svn commit: r354239 - head/contrib/gdb/gdb

[luporl]

The kernel parts were fixed by r354213 and r354214.
I've used old kgdb to test remote debugging through serial only, not for
inspecting crash dumps.

On Fri, Nov 1, 2019 at 4:34 PM John Baldwin <jhb at freebsd.org> wrote:

> On 11/1/19 12:26 PM, luporl wrote:
> > Well, after evaluating remote kernel debugging through serial port, on
> > amd64, I've run into several issues while using latest ports gdb/kgdb.
> > I don't remember all of them, but were things like step/next not always
> > working, connection being lost, and similar things.
> > OTOH, /usr/libexec/kgdb worked fine and reliably, although older and more
> > limited.
> > This is probably due to some incompatibility in GDB Remote Serial
> Protocol,
> > between the kernel backend and newer GDB from ports.
> >
> > So, that's why I chose to use /usr/libexec/kgdb while fixing/enabling
> > remote debugging on PPC64, because it works reasonably well, and I could
> > focus on testing/fixing other parts first.
> > With only this change on gdb, it is now possible to use it to test some
> > basic functionality, like remote debugger attach, backtrace and data
> > inspection.
> >
> > My goal is not to fix every issue in /usr/libexec/kgdb, but just to get
> the
> > basics working, to then move on and switch to ports' GDB.
>
> What's odd about this commit is it only affects userland binaries, not the
> kernel, so a bit odd for kgdb, especially since the old kgdb in the tree
> doesn't include user support IIRC, only kernel bits (in modern gdb, kgdb
> is just a wrapper, and you can use 'target vmcore' from within gdb itself
> against a crash dump, etc.)
>
> --
> John Baldwin
>