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/bug.h> 52 53 extern bool static_key_initialized; 54 55 #define STATIC_KEY_CHECK_USE() WARN(!static_key_initialized, \ 56 "%s used before call to jump_label_init", \ 57 __func__) 58 59 #if defined(CC_HAVE_ASM_GOTO) && defined(CONFIG_JUMP_LABEL) 60 61 struct static_key { 62 atomic_t enabled; 63 /* Set lsb bit to 1 if branch is default true, 0 ot */ 64 struct jump_entry *entries; 65 #ifdef CONFIG_MODULES 66 struct static_key_mod *next; 67 #endif 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 #include <linux/atomic.h> 82 #ifdef HAVE_JUMP_LABEL 83 84 #define JUMP_LABEL_TRUE_BRANCH 1UL 85 86 static 87 inline struct jump_entry *jump_label_get_entries(struct static_key *key) 88 { 89 return (struct jump_entry *)((unsigned long)key->entries 90 & ~JUMP_LABEL_TRUE_BRANCH); 91 } 92 93 static inline bool jump_label_get_branch_default(struct static_key *key) 94 { 95 if ((unsigned long)key->entries & JUMP_LABEL_TRUE_BRANCH) 96 return true; 97 return false; 98 } 99 100 static __always_inline bool static_key_false(struct static_key *key) 101 { 102 return arch_static_branch(key); 103 } 104 105 static __always_inline bool static_key_true(struct static_key *key) 106 { 107 return !static_key_false(key); 108 } 109 110 extern struct jump_entry __start___jump_table[]; 111 extern struct jump_entry __stop___jump_table[]; 112 113 extern void jump_label_init(void); 114 extern void jump_label_lock(void); 115 extern void jump_label_unlock(void); 116 extern void arch_jump_label_transform(struct jump_entry *entry, 117 enum jump_label_type type); 118 extern void arch_jump_label_transform_static(struct jump_entry *entry, 119 enum jump_label_type type); 120 extern int jump_label_text_reserved(void *start, void *end); 121 extern void static_key_slow_inc(struct static_key *key); 122 extern void static_key_slow_dec(struct static_key *key); 123 extern void jump_label_apply_nops(struct module *mod); 124 125 #define STATIC_KEY_INIT_TRUE ((struct static_key) \ 126 { .enabled = ATOMIC_INIT(1), .entries = (void *)1 }) 127 #define STATIC_KEY_INIT_FALSE ((struct static_key) \ 128 { .enabled = ATOMIC_INIT(0), .entries = (void *)0 }) 129 130 #else /* !HAVE_JUMP_LABEL */ 131 132 struct static_key { 133 atomic_t enabled; 134 }; 135 136 static __always_inline void jump_label_init(void) 137 { 138 static_key_initialized = true; 139 } 140 141 static __always_inline bool static_key_false(struct static_key *key) 142 { 143 if (unlikely(atomic_read(&key->enabled) > 0)) 144 return true; 145 return false; 146 } 147 148 static __always_inline bool static_key_true(struct static_key *key) 149 { 150 if (likely(atomic_read(&key->enabled) > 0)) 151 return true; 152 return false; 153 } 154 155 static inline void static_key_slow_inc(struct static_key *key) 156 { 157 STATIC_KEY_CHECK_USE(); 158 atomic_inc(&key->enabled); 159 } 160 161 static inline void static_key_slow_dec(struct static_key *key) 162 { 163 STATIC_KEY_CHECK_USE(); 164 atomic_dec(&key->enabled); 165 } 166 167 static inline int jump_label_text_reserved(void *start, void *end) 168 { 169 return 0; 170 } 171 172 static inline void jump_label_lock(void) {} 173 static inline void jump_label_unlock(void) {} 174 175 static inline int jump_label_apply_nops(struct module *mod) 176 { 177 return 0; 178 } 179 180 #define STATIC_KEY_INIT_TRUE ((struct static_key) \ 181 { .enabled = ATOMIC_INIT(1) }) 182 #define STATIC_KEY_INIT_FALSE ((struct static_key) \ 183 { .enabled = ATOMIC_INIT(0) }) 184 185 #endif /* HAVE_JUMP_LABEL */ 186 187 #define STATIC_KEY_INIT STATIC_KEY_INIT_FALSE 188 #define jump_label_enabled static_key_enabled 189 190 static inline bool static_key_enabled(struct static_key *key) 191 { 192 return (atomic_read(&key->enabled) > 0); 193 } 194 195 #endif /* _LINUX_JUMP_LABEL_H */ 196