Re: [PATCH v4 2/5] RISC-V: add helpers for J-type immediate handling

[Andrew Jones <ajones@ventanamicro.com>]

On Mon, Jan 09, 2023 at 07:17:52PM +0100, Heiko Stuebner wrote:
> From: Heiko Stuebner <heiko.stuebner@vrull.eu>
> 
> Similar to the helper for the u-type + i-type imm handling, add helper-
> functions for j-type immediates.
> 
> While it also would be possible to open-code that bit of imm wiggling
> using the macros already provided in insn.h, it's way better to have
> consistency on how we handle this across all function encoding/decoding.
> 
> Signed-off-by: Heiko Stuebner <heiko.stuebner@vrull.eu>
> ---
>  arch/riscv/include/asm/insn.h | 26 ++++++++++++++++++++++++++
>  1 file changed, 26 insertions(+)
> 
> diff --git a/arch/riscv/include/asm/insn.h b/arch/riscv/include/asm/insn.h
> index 0455b4dcb0a7..9eea61a3028f 100644
> --- a/arch/riscv/include/asm/insn.h
> +++ b/arch/riscv/include/asm/insn.h
> @@ -301,6 +301,32 @@ static __always_inline bool riscv_insn_is_branch(u32 code)
>  	(RVC_X(x_, RVC_B_IMM_7_6_OPOFF, RVC_B_IMM_7_6_MASK) << RVC_B_IMM_7_6_OFF) | \
>  	(RVC_IMM_SIGN(x_) << RVC_B_IMM_SIGN_OFF); })
>  
> +/*
> + * Get the immediate from a J-type instruction.
> + *
> + * @insn: instruction to process
> + * Return: immediate
> + */
> +static inline s32 riscv_insn_extract_jtype_imm(u32 insn)
> +{
> +	return RV_EXTRACT_JTYPE_IMM(insn);
> +}
> +
> +/*
> + * Update a J-type instruction with an immediate value.
> + *
> + * @insn: pointer to the jtype instruction
> + * @imm: the immediate to insert into the instruction
> + */
> +static inline void riscv_insn_insert_jtype_imm(u32 *insn, s32 imm)
> +{
> +	*insn &= ~GENMASK(31, 12);
> +	*insn |= (((imm & (RV_J_IMM_10_1_MASK << RV_J_IMM_10_1_OFF)) << RV_I_IMM_11_0_OPOFF) |
                                                                        ^ RV_J_IMM_10_1_OPOFF
									(as pointed out by Conor)

> +		  ((imm & (RV_J_IMM_11_MASK << RV_J_IMM_11_OFF)) << RV_J_IMM_11_OPOFF) |
> +		  ((imm & (RV_J_IMM_19_12_OPOFF << RV_J_IMM_19_12_OFF)) << RV_J_IMM_19_12_OPOFF) |
                           ^ RV_J_IMM_19_12_MASK


> +		  ((imm & (1 << RV_J_IMM_SIGN_OFF)) << RV_J_IMM_SIGN_OPOFF));

nit: can drop the outermost ()

> +}
> +
>  /*
>   * Put together one immediate from a U-type and I-type instruction pair.
>   *
> -- 
> 2.35.1
> 

Thanks,
drew

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