Hello all! Thank you to everyone in the community for building/working on such a great tool! I am helping build a userspace implementation of eBPF and following Dave's standardization process closely. I was investigating how endianness affects the order of the components of instructions in memory. In particular, the order of the src/dest fields. In the IETF mailing list archives I found Jose's excellent pointer to the implementation-defined nature of the order of bit fields (https://mailarchive.ietf.org/arch/msg/bpf/I7abyqaiXj_DYuoLln5joMw90k0/) and spent the better part of today digging through gcc's source code to find the *actual* logic that controls the order (yes, I believe that I ultimately found it!). Nevertheless, given that there is a reliance on the behavior of gcc and clang, would you be interested in having additional documentation about it? I would love to write it but don't want to waste your time. I was thinking: 1. Adding documentation about field order to include/uapi/linux/bpf.h where the insn struct is defined. 2. Adding documentation to the design QA (Documentation/bpf/bpf_design_QA.rst) 3. Anything else that others might want. I apologize for the long email and I just want to be helpful. If this seems worthwhile, please let me know. Otherwise, I will defer and not bother you all further. Thanks! Will
