From: James Morse james.morse@arm.com
commit 91a5cefa2f98bdd3404c2fba57048c4fa225cc37 upstream.
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 Signed-off-by: David Brown david.brown@linaro.org --- arch/arm64/include/asm/alternative.h | 28 +++++++++++++++++++++++++--- 1 file changed, 25 insertions(+), 3 deletions(-)
diff --git a/arch/arm64/include/asm/alternative.h b/arch/arm64/include/asm/alternative.h index c4243a4..4e3d4c8 100644 --- a/arch/arm64/include/asm/alternative.h +++ b/arch/arm64/include/asm/alternative.h @@ -3,6 +3,7 @@
#ifndef __ASSEMBLY__
+#include <linux/kconfig.h> #include <linux/types.h> #include <linux/stddef.h> #include <linux/stringify.h> @@ -39,7 +40,8 @@ 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" \ @@ -52,7 +54,11 @@ 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
@@ -64,7 +70,8 @@ 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 @@ -74,6 +81,7 @@ void free_alternatives_memory(void); 664: .popsection .org . - (664b-663b) + (662b-661b) .org . - (662b-661b) + (664b-663b) + .endif .endm
/* @@ -117,6 +125,20 @@ 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 */