linux-kernel - Re: [PATCH v5 4/9] riscv/kprobe: Add common RVI and RVC instruction decoder code

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Message-ID: <871qoasmmw.fsf@all.your.base.are.belong.to.us>
Date:   Wed, 04 Jan 2023 09:57:11 +0100
From:   Björn Töpel <bjorn@...nel.org>
To:     "liaochang (A)" <liaochang1@...wei.com>,
        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
Subject: Re: [PATCH v5 4/9] riscv/kprobe: Add common RVI and RVC instruction
 decoder code

"liaochang (A)" <liaochang1@...wei.com> writes:

>> Shouldn't the mask be 0xf003?
>
> Actually, the mask should be 0xf003 indeedly, but it also bring another problem that
> it can't tell C.MV and C.JR via the mask and value parts. Look opcodes below:
>
>       15 14 13 12 | 11 10  9  8 | 7 6 5 4 | 3 2  1 0
> C.JR:  1  0  0  0 |             rs1           0  1 0
> C.MV:  1  0  0  0 |              rd         rs2  1 0
>
> The only differece between C.MV and C.JR is the bits[2~6], these bitfield of C.JR is zero,
> the ones of C.MV is rs2 which never be zero. In order to tell C.MV and C.JR correclty, it
> is better to adjust the mask of C.JR to be 0xf07f as your patch(riscv, kprobe: Stricter c.jr/c.jalr decoding)
>
> Looking forward to your feedback.

Yup, that was the reason I submitted the fix! Let's wait for the fix to
be applied, and not include that fix in your feature series.


Björn