1 #ifndef _LINUX_JUMP_LABEL_H 2 #define _LINUX_JUMP_LABEL_H 3 4 /* 5 * Jump label support 6 * 7 * Copyright (C) 2009-2012 Jason Baron <[email protected]> 8 * Copyright (C) 2011-2012 Peter Zijlstra <[email protected]> 9 * 10 * Jump labels provide an interface to generate dynamic branches using 11 * self-modifying code. Assuming toolchain and architecture support the result 12 * of a "if (static_key_false(&key))" statement is a unconditional branch (which 13 * defaults to false - and the true block is placed out of line). 14 * 15 * However at runtime we can change the branch target using 16 * static_key_slow_{inc,dec}(). These function as a 'reference' count on the key 17 * object and for as long as there are references all branches referring to 18 * that particular key will point to the (out of line) true block. 19 * 20 * Since this relies on modifying code the static_key_slow_{inc,dec}() functions 21 * must be considered absolute slow paths (machine wide synchronization etc.). 22 * OTOH, since the affected branches are unconditional their runtime overhead 23 * will be absolutely minimal, esp. in the default (off) case where the total 24 * effect is a single NOP of appropriate size. The on case will patch in a jump 25 * to the out-of-line block. 26 * 27 * When the control is directly exposed to userspace it is prudent to delay the 28 * decrement to avoid high frequency code modifications which can (and do) 29 * cause significant performance degradation. Struct static_key_deferred and 30 * static_key_slow_dec_deferred() provide for this. 31 * 32 * Lacking toolchain and or architecture support, it falls back to a simple 33 * conditional branch. 34 * 35 * struct static_key my_key = STATIC_KEY_INIT_TRUE; 36 * 37 * if (static_key_true(&my_key)) { 38 * } 39 * 40 * will result in the true case being in-line and starts the key with a single 41 * reference. Mixing static_key_true() and static_key_false() on the same key is not 42 * allowed. 43 * 44 * Not initializing the key (static data is initialized to 0s anyway) is the 45 * same as using STATIC_KEY_INIT_FALSE. 46 * 47 */ 48 49 #include <linux/types.h> 50 #include <linux/compiler.h> 51 #include <linux/workqueue.h> 52 53 #if defined(CC_HAVE_ASM_GOTO) && defined(CONFIG_JUMP_LABEL) 54 55 struct static_key { 56 atomic_t enabled; 57 /* Set lsb bit to 1 if branch is default true, 0 ot */ 58 struct jump_entry *entries; 59 #ifdef CONFIG_MODULES 60 struct static_key_mod *next; 61 #endif 62 }; 63 64 struct static_key_deferred { 65 struct static_key key; 66 unsigned long timeout; 67 struct delayed_work work; 68 }; 69 70 # include <asm/jump_label.h> 71 # define HAVE_JUMP_LABEL 72 #endif /* CC_HAVE_ASM_GOTO && CONFIG_JUMP_LABEL */ 73 74 enum jump_label_type { 75 JUMP_LABEL_DISABLE = 0, 76 JUMP_LABEL_ENABLE, 77 }; 78 79 struct module; 80 81 #ifdef HAVE_JUMP_LABEL 82 83 #define JUMP_LABEL_TRUE_BRANCH 1UL 84 85 static 86 inline struct jump_entry *jump_label_get_entries(struct static_key *key) 87 { 88 return (struct jump_entry *)((unsigned long)key->entries 89 & ~JUMP_LABEL_TRUE_BRANCH); 90 } 91 92 static inline bool jump_label_get_branch_default(struct static_key *key) 93 { 94 if ((unsigned long)key->entries & JUMP_LABEL_TRUE_BRANCH) 95 return true; 96 return false; 97 } 98 99 static __always_inline bool static_key_false(struct static_key *key) 100 { 101 return arch_static_branch(key); 102 } 103 104 static __always_inline bool static_key_true(struct static_key *key) 105 { 106 return !static_key_false(key); 107 } 108 109 extern struct jump_entry __start___jump_table[]; 110 extern struct jump_entry __stop___jump_table[]; 111 112 extern void jump_label_init(void); 113 extern void jump_label_lock(void); 114 extern void jump_label_unlock(void); 115 extern void arch_jump_label_transform(struct jump_entry *entry, 116 enum jump_label_type type); 117 extern void arch_jump_label_transform_static(struct jump_entry *entry, 118 enum jump_label_type type); 119 extern int jump_label_text_reserved(void *start, void *end); 120 extern void static_key_slow_inc(struct static_key *key); 121 extern void static_key_slow_dec(struct static_key *key); 122 extern void static_key_slow_dec_deferred(struct static_key_deferred *key); 123 extern void jump_label_apply_nops(struct module *mod); 124 extern void 125 jump_label_rate_limit(struct static_key_deferred *key, unsigned long rl); 126 127 #define STATIC_KEY_INIT_TRUE ((struct static_key) \ 128 { .enabled = ATOMIC_INIT(1), .entries = (void *)1 }) 129 #define STATIC_KEY_INIT_FALSE ((struct static_key) \ 130 { .enabled = ATOMIC_INIT(0), .entries = (void *)0 }) 131 132 #else /* !HAVE_JUMP_LABEL */ 133 134 #include <linux/atomic.h> 135 136 struct static_key { 137 atomic_t enabled; 138 }; 139 140 static __always_inline void jump_label_init(void) 141 { 142 } 143 144 struct static_key_deferred { 145 struct static_key key; 146 }; 147 148 static __always_inline bool static_key_false(struct static_key *key) 149 { 150 if (unlikely(atomic_read(&key->enabled)) > 0) 151 return true; 152 return false; 153 } 154 155 static __always_inline bool static_key_true(struct static_key *key) 156 { 157 if (likely(atomic_read(&key->enabled)) > 0) 158 return true; 159 return false; 160 } 161 162 static inline void static_key_slow_inc(struct static_key *key) 163 { 164 atomic_inc(&key->enabled); 165 } 166 167 static inline void static_key_slow_dec(struct static_key *key) 168 { 169 atomic_dec(&key->enabled); 170 } 171 172 static inline void static_key_slow_dec_deferred(struct static_key_deferred *key) 173 { 174 static_key_slow_dec(&key->key); 175 } 176 177 static inline int jump_label_text_reserved(void *start, void *end) 178 { 179 return 0; 180 } 181 182 static inline void jump_label_lock(void) {} 183 static inline void jump_label_unlock(void) {} 184 185 static inline int jump_label_apply_nops(struct module *mod) 186 { 187 return 0; 188 } 189 190 static inline void 191 jump_label_rate_limit(struct static_key_deferred *key, 192 unsigned long rl) 193 { 194 } 195 196 #define STATIC_KEY_INIT_TRUE ((struct static_key) \ 197 { .enabled = ATOMIC_INIT(1) }) 198 #define STATIC_KEY_INIT_FALSE ((struct static_key) \ 199 { .enabled = ATOMIC_INIT(0) }) 200 201 #endif /* HAVE_JUMP_LABEL */ 202 203 #define STATIC_KEY_INIT STATIC_KEY_INIT_FALSE 204 #define jump_label_enabled static_key_enabled 205 206 static inline bool static_key_enabled(struct static_key *key) 207 { 208 return (atomic_read(&key->enabled) > 0); 209 } 210 211 #endif /* _LINUX_JUMP_LABEL_H */ 212