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jump_label: Provide CONFIG-driven build state defaults

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As shown in the comment in jump_label.h, choosing the initial state of
static branches changes the assembly layout. If the condition is expected
to be likely it's inline, and if unlikely it is out of line via a jump.

A few places in the kernel use (or could be using) a CONFIG to choose the
default state, which would give a small performance benefit to their
compile-time declared default. Provide the infrastructure to do this.

Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20210401232347.2791257-2-keescook@chromium.org
This commit is contained in:
Kees Cook 2021-04-01 16:23:42 -07:00 committed by Thomas Gleixner
parent e49d033bdd
commit 0d66ccc162
1 changed files with 19 additions and 0 deletions
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19
include/linux/jump_label.h
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@ -382,6 +382,21 @@ struct static_key_false {
[0 ... (count) - 1] = STATIC_KEY_FALSE_INIT, \
}
#define _DEFINE_STATIC_KEY_1(name) DEFINE_STATIC_KEY_TRUE(name)
#define _DEFINE_STATIC_KEY_0(name) DEFINE_STATIC_KEY_FALSE(name)
#define DEFINE_STATIC_KEY_MAYBE(cfg, name) \
__PASTE(_DEFINE_STATIC_KEY_, IS_ENABLED(cfg))(name)
#define _DEFINE_STATIC_KEY_RO_1(name) DEFINE_STATIC_KEY_TRUE_RO(name)
#define _DEFINE_STATIC_KEY_RO_0(name) DEFINE_STATIC_KEY_FALSE_RO(name)
#define DEFINE_STATIC_KEY_MAYBE_RO(cfg, name) \
__PASTE(_DEFINE_STATIC_KEY_RO_, IS_ENABLED(cfg))(name)
#define _DECLARE_STATIC_KEY_1(name) DECLARE_STATIC_KEY_TRUE(name)
#define _DECLARE_STATIC_KEY_0(name) DECLARE_STATIC_KEY_FALSE(name)
#define DECLARE_STATIC_KEY_MAYBE(cfg, name) \
__PASTE(_DECLARE_STATIC_KEY_, IS_ENABLED(cfg))(name)
extern bool ____wrong_branch_error(void);
#define static_key_enabled(x) \
@ -482,6 +497,10 @@ extern bool ____wrong_branch_error(void);
#endif /* CONFIG_JUMP_LABEL */
#define static_branch_maybe(config, x) \
(IS_ENABLED(config) ? static_branch_likely(x) \
: static_branch_unlikely(x))
/*
* Advanced usage; refcount, branch is enabled when: count != 0
*/