LCOV - code coverage report
Current view: top level - include/linux - jump_label.h (source / functions) Hit Total Coverage
Test: coverage.info Lines: 1 7 14.3 %
Date: 2014-02-18 Functions: 0 0 -
Branches: 112 290 38.6 %

           Branch data     Line data    Source code
       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 <jbaron@redhat.com>
       8                 :            :  * Copyright (C) 2011-2012 Peter Zijlstra <pzijlstr@redhat.com>
       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                 :          0 :         static_key_initialized = true;
     139                 :            : }
     140                 :            : 
     141                 :            : static __always_inline bool static_key_false(struct static_key *key)
     142                 :            : {
     143    [ + ][ +  + ]: 1784933431 :         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 [ #  # ][ #  # ]:          0 :         STATIC_KEY_CHECK_USE();
                 [ #  # ]
     158                 :          0 :         atomic_inc(&key->enabled);
     159                 :            : }
     160                 :            : 
     161                 :            : static inline void static_key_slow_dec(struct static_key *key)
     162                 :            : {
     163 [ #  # ][ #  # ]:          0 :         STATIC_KEY_CHECK_USE();
                 [ #  # ]
     164                 :          0 :         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                 :          0 :         return (atomic_read(&key->enabled) > 0);
     193                 :            : }
     194                 :            : 
     195                 :            : #endif  /* _LINUX_JUMP_LABEL_H */

Generated by: LCOV version 1.9