Subject: [PATCH v2 01/19] arm64: alternative: Allow alternative_insn to always issue the first instruction

From: Catalin Marinas <[email-masked]>
Date: Wed, 26 Feb 2020 18:05:08 +0000

There are situations where we do not want to disable the whole block
based on a config option, only the alternative part while keeping the
first instruction. Improve the alternative_insn assembler macro to take
a 'first_insn' argument, default 0 to preserve the current behaviour.

Signed-off-by: Catalin Marinas <[email-masked]>
---
 arch/arm64/include/asm/alternative.h | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/include/asm/alternative.h b/arch/arm64/include/asm/alternative.h
index 324e7d5ab37e..44083424d7aa 100644
--- a/arch/arm64/include/asm/alternative.h
+++ b/arch/arm64/include/asm/alternative.h
@@ -111,7 +111,11 @@ static inline void apply_alternatives_module(void *start, size_t length) { }
 	.byte \alt_len
 .endm
 
-.macro alternative_insn insn1, insn2, cap, enable = 1
+/*
+ * Disable the whole block if enable == 0, unless first_insn == 1 in which
+ * case insn1 will always be issued but without an alternative insn2.
+ */
+.macro alternative_insn insn1, insn2, cap, enable = 1, first_insn = 0
 	.if \enable
 661:	\insn1
 662:	.pushsection .altinstructions, "a"
@@ -122,6 +126,8 @@ static inline void apply_alternatives_module(void *start, size_t length) { }
 664:	.popsection
 	.org	. - (664b-663b) + (662b-661b)
 	.org	. - (662b-661b) + (664b-663b)
+	.elseif \first_insn
+	\insn1
 	.endif
 .endm

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