAY_TRUE(keys, count); |
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* DEFINE_STATIC_KEY_ARRAY_FALSE(keys, count); |
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* static_branch_likely() |
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* static_branch_unlikely() |
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* |
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* Jump labels provide an interface to generate dynamic branches using |
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* self-modifying code. Assuming toolchain and architecture support, if we |
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* define a "key" that is initially false via "DEFINE_STATIC_KEY_FALSE(key)", |
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* an "if (static_branch_unlikely(&key))" statement is an unconditional branch |
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* (which defaults to false - and the true block is placed out of line). |
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* Similarly, we can define an initially true key via |
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* "DEFINE_STATIC_KEY_TRUE(key)", and use it in the same |
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* "if (static_branch_unlikely(&key))", in which case we will generate an |
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* unconditional branch to the out-of-line true branch. Keys that are |
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* initially true or false can be using in both static_branch_unlikely() |
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* and static_branch_likely() statements. |
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* |
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* At runtime we can change the branch target by setting the key |
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* to true via a call to static_branch_enable(), or false using |
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* static_branch_disable(). If the direction of the branch is switched by |
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* these calls then we run-time modify the branch target via a |
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* no-op -> jump or jump -> no-op conversion. For example, for an |
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* initially false key that is used in an "if (static_branch_unlikely(&key))" |
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* statement, setting the key to true requires us to patch in a jump |
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* to the out-of-line of true branch. |
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* |
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* In addition to static_branch_{enable,disable}, we can also reference count |
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* the key or branch direction via static_branch_{inc,dec}. Thus, |
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* static_branch_inc() can be thought of as a 'make more true' and |
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* static_branch_dec() as a 'make more false'. |
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* |
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* Since this relies on modifying code, the branch modifying functions |
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* must be considered absolute slow paths (machine wide synchronization etc.). |
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* OTOH, since the affected branches are unconditional, their runtime overhead |
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* will be absolutely minimal, esp. in the default (off) case where the total |
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* effect is a single NOP of appropriate size. The on case will patch in a jump |
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* to the out-of-line block. |
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* |
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* When the control is directly exposed to userspace, it is prudent to delay the |
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* decrement to avoid high frequency code modifications which can (and do) |
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* cause significant performance degradation. Struct static_key_deferred and |
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* static_key_slow_dec_deferred() provide for this. |
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* |
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* Lacking toolchain and or architecture support, static keys fall back to a |
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* simple conditional branch. |
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* |
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* Additional babbling in: Documentation/staging/static-keys.rst |
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*/ |
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#ifndef __ASSEMBLY__ |
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#include <linux/types.h> |
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#include <linux/compiler.h> |
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extern bool static_key_initialized; |
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#define STATIC_KEY_CHECK_USE(key) WARN(!static_key_initialized, \ |
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"%s(): static key '%pS' used before call to jump_label_init()", \ |
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__func__, (key)) |
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#ifdef CONFIG_JUMP_LABEL |
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struct static_key { |
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atomic_t enabled; |
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/* |
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* Note: |
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* To make anonymous unions work with old compilers, the static |
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* initialization of them requires brackets. This creates a dependency |
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* on the order of the struct with the initializers. If any fields |
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* are added, STATIC_KEY_INIT_TRUE and STATIC_KEY_INIT_FALSE may need |
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* to be modified. |
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* |
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* bit 0 => 1 if key is initially true |
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* 0 if initially false |
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* bit 1 => 1 if points to struct static_key_mod |
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* 0 if points to struct jump_entry |
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*/ |
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union { |
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unsigned long type; |
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struct jump_entry *entries; |
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struct static_key_mod *next; |
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}; |
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}; |
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#else |
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struct static_key { |
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atomic_t enabled; |
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}; |
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#endif /* CONFIG_JUMP_LABEL */ |
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#endif /* __ASSEMBLY__ */ |
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#ifdef CONFIG_JUMP_LABEL |
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#include <asm/jump_label.h> |
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#ifndef __ASSEMBLY__ |
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#ifdef CONFIG_HAVE_ARCH_JUMP_LABEL_RELATIVE |
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struct jump_entry { |
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s32 code; |
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s32 target; |
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long key; // key may be far away from the core kernel under KASLR |
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}; |
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static inline unsigned long jump_entry_code(const struct jump_entry *entry) |
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{ |
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return (unsigned long)&entry->code + entry->code; |
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} |
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static inline unsigned long jump_entry_target(const struct jump_entry *entry) |
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{ |
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return (unsigned long)&entry->target + entry->target; |
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} |
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static inline struct static_key *jump_entry_key(const struct jump_entry *entry) |
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{ |
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long offset = entry->key & ~3L; |
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return (struct static_key *)((unsigned long)&entry->key + offset); |
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} |
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#else |
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static inline unsigned long jump_entry_code(const struct jump_entry *entry) |
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{ |
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return entry->code; |
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} |
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static inline unsigned long jump_entry_target(const struct jump_entry *entry) |
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{ |
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return entry->target; |
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} |
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static inline struct static_key *jump_entry_key(const struct jump_entry *entry) |
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{ |
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return (struct static_key *)((unsigned long)entry->key & ~3UL); |
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} |
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#endif |
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static inline bool jump_entry_is_branch(const struct jump_entry *entry) |
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{ |
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return (unsigned long)entry->key & 1UL; |
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} |
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static inline bool jump_entry_is_init(const struct jump_entry *entry) |
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{ |
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return (unsigned long)entry->key & 2UL; |
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} |
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static inline void jump_entry_set_init(struct jump_entry *entry) |
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{ |
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entry->key |= 2; |
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} |
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#endif |
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#endif |
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#ifndef __ASSEMBLY__ |
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enum jump_label_type { |
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JUMP_LABEL_NOP = 0, |
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JUMP_LABEL_JMP, |
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}; |
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struct module; |
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#ifdef CONFIG_JUMP_LABEL |
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#define JUMP_TYPE_FALSE 0UL |
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#define JUMP_TYPE_TRUE 1UL |
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#define JUMP_TYPE_LINKED 2UL |
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#define JUMP_TYPE_MASK 3UL |
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static __always_inline bool static_key_false(struct static_key *key) |
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{ |
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return arch_static_branch(key, false); |
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} |
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static __always_inline bool static_key_true(struct static_key *key) |
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{ |
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return !arch_static_branch(key, true); |
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} |
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extern struct jump_entry __start___jump_table[]; |
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extern struct jump_entry __stop___jump_table[]; |
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extern void jump_label_init(void); |
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extern void jump_label_lock(void); |
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extern void jump_label_unlock(void); |
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extern void arch_jump_label_transform(struct jump_entry *entry, |
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enum jump_label_type type); |
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extern void arch_jump_label_transform_static(struct jump_entry *entry, |
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enum jump_label_type type); |
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extern bool arch_jump_label_transform_queue(struct jump_entry *entry, |
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enum jump_label_type type); |
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extern void arch_jump_label_transform_apply(void); |
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extern int jump_label_text_reserved(void *start, void *end); |
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extern void static_key_slow_inc(struct static_key *key); |
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extern void static_key_slow_dec(struct static_key *key); |
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extern void static_key_slow_inc_cpuslocked(struct static_key *key); |
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extern void static_key_slow_dec_cpuslocked(struct static_key *key); |
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extern void jump_label_apply_nops(struct module *mod); |
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extern int static_key_count(struct static_key *key); |
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extern void static_key_enable(struct static_key *key); |
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extern void static_key_disable(struct static_key *key); |
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extern void static_key_enable_cpuslocked(struct static_key *key); |
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extern void static_key_disable_cpuslocked(struct static_key *key); |
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/* |
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* We should be using ATOMIC_INIT() for initializing .enabled, but |
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* the inclusion of atomic.h is problematic for inclusion of jump_label.h |
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* in 'low-level' headers. Thus, we are initializing .enabled with a |
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* raw value, but have added a BUILD_BUG_ON() to catch any issues in |
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* jump_label_init() see: kernel/jump_label.c. |
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*/ |
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#define STATIC_KEY_INIT_TRUE \ |
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{ .enabled = { 1 }, \ |
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{ .entries = (void *)JUMP_TYPE_TRUE } } |
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#define STATIC_KEY_INIT_FALSE \ |
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{ .enabled = { 0 }, \ |
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{ .entries = (void *)JUMP_TYPE_FALSE } } |
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#else /* !CONFIG_JUMP_LABEL */ |
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#include <linux/atomic.h> |
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#include <linux/bug.h> |
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static inline int static_key_count(struct static_key *key) |
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{ |
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return atomic_read(&key->enabled); |
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} |
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static __always_inline void jump_label_init(void) |
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{ |
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static_key_initialized = true; |
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} |
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static __always_inline bool static_key_false(struct static_key *key) |
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{ |
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if (unlikely_notrace(static_key_count(key) > 0)) |
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return true; |
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return false; |
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} |
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static __always_inline bool static_key_true(struct static_key *key) |
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{ |
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if (likely_notrace(static_key_count(key) > 0)) |
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return true; |
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return false; |
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} |
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static inline void static_key_slow_inc(struct static_key *key) |
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{ |
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STATIC_KEY_CHECK_USE(key); |
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atomic_inc(&key->enabled); |
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} |
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static inline void static_key_slow_dec(struct static_key *key) |
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{ |
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STATIC_KEY_CHECK_USE(key); |
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atomic_dec(&key->enabled); |
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} |
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#define static_key_slow_inc_cpuslocked(key) static_key_slow_inc(key) |
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#define static_key_slow_dec_cpuslocked(key) static_key_slow_dec(key) |
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static inline int jump_label_text_reserved(void *start, void *end) |
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{ |
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return 0; |
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} |
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static inline void jump_label_lock(void) {} |
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static inline void jump_label_unlock(void) {} |
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static inline int jump_label_apply_nops(struct module *mod) |
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{ |
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return 0; |
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} |
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static inline void static_key_enable(struct static_key *key) |
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{ |
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STATIC_KEY_CHECK_USE(key); |
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if (atomic_read(&key->enabled) != 0) { |
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WARN_ON_ONCE(atomic_read(&key->enabled) != 1); |
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return; |
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} |
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atomic_set(&key->enabled, 1); |
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} |
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static inline void static_key_disable(struct static_key *key) |
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{ |
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STATIC_KEY_CHECK_USE(key); |
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if (atomic_read(&key->enabled) != 1) { |
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WARN_ON_ONCE(atomic_read(&key->enabled) != 0); |
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return; |
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} |
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atomic_set(&key->enabled, 0); |
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} |
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#define static_key_enable_cpuslocked(k) static_key_enable((k)) |
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#define static_key_disable_cpuslocked(k) static_key_disable((k)) |
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#define STATIC_KEY_INIT_TRUE { .enabled = ATOMIC_INIT(1) } |
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#define STATIC_KEY_INIT_FALSE { .enabled = ATOMIC_INIT(0) } |
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#endif /* CONFIG_JUMP_LABEL */ |
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#define STATIC_KEY_INIT STATIC_KEY_INIT_FALSE |
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#define jump_label_enabled static_key_enabled |
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/* -------------------------------------------------------------------------- */ |
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/* |
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* Two type wrappers around static_key, such that we can use compile time |
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* type differentiation to emit the right code. |
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* |
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* All the below code is macros in order to play type games. |
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*/ |
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struct static_key_true { |
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struct static_key key; |
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}; |
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struct static_key_false { |
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struct static_key key; |
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}; |
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#define STATIC_KEY_TRUE_INIT (struct static_key_true) { .key = STATIC_KEY_INIT_TRUE, } |
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#define STATIC_KEY_FALSE_INIT (struct static_key_false){ .key = STATIC_KEY_INIT_FALSE, } |
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#define DEFINE_STATIC_KEY_TRUE(name) \ |
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struct static_key_true name = STATIC_KEY_TRUE_INIT |
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#define DEFINE_STATIC_KEY_TRUE_RO(name) \ |
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struct static_key_true name __ro_after_init = STATIC_KEY_TRUE_INIT |
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#define DECLARE_STATIC_KEY_TRUE(name) \ |
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extern struct static_key_true name |
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#define DEFINE_STATIC_KEY_FALSE(name) \ |
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struct static_key_false name = STATIC_KEY_FALSE_INIT |
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#define DEFINE_STATIC_KEY_FALSE_RO(name) \ |
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struct static_key_false name __ro_after_init = STATIC_KEY_FALSE_INIT |
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#define DECLARE_STATIC_KEY_FALSE(name) \ |
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extern struct static_key_false name |
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#define DEFINE_STATIC_KEY_ARRAY_TRUE(name, count) \ |
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struct static_key_true name[count] = { \ |
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[0 ... (count) - 1] = STATIC_KEY_TRUE_INIT, \ |
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} |
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#define DEFINE_STATIC_KEY_ARRAY_FALSE(name, count) \ |
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struct static_key_false name[count] = { \ |
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[0 ... (count) - 1] = STATIC_KEY_FALSE_INIT, \ |
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} |
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extern bool ____wrong_branch_error(void); |
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#define static_key_enabled(x) \ |
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({ \ |
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if (!__builtin_types_compatible_p(typeof(*x), struct static_key) && \ |
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!__builtin_types_compatible_p(typeof(*x), struct static_key_true) &&\ |
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!__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \ |
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____wrong_branch_error(); \ |
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static_key_count((struct static_key *)x) > 0; \ |
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}) |
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#ifdef CONFIG_JUMP_LABEL |
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/* |
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* Combine the right initial value (type) with the right branch order |
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* to generate the desired result. |
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* |
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* |
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* type\branch| likely (1) | unlikely (0) |
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* -----------+-----------------------+------------------ |
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* | | |
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* true (1) | ... | ... |
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* | NOP | JMP L |
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* | <br-stmts> | 1: ... |
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* | L: ... | |
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* | | |
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* | | L: <br-stmts> |
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* | | jmp 1b |
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* | | |
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* -----------+-----------------------+------------------ |
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* | | |
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* false (0) | ... | ... |
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* | JMP L | NOP |
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* | <br-stmts> | 1: ... |
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* | L: ... | |
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* | | |
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* | | L: <br-stmts> |
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* | | jmp 1b |
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* | | |
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* -----------+-----------------------+------------------ |
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* |
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* The initial value is encoded in the LSB of static_key::entries, |
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* type: 0 = false, 1 = true. |
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* |
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* The branch type is encoded in the LSB of jump_entry::key, |
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* branch: 0 = unlikely, 1 = likely. |
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* |
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* This gives the following logic table: |
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* |
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* enabled type branch instuction |
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* -----------------------------+----------- |
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* 0 0 0 | NOP |
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* 0 0 1 | JMP |
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* 0 1 0 | NOP |
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* 0 1 1 | JMP |
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* |
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* 1 0 0 | JMP |
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* 1 0 1 | NOP |
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* 1 1 0 | JMP |
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* 1 1 1 | NOP |
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* |
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* Which gives the following functions: |
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* |
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* dynamic: instruction = enabled ^ branch |
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* static: instruction = type ^ branch |
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* |
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* See jump_label_type() / jump_label_init_type(). |
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*/ |
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#define static_branch_likely(x) \ |
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({ \ |
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bool branch; \ |
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if (__builtin_types_compatible_p(typeof(*x), struct static_key_true)) \ |
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branch = !arch_static_branch(&(x)->key, true); \ |
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else if (__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \ |
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branch = !arch_static_branch_jump(&(x)->key, true); \ |
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else \ |
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branch = ____wrong_branch_error(); \ |
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likely_notrace(branch); \ |
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}) |
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#define static_branch_unlikely(x) \ |
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({ \ |
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bool branch; \ |
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if (__builtin_types_compatible_p(typeof(*x), struct static_key_true)) \ |
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branch = arch_static_branch_jump(&(x)->key, false); \ |
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else if (__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \ |
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branch = arch_static_branch(&(x)->key, false); \ |
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else \ |
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branch = ____wrong_branch_error(); \ |
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unlikely_notrace(branch); \ |
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}) |
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#else /* !CONFIG_JUMP_LABEL */ |
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#define static_branch_likely(x) likely_notrace(static_key_enabled(&(x)->key)) |
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#define static_branch_unlikely(x) unlikely_notrace(static_key_enabled(&(x)->key)) |
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#endif /* CONFIG_JUMP_LABEL */ |
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/* |
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* Advanced usage; refcount, branch is enabled when: count != 0 |
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*/ |
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#define static_branch_inc(x) static_key_slow_inc(&(x)->key) |
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#define static_branch_dec(x) static_key_slow_dec(&(x)->key) |
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#define static_branch_inc_cpuslocked(x) static_key_slow_inc_cpuslocked(&(x)->key) |
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#define static_branch_dec_cpuslocked(x) static_key_slow_dec_cpuslocked(&(x)->key) |
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/* |
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* Normal usage; boolean enable/disable. |
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*/ |
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#define static_branch_enable(x) static_key_enable(&(x)->key) |
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#define static_branch_disable(x) static_key_disable(&(x)->key) |
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#define static_branch_enable_cpuslocked(x) static_key_enable_cpuslocked(&(x)->key) |
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#define static_branch_disable_cpuslocked(x) static_key_disable_cpuslocked(&(x)->key) |
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#endif /* __ASSEMBLY__ */ |
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#endif /* _LINUX_JUMP_LABEL_H */
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