linux-kernel - Re: [PATCH v6 06/13] riscv/kprobe: Add code to check if kprobe can be optimized

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Message-ID: <87wn51tsx2.fsf@all.your.base.are.belong.to.us>
Date:   Wed, 01 Feb 2023 14:30:01 +0100
From:   Björn Töpel <bjorn@...nel.org>
To:     Chen Guokai <chenguokai17@...ls.ucas.ac.cn>,
        paul.walmsley@...ive.com, palmer@...belt.com,
        aou@...s.berkeley.edu, rostedt@...dmis.org, mingo@...hat.com,
        sfr@...b.auug.org.au
Cc:     linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        liaochang1@...wei.com, Chen Guokai <chenguokai17@...ls.ucas.ac.cn>
Subject: Re: [PATCH v6 06/13] riscv/kprobe: Add code to check if kprobe can
 be optimized

Chen Guokai <chenguokai17@...ls.ucas.ac.cn> writes:

> From: Liao Chang <liaochang1@...wei.com>
>
> For the RVI and RVC hybrid encoding kernel, although AUIPC/JALR just
> occupy 8 bytes space, the patched code is 10 bytes at the worst case
> to ensure no RVI is truncated, so to check if kprobe satisfies the
> requirement of jump optimization, it has to find out an instruction
> window large enough to patch AUIPC/JALR(and padding C.NOP), and ensure
> no instruction nearby jumps into the patching window.
>
> Besides that, this series does not support the simulation of pc-relative
> instruction in optprobe handler yet, so the patching window should not
> includes pc-relative instruction.
>
> Signed-off-by: Liao Chang <liaochang1@...wei.com>
> Co-developed-by: Chen Guokai <chenguokai17@...ls.ucas.ac.cn>
> Signed-off-by: Chen Guokai <chenguokai17@...ls.ucas.ac.cn>

Reviewed-by: Björn Töpel <bjorn@...nel.org>