/* SPDX-License-Identifier: GPL-2.0 */
#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 Red Hat, Inc., Peter Zijlstra
*
* 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);
* DEFINE_STATIC_KEY_ARRAY_TRUE(keys, count);
* DEFINE_STATIC_KEY_ARRAY_FALSE(keys, count);
* 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
*/
#ifndef __ASSEMBLY__
#include <linux/types.h>
#include <linux/compiler.h>
extern bool static_key_initialized;
#define STATIC_KEY_CHECK_USE(key) WARN(!static_key_initialized, \
"%s(): static key '%pS' used before call to jump_label_init()", \
__func__, (key))
#ifdef CONFIG_JUMP_LABEL
struct static_key {
atomic_t enabled;
/*
* Note:
* To make anonymous unions work with old compilers, the static
* initialization of them requires brackets. This creates a dependency
* on the order of the struct with the initializers. If any fields
* are added, STATIC_KEY_INIT_TRUE and STATIC_KEY_INIT_FALSE may need
* to be modified.
*
* bit 0 => 1 if key is initially true
* 0 if initially false
* bit 1 => 1 if points to struct static_key_mod
* 0 if points to struct jump_entry
*/
union {
unsigned long type;
struct jump_entry *entries;
struct static_key_mod *next;
};
};
#else
struct static_key {
atomic_t enabled;
};
#endif /* CONFIG_JUMP_LABEL */
#endif /* __ASSEMBLY__ */
#ifdef CONFIG_JUMP_LABEL
#include <asm/jump_label.h>
#ifndef __ASSEMBLY__
#ifdef CONFIG_HAVE_ARCH_JUMP_LABEL_RELATIVE
struct jump_entry {
s32 code;
s32 target;
long key; // key may be far away from the core kernel under KASLR
};
static inline unsigned long jump_entry_code(const struct jump_entry *entry)
{
return (unsigned long)&entry->code + entry->code;
}
static inline unsigned long jump_entry_target(const struct jump_entry *entry)
{
return (unsigned long)&entry->target + entry->target;
}
static inline struct static_key *jump_entry_key(const struct jump_entry *entry)
{
long offset = entry->key & ~3L;
return (struct static_key *)((unsigned long)&entry->key + offset);
}
#else
static inline unsigned long jump_entry_code(const struct jump_entry *entry)
{
return entry->code;
}
static inline unsigned long jump_entry_target(const struct jump_entry *entry)
{
return entry->target;
}
static inline struct static_key *jump_entry_key(const struct jump_entry *entry)
{
return (struct static_key *)((unsigned long)entry->key & ~3UL);
}
#endif
static inline bool jump_entry_is_branch(const struct jump_entry *entry)
{
return (unsigned long)entry->key & 1UL;
}
static inline bool jump_entry_is_init(const struct jump_entry *entry)
{
return (unsigned long)entry->key & 2UL;
}
static inline void jump_entry_set_init(struct jump_entry *entry)
{
entry->key |= 2;
}
#endif
#endif
#ifndef __ASSEMBLY__
enum jump_label_type {
JUMP_LABEL_NOP = 0,
JUMP_LABEL_JMP,
};
struct module;
#ifdef CONFIG_JUMP_LABEL
#define JUMP_TYPE_FALSE 0UL
#define JUMP_TYPE_TRUE 1UL
#define JUMP_TYPE_LINKED 2UL
#define JUMP_TYPE_MASK 3UL
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 bool arch_jump_label_transform_queue(struct jump_entry *entry,
enum jump_label_type type);
extern void arch_jump_label_transform_apply(void);
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 static_key_slow_inc_cpuslocked(struct static_key *key);
extern void static_key_slow_dec_cpuslocked(struct static_key *key);
extern void jump_label_apply_nops(struct module *mod);
extern int static_key_count(struct static_key *key);
extern void static_key_enable(struct static_key *key);
extern void static_key_disable(struct static_key *key);
extern void static_key_enable_cpuslocked(struct static_key *key);
extern void static_key_disable_cpuslocked(struct static_key *key);
/*
* We should be using ATOMIC_INIT() for initializing .enabled, but
* the inclusion of atomic.h is problematic for inclusion of jump_label.h
* in 'low-level' headers. Thus, we are initializing .enabled with a
* raw value, but have added a BUILD_BUG_ON() to catch any issues in
* jump_label_init() see: kernel/jump_label.c.
*/
#define STATIC_KEY_INIT_TRUE \
{ .enabled = { 1 }, \
{ .entries = (void *)JUMP_TYPE_TRUE } }
#define STATIC_KEY_INIT_FALSE \
{ .enabled = { 0 }, \
{ .entries = (void *)JUMP_TYPE_FALSE } }
#else /* !CONFIG_JUMP_LABEL */
#include <linux/atomic.h>
#include <linux/bug.h>
static inline int static_key_count(struct static_key *key)
{
return atomic_read(&key->enabled);
}
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(key);
atomic_inc(&key->enabled);
}
static inline void static_key_slow_dec(struct static_key *key)
{
STATIC_KEY_CHECK_USE(key);
atomic_dec(&key->enabled);
}
#define static_key_slow_inc_cpuslocked(key) static_key_slow_inc(key)
#define static_key_slow_dec_cpuslocked(key) static_key_slow_dec(key)
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;
}
static inline void static_key_enable(struct static_key *key)
{
STATIC_KEY_CHECK_USE(key);
if (atomic_read(&key->enabled) != 0) {
WARN_ON_ONCE(atomic_read(&key->enabled) != 1);
return;
}
atomic_set(&key->enabled, 1);
}
static inline void static_key_disable(struct static_key *key)
{
STATIC_KEY_CHECK_USE(key);
if (atomic_read(&key->enabled) != 1) {
WARN_ON_ONCE(atomic_read(&key->enabled) != 0);
return;
}
atomic_set(&key->enabled, 0);
}
#define static_key_enable_cpuslocked(k) static_key_enable((k))
#define static_key_disable_cpuslocked(k) static_key_disable((k))
#define STATIC_KEY_INIT_TRUE { .enabled = ATOMIC_INIT(1) }
#define STATIC_KEY_INIT_FALSE { .enabled = ATOMIC_INIT(0) }
#endif /* CONFIG_JUMP_LABEL */
#define STATIC_KEY_INIT STATIC_KEY_INIT_FALSE
#define jump_label_enabled static_key_enabled
/* -------------------------------------------------------------------------- */
/*
* 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_TRUE_RO(name) \
struct static_key_true name __ro_after_init = STATIC_KEY_TRUE_INIT
#define DECLARE_STATIC_KEY_TRUE(name) \
extern struct static_key_true name
#define DEFINE_STATIC_KEY_FALSE(name) \
struct static_key_false name = STATIC_KEY_FALSE_INIT
#define DEFINE_STATIC_KEY_FALSE_RO(name) \
struct static_key_false name __ro_after_init = STATIC_KEY_FALSE_INIT
#define DECLARE_STATIC_KEY_FALSE(name) \
extern struct static_key_false name
#define DEFINE_STATIC_KEY_ARRAY_TRUE(name, count) \
struct static_key_true name[count] = { \
[0 ... (count) - 1] = STATIC_KEY_TRUE_INIT, \
}
#define DEFINE_STATIC_KEY_ARRAY_FALSE(name, count) \
struct static_key_false name[count] = { \
[0 ... (count) - 1] = 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 CONFIG_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(); \
likely(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(); \
unlikely(branch); \
})
#else /* !CONFIG_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 /* CONFIG_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)
#define static_branch_inc_cpuslocked(x) static_key_slow_inc_cpuslocked(&(x)->key)
#define static_branch_dec_cpuslocked(x) static_key_slow_dec_cpuslocked(&(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)
#define static_branch_enable_cpuslocked(x) static_key_enable_cpuslocked(&(x)->key)
#define static_branch_disable_cpuslocked(x) static_key_disable_cpuslocked(&(x)->key)
#endif /* __ASSEMBLY__ */
#endif /* _LINUX_JUMP_LABEL_H */
