LoongArch: BPF: Support sign-extension mov instructions

Add support for sign-extension mov instructions.
Signed-off-by: Hengqi Chen <hengqi.chen@gmail.com>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

arch/loongarch/net/bpf_jit.c

@@ -472,9 +472,24 @@ static int build_insn(const struct bpf_insn *insn, struct jit_ctx *ctx, bool ext
 	/* dst = src */
 	case BPF_ALU | BPF_MOV | BPF_X:
 	case BPF_ALU64 | BPF_MOV | BPF_X:
+		switch (off) {
+		case 0:
 			move_reg(ctx, dst, src);
 			emit_zext_32(ctx, dst, is32);
 			break;
+		case 8:
+			move_reg(ctx, t1, src);
+			emit_insn(ctx, extwb, dst, t1);
+			break;
+		case 16:
+			move_reg(ctx, t1, src);
+			emit_insn(ctx, extwh, dst, t1);
+			break;
+		case 32:
+			emit_insn(ctx, addw, dst, src, LOONGARCH_GPR_ZERO);
+			break;
+		}
+		break;
 
 	/* dst = imm */
 	case BPF_ALU | BPF_MOV | BPF_K: