linux-kernel - Re: [PATCH 1/3] riscv: kprobes: simulate c.j instruction

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Message-ID: <ZNLmX1wXu3ZivilA@ghost>
Date:   Tue, 8 Aug 2023 18:05:35 -0700
From:   Charlie Jenkins <charlie@...osinc.com>
To:     Nam Cao <namcaov@...il.com>
Cc:     Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] riscv: kprobes: simulate c.j instruction

On Tue, Aug 08, 2023 at 05:11:48PM -0700, Charlie Jenkins wrote:
> On Sun, Jul 30, 2023 at 10:27:07AM +0200, Nam Cao wrote:
> > kprobes currently rejects c.j instruction. Implement it.
> > 
> > Signed-off-by: Nam Cao <namcaov@...il.com>
> > ---
> >  arch/riscv/kernel/probes/decode-insn.c   |  3 ++-
> >  arch/riscv/kernel/probes/simulate-insn.c | 24 ++++++++++++++++++++++++
> >  arch/riscv/kernel/probes/simulate-insn.h |  1 +
> >  3 files changed, 27 insertions(+), 1 deletion(-)
> > 
> > diff --git a/arch/riscv/kernel/probes/decode-insn.c b/arch/riscv/kernel/probes/decode-insn.c
> > index 64f6183b4717..39adb07a342d 100644
> > --- a/arch/riscv/kernel/probes/decode-insn.c
> > +++ b/arch/riscv/kernel/probes/decode-insn.c
> > @@ -29,13 +29,14 @@ riscv_probe_decode_insn(probe_opcode_t *addr, struct arch_probe_insn *api)
> >  	 * TODO: the REJECTED ones below need to be implemented
> >  	 */
> >  #ifdef CONFIG_RISCV_ISA_C
> > -	RISCV_INSN_REJECTED(c_j,		insn);
> >  	RISCV_INSN_REJECTED(c_jr,		insn);
> >  	RISCV_INSN_REJECTED(c_jal,		insn);
> >  	RISCV_INSN_REJECTED(c_jalr,		insn);
> >  	RISCV_INSN_REJECTED(c_beqz,		insn);
> >  	RISCV_INSN_REJECTED(c_bnez,		insn);
> >  	RISCV_INSN_REJECTED(c_ebreak,		insn);
> > +
> > +	RISCV_INSN_SET_SIMULATE(c_j,		insn);
> >  #endif
> >  
> >  	RISCV_INSN_SET_SIMULATE(jal,		insn);
> > diff --git a/arch/riscv/kernel/probes/simulate-insn.c b/arch/riscv/kernel/probes/simulate-insn.c
> > index 7441ac8a6843..3ba45c612cd8 100644
> > --- a/arch/riscv/kernel/probes/simulate-insn.c
> > +++ b/arch/riscv/kernel/probes/simulate-insn.c
> > @@ -188,3 +188,27 @@ bool __kprobes simulate_branch(u32 opcode, unsigned long addr, struct pt_regs *r
> >  
> >  	return true;
> >  }
> > +
> > +bool __kprobes simulate_c_j(u32 opcode, unsigned long addr, struct pt_regs *regs)
> > +{
> > +	/*
> > +	 *  15    13 12                            2 1      0
> > +	 * | funct3 | offset[11|4|9:8|10|6|7|3:1|5] | opcode |
> > +	 *     3                   11                    2
> > +	 */
> > +
> > +	s32 offset;
> > +
> > +	offset  = ((opcode >> 3)  & 0x7) << 1;
> > +	offset |= ((opcode >> 11) & 0x1) << 4;
> > +	offset |= ((opcode >> 2)  & 0x1) << 5;
> > +	offset |= ((opcode >> 7)  & 0x1) << 6;
> > +	offset |= ((opcode >> 6)  & 0x1) << 7;
> > +	offset |= ((opcode >> 9)  & 0x3) << 8;
> > +	offset |= ((opcode >> 8)  & 0x1) << 10;
> > +	offset |= ((opcode >> 12) & 0x1) << 11;
> > +
> > +	instruction_pointer_set(regs, addr + sign_extend32(offset, 11));
> Can you use riscv_insn_insert_jtype_imm() from insn.h since it is
> already created? It will also sign extend for you. Don't worry about
> creating a similar function for the branches, I am in the process of
> refactoring the insn.h file.
> > +
> > +	return true;
> > +}
> > diff --git a/arch/riscv/kernel/probes/simulate-insn.h b/arch/riscv/kernel/probes/simulate-insn.h
> > index 61e35db31001..4bd6c266e7d3 100644
> > --- a/arch/riscv/kernel/probes/simulate-insn.h
> > +++ b/arch/riscv/kernel/probes/simulate-insn.h
> > @@ -24,5 +24,6 @@ bool simulate_auipc(u32 opcode, unsigned long addr, struct pt_regs *regs);
> >  bool simulate_branch(u32 opcode, unsigned long addr, struct pt_regs *regs);
> >  bool simulate_jal(u32 opcode, unsigned long addr, struct pt_regs *regs);
> >  bool simulate_jalr(u32 opcode, unsigned long addr, struct pt_regs *regs);
> > +bool simulate_c_j(u32 opcode, unsigned long addr, struct pt_regs *regs);
> >  
> >  #endif /* _RISCV_KERNEL_PROBES_SIMULATE_INSN_H */
> > -- 
> > 2.34.1
> > 
> > 
> > _______________________________________________
> > linux-riscv mailing list
> > linux-riscv@...ts.infradead.org
> > http://lists.infradead.org/mailman/listinfo/linux-riscv
> Thanks,
> Charlie
Oh sorry, I forgot this was compressed. You can ignore the last message.
The changes look good. You can add:

Reviewed-by: Charlie Jenkins <charlie@...osinc.com>

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