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Date: Fri, 13 Nov 2015 18:39:33 -0800
Message-ID: <CABg9mcvomep=M1As_Vj=XuTNk=jiGwXQqQWbjotMXP2csKX=Bg@mail.gmail.com>
Subject: Re: [PATCH V3 2/2] arm64: bpf: make BPF prologue and epilogue align
 with ARM64 AAPCS
From: Z Lim <zlim.lnx@gmail.com>
To: Yang Shi <yang.shi@linaro.org>
Cc: Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will.deacon@arm.com>, Xi Wang <xi.wang@gmail.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Network Development <netdev@vger.kernel.org>,
        "linux-arm-kernel@lists.infradead.org" 
	<linux-arm-kernel@lists.infradead.org>,
        linaro-kernel@lists.linaro.org
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Yang, I noticed another thing...

On Fri, Nov 13, 2015 at 10:09 AM, Yang Shi <yang.shi@linaro.org> wrote:
> Save and restore FP/LR in BPF prog prologue and epilogue, save SP to FP
> in prologue in order to get the correct stack backtrace.
>
> However, ARM64 JIT used FP (x29) as eBPF fp register, FP is subjected to
> change during function call so it may cause the BPF prog stack base address
> change too.
>
> Use x25 to replace FP as BPF stack base register (fp). Since x25 is callee
> saved register, so it will keep intact during function call.

Can you please add save/restore for x25 also? :)

> It is initialized in BPF prog prologue when BPF prog is started to run
> everytime. When BPF prog exits, it could be just tossed.
>
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