Messages in this thread | | | Subject | Re: [PATCH v2 1/5] arm64: alternative: Provide if/else/endif assembler macros | From | Daniel Thompson <> | Date | Wed, 22 Jul 2015 12:08:00 +0100 |
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On 20/07/15 18:12, Will Deacon wrote: >> diff --git a/arch/arm64/include/asm/alternative.h b/arch/arm64/include/asm/alternative.h >> index c385a0c4057f..31b19ad18f7e 100644 >> --- a/arch/arm64/include/asm/alternative.h >> +++ b/arch/arm64/include/asm/alternative.h >> @@ -77,6 +77,46 @@ void free_alternatives_memory(void); >> .org . - (662b-661b) + (664b-663b) >> .endm >> >> +/* >> + * Begin an alternative code sequence. >> + * >> + * The code that follows this marco will be assembled and linked as >> + * normal. There are no restrictions on this code. > > s/marco/macro/
Will fix this.
> >> + */ >> +.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 jump to local labels defined outside of the alternative >> + * sequence. > > Actually, we fix up the branch target during patching. What you can't do > is jump into *another* alternative sequence.
Ok. I will update this.
I saw that there must be branch target patching (due to branches to __save_vgic_v3_state) but got it into my head that branches to local labels confused the assembler. I guess I must made an unrelated syntax error because I just done a few tests and can't reproduce anything like that.
Daniel.
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