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Commit 91a5cefa authored by James Morse's avatar James Morse Committed by Will Deacon
Browse files

arm64: kernel: Add optional CONFIG_ parameter to ALTERNATIVE() 



Some uses of ALTERNATIVE() may depend on a feature that is disabled at
compile time by a Kconfig option. In this case the unused alternative
instructions waste space, and if the original instruction is a nop, it
wastes time and space.

This patch adds an optional 'config' option to ALTERNATIVE() and
alternative_insn that allows the compiler to remove both the original
and alternative instructions if the config option is not defined.

Suggested-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
Acked-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
Signed-off-by: default avatarJames Morse <james.morse@arm.com>
Signed-off-by: default avatarWill Deacon <will.deacon@arm.com>
parent 18ffa046

arch/arm64/include/asm/alternative.h

+25 −3
Original line number Diff line number Diff line
@@ -3,6 +3,7 @@ 


#ifndef __ASSEMBLY__



#include <linux/kconfig.h>

#include <linux/types.h>

#include <linux/stddef.h>

#include <linux/stringify.h>
@@ -40,7 +41,8 @@ void free_alternatives_memory(void); 
 * be fixed in a binutils release posterior to 2.25.51.0.2 (anything

 * containing commit 4e4d08cf7399b606 or c1baaddf8861).

 */

#define ALTERNATIVE(oldinstr, newinstr, feature)			\

#define __ALTERNATIVE_CFG(oldinstr, newinstr, feature, cfg_enabled)	\

	".if "__stringify(cfg_enabled)" == 1\n"				\

	"661:\n\t"							\

	oldinstr "\n"							\

	"662:\n"							\
@@ -53,7 +55,11 @@ void free_alternatives_memory(void); 
	"664:\n\t"							\

	".popsection\n\t"						\

	".org	. - (664b-663b) + (662b-661b)\n\t"			\

	".org	. - (662b-661b) + (664b-663b)\n"

	".org	. - (662b-661b) + (664b-663b)\n"			\

	".endif\n"



#define _ALTERNATIVE_CFG(oldinstr, newinstr, feature, cfg, ...)	\

	__ALTERNATIVE_CFG(oldinstr, newinstr, feature, IS_ENABLED(cfg))



#else
@@ -65,7 +71,8 @@ void free_alternatives_memory(void); 
	.byte \alt_len

.endm



.macro alternative_insn insn1 insn2 cap

.macro alternative_insn insn1, insn2, cap, enable = 1

	.if \enable

661:	\insn1

662:	.pushsection .altinstructions, "a"

	altinstruction_entry 661b, 663f, \cap, 662b-661b, 664f-663f
@@ -75,6 +82,7 @@ void free_alternatives_memory(void); 
664:	.popsection

	.org	. - (664b-663b) + (662b-661b)

	.org	. - (662b-661b) + (664b-663b)

	.endif

.endm



/*
@@ -118,6 +126,20 @@ void free_alternatives_memory(void); 
	.org	. - (662b-661b) + (664b-663b)

.endm



#define _ALTERNATIVE_CFG(insn1, insn2, cap, cfg, ...)	\

	alternative_insn insn1, insn2, cap, IS_ENABLED(cfg)





#endif  /*  __ASSEMBLY__  */



/*

 * Usage: asm(ALTERNATIVE(oldinstr, newinstr, feature));

 *

 * Usage: asm(ALTERNATIVE(oldinstr, newinstr, feature, CONFIG_FOO));

 * N.B. If CONFIG_FOO is specified, but not selected, the whole block

 *      will be omitted, including oldinstr.

 */

#define ALTERNATIVE(oldinstr, newinstr, ...)   \

	_ALTERNATIVE_CFG(oldinstr, newinstr, __VA_ARGS__, 1)



#endif /* __ASM_ALTERNATIVE_H */