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 an 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, jump labels fall 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 #include <linux/types.h> 49 #include <linux/compiler.h> 50 #include <linux/bug.h> 51 52 extern bool static_key_initialized; 53 54 #define STATIC_KEY_CHECK_USE() WARN(!static_key_initialized, \ 55 "%s used before call to jump_label_init", \ 56 __func__) 57 58 #if defined(CC_HAVE_ASM_GOTO) && defined(CONFIG_JUMP_LABEL) 59 60 struct static_key { 61 atomic_t enabled; 62 /* Set lsb bit to 1 if branch is default true, 0 ot */ 63 struct jump_entry *entries; 64 #ifdef CONFIG_MODULES 65 struct static_key_mod *next; 66 #endif 67 }; 68 69 # include <asm/jump_label.h> 70 # define HAVE_JUMP_LABEL 71 #else 72 struct static_key { 73 atomic_t enabled; 74 }; 75 #endif /* CC_HAVE_ASM_GOTO && CONFIG_JUMP_LABEL */ 76 77 enum jump_label_type { 78 JUMP_LABEL_DISABLE = 0, 79 JUMP_LABEL_ENABLE, 80 }; 81 82 struct module; 83 84 #include <linux/atomic.h> 85 86 static inline int static_key_count(struct static_key *key) 87 { 88 return atomic_read(&key->enabled); 89 } 90 91 #ifdef HAVE_JUMP_LABEL 92 93 #define JUMP_LABEL_TYPE_FALSE_BRANCH 0UL 94 #define JUMP_LABEL_TYPE_TRUE_BRANCH 1UL 95 #define JUMP_LABEL_TYPE_MASK 1UL 96 97 static 98 inline struct jump_entry *jump_label_get_entries(struct static_key *key) 99 { 100 return (struct jump_entry *)((unsigned long)key->entries 101 & ~JUMP_LABEL_TYPE_MASK); 102 } 103 104 static inline bool jump_label_get_branch_default(struct static_key *key) 105 { 106 if (((unsigned long)key->entries & JUMP_LABEL_TYPE_MASK) == 107 JUMP_LABEL_TYPE_TRUE_BRANCH) 108 return true; 109 return false; 110 } 111 112 static __always_inline bool static_key_false(struct static_key *key) 113 { 114 return arch_static_branch(key); 115 } 116 117 static __always_inline bool static_key_true(struct static_key *key) 118 { 119 return !static_key_false(key); 120 } 121 122 extern struct jump_entry __start___jump_table[]; 123 extern struct jump_entry __stop___jump_table[]; 124 125 extern void jump_label_init(void); 126 extern void jump_label_lock(void); 127 extern void jump_label_unlock(void); 128 extern void arch_jump_label_transform(struct jump_entry *entry, 129 enum jump_label_type type); 130 extern void arch_jump_label_transform_static(struct jump_entry *entry, 131 enum jump_label_type type); 132 extern int jump_label_text_reserved(void *start, void *end); 133 extern void static_key_slow_inc(struct static_key *key); 134 extern void static_key_slow_dec(struct static_key *key); 135 extern void jump_label_apply_nops(struct module *mod); 136 137 #define STATIC_KEY_INIT_TRUE ((struct static_key) \ 138 { .enabled = ATOMIC_INIT(1), \ 139 .entries = (void *)JUMP_LABEL_TYPE_TRUE_BRANCH }) 140 #define STATIC_KEY_INIT_FALSE ((struct static_key) \ 141 { .enabled = ATOMIC_INIT(0), \ 142 .entries = (void *)JUMP_LABEL_TYPE_FALSE_BRANCH }) 143 144 #else /* !HAVE_JUMP_LABEL */ 145 146 static __always_inline void jump_label_init(void) 147 { 148 static_key_initialized = true; 149 } 150 151 static __always_inline bool static_key_false(struct static_key *key) 152 { 153 if (unlikely(static_key_count(key) > 0)) 154 return true; 155 return false; 156 } 157 158 static __always_inline bool static_key_true(struct static_key *key) 159 { 160 if (likely(static_key_count(key) > 0)) 161 return true; 162 return false; 163 } 164 165 static inline void static_key_slow_inc(struct static_key *key) 166 { 167 STATIC_KEY_CHECK_USE(); 168 atomic_inc(&key->enabled); 169 } 170 171 static inline void static_key_slow_dec(struct static_key *key) 172 { 173 STATIC_KEY_CHECK_USE(); 174 atomic_dec(&key->enabled); 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 #define STATIC_KEY_INIT_TRUE ((struct static_key) \ 191 { .enabled = ATOMIC_INIT(1) }) 192 #define STATIC_KEY_INIT_FALSE ((struct static_key) \ 193 { .enabled = ATOMIC_INIT(0) }) 194 195 #endif /* HAVE_JUMP_LABEL */ 196 197 #define STATIC_KEY_INIT STATIC_KEY_INIT_FALSE 198 #define jump_label_enabled static_key_enabled 199 200 static inline bool static_key_enabled(struct static_key *key) 201 { 202 return static_key_count(key) > 0; 203 } 204 205 #endif /* _LINUX_JUMP_LABEL_H */ 206