On Mon, 2023-11-27 at 14:45 -0600, Daniel Xu wrote: [...] > IIUC uapi structs look the same in BTF as any other struct. Yes, and all share preserve_access_index attribute because of the way attribute push/pop directives are generated in vmlinux.h. > Just wondering, though: will bpftool be able to generate the appropriate > annotations for uapi structs? The problem is that there is no easy way to identify if structure is uapi in DWARF (from which BTF is generated). One way to do this: - modify pahole to check DW_AT_decl_file for each struct DWARF entry and generate some special decl tag in BTF; - modify bpftool to interpret this tag as a marker to not generate preserve_access_index for a structure. The drawback is that such behavior hardcodes some kernel specific assumptions both in pahole and in bpftool. It also remains to be seen if DW_AT_decl_file tags are consistent. It might be the case that allowing excessive CO-RE relocations is a better option. (And maybe tweak something about bitfield access generation to avoid such issues as in this thread). Thanks, Eduard
