Reasoning on pure machine code or disassembly is still hit and miss. For better results you can run the binary through a disassembler, then ask an llm to turn that into an equivalent c program, then ask it to work on that. But some of the subtleties might get lost in translation

If you put codex in Xhigh and allow it access to tools, it will take an hour but it will eventually give you back quality recompiled code, with the same issues the original had (here quality means readable)