Abstract: Researchers have shown that offloading software middleboxes (e.g., NAT, firewall, load balancer) to programmable switches can yield orders-of-magnitude performance gains. However, it requires manually selecting the middle-box components to offload and rewriting the offloaded code in P4, a domain-specific language for programmable switches. We design and implement Gallium, a compiler that transforms an input software middlebox into two parts—a P4 program that runs on a programmable switch and an x86 non-offloaded program that runs on a regular middlebox server. Gallium ensures that (1) the combined effect of the P4 program and the non-offloaded program is functionally equivalent to the input middlebox program, (2) the P4 program respects the resource constraints in the programmable switch, and (3) the run-to-completion semantics are met under concurrent execution. Our evaluations show that Gallium saves 21-79