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Date:   Tue, 3 Jan 2023 10:33:20 +0000
From:   Conor Dooley <conor@kernel.org>
To:     =?iso-8859-1?Q?Bj=F6rn_T=F6pel?= <bjorn@kernel.org>
Cc:     Paul Walmsley <paul.walmsley@sifive.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Albert Ou <aou@eecs.berkeley.edu>,
        linux-riscv@lists.infradead.org, Guo Ren <guoren@kernel.org>,
        =?iso-8859-1?Q?Bj=F6rn_T=F6pel?= <bjorn@rivosinc.com>,
        linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org
Subject: Re: [PATCH] riscv, kprobes: Stricter c.jr/c.jalr decoding
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References: <20230102160748.1307289-1-bjorn@kernel.org>
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 <87sfgsp15q.fsf@all.your.base.are.belong.to.us>
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On Tue, Jan 03, 2023 at 07:44:49AM +0100, Bj=F6rn T=F6pel wrote:
> Conor Dooley <conor@kernel.org> writes:
> > On Mon, Jan 02, 2023 at 05:07:48PM +0100, Bj=F6rn T=F6pel wrote:
> >> From: Bj=F6rn T=F6pel <bjorn@rivosinc.com>
> >> diff --git a/arch/riscv/kernel/probes/simulate-insn.h b/arch/riscv/ker=
nel/probes/simulate-insn.h
> >> index cb6ff7dccb92..de8474146a9b 100644
> >> --- a/arch/riscv/kernel/probes/simulate-insn.h
> >> +++ b/arch/riscv/kernel/probes/simulate-insn.h
> >> @@ -31,9 +31,9 @@ __RISCV_INSN_FUNCS(fence,	0x7f, 0x0f);
> >>  	} while (0)
> >> =20
> >>  __RISCV_INSN_FUNCS(c_j,		0xe003, 0xa001);
> >> -__RISCV_INSN_FUNCS(c_jr,	0xf007, 0x8002);
> >
> > Hmm, I wonder where the mask originally came from!
>=20
> I think it's just a simple bug -- missing that "rs2" must be zero.
>=20
> > I had a look at the compressed spec, of which the version google gave to
> > me was v1.9 [1], and Table 1.6 in that (Instruction listing for RVC,
> > Quadrant 2) seems to list them all together.

> > [1] -
> > https://riscv.org/wp-content/uploads/2015/11/riscv-compressed-spec-v1.9=
=2Epdf
>=20
> C-ext is part of the unpriv spec:
> https://github.com/riscv/riscv-isa-manual/releases

Yah, I was trying to see if there was some period piece which was
misleading that would have explained the mask. I looked again & the v1.7
spec doesn't have that table, but also has no reason to suggest the
current mask either. Guess it was just a mistake :)

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