riscv, bpf: Support sign-extension mov insns

Add support sign-extension mov instructions for RV64.
Signed-off-by: Pu Lehui <pulehui@huawei.com>
Acked-by: Björn Töpel <bjorn@kernel.org>
Link: https://lore.kernel.org/r/20230824095001.3408573-4-pulehui@huaweicloud.comSigned-off-by: Alexei Starovoitov <ast@kernel.org>

arch/riscv/net/bpf_jit_comp64.c

@@ -1047,7 +1047,19 @@ int bpf_jit_emit_insn(const struct bpf_insn *insn, struct rv_jit_context *ctx,
 			emit_zext_32(rd, ctx);
 			break;
 		}
+		switch (insn->off) {
+		case 0:
 			emit_mv(rd, rs, ctx);
+			break;
+		case 8:
+		case 16:
+			emit_slli(RV_REG_T1, rs, 64 - insn->off, ctx);
+			emit_srai(rd, RV_REG_T1, 64 - insn->off, ctx);
+			break;
+		case 32:
+			emit_addiw(rd, rs, 0, ctx);
+			break;
+		}
 		if (!is64 && !aux->verifier_zext)
 			emit_zext_32(rd, ctx);
 		break;