Commit 0d66ccc1 authored by Kees Cook's avatar Kees Cook Committed by Thomas Gleixner
Browse files

jump_label: Provide CONFIG-driven build state defaults 



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: default avatarKees Cook <keescook@chromium.org>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Acked-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20210401232347.2791257-2-keescook@chromium.org
parent e49d033b

include/linux/jump_label.h

+19 −0
Original line number Diff line number Diff line
@@ -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

 */