[PATCH bpf-next v2 2/3] riscv, bpf: Fix support for BPF_MOVSX in RV32 JIT

[Pu Lehui]

On 2026/5/12 6:16, Kuan-Wei Chiu wrote:
> The current rv32 bpf jit compiler incorrectly treats BPF_MOVSX as a
> standard zero-extended move operation. The bpf instruction set allows
> sign-extension moves by reusing the BPF_MOV opcode with the instruction
> offset set to 8, 16, or 32.
> 
> Update the bpf_jit_emit_insn() function to check the offset field for
> both ALU and ALU64 MOV operations. If the offset is non-zero, emit the
> correct slli and srai instructions to perform the sign extension.
> 
> Before this patch:
> [   19.549705] test_bpf: #82 ALU_MOVSX | BPF_B jited:1 ret 2 != 1 (0x2 != 0x1)FAIL (1 times)
> [   19.551354] test_bpf: #83 ALU_MOVSX | BPF_H jited:1 ret 2 != 1 (0x2 != 0x1)FAIL (1 times)
> [   19.552576] test_bpf: #84 ALU64_MOVSX | BPF_B jited:1 ret 2 != 1 (0x2 != 0x1)FAIL (1 times)
> [   19.553542] test_bpf: #85 ALU64_MOVSX | BPF_H jited:1 ret 2 != 1 (0x2 != 0x1)FAIL (1 times)
> [   19.554807] test_bpf: #86 ALU64_MOVSX | BPF_W jited:1 ret 2 != 1 (0x2 != 0x1)FAIL (1 times)
> 
> After this patch:
> [   17.931172] test_bpf: #82 ALU_MOVSX | BPF_B jited:1 125 PASS
> [   17.932198] test_bpf: #83 ALU_MOVSX | BPF_H jited:1 124 PASS
> [   17.933039] test_bpf: #84 ALU64_MOVSX | BPF_B jited:1 124 PASS
> [   17.933918] test_bpf: #85 ALU64_MOVSX | BPF_H jited:1 124 PASS
> [   17.934751] test_bpf: #86 ALU64_MOVSX | BPF_W jited:1 122 PASS
> 
> Fixes: 8100928c8814 ("bpf: Support new sign-extension mov insns")

not a fix, the fixes tag should remove. And the title should `Add 
support for xxx`

others lgtm,

Reviewed-by: Pu Lehui <pulehui at huawei.com>

> Signed-off-by: Kuan-Wei Chiu <visitorckw at gmail.com>
> ---
>   arch/riscv/net/bpf_jit_comp32.c | 32 ++++++++++++++++++++++++++++++++
>   1 file changed, 32 insertions(+)
> 
> diff --git a/arch/riscv/net/bpf_jit_comp32.c b/arch/riscv/net/bpf_jit_comp32.c
> index 7396899ea276..f8509950fed4 100644
> --- a/arch/riscv/net/bpf_jit_comp32.c
> +++ b/arch/riscv/net/bpf_jit_comp32.c
> @@ -974,6 +974,24 @@ int bpf_jit_emit_insn(const struct bpf_insn *insn, struct rv_jit_context *ctx,
>   
>   	switch (code) {
>   	case BPF_ALU64 | BPF_MOV | BPF_X:
> +		if (insn->off != 0) {
> +			const s8 *rd = bpf_get_reg64(dst, tmp1, ctx);
> +			const s8 *rs = bpf_get_reg64(src, tmp2, ctx);
> +
> +			if (insn->off == 8) {
> +				emit(rv_slli(lo(rd), lo(rs), 24), ctx);
> +				emit(rv_srai(lo(rd), lo(rd), 24), ctx);
> +			} else if (insn->off == 16) {
> +				emit(rv_slli(lo(rd), lo(rs), 16), ctx);
> +				emit(rv_srai(lo(rd), lo(rd), 16), ctx);
> +			} else {
> +				emit(rv_addi(lo(rd), lo(rs), 0), ctx);
> +			}
> +			emit(rv_srai(hi(rd), lo(rd), 31), ctx);
> +			bpf_put_reg64(dst, rd, ctx);
> +			break;
> +		}
> +		fallthrough;
>   
>   	case BPF_ALU64 | BPF_ADD | BPF_X:
>   	case BPF_ALU64 | BPF_ADD | BPF_K:
> @@ -1024,6 +1042,20 @@ int bpf_jit_emit_insn(const struct bpf_insn *insn, struct rv_jit_context *ctx,
>   			emit_zext64(dst, ctx);
>   			break;
>   		}
> +		if (insn->off != 0) {
> +			const s8 *rd = bpf_get_reg32(dst, tmp1, ctx);
> +			const s8 *rs = bpf_get_reg32(src, tmp2, ctx);
> +
> +			if (insn->off == 8) {
> +				emit(rv_slli(lo(rd), lo(rs), 24), ctx);
> +				emit(rv_srai(lo(rd), lo(rd), 24), ctx);
> +			} else if (insn->off == 16) {
> +				emit(rv_slli(lo(rd), lo(rs), 16), ctx);
> +				emit(rv_srai(lo(rd), lo(rd), 16), ctx);
> +			}
> +			bpf_put_reg32(dst, rd, ctx);
> +			break;
> +		}
>   		fallthrough;
>   
>   	case BPF_ALU | BPF_ADD | BPF_X: