Re: [PATCH bpf-next v2 1/2] bpf, riscv: Add support for signed arena loads

> diff --git a/arch/riscv/net/bpf_jit_comp64.c b/arch/riscv/net/bpf_jit_comp64.c
> index 74efe4b138d2..56196b001286 100644
> --- a/arch/riscv/net/bpf_jit_comp64.c
> +++ b/arch/riscv/net/bpf_jit_comp64.c

[ ... ]

> @@ -1908,13 +1910,19 @@ int bpf_jit_emit_insn(const struct bpf_insn *insn, struct rv_jit_context *ctx,
>  	case BPF_LDX | BPF_PROBE_MEM32 | BPF_H:
>  	case BPF_LDX | BPF_PROBE_MEM32 | BPF_W:
>  	case BPF_LDX | BPF_PROBE_MEM32 | BPF_DW:
> +	/* LDX | PROBE_MEM32SX: sign-extending arena load */
> +	case BPF_LDX | BPF_PROBE_MEM32SX | BPF_B:
> +	case BPF_LDX | BPF_PROBE_MEM32SX | BPF_H:
> +	case BPF_LDX | BPF_PROBE_MEM32SX | BPF_W:
>  	{
>  		bool sign_ext;
>
>  		sign_ext = BPF_MODE(insn->code) == BPF_MEMSX ||
> -			   BPF_MODE(insn->code) == BPF_PROBE_MEMSX;
> +			   BPF_MODE(insn->code) == BPF_PROBE_MEMSX ||
> +			   BPF_MODE(insn->code) == BPF_PROBE_MEM32SX;
>
> -		if (BPF_MODE(insn->code) == BPF_PROBE_MEM32) {
> +		if (BPF_MODE(insn->code) == BPF_PROBE_MEM32 ||
> +		    BPF_MODE(insn->code) == BPF_PROBE_MEM32SX) {
>  			emit_add(RV_REG_T2, rs, RV_REG_ARENA, ctx);
>  			rs = RV_REG_T2;
>  		}

This isn't a bug, but would the comment fit the surrounding style better as
an expression? The neighbouring case-group comments all spell the access
out in pseudo-code form:

    /* LDX: dst = *(unsigned size *)(src + off) */
    /* LDSX: dst = *(signed size *)(src + off) */
    /* LDX | PROBE_MEM32: dst = *(unsigned size *)(src + RV_REG_ARENA + off) */
    /* ST | PROBE_MEM32: *(size *)(dst + RV_REG_ARENA + off) = imm */
    /* STX | PROBE_MEM32: *(size *)(dst + RV_REG_ARENA + off) = src */

Something like this would match the pattern:

    /* LDX | PROBE_MEM32SX: dst = *(signed size *)(src + RV_REG_ARENA + off) */


---
AI reviewed your patch. Please fix the bug or email reply why it's not a bug.
See: https://github.com/kernel-patches/vmtest/blob/master/ci/claude/README.md

CI run summary: https://github.com/kernel-patches/bpf/actions/runs/32235574103

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