cregit-Linux how code gets into the kernel

Release 4.12 include/linux/jump_label.h

Directory: include/linux
#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
 */

#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>

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;
/*
 * 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	/* 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;

#ifdef HAVE_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); }

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Ingo Molnar1890.00%150.00%
Peter Zijlstra210.00%150.00%
Total20100.00%2100.00%


static __always_inline bool static_key_true(struct static_key *key) { return !arch_static_branch(key, true); }

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Ingo Molnar1885.71%150.00%
Peter Zijlstra314.29%150.00%
Total21100.00%2100.00%

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); 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); /* * 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 /* !HAVE_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); }

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Paolo Bonzini21100.00%1100.00%
Total21100.00%1100.00%


static __always_inline void jump_label_init(void) { static_key_initialized = true; }

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Jeremy Fitzhardinge753.85%150.00%
Hannes Frederic Sowa646.15%150.00%
Total13100.00%2100.00%


static __always_inline bool static_key_false(struct static_key *key) { if (unlikely(static_key_count(key) > 0)) return true; return false; }

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Ingo Molnar2893.33%133.33%
Roel Kluin13.33%133.33%
Mel Gorman13.33%133.33%
Total30100.00%3100.00%


static __always_inline bool static_key_true(struct static_key *key) { if (likely(static_key_count(key) > 0)) return true; return false; }

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Ingo Molnar2893.33%133.33%
Mel Gorman13.33%133.33%
Roel Kluin13.33%133.33%
Total30100.00%3100.00%


static inline void static_key_slow_inc(struct static_key *key) { STATIC_KEY_CHECK_USE(); atomic_inc(&key->enabled); }

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Jason Baron1878.26%250.00%
Hannes Frederic Sowa313.04%125.00%
Ingo Molnar28.70%125.00%
Total23100.00%4100.00%


static inline void static_key_slow_dec(struct static_key *key) { STATIC_KEY_CHECK_USE(); atomic_dec(&key->enabled); }

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PersonTokensPropCommitsCommitProp
Jason Baron1878.26%250.00%
Hannes Frederic Sowa313.04%125.00%
Ingo Molnar28.70%125.00%
Total23100.00%4100.00%


static inline int jump_label_text_reserved(void *start, void *end) { return 0; }

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Jason Baron18100.00%1100.00%
Total18100.00%1100.00%


static inline void jump_label_lock(void) {}

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Jason Baron8100.00%1100.00%
Total8100.00%1100.00%


static inline void jump_label_unlock(void) {}

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Jason Baron8100.00%1100.00%
Total8100.00%1100.00%


static inline int jump_label_apply_nops(struct module *mod) { return 0; }

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Jason Baron15100.00%1100.00%
Total15100.00%1100.00%


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); }

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Peter Zijlstra41100.00%1100.00%
Total41100.00%1100.00%


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); }

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Peter Zijlstra40100.00%1100.00%
Total40100.00%1100.00%

#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 /* -------------------------------------------------------------------------- */ /* * 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 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 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 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 /* __ASSEMBLY__ */ #endif /* _LINUX_JUMP_LABEL_H */

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Jason Baron27935.54%623.08%
Peter Zijlstra21026.75%415.38%
Ingo Molnar10813.76%13.85%
Anton Blanchard394.97%13.85%
Jeremy Fitzhardinge293.69%27.69%
Paolo Bonzini243.06%13.85%
Hannes Frederic Sowa212.68%13.85%
Catalin Marinas212.68%13.85%
Tony Luck162.04%13.85%
Mel Gorman121.53%13.85%
Tejun Heo121.53%13.85%
Jiang Liu60.76%13.85%
Roel Kluin20.25%13.85%
Boris Ostrovsky20.25%13.85%
Luis R. Rodriguez20.25%13.85%
Steven Rostedt10.13%13.85%
Gleb Natapov10.13%13.85%
Total785100.00%26100.00%
Directory: include/linux
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