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From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug debug/108996] Proposal for adding DWARF call site information
 in GCC with -O0
Date: Tue, 07 Mar 2023 08:53:28 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D108996

--- Comment #10 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
(In reply to Ulrich Weigand from comment #8)
> (In reply to Jakub Jelinek from comment #5)
> > Though, relying on DW_OP_entry_value is not reliable, if e.g. tail call=
s are
> > (or could be) involved, then GDB needs to punt.
>=20
> The only way a tail call could happen is if the return value is
> passed through directly to the (caller's) caller, so the return
> buffer address should still be correct, right?

If there is just a single possible tail call, I think GDB still handles it,
so that would be ok.  But if you have multiple possible tail calls, I think=
 GDB
for DW_OP_entry_value evaluation punts (at least should, because it doesn't
know which
sequence of calls has been taken).

> I don't think it is possible to track the value in the callee - the value
> may not be available *anywhere* because it is no longer needed.  (Also, I
> don't think the implicit return buffer address is guaranteed to be spilled
> to the stack even at -O0.)

Well, at -O0 we can certainly guarantee it is available somewhere, even if =
we
currently don't do it already (it would surprise me if it is not spilled).=