Re: [patch 00/12] entryval: Fix x86_64 <optimized out> parameters, virtual tail call frames

[Tom Tromey <tromey@redhat.com>]

>>>>> "Jan" == Jan Kratochvil <jan.kratochvil@redhat.com> writes:

Jan> It may have been discussed - it is not in `(gdb)Rationale' - why
Jan> isn't AX at least derived from DWARF?  But I guess the answer is
Jan> the part of DWARF expressions compatible with `(gdb)Rationale' ---
Jan> the AX requirements - is negligibly small.

I don't know, but we've collected a number of issues with AX as it now
stands.  These aren't merely theoretical, either, but problems with code
actually generated by GCC.  Those missing opcodes aren't missing out of
laziness, but rather because for the most part they aren't efficiently
implementable.  (One exception is the typed DWARF extension -- but we
could only handle integral types, which is probably not an interesting
subset.)

AX needs some big upgrades, or maybe an "AX 2.0" explicitly based on
DWARF.  I think the blocker here is that we (Red Hat) are on the cutting
edge for compilers and debuginfo, but don't currently have many users
using AX; but shops where the users are using AX are often (just
guessing) a few compiler revisions behind -- so nobody has really felt
the pain yet.


A related problem closer to home is that watchpoints don't respect
location lists.  Whoops.  I don't have a test case but I think one
should be constructible.  (I consider this related because it is another
spot where DWARF expressiveness has not propagated throughout GDB.)

Tom