Re: Debugging 32 bit ARM guests running under QEMU KVM on 64 bit ARM hosts with gdb

[alarson]

"Alex Bennée"
<alex.bennee@linaro.org> wrote on 01/12/2021 06:26:50 AM:

> From: "Alex Bennée" <alex.bennee@linaro.org>
> To: alarson@ddci.com
> Cc: "Berto
Furth" <bertofurth@sent.com>, qemu-discuss@nongnu.org
> Date: 01/12/2021
06:29 AM
> Subject:
Re: Debugging 32 bit ARM guests running under QEMU KVM on 
> 64 bit ARM hosts with gdb
> 
> 
> alarson@ddci.com writes:
> 
> >> From: "Berto Furth" <bertofurth@sent.com>
> >> To: qemu-discuss@nongnu.org
> >> Date: 01/08/2021 05:48 AM
> >> Subject: Debugging 32 bit ARM guests running under QEMU KVM
on 64 
> >> bit ARM hosts with gdb
> >
> >> I have noticed that when debugging a 32 bit arm (AA32) kvm
guest 
> >> running in a 64 bit ARM (aarch64 / AA64) host with "qemu-system-
> >> aarch64" and the "aarch64=off" flag set that
a remote gdb debugger 
> >> still thinks that it's debugging ARM64. ...
> >
> > Just FYI, my group has been maintaining a similar patch so we
can debug
> > 32-bit guests.  I don't have qemu commit privileges (and
I shouldn't),
> > but I would be willing to support this activity in terms of testing
> > patches, which I can do on arm, ppc, and x86 guests.  We
haven't updated
> > to recent QEMU versions recently, but for this I would.
> 
> Re-reading the old thread I think this stalled because it wasn't
> entirely clear moving the gdbstub initialisation in the second patch
was
> the cleanest way to deal with things.
> 
> Does you patch take a similar approach?

Sadly our patch
is pretty brutal.  It hard wires the GDB stub to 32-bit.
We ran into several
problems with the Eclipse version (at the time) stepping
between 32 and
64-bit code.  Since most of our code was 32-bit we just forced
32-bit access
always.  More recently we have more 64-bit code, hence the
interest in looking
for something that handles both more gracefully.  I'm
hoping the issues
with Eclipse have been resolved in the mean time.