linux-kernel - Re: [PATCH v5 1/9] riscv/kprobe: Prepare the skeleton to implement RISCV OPTPROBES feature

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Date:   Mon, 02 Jan 2023 19:03:17 +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 v5 1/9] riscv/kprobe: Prepare the skeleton to implement
 RISCV OPTPROBES feature

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

> From: Liao Chang <liaochang1@...wei.com>
>
> Prepare skeleton to implement optimized kprobe on RISCV, it is consist
> of Makfile, Kconfig and some architecture specific files: kprobe.h and
> opt.c opt.c include some macro, type definition and functions required
> by kprobe framework, opt_trampoline.S provide a piece of assembly code
> template used to construct the detour buffer as the target of long jump
> instruction(s) for each optimzed kprobe.

This is pretty much just reiterating what diff-stat says. Please try to
explain why a certain change is done, instead of what. What is already
in the patch.

> Since the jump range of PC-relative instruction JAL is +/-2M, that is
> too small to reach the detour buffer, hence the foudamental idea to
> address OPTPROBES on RISCV is replace 'EBREAK' with 'AUIPC/JALR'. which
> means it needs to clobber one more instruction beside the kprobe
> instruction, furthermore, RISCV supports hybird RVI and RVC in single
> kernel binary, so in theory a pair of 'AUIPC/JALR' is about to clobber
> 10 bytes(3 RVC and 1 RVI, 2 bytes is padding for alignment) at worst
> case. The second hardsome problem is looking for one integer register as
> the destination of 'AUIPC/JALR' without any side-effect.

There are a number of spelling errors, please use a spellchecker and if
you reference a file (e.g. Makefile), make sure it is correctly spelled
out.

The comments above applies to all the commit messages of this series.


Björn