remill VS revng-qa

Usually such things are called lifters. Wonder how this tool compares to other existing LLVM IR lifters, such as remill[0] and rellume[1].

0: https://github.com/lifting-bits/remill

> the binary code to LLVM IR uplifting loses a lot of context

Losing context is good in order to ensure you properly decoupled the frontend from the rest of the pipeline.

We don't even keep track of what a "call" instruction is, we re-detect it on the LLVM IR.

One reason you may want to preserve context is to let the user know where a specific piece of lifted code originated from. In order to preserve this information, we exploit LLVM's debugging metadata and it works pretty well. There's some loss there, but LLVM transformations strive to preserve it.

After all, imagine you have `add rax, 4; add rax, 4`, you'll want to optimize it to a +8 and you'll either have to decide if you want to associate your +8 operation with the first or the second instruction.

> the binary code to LLVM IR uplifting loses a lot of [...] semantics information

Not sure what you mean here, we use QEMU as a lifter and that's very accurate in terms of semantics.

I'm not sure what MIR and Swift IR have to do with the discussion, those are higher level IRs for specific languages. LLVM is rather low level and it's language agnostic.

However, for going beyond lifting, i.e., decompilation, it's true that LLVM shows some significant limitations. That's why we're rolling our own MLIR dialect, but we can still benefit of all the MLIR/LLVM infrastructure, optimizations and analyses. We're not starting from scratch.

> emulating pieces of the code sparsely to figure out indirect jumps and so on

It's hard to emulate without starting from the beginning. Maybe you're thinking about symbolic execution?

In any case, rev.ng does not emulate and does not do any symbolic execution: we have a data-flow analysis that detects destinations of indirect jumps and it's pretty scalable and effective. Example of things we handle: https://github.com/revng/revng-qa/blob/master/share/revng/te...