> On Wed, Apr 24, 2024 at 5:25 AM Jose E. Marchesi
> <jose.marchesi@xxxxxxxxxx> wrote:
>>
>>
>> Hello.
>> The following function in the BPF selftest progs/test_xdp_noinline.c:
>>
>> /* don't believe your eyes!
>> * below function has 6 arguments whereas bpf and llvm allow maximum of 5
>> * but since it's _static_ llvm can optimize one argument away
>> */
>> __attribute__ ((noinline))
>> static int process_l3_headers_v6(struct packet_description *pckt,
>> __u8 *protocol, __u64 off,
>> __u16 *pkt_bytes, void *data,
>> void *data_end)
>> {
>> struct ipv6hdr *ip6h;
>> __u64 iph_len;
>> int action;
>>
>> ip6h = data + off;
>> if (ip6h + 1 > data_end)
>> return XDP_DROP;
>> iph_len = sizeof(struct ipv6hdr);
>> *protocol = ip6h->nexthdr;
>> pckt->flow.proto = *protocol;
>> *pkt_bytes = bpf_ntohs(ip6h->payload_len);
>> off += iph_len;
>> if (*protocol == 45) {
>> return XDP_DROP;
>> } else if (*protocol == 59) {
>> action = parse_icmpv6(data, data_end, off, pckt);
>> if (action >= 0)
>> return action;
>> } else {
>> memcpy(pckt->flow.srcv6, ip6h->saddr.in6_u.u6_addr32, 16);
>> memcpy(pckt->flow.dstv6, ip6h->daddr.in6_u.u6_addr32, 16);
>> }
>> return -1;
>> }
>>
>> Relies, as acknowledged in the comment block, on LLVM optimizing out one
>> of the arguments. As it happens GCC doesn't optimize that argument out,
>> and as a result it fails at compile-time when building
>> tst_xdp_noinline.c.
>>
>> Would it be possible to rewrite this particular test to not rely on that
>> particular optimization?
>
> Feel free to send a patch that reduces it to 5 args.
> This test was a copy paste of katran.
> There was no intent to test this 6->5 llvm optimization.
Ok perfect. Will do. Thanks!
