380 lines
11 KiB
C
380 lines
11 KiB
C
#ifndef _LINUX_JUMP_LABEL_H
|
|
#define _LINUX_JUMP_LABEL_H
|
|
|
|
/*
|
|
* Jump label support
|
|
*
|
|
* Copyright (C) 2009-2012 Jason Baron <jbaron@redhat.com>
|
|
* Copyright (C) 2011-2012 Peter Zijlstra <pzijlstr@redhat.com>
|
|
*
|
|
* DEPRECATED API:
|
|
*
|
|
* The use of 'struct static_key' directly, is now DEPRECATED. In addition
|
|
* static_key_{true,false}() is also DEPRECATED. IE DO NOT use the following:
|
|
*
|
|
* struct static_key false = STATIC_KEY_INIT_FALSE;
|
|
* struct static_key true = STATIC_KEY_INIT_TRUE;
|
|
* static_key_true()
|
|
* static_key_false()
|
|
*
|
|
* The updated API replacements are:
|
|
*
|
|
* DEFINE_STATIC_KEY_TRUE(key);
|
|
* DEFINE_STATIC_KEY_FALSE(key);
|
|
* static_branch_likely()
|
|
* static_branch_unlikely()
|
|
*
|
|
* Jump labels provide an interface to generate dynamic branches using
|
|
* self-modifying code. Assuming toolchain and architecture support, if we
|
|
* define a "key" that is initially false via "DEFINE_STATIC_KEY_FALSE(key)",
|
|
* an "if (static_branch_unlikely(&key))" statement is an unconditional branch
|
|
* (which defaults to false - and the true block is placed out of line).
|
|
* Similarly, we can define an initially true key via
|
|
* "DEFINE_STATIC_KEY_TRUE(key)", and use it in the same
|
|
* "if (static_branch_unlikely(&key))", in which case we will generate an
|
|
* unconditional branch to the out-of-line true branch. Keys that are
|
|
* initially true or false can be using in both static_branch_unlikely()
|
|
* and static_branch_likely() statements.
|
|
*
|
|
* At runtime we can change the branch target by setting the key
|
|
* to true via a call to static_branch_enable(), or false using
|
|
* static_branch_disable(). If the direction of the branch is switched by
|
|
* these calls then we run-time modify the branch target via a
|
|
* no-op -> jump or jump -> no-op conversion. For example, for an
|
|
* initially false key that is used in an "if (static_branch_unlikely(&key))"
|
|
* statement, setting the key to true requires us to patch in a jump
|
|
* to the out-of-line of true branch.
|
|
*
|
|
* In addition to static_branch_{enable,disable}, we can also reference count
|
|
* the key or branch direction via static_branch_{inc,dec}. Thus,
|
|
* static_branch_inc() can be thought of as a 'make more true' and
|
|
* static_branch_dec() as a 'make more false'.
|
|
*
|
|
* Since this relies on modifying code, the branch modifying functions
|
|
* must be considered absolute slow paths (machine wide synchronization etc.).
|
|
* OTOH, since the affected branches are unconditional, their runtime overhead
|
|
* will be absolutely minimal, esp. in the default (off) case where the total
|
|
* effect is a single NOP of appropriate size. The on case will patch in a jump
|
|
* to the out-of-line block.
|
|
*
|
|
* When the control is directly exposed to userspace, it is prudent to delay the
|
|
* decrement to avoid high frequency code modifications which can (and do)
|
|
* cause significant performance degradation. Struct static_key_deferred and
|
|
* static_key_slow_dec_deferred() provide for this.
|
|
*
|
|
* Lacking toolchain and or architecture support, static keys fall back to a
|
|
* simple conditional branch.
|
|
*
|
|
* Additional babbling in: Documentation/static-keys.txt
|
|
*/
|
|
|
|
#if defined(CC_HAVE_ASM_GOTO) && defined(CONFIG_JUMP_LABEL)
|
|
# define HAVE_JUMP_LABEL
|
|
#endif
|
|
|
|
#ifndef __ASSEMBLY__
|
|
|
|
#include <linux/types.h>
|
|
#include <linux/compiler.h>
|
|
#include <linux/bug.h>
|
|
|
|
extern bool static_key_initialized;
|
|
|
|
#define STATIC_KEY_CHECK_USE() WARN(!static_key_initialized, \
|
|
"%s used before call to jump_label_init", \
|
|
__func__)
|
|
|
|
#ifdef HAVE_JUMP_LABEL
|
|
|
|
struct static_key {
|
|
atomic_t enabled;
|
|
/* Set lsb bit to 1 if branch is default true, 0 ot */
|
|
struct jump_entry *entries;
|
|
#ifdef CONFIG_MODULES
|
|
struct static_key_mod *next;
|
|
#endif
|
|
};
|
|
|
|
#else
|
|
struct static_key {
|
|
atomic_t enabled;
|
|
};
|
|
#endif /* HAVE_JUMP_LABEL */
|
|
#endif /* __ASSEMBLY__ */
|
|
|
|
#ifdef HAVE_JUMP_LABEL
|
|
#include <asm/jump_label.h>
|
|
#endif
|
|
|
|
#ifndef __ASSEMBLY__
|
|
|
|
enum jump_label_type {
|
|
JUMP_LABEL_NOP = 0,
|
|
JUMP_LABEL_JMP,
|
|
};
|
|
|
|
struct module;
|
|
|
|
#include <linux/atomic.h>
|
|
|
|
static inline int static_key_count(struct static_key *key)
|
|
{
|
|
return atomic_read(&key->enabled);
|
|
}
|
|
|
|
#ifdef HAVE_JUMP_LABEL
|
|
|
|
#define JUMP_TYPE_FALSE 0UL
|
|
#define JUMP_TYPE_TRUE 1UL
|
|
#define JUMP_TYPE_MASK 1UL
|
|
|
|
static __always_inline bool static_key_false(struct static_key *key)
|
|
{
|
|
return arch_static_branch(key, false);
|
|
}
|
|
|
|
static __always_inline bool static_key_true(struct static_key *key)
|
|
{
|
|
return !arch_static_branch(key, true);
|
|
}
|
|
|
|
extern struct jump_entry __start___jump_table[];
|
|
extern struct jump_entry __stop___jump_table[];
|
|
|
|
extern void jump_label_init(void);
|
|
extern void jump_label_lock(void);
|
|
extern void jump_label_unlock(void);
|
|
extern void arch_jump_label_transform(struct jump_entry *entry,
|
|
enum jump_label_type type);
|
|
extern void arch_jump_label_transform_static(struct jump_entry *entry,
|
|
enum jump_label_type type);
|
|
extern int jump_label_text_reserved(void *start, void *end);
|
|
extern void static_key_slow_inc(struct static_key *key);
|
|
extern void static_key_slow_dec(struct static_key *key);
|
|
extern void jump_label_apply_nops(struct module *mod);
|
|
|
|
#define STATIC_KEY_INIT_TRUE \
|
|
{ .enabled = ATOMIC_INIT(1), \
|
|
.entries = (void *)JUMP_TYPE_TRUE }
|
|
#define STATIC_KEY_INIT_FALSE \
|
|
{ .enabled = ATOMIC_INIT(0), \
|
|
.entries = (void *)JUMP_TYPE_FALSE }
|
|
|
|
#else /* !HAVE_JUMP_LABEL */
|
|
|
|
static __always_inline void jump_label_init(void)
|
|
{
|
|
static_key_initialized = true;
|
|
}
|
|
|
|
static __always_inline bool static_key_false(struct static_key *key)
|
|
{
|
|
if (unlikely(static_key_count(key) > 0))
|
|
return true;
|
|
return false;
|
|
}
|
|
|
|
static __always_inline bool static_key_true(struct static_key *key)
|
|
{
|
|
if (likely(static_key_count(key) > 0))
|
|
return true;
|
|
return false;
|
|
}
|
|
|
|
static inline void static_key_slow_inc(struct static_key *key)
|
|
{
|
|
STATIC_KEY_CHECK_USE();
|
|
atomic_inc(&key->enabled);
|
|
}
|
|
|
|
static inline void static_key_slow_dec(struct static_key *key)
|
|
{
|
|
STATIC_KEY_CHECK_USE();
|
|
atomic_dec(&key->enabled);
|
|
}
|
|
|
|
static inline int jump_label_text_reserved(void *start, void *end)
|
|
{
|
|
return 0;
|
|
}
|
|
|
|
static inline void jump_label_lock(void) {}
|
|
static inline void jump_label_unlock(void) {}
|
|
|
|
static inline int jump_label_apply_nops(struct module *mod)
|
|
{
|
|
return 0;
|
|
}
|
|
|
|
#define STATIC_KEY_INIT_TRUE { .enabled = ATOMIC_INIT(1) }
|
|
#define STATIC_KEY_INIT_FALSE { .enabled = ATOMIC_INIT(0) }
|
|
|
|
#endif /* HAVE_JUMP_LABEL */
|
|
|
|
#define STATIC_KEY_INIT STATIC_KEY_INIT_FALSE
|
|
#define jump_label_enabled static_key_enabled
|
|
|
|
static inline void static_key_enable(struct static_key *key)
|
|
{
|
|
int count = static_key_count(key);
|
|
|
|
WARN_ON_ONCE(count < 0 || count > 1);
|
|
|
|
if (!count)
|
|
static_key_slow_inc(key);
|
|
}
|
|
|
|
static inline void static_key_disable(struct static_key *key)
|
|
{
|
|
int count = static_key_count(key);
|
|
|
|
WARN_ON_ONCE(count < 0 || count > 1);
|
|
|
|
if (count)
|
|
static_key_slow_dec(key);
|
|
}
|
|
|
|
/* -------------------------------------------------------------------------- */
|
|
|
|
/*
|
|
* Two type wrappers around static_key, such that we can use compile time
|
|
* type differentiation to emit the right code.
|
|
*
|
|
* All the below code is macros in order to play type games.
|
|
*/
|
|
|
|
struct static_key_true {
|
|
struct static_key key;
|
|
};
|
|
|
|
struct static_key_false {
|
|
struct static_key key;
|
|
};
|
|
|
|
#define STATIC_KEY_TRUE_INIT (struct static_key_true) { .key = STATIC_KEY_INIT_TRUE, }
|
|
#define STATIC_KEY_FALSE_INIT (struct static_key_false){ .key = STATIC_KEY_INIT_FALSE, }
|
|
|
|
#define DEFINE_STATIC_KEY_TRUE(name) \
|
|
struct static_key_true name = STATIC_KEY_TRUE_INIT
|
|
|
|
#define DEFINE_STATIC_KEY_FALSE(name) \
|
|
struct static_key_false name = STATIC_KEY_FALSE_INIT
|
|
|
|
extern bool ____wrong_branch_error(void);
|
|
|
|
#define static_key_enabled(x) \
|
|
({ \
|
|
if (!__builtin_types_compatible_p(typeof(*x), struct static_key) && \
|
|
!__builtin_types_compatible_p(typeof(*x), struct static_key_true) &&\
|
|
!__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \
|
|
____wrong_branch_error(); \
|
|
static_key_count((struct static_key *)x) > 0; \
|
|
})
|
|
|
|
#ifdef HAVE_JUMP_LABEL
|
|
|
|
/*
|
|
* Combine the right initial value (type) with the right branch order
|
|
* to generate the desired result.
|
|
*
|
|
*
|
|
* type\branch| likely (1) | unlikely (0)
|
|
* -----------+-----------------------+------------------
|
|
* | |
|
|
* true (1) | ... | ...
|
|
* | NOP | JMP L
|
|
* | <br-stmts> | 1: ...
|
|
* | L: ... |
|
|
* | |
|
|
* | | L: <br-stmts>
|
|
* | | jmp 1b
|
|
* | |
|
|
* -----------+-----------------------+------------------
|
|
* | |
|
|
* false (0) | ... | ...
|
|
* | JMP L | NOP
|
|
* | <br-stmts> | 1: ...
|
|
* | L: ... |
|
|
* | |
|
|
* | | L: <br-stmts>
|
|
* | | jmp 1b
|
|
* | |
|
|
* -----------+-----------------------+------------------
|
|
*
|
|
* The initial value is encoded in the LSB of static_key::entries,
|
|
* type: 0 = false, 1 = true.
|
|
*
|
|
* The branch type is encoded in the LSB of jump_entry::key,
|
|
* branch: 0 = unlikely, 1 = likely.
|
|
*
|
|
* This gives the following logic table:
|
|
*
|
|
* enabled type branch instuction
|
|
* -----------------------------+-----------
|
|
* 0 0 0 | NOP
|
|
* 0 0 1 | JMP
|
|
* 0 1 0 | NOP
|
|
* 0 1 1 | JMP
|
|
*
|
|
* 1 0 0 | JMP
|
|
* 1 0 1 | NOP
|
|
* 1 1 0 | JMP
|
|
* 1 1 1 | NOP
|
|
*
|
|
* Which gives the following functions:
|
|
*
|
|
* dynamic: instruction = enabled ^ branch
|
|
* static: instruction = type ^ branch
|
|
*
|
|
* See jump_label_type() / jump_label_init_type().
|
|
*/
|
|
|
|
#define static_branch_likely(x) \
|
|
({ \
|
|
bool branch; \
|
|
if (__builtin_types_compatible_p(typeof(*x), struct static_key_true)) \
|
|
branch = !arch_static_branch(&(x)->key, true); \
|
|
else if (__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \
|
|
branch = !arch_static_branch_jump(&(x)->key, true); \
|
|
else \
|
|
branch = ____wrong_branch_error(); \
|
|
branch; \
|
|
})
|
|
|
|
#define static_branch_unlikely(x) \
|
|
({ \
|
|
bool branch; \
|
|
if (__builtin_types_compatible_p(typeof(*x), struct static_key_true)) \
|
|
branch = arch_static_branch_jump(&(x)->key, false); \
|
|
else if (__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \
|
|
branch = arch_static_branch(&(x)->key, false); \
|
|
else \
|
|
branch = ____wrong_branch_error(); \
|
|
branch; \
|
|
})
|
|
|
|
#else /* !HAVE_JUMP_LABEL */
|
|
|
|
#define static_branch_likely(x) likely(static_key_enabled(&(x)->key))
|
|
#define static_branch_unlikely(x) unlikely(static_key_enabled(&(x)->key))
|
|
|
|
#endif /* HAVE_JUMP_LABEL */
|
|
|
|
/*
|
|
* Advanced usage; refcount, branch is enabled when: count != 0
|
|
*/
|
|
|
|
#define static_branch_inc(x) static_key_slow_inc(&(x)->key)
|
|
#define static_branch_dec(x) static_key_slow_dec(&(x)->key)
|
|
|
|
/*
|
|
* Normal usage; boolean enable/disable.
|
|
*/
|
|
|
|
#define static_branch_enable(x) static_key_enable(&(x)->key)
|
|
#define static_branch_disable(x) static_key_disable(&(x)->key)
|
|
|
|
#endif /* _LINUX_JUMP_LABEL_H */
|
|
|
|
#endif /* __ASSEMBLY__ */
|