linux-kernel - Re: [PATCH V1 0/5] riscv: Add k/uprobe supported

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Date:   Sat, 4 Jul 2020 09:39:50 +0300
From:   Pekka Enberg <penberg@...il.com>
To:     guoren@...nel.org
Cc:     palmerdabbelt@...gle.com, Paul Walmsley <paul.walmsley@...ive.com>,
        Anup Patel <anup@...infault.org>, greentime.hu@...ive.com,
        zong.li@...ive.com, me@...ki.ch, bjorn.topel@...il.com,
        atish.patra@....com, linux-riscv@...ts.infradead.org,
        Guo Ren <guoren@...ux.alibaba.com>,
        LKML <linux-kernel@...r.kernel.org>, linux-csky@...r.kernel.org
Subject: Re: [PATCH V1 0/5] riscv: Add k/uprobe supported

On Sat, Jul 4, 2020 at 6:34 AM <guoren@...nel.org> wrote:
> The patchset includes kprobe/uprobe support and some related fixups.

Nice!

On Sat, Jul 4, 2020 at 6:34 AM <guoren@...nel.org> wrote:
> There is no single step exception in riscv ISA, so utilize ebreak to
> simulate. Some pc related instructions couldn't be executed out of line
> and some system/fence instructions couldn't be a trace site at all.
> So we give out a reject list and simulate list in decode-insn.c.

Can you elaborate on what you mean by this? Why would you need a
single-step facility for kprobes? Is it for executing the instruction
that was replaced with a probe breakpoint?

Also, the "Debug Specification" [1] specifies a single-step facility
for RISC-V -- why is that not useful for implementing kprobes?

1. https://riscv.org/specifications/debug-specification/

- Pekka