linux-kernel - Re: [PATCH] riscv: correct riscv_insn_is_c_jr() and riscv_insn_is_c

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Message-ID: <87o7j9g73d.fsf@all.your.base.are.belong.to.us>
Date:   Mon, 14 Aug 2023 14:07:50 +0200
From:   Björn Töpel <bjorn@...nel.org>
To:     Nam Cao <namcaov@...il.com>,
        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
Cc:     Nam Cao <namcaov@...il.com>, charlie@...osinc.com
Subject: Re: [PATCH] riscv: correct riscv_insn_is_c_jr() and
 riscv_insn_is_c_jalr()

Nam Cao <namcaov@...il.com> writes:

> The instructions c.jr and c.jalr must have rs1 != 0, but
> riscv_insn_is_c_jr() and riscv_insn_is_c_jalr() do not check for this. So,
> riscv_insn_is_c_jr() can match a reserved encoding, while
> riscv_insn_is_c_jalr() can match the c.ebreak instruction.
>
> Rewrite them with check for rs1 != 0.
>
> Signed-off-by: Nam Cao <namcaov@...il.com>
> ---
>  arch/riscv/include/asm/insn.h | 15 +++++++++++++--
>  1 file changed, 13 insertions(+), 2 deletions(-)
>
> diff --git a/arch/riscv/include/asm/insn.h b/arch/riscv/include/asm/insn.h
> index 4e1505cef8aa..fce00400c9bc 100644
> --- a/arch/riscv/include/asm/insn.h
> +++ b/arch/riscv/include/asm/insn.h
> @@ -110,6 +110,7 @@
>  #define RVC_INSN_FUNCT4_OPOFF	12
>  #define RVC_INSN_FUNCT3_MASK	GENMASK(15, 13)
>  #define RVC_INSN_FUNCT3_OPOFF	13
> +#define RVC_INSN_J_RS1_MASK	GENMASK(11, 7)
>  #define RVC_INSN_J_RS2_MASK	GENMASK(6, 2)
>  #define RVC_INSN_OPCODE_MASK	GENMASK(1, 0)
>  #define RVC_ENCODE_FUNCT3(f_)	(RVC_FUNCT3_##f_ << RVC_INSN_FUNCT3_OPOFF)
> @@ -245,8 +246,6 @@ __RISCV_INSN_FUNCS(c_jal, RVC_MASK_C_JAL, RVC_MATCH_C_JAL)
>  __RISCV_INSN_FUNCS(auipc, RVG_MASK_AUIPC, RVG_MATCH_AUIPC)
>  __RISCV_INSN_FUNCS(jalr, RVG_MASK_JALR, RVG_MATCH_JALR)
>  __RISCV_INSN_FUNCS(jal, RVG_MASK_JAL, RVG_MATCH_JAL)
> -__RISCV_INSN_FUNCS(c_jr, RVC_MASK_C_JR, RVC_MATCH_C_JR)
> -__RISCV_INSN_FUNCS(c_jalr, RVC_MASK_C_JALR, RVC_MATCH_C_JALR)
>  __RISCV_INSN_FUNCS(c_j, RVC_MASK_C_J, RVC_MATCH_C_J)
>  __RISCV_INSN_FUNCS(beq, RVG_MASK_BEQ, RVG_MATCH_BEQ)
>  __RISCV_INSN_FUNCS(bne, RVG_MASK_BNE, RVG_MATCH_BNE)
> @@ -273,6 +272,18 @@ static __always_inline bool riscv_insn_is_branch(u32 code)
>  	return (code & RV_INSN_OPCODE_MASK) == RVG_OPCODE_BRANCH;
>  }
>  
> +static __always_inline bool riscv_insn_is_c_jr(u32 code)
> +{
> +	return (code & RVC_MASK_C_JR) == RVC_MATCH_C_JR &&
> +	       (code & RVC_INSN_J_RS1_MASK) != 0;
> +}
> +
> +static __always_inline bool riscv_insn_is_c_jalr(u32 code)
> +{
> +	return (code & RVC_MASK_C_JALR) == RVC_MATCH_C_JALR &&
> +	       (code & RVC_INSN_J_RS1_MASK) != 0;
> +}
> +

Nice one!

In the future, add a Fixes-tag for these kind of changes!
Fixes: ec5f90877516 ("RISC-V: Move riscv_insn_is_* macros into a common header")

(No need for a respin, b4 will pick up the Fixes above.)


Björn