linux-kernel - Re: [PATCH] arm64: bpf: fix JIT stack setup

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Message-ID: <564249A2.1070903@linaro.org>
Date:	Tue, 10 Nov 2015 11:46:42 -0800
From:	"Shi, Yang" <yang.shi@...aro.org>
To:	Z Lim <zlim.lnx@...il.com>
CC:	Alexei Starovoitov <alexei.starovoitov@...il.com>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	Alexei Starovoitov <ast@...nel.org>, daniel@...earbox.net,
	Xi Wang <xi.wang@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Network Development <netdev@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	linaro-kernel@...ts.linaro.org
Subject: Re: [PATCH] arm64: bpf: fix JIT stack setup

On 11/9/2015 12:00 PM, Z Lim wrote:
> On Mon, Nov 9, 2015 at 10:08 AM, Shi, Yang <yang.shi@...aro.org> wrote:
>> I added it to stay align with ARMv8 AAPCS to maintain the correct FP during
>> function call. It makes us get correct stack backtrace.
>>
>> I think we'd better to keep compliant with ARMv8 AAPCS in BPF JIT prologue
>> too.
>>
>> If nobody thinks it is necessary, we definitely could remove that change.
>
> Oh no, I don't think anyone will say it's unnecessary!
> I agree the A64_FP-related change is a good idea, so stack unwinding works.
>
> How about splitting this into two patches? One for the BPF-related
> bug, and another for A64 FP-handling.

I'm not sure if this is a good approach or not. IMHO, they are kind of 
atomic. Without A64 FP-handling, that fix looks incomplete and 
introduces another problem (stack backtrace).

Thanks,
Yang

>
> Thanks again for tracking this down and improving things overall for arm64 :)
>
>>
>> Thanks,
>> Yang
>>
>>

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