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

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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: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: James Morse <james.morse@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
This commit is contained in:
James Morse 2015-07-21 13:23:30 +01:00 committed by Will Deacon
parent 18ffa046c5
commit 91a5cefa2f
1 changed files with 25 additions and 3 deletions
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28
arch/arm64/include/asm/alternative.h
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@ -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 */