Re: [Qemu-devel] [PATCH] scripts/qemugdb: support coroutine backtrace in coredumps

Stefan Hajnoczi <[email protected]> Wed, 2 Jan 2019 14:01:39 +0000

Newsgroups	gmane.comp.gdb.devel,gmane.comp.emulators.qemu
Message-ID	<[email protected]>

On Thu, Dec 27, 2018 at 05:36:04PM +0000, Vladimir Sementsov-Ogievskiy wrote:
> 23.04.2018 16:28, Pedro Alves wrote:
> > On 04/23/2018 02:37 AM, Simon Marchi wrote:
> >> On 2018-04-09 10:08 PM, Stefan Hajnoczi wrote:
> >>> I wonder what the point of select-frame is then...
> >>>
> >>> I have CCed the GDB mailing list.  Maybe someone can help us.  Context:
> >>>
> >>> QEMU implements coroutines using jmpbuf.  We'd like to print coroutine
> >>> call stacks in GDB and have a script that works when a process is being
> >>> debugged (it sets the registers).
> >>>
> >>> Now we'd like to extend the script to work on core dumps where it's not
> >>> possible to set registers (since there is no process being debugged).
> >>>
> >>> Is there a way to backtrace an arbitrary call stack in a core dump?
> >>
> >> Not that I know of.  The "frame <stack-addr> <pc-addr>" form of the frame
> >> command sounds like it should be usable to achieve that, but it doesn't
> >> seem to work in that way.  I really wonder if it's working as it was
> >> intended initially.  I guess using that form of the frame command should
> >> override/mask the real current values of $sp and $pc?
> > 
> > Yeah, "frame <args>" has a lot of problems.
> > 
> > This series was working toward sorting out the "frame" command:
> > 
> >    https://sourceware.org/ml/gdb-patches/2015-09/msg00248.html
> > 
> > Follow the urls there for more background.
> > 
> > To me, the important questions to answer are here:
> >   https://sourceware.org/ml/gdb-patches/2015-09/msg00658.html
> > 
> > Unfortunately, I don't think the series moved past that point.
> > 
> > Thanks,
> > Pedro Alves
> > 
> 
> 
> Hi Pedro!
> 
> Hmm, returned to this topic. I've spent this day digging in gdb code, and found it much
> more difficult than qemu)..
> 
> I've failed to find something like
> 
> create_frame_with_registers, or create_thread_with_registers.. Looks like registers comes
> from some register caches, backed by different sources of registers or something like this.
> 
> So, I'd like to ask several questions:
> 
> 1. Any news on the topic since April?

Not on my side, sorry.

Stefan

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