Re: [PATCH v2] Add Guile frame unwinder interface

[Eli Zaretskii <eliz@gnu.org>]

> Date: Mon, 09 Mar 2015 15:41:21 +0000
> From: Pedro Alves <palves@redhat.com>
> CC: asmundak@google.com
> 
> >From a glimpse over the code, I think this actually marks it as
> "<not saved>" (optimized out), right?  That would be the correct
> thing to do.  Marking a register as "<unavailable>" is also possible,
> but it is a different thing -- it means the value exists, but gdb
> couln't get to it, because e.g., the core file is trimmed, or the
> ptrace interface is missing access to some registers.

Actually, from past discussions I understand that "optimized out" more
often than not means "value exists, but GDB is not smart enough to
interpret the DWARF info to find it and/or GCC didn't put enough of
the info there to begin with".  So I wish we would at some point says
something different when this is the case, instead of hiding behind
unnamed "optimizations".