On 07/29, sdf@xxxxxxxxxx wrote:
As discussed in https://docs.google.com/presentation/d/1A9Anx8JPHl_pK1aXy8hlxs3V5pkrKwHHtkPf_-HeYTc during BPF office hours, we'd like to attach arbitrary auxiliary metadata to the program, for example, the build timestamp or the commit hash.
IIRC, the suggestion was to explore BTF and .BTF.ext section in particular. We've spent some time looking at the BTF encoding and BTF.ext section and we don't see how we can put this data into .BTF.ext or even .BTF without any kernel changes.
The reasoning (at least how we see it): * .BTF.ext is just a container with func_info/line_info/relocation_info and libbpf extracts the data form this section and passes it to sys_bpf(BPF_PROG_LOAD); the important note is that it doesn't pass the whole container to the kernel, but passes the data that's been extracted from the appropriate sections * .BTF can be used for metadata, but it looks like we'd have to add another BTF_INFO_KIND() to make it a less messy (YiFei, feel free to correct me)
So the question is: are we missing something? Is there some way to add key=value metadata to BTF that doesn't involve a lot of kernel changes?
If the restrictions above are correct, should we go back to trying to put this metadata into .data section (or maybe even the new .metadata section)? The only missing piece of the puzzle in that case is the ability to extend BPF_PROG_LOAD with a way to say 'hold this map unconditionally'.
Should we have a short discussion about that this Thu during the office hours? I don't see this week's sheet page in there yet :-(
