linux-kernel - Re: [PATCH v1 1/3] arm64: add a macro for SError synchronization

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Message-ID: <d7b8b779-9e00-8e8f-b44e-48e3d7e37058@huawei.com>
Date:   Wed, 1 Nov 2017 20:54:44 +0800
From:   gengdongjiu <gengdongjiu@...wei.com>
To:     Robin Murphy <robin.murphy@....com>, <catalin.marinas@....com>,
        <will.deacon@....com>, <marc.zyngier@....com>,
        <christoffer.dall@...aro.org>, <james.morse@....com>,
        <mark.rutland@....com>, <ard.biesheuvel@...aro.org>,
        <cov@...eaurora.org>, <Dave.Martin@....com>,
        <suzuki.poulose@....com>, <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <kvmarm@...ts.cs.columbia.edu>
Subject: Re: [PATCH v1 1/3] arm64: add a macro for SError synchronization

Hi Robin,

On 2017/11/1 19:24, Robin Murphy wrote:
>> +	esb
>> +alternative_else_nop_endif
>> +1:
>> +	.endm
> Having a branch in here is pretty horrible, and furthermore using label
> number 1 has a pretty high chance of subtly breaking code where this
> macro is inserted.
> 
> Can we not somehow nest or combine the alternative conditions here?

I found it will report error if combine the alternative conditions here.

For example:

+	.macro	error_synchronize
+alternative_if ARM64_HAS_IESB
+alternative_if ARM64_HAS_RAS_EXTN
+	esb
+alternative_else_nop_endif
+alternative_else_nop_endif
+	.endm

And even using b.eq/cbz instruction in the alternative instruction in arch/arm64/kernel/entry.S,
it will report Error.

For example below

alternative_if ARM64_HAS_PAN
	xxxxxxxxxxxxxxxxxxxx
        b.eq    xxxxx
alternative_else_nop_endif

I do not dig it deeply, do you know the reason about it or good suggestion about that?
Thanks a lot in advance.


> 
> Robin.
> 
>>  #endif	/* __ASM_ASSEMBLER_H */