>> For a moment, for the sake of this question, if we establish that CTF/BTF >> generation always feeds off DWARF DIEs (so there is no need to access >> type/decl tree nodes), what will it take to keep LTO support while keeping >> ctf_debug_finalize in dwarf2out_finish ? > > I don't think it's possible without major surgery. Now, it looks like > you want to emit .ctf at the LTO compile stage and BTF at the LTRANS > stage. Note you do not have access to the CTF data produced at the > LTRANS stage. What DWARF has access to is pointers (symbol name + offset) > to the early DWARF generated DIEs for GCCs tree decls from what it > adds DW_AT_abstract_origin references and then amending those entities > with furthr DWARF attributes. > > Now, the "major surgery" could for example entail streaming the CTF > data you produce from compile through WPA to the LTRANS stage. Or > alternatively simply reading it from the compile time produced objects > by means of the DWARF DIE references. I don't know what kind of (if any) > references you need to produce from BTF to the CTF data (I suppose they > might share indexes into a same symbol table...).
I am thinking, given that we have both "early DWARF" and "late DWARF", we may want to have three init/fini hooks for debug formats instead of two: DEBUG_FORMAT_initialize (called in dwarf2out_early_finish) [... traverse early DWARF (DEBUG_FORMAT_do_die) ...] DEBUG_FORMAT_early_finish (called in dwarf2out_early_finish) DEBUG_FORMAT_finish (called in dwarf2out_finish) Note that CTF and BTF share the ctfc internal data structure (which is built from traversing the early DWARF) but these are otherwise distinct debug formats: CTF can be completely emitted in ctf_early_finish, whereas BTF needs additional information that is only available in ctf_finish.)
