eBPF Is Awesome
Most examples of BPF code are written in a mix of Python and C using BCC, the "BPF Compiler Collection", which essentially treats all of LLVM and clang as a library callable from Python code.<p>I can't get my head around using it that way, and have found it pretty straightforward to just write C programs, compiled with clang `-target bpf`. Until very recently, writing anything interesting this way required you to declare all functions inline, compile into a single ELF .o, and, of course, avoid most loops. But most of the kinds of things you'd write in BPF tend not to be especially loopy (you can factor most algorithmic code out into userland, communicating with BPF using maps).<p>A big issue for this kind of development is kernel compat; struct layouts can change from release to release, for instance. This isn't a problem for us at Fly, because we just run the same kernel everywhere, but it's a real problem if you're trying to ship a tool for other people's systems. But that's changing with CO-RE; recent kernels can export a simplified symbol table in a BPF-legible format called BTF, and  the leader can perform relocations. Facebook has written a bunch of good stuff about this:<p><a href="https://facebookmicrosites.github.io/bpf/blog/2020/02/20/bcc-to-libbpf-howto-guide.html" rel="nofollow">https://facebookmicrosites.github.io/bpf/blog/2020/02/20/bcc...</a>