svn commit: r294011 - head/share/man/man4

[Slawa Olhovchenkov]

On Fri, Jan 15, 2016 at 06:27:05AM +1100, Bruce Evans wrote:

> On Thu, 14 Jan 2016, Warner Losh wrote:
> 
> > Log:
> >  Document how to enter the debugger here. I'm sure there's some better
> >  canonical place, and the nit-pickers are welcome to move this
> >  information there with a cross reference.
> > ...
> > Modified: head/share/man/man4/ddb.4
> > ==============================================================================
> > --- head/share/man/man4/ddb.4	Thu Jan 14 16:21:58 2016	(r294010)
> > +++ head/share/man/man4/ddb.4	Thu Jan 14 16:23:07 2016	(r294011)
> > @@ -1435,6 +1435,47 @@ The NMI allows one to break into the deb
> > ...
> > +.Pp
> > +For serial consoles, you can break to the debugger by sending a BREAK
> > +condition on the serial line if
> > +.Cd options BREAK_TO_DEBUGGER
> > +is specified in the kernel.
> > +Most terminal emulation programs can send a break sequence with a
> > +special key sequence or via a menu item.
> > +However, in some setups, sending the break can be difficult to arrange
> > +or happens spuriously, so if the kernel contains
> 
> This is all quite broken, though the above description is almost correct.
> 
> The BREAK_TO_DEBUGGER option used to mean: enter (not break into) the
> debugger using a serial line break.  This is a good method, except it
> is too easy to get serial line breaks.  Unplugging the cable usually
> gives on, and turning off the other end might give one.  So this method
> is only usable on local systems with secure cables that you don't trip
> over or otherwise disconnect).
> 
> This option was broken to mean: the default for the sysctl that controls
> "breaking into" the debugger using either a serial line break or the console
> key for "breaking into" the debugger.  For almost perfection confusion,
> this key is normally the "Ctrl-Print Screen" key on PC keyboards and
> there is a "Break" key nearby.  Ctrl-Alt-Esc also works.  syscons(4)

On may keyboard "Break" subscribe to "Pause", to "Print Screen"
subscribe "SysReq".