From: Daniel Thompson daniel.thompson@linaro.org
commit 63e40815f02584ba8174e0f6af40924b2b335cae upstream.
The existing alternative_insn macro has some limitations that make it hard to work with. In particular the fact it takes instructions from it own macro arguments means it doesn't play very nicely with C pre-processor macros because the macro arguments look like a string to the C pre-processor. Workarounds are (probably) possible but things start to look ugly.
Introduce an alternative set of macros that allows instructions to be presented to the assembler as normal and switch everything over to the new macros.
Signed-off-by: Daniel Thompson daniel.thompson@linaro.org Signed-off-by: Will Deacon will.deacon@arm.com Signed-off-by: David Brown david.brown@linaro.org --- arch/arm64/include/asm/alternative.h | 41 ++++++++++++++++++++++++++++++++++++ 1 file changed, 41 insertions(+)
diff --git a/arch/arm64/include/asm/alternative.h b/arch/arm64/include/asm/alternative.h index ec12951..c4243a4 100644 --- a/arch/arm64/include/asm/alternative.h +++ b/arch/arm64/include/asm/alternative.h @@ -76,6 +76,47 @@ void free_alternatives_memory(void); .org . - (662b-661b) + (664b-663b) .endm
+/* + * Begin an alternative code sequence. + * + * The code that follows this macro will be assembled and linked as + * normal. There are no restrictions on this code. + */ +.macro alternative_if_not cap + .pushsection .altinstructions, "a" + altinstruction_entry 661f, 663f, \cap, 662f-661f, 664f-663f + .popsection +661: +.endm + +/* + * Provide the alternative code sequence. + * + * The code that follows this macro is assembled into a special + * section to be used for dynamic patching. Code that follows this + * macro must: + * + * 1. Be exactly the same length (in bytes) as the default code + * sequence. + * + * 2. Not contain a branch target that is used outside of the + * alternative sequence it is defined in (branches into an + * alternative sequence are not fixed up). + */ +.macro alternative_else +662: .pushsection .altinstr_replacement, "ax" +663: +.endm + +/* + * Complete an alternative code sequence. + */ +.macro alternative_endif +664: .popsection + .org . - (664b-663b) + (662b-661b) + .org . - (662b-661b) + (664b-663b) +.endm + #endif /* __ASSEMBLY__ */
#endif /* __ASM_ALTERNATIVE_H */