honey-potion VS qbe-rs

Hi all! We are working on an eBPF backend for Elixir. It's called Honey Potion. The project is under development, but it is possible to write some useful programs at this point. For instance, in this video, one of the guys involved explains how to write a program to count system calls.

We have been working on an eBPF backend for the Elixir programming language. The current implementation is on this branch. EBPF is a bit like a virtual machine that runs on the Linux kernel. EBPF programs are typically used to implement network applications. The most interesting aspect of the backend is that Linux uses a verifier to ensure that eBPF programs always terminate and only access memory within allocated bounds.

Hi! We have been translating Elixir to C (which we translate to eBPF) in HoneyPotion. We used mostly Chapter 15 of Appel's Modern Compiler Implementation in Java to implement the code generator (that's "15. Functional Programming Languages"). I think the choice of C has been good thus far. The implementation of Elixir's pattern matching took much work, but if we had chosen a higher level target, we would still have to translate that to eBPF. Here's the entry point for the translator.

We have been working on a tool that translates Elixir to eBPF. We actually translate eBPF to C. Now that we have more stuff working, I really wonder if generating C was a good choice.

That's exactly what Honey Potion does, when we translate Elixir into Linux' eBPF!

> I think it uses a different backend than LLVM

harec uses https://c9x.me/compile/

Have you considered QBE?

I really hope other new projects (like QBE) can really grow and become widely used

I really liked targetting QBE (https://c9x.me/compile/) as an IR, as it gave me lots of back-end optimisations for free 😊.

There is: QBE.

You might be underestimating the accuracy of the CPU models LLVM uses.

For x86, the same data the code generator uses drives llvm-mca[1], which given a loop body can tell you the throughput, latency, and microarchitectural bottlenecks (decoding, ports, dependencies, store forwarding, etc.)—if not always precisely, then still not worse then IACA, the tool written at Intel by people who presumably knew how the CPUs work, unlike LLVM contributors and the rest of us who can only guess and measure. This separately for Haswell, Sandy Bridge, Skylake, etc.; not “x86”.

Now, is this the best model you can get? Not exactly[2], but it’s close enough to not matter. Do we often need machine code to be optimized to that level of detail? Perhaps not[3], and with that in mind you can shave at least a factor of ten off LLVM’s considerable bulk at the cost of 20—30% of performance[4,5]. But if you do want those as well, it seems that the complexity of LLVM is a fair price, or has the right order of magnitude at least.

(Frontend not included, C++ frontend required to bootstrap sold separately, at a similar markup compared to a C-only frontend with somewhat worse ergonomics.)

[1] https://llvm.org/docs/CommandGuide/llvm-mca.html

[2] https://www.uops.info/

[3] https://briancallahan.net/blog/20211010.html

[4] https://c9x.me/compile/

[5] https://drewdevault.com/talks/qbe.html

You can try buildling you own backend like llvm. A good example or starting point is probably QBE since it is extremely small but very functional.

How big is the whole backend? I've heard that it is small but I wanted to compare it to QBE which is around 8 KLoC and it is quite interesting too.