KADB(4)                     BSD Programmer's Manual                    KADB(4)

NAME
     kdb - kernel debugging facility

SYNOPSIS
     options
     KADB

DESCRIPTION
     Kdb is a debugging facility for the kernel based on adb(1).  Kdb may be
     used to symbolically examine and modify memory locations, set break-
     points, and single step the system.

     Several boot time options are used in conjunction with the debugger.  To
     ``enable'' the debugger, the system must be booted with the RB_KDB flag
     (0x40) specified in the boothowto register.  When the debugger is enabled
     the system will read in and initialize the symbol table from the booted
     system.  If the RB_HALT flag (0x08) is also specified, the system will
     enter the debugger at the earliest possible time to allow breakpoints to
     be set before the system starts operation.  From that point on, if the
     RB_NOSYNC flag (0x04) is set, typing `^[k', `^[K', or `^[^K' at the con-
     sole causes a trap into the debugger.

     Kdb supports most of the adb command language.  The output formats `f',
     `F', `Y', are not supported.  The address space maps do not exist, thus
     the `m', `m', and `m' commands do not exist.  Shell escapes and command
     files are not supported.  The `r' and `k' commands make no sense and are
     not recognized.  Finally, the signal arguments to the continue and single
     step commands are ignored.

NOTES
     Kdb normally runs at a priority level below the interrupt level of the
     clock and all devices; the level of the highest priority software inter-
     rupt.  If the debugger is entered on the kernel's per-process stack at an
     ipl below its normal operating level it automatically switches to the in-
     terrupt stack to avoid potential overflow of the kernel stack.  Should
     the debugger operate on the kernel stack the message `(on kernel stack)'
     will be printed on entry.

     Note also that because kdb uses input from the console to force entry to
     the debugger it may not be possible to force entry if the system hangs at
     a priority level higher than the console receiver interrupt.

SEE ALSO
     adb(1)

HISTORY
     The kdb debugging facility currently under development.

BSDI BSD/386                    March 27, 1993                               1