KGDB connection failure - Please help, I'm desparate! (=> or desperate)

[Peter Craft]

First off - Make that "desperate".  Sorry.

Second, an update..

I've modified remote.c in gdb to print the data coming across the
serial line.  When I boot with -d and enter "gdb" followed by "s", absolutely
nothing comes across the serial line - readchar times out every time.

If I then reboot without -d (with the same modified gdb running) and set console=comconsole
I see all of the expected console characters read by readchar.

So it appears that the gdb stub on the target isn't outputing any data to
the serial line whatsoever.  Again, I have KDB, DDB, and GDB set in the
configuration file and the sio flags set to 0x90 (I've tried 0xc0 as well)
in the loader.conf file.  Furthermore, when I boot with -d I see the
message:
    GDB: Current port: sio

Can anyone think of a reason why the target isn't outputting debug packets to
the serial port?  Can anyone suggest a method to debug a debugger?

Thanks


  ----- Original Message ----- 
  From: Peter Craft 
  To: freebsd-questions at freebsd.org 
  Sent: Friday, February 20, 2009 3:28 PM
  Subject: KGDB connection failure - Please help, I'm desparate!



  I've been trying for three days to get KGDB to work.

  I've followed the instructions here:
  http://www.freebsd.org/doc/en_US.ISO8859-1/books/developers-handbook/kerneldebug-online-gdb.html

  and here:
  http://www.lemis.com/grog/Papers/Debug-tutorial/tutorial.pdf

  without success.  Specifically, I've rebuilt my kernel with:
  makeoptions     DEBUG=-g                # Build kernel with gdb(1) debug symbols
  ..
  options         KDB
  options         DDB
  options         GDB

  My "boot.config" file contains -P and my /boot/loader.conf file contains:
  hint.sio.0.flags="0x90"

  When I issue the "boot -d" on the target, the system breaks in to the "db" prompt
  as expected, at which point I enter "gdb" followed by "s".  All of which seems to
  work perfectly.

  On the debugger side I enter kgdb with "kgdb -r /dev/cuad0 -v kernel.debug"
  from the build directory and I get:

  Ignoring packet error, continuing...
  Ignoring packet error, continuing...
  Ignoring packet error, continuing...
  Couldn't establish connection to remote target
  Malformed response to offset query, timeout

  If I boot the remote system with "set console=comconsole", I'm able to communicate
  across the serial line as a console, so I believe that the serial ports and cable are
  functioning properly.  I just can't get gdb to connect.

  Can anyone offer any suggestion on what to try next?  Or tips on how to go
  about debugging the problem?  This is with FreeBSD 7.1.

  Thanks in advance,

  Pete