On 05/24/2019 02:26 AM, Richard Biener wrote:
Currently, it does look like CTF for possibly to-be-omitted symbols will be
generated... I assume even DWARF needs to handle this case. Can you point me to
how DWARF does this ?
It emits the debug information. DWARF outputs a representation of the source,
not only emitted objects. We prune some "unused" bits if the user prefers us
to do that but we do not omit information on types or decls that are used in
the source but later eventually optimized away.
It seems to me that linker support to garbage collect
unused entries would be the way to go forward (probably easy for the
declarations
but not so for the types)?
Hmm, garbage collecting unused types in linker - Let me get back to you on
this. It does not look easy. Decl should be doable though.
For example DWARF has something like type units that can be refered
to via hashes. GCC can output those into separate sections and I can
envision outputting separate debug (CTF) sections for each declaration.
The linker could then merge sections for declarations that survived
and pick up all referenced type sections. Restrictions on ordering
for CTF may make this a bit difficult though, essentially forcing a
separate intermediate "unlinked" format and the linker regenerating
the final one. OTOH CTF probably simply concatenates data from
different CUs?
Yes, I cannot see this happening with CTF easily without some format changes.
At link-time, there needs to be de-duplication of CTF types across CUs. This
linker component needs work at this time, although we do have a working
prototype.
Regarding the type units in DWARF, are the shared/common types duplicated
across the type units ? If not duplicated, how are the referenced types
maintained/denoted across type units ?
Thanks!
Indu
