How frame command with address works

[Simon Marchi]

On 2/8/23 05:01, Roger Phillips via Gdb wrote:
> Greetings,
> 
> I have to analyze a coredump on an Aarch64 system. The callstack is
> broken so I only see the bottom frame. However, if I manually unwind
> the stack via $x29 register then I see what looks like intact stack
> frames. Now I try to use the frame / frame address command with the
> addresses from the $x29 registers which should point to the bases of
> the stackframes (the location where the address of the next frame is).
> However it always tells me "No frame at address ...".
> 
> What does frame address need to correctly parse a frame?

I think you want to use the "frame view" or "select-frame view"
command, which lets you specify arbitrary SP and PC addresses.  GDB
makes a frame_info object out of those and shows it to you.

It used to be that "frame <ADDRESS>" would do that, but it was
error-prone, as explained here, so was chanted to "frame view" and
"select-frame view":

  https://gitlab.com/gnutools/binutils-gdb/-/commit/f67ffa6a785bee26bc23550670f85c6db578641f

I know a bit about that feature because it was in the way of some change
I wanted to do recently (frame_info_ptr, if someone wants to search the
git log).  I think the intent of the feature is exactly your scenario.
However, I'm under the impression that it's a bit broken right now.
When selecting an arbitrary frame with "select-frame view", you can't do
up/down to see callers of that frame, and "backtrace" shows you the
"real" stack.  I've been told that these commands used to work with
user-created frames though, probably a long time ago.  But since that
feature wasn't tested at all, I guess it got broken.

Simon