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

Stefan Hajnoczi <[email protected]> Mon, 23 Apr 2018 10:33:34 +0100

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

On Sun, Apr 22, 2018 at 09:37:52PM -0400, 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?

Yes, that is what I was expecting.

Vladimir has a script to copy the coredump file and manipulate the
registers on disk, but it would be nicer to do stack-switching inside
the GDB session without needing to create another coredump file.

Vladimir: Would you like to write a GDB patch?  If GDB is fixed then
workaround won't be necessary.

Stefan

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