Re: kgdb support in vanilla 2.6.2

[Tom Rini <trini@kernel.crashing.org>]

On Thu, Mar 04, 2004 at 12:54:12PM -0800, George Anzinger wrote:
> Amit S. Kale wrote:
> >On Thursday 04 Mar 2004 10:48 am, Andrew Morton wrote:
> >
> >>"Amit S. Kale" <amitkale@emsyssoft.com> wrote:
> >>
> >>>Flashing keyboard lights is easy on x86 and x86_64 platforms.
> >>
> >>Please, no keyboards.  Some people want to be able to use kgdboe
> >>to find out why machine number 324 down the corridor just died.
> >>
> >>How about just doing
> >>
> >>
> >>char *why_i_crashed;
> >>
> >>
> >>{
> >>	...
> >>	if (expr1)
> >>		why_i_crashed = "hit a BUG";
> >>	else if (expr2)
> >>		why_i_crashed = "divide by zero";
> >>	else ...
> >>}
> >>
> >>then provide a gdb macro which prints out the string at *why_i_crashed?
> >
> >
> >If we can afford to do this (in terms of actions that can be done with the 
> >machine being unstable) we can certainly print a console message through 
> >gdb.
> 
> Not once you are connected to gdb.  The "O" packet can only be sent if the 
> program (i.e. kernel) is running as far as gdb knows.  So you could preceed 
> a connection with this, but could not used it after gdb knows the kernel is 
> stopped.

If GDB is already connected and sitting by waiting, you can send the O
packet.  If it is not, you could delay sending the O packet until you
know that GDB has now connected.

This isn't an unworkable idea, but it's probably better to just set
*why_i_crashed (think work work work, oh wait, what caused this again?)
and provide some handy macros (which we should be in the docs anyhow).

-- 
Tom Rini
http://gate.crashing.org/~trini/