eBPF backend doesn't generate emit in if statement correctly

[vbnogueira]

In the eBPF backend, if the user attempts to write an emit inside an if statement in the deparser's apply block, the generated code is semantically different from the original. For example the following snippet:

control IngressDeparserImpl(packet_out packet,
                            out empty_t clone_i2e_meta,
                            out empty_t resubmit_meta,
                            out empty_t normal_meta,
                            inout headers hdr,
                            in metadata meta,
                            in psa_ingress_output_metadata_t istd)
{
    apply {
        if (meta.mymd == 0) {
            packet.emit(hdr.ethernet);
        }


        packet.emit(hdr.ipv4);
    }   
}

Will generate and empty if statement:

if (meta->mymd == 0) { 
;            }

and completely ignore the emit for the ethernet header

Below is the link to a tarball which has both the P4 program used to reproduce the issue and the generated C eBPF file that will illustrate the bug:
emit-bug.tar.gz

The command used to compile was:

./p4c-ebpf --arch psa emit-bug.p4 -o emit-bug.c

I compiled p4c with commit 8273608

[fruffy]

Just a heads-up: the eBPF back end currently does not have an active maintainer who would take on this bug.

[vbnogueira]

Just a heads-up: the eBPF back end currently does not have an active maintainer who would take on this bug.

Ohh, I see
From what I understood, the tc backend uses the same deparser code and shares the same bug
So we can make it also a tc backend issue