Jason Wessel writes:

I suppose the argument could be made to remove the check in the compiled 
file, but it does serve as a way to protect kgdb for now if someone 
tries to hard compile in xmon and kgdb.  Completely unpredictable 
results will occur with the debugger unless some pieces are fixed.  I 
would rather make sure until that happens there is no way head down the 
rat hole.

It should all work provided kgdb plays nicely.  We used to be able to
compile in both xmon and kdb and select at runtime which one gets
used.

That issue aside would it be useful to have xmon+kgdb?  After having 
looked at the hook points for xmon, if a command was added to xmon to 
provide an "detach" it would be easy enough to have kgdb and xmon in the 
same kernel.  Obviously only one or the other can be used at any given time.

Well, xmon_init(0) will do a detach.  However, I don't see that it is
needed; there is plenty of flexibility to choose to have xmon or not
using the CONFIG_XMON_DEFAULT config option and the xmon= boot command
line option.

Paul.