.\"	$NetBSD: ddb.4,v 1.16 1997/11/23 18:37:33 chopps Exp $
.\"
.\" Copyright (c) 1997 The NetBSD Foundation, Inc.
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.\" This code is derived from software contributed to The NetBSD Foundation
.\" by Luke Mewburn
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.\"    must display the following acknowledgement:
.\"        This product includes software developed by the NetBSD
.\"        Foundation, Inc. and its contributors.
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.\"    contributors may be used to endorse or promote products derived
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.\" ---
.\"	This manual page was derived from a -man.old document which bore
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.\"
.\" Mach Operating System
.\" Copyright (c) 1991,1990 Carnegie Mellon University
.\" All Rights Reserved.
.\" 
.\" Permission to use, copy, modify and distribute this software and its
.\" documentation is hereby granted, provided that both the copyright
.\" notice and this permission notice appear in all copies of the
.\" software, derivative works or modified versions, and any portions
.\" thereof, and that both notices appear in supporting documentation.
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.\" CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
.\" CONDITION.  CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND FOR
.\" ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
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.\" Carnegie Mellon requests users of this software to return to
.\" 
.\"  Software Distribution Coordinator  or  Software.Distribution@CS.CMU.EDU
.\"  School of Computer Science
.\"  Carnegie Mellon University
.\"  Pittsburgh PA 15213-3890
.\" 
.\" any improvements or extensions that they make and grant Carnegie Mellon
.\" the rights to redistribute these changes.
.\"
.Dd November 17, 1997
.Dt DDB 4
.Os NetBSD
.Sh NAME
.Nm ddb
.Nd in-kernel debugger
.Sh SYNOPSIS
.Cd options DDB
.Pp
To enable history editing:
.Cd options DDB_HISTORY_SIZE=integer
.Pp
To disable entering
.Nm
upon kernel panic:
.Cd options DDB_ONPANIC=0
.Sh DESCRIPTION
.Nm
is the in-kernel debugger.
It may be entered at any time via a special key sequence, and
optionally may be invoked when the kernel panics.
.Pp
The current memory location being edited is referred to as
.Ar dot ,
and the next location is
.Ar next .
They are displayed as hexadecimal numbers.
.Pp
Commands that examine and/or modify memory update
.Ar dot
to the address of the last line examined or the last location
modified, and set
.Ar next
to the next location to be examined or modified.
Other commands don't change
.Ar dot ,
and set
.Ar next
to be the same as
.Ar dot .
.Pp
The general command syntax is:
.Bd -ragged -offset indent
.Ic command Ns Op Cm / Ns Ar modifier
.Ar address
.Op Cm , Ns Ar count
.Ed
.Pp
A blank line repeats the previous command from the address
.Ar next
with a
.Cm count
of 1 and no modifiers.
Specifying
.Cm address
sets
.Em dot
to the address.
If 
.Cm address
is omitted,
.Em dot
is used.
A missing
.Cm count
is taken to be 1 for printing commands, and infinity for stack traces.
.Pp
.Nm
has a
.Xr more 1 -like
functionality; if a number of lines in a command's output exceeds the number
defined in the
.Va lines
variable, then
.Nm
displays
.Dq "--db more--"
and waits for a response, which may be one of:
.Bl -tag -offset indent -width "<return>"
.It <return>
one more line.
.It <space>
one more page.
.It Ic q 
abort the current command, and return to the command input mode.
.El
.Pp
If 
.Nm
history editing is enabled (by defining the
.D1 Cd options DDB_HISTORY_SIZE=num
kernel option), then a history of the last
.Cm num
commands is kept.
The history can be manipulated with the following key sequences:
.Bl -tag -offset indent -width "<Ctrl>-P"
.It <Ctrl>-P
retrieve previous command in history (if any).
.It <Ctrl>-N
retrieve next command in history (if any).
.El
.Sh COMMANDS
.Nm
supports the following commands:
.Bl -tag -width 5n
.It Xo
.Ic examine Ns Op Cm / Ns Ar modifier
.Ar address Ns Op Cm , Ns Ar count
.Xc
Display the address locations according to the format in 
.Ar modifier .
Multiple modifier formats display multiple locations.
If
.Ar modifier
isn't specified, the modifier from the last use of
.Ic examine
is used.
.Pp
The valid format characters for
.Ar modifier
are:
.Bl -tag -offset indent -width 2n
.It Cm b
examine bytes (8 bits).
.It Cm h
examine half-words (16 bits).
.It Cm l
examine long-words (32 bits).
.It Cm a
print the location being examined.
.It Cm A
print the location with a line number if possible.
.It Cm x
display in unsigned hex.
.It Cm z
display in signed hex.
.It Cm o
display in unsigned octal.
.It Cm d
display in signed decimal.
.It Cm u
display in unsigned decimal.
.It Cm r
display in current radix, signed.
.It Cm c
display low 8 bits as a character.
Non-printing characters as displayed as an octal escape code
(e.g.,
.Sq \e000 ) .
.It Cm s
display the NUL terminated string at the location.
Non-printing characters are displayed as octal escapes.
.It Cm m
display in unsigned hex with a character dump at the end of each line.
The location is displayed as hex at the beginning of each line.
.It Cm i
display as a machine instruction.
.It Cm I
display as a machine instruction, with possible alternative formats
depending upon the machine:
.Bl -tag -offset indent -width "sparc"
.It i386
don't round to the next long word boundary
.It mips
print register contents
.It vax
don't assume that each external label is a procedure entry mask
.El
.El
.It Xo
.Ic x Ns Op Cm / Ns Ar modifier
.Ar address Ns Op Cm , Ns Ar count
.Xc
A synonym for
.Ic examine .
.It Ic xf
Examine forward.
.Ic xf
re-executes the most recent
.Ic execute
command with the same parameters except that
.Ar address
is set to
.Ar next .
.It Ic xb
Examine backward.
.Ic xb
re-executes the most recent
.Ic execute
command with the same parameters, except that
.Ar address
is set to the last start address minus its size.
.It Xo
.Ic print Ns Op Cm /axzodurc
.Ar address Op Ar address ...
.Xc
Print addresses
.Ar address
according to the modifier character, as per
.Ic examine .
Valid modifiers are:
.Cm /a ,
.Cm /x ,
.Cm /z ,
.Cm /o ,
.Cm /d ,
.Cm /u ,
.Cm /r ,
and
.Cm /c
(as per
.Ic examine ) .
If no modifier is specified, the most recent one specified is used.
.Ar address
may be a string, and is printed
.Dq as-is .
For example:
.Bd -literal -offset indent
print/x "eax = " $eax "\enecx = " $ecx "\en"
.Ed
.Pp
will produce:
.Bd -literal -offset indent
eax = xxxxxx
ecx = yyyyyy
.Ed
.It Xo
.Ic write Ns Op Cm /bhl
.Ar address
.Ar expression Op Ar expression ...
.Xc
Write the
.Ar expression Ns s
at succeeding locations.
The unit size is specified with a modifier character, as per
.Ic examine .
Valid modifiers are:
.Cm /b ,
.Cm /h ,
and
.Cm /l .
If no modifier is specified,
.Cm /l
is used.
.Pp
Warning: since there is no delimiter between
.Ar expression Ns s ,
strange things may occur.
It's best to enclose each
.Ar expression
in parentheses.
.It Xo
.Ic set
.Cm $ Ns Ar variable
.Op Cm =
.Ar expression
.Xc
Set the named variable or register to the value of
.Ar expression .
Valid variable names are described in
.Sx VARIABLES .
.It Xo
.Cm break Ns Op Cm /u
.Ar address Ns Op Cm , Ns Ar count
.Xc
Set a breakpoint at
.Ar address .
If
.Ar count
is supplied, continues
.Pq Ar count Ns -1
times before stopping at the breakpoint.
If the breakpoint is set, a breakpoint number is printed with
.Sq # .
This number can be used to
.Ic delete
the breakpoint, or to add
conditions to it.
.Pp
If
.Cm /u
is specified,
set a breakpoint at a user-space address.
Without
.Cm /u ,
.Ar address
is considered to be in the kernel-space, and an address in the wrong
space will be rejected, and an error message will be emitted.
This modifier may only be used if it is supported by machine dependent
routines.
.Pp
Warning: if a user text is shadowed by a normal user-space debugger,
user-space breakpoints may not work correctly.
Setting a breakpoint at the low-level code paths may also cause
strange behavior.
.It Xo
.Ic delete
.Ar "address" |
.Cm # Ns Ar number
.Xc
Delete a breakpoint.
The target breakpoint may be specified by
.Ar address ,
as per
.Ic break ,
or by the breakpoint number returned by
.Ic break
if it's prefixed with
.Sq Cm # .
.It Xo
.Ic step Ns Op Cm /p
.Op Cm , Ns Ar count
.Xc
Single-step
.Ar count
times.
If
.Cm /p
is specified, print each instruction at each step.
Otherwise, only print the last instruction.
.Pp
Warning: depending on the machine type, it may not be possible
to single-step through some low-level code paths or user-space
code.
On machines with software-emulated single-stepping (e.g., pmax),
stepping through code executed by interrupt handlers will probably
do the wrong thing.
.It Ic continue Ns Op Cm /c
Continue execution until a breakpoint or watchpoint.
If
.Cm /c
is specified, count instructions while executing.
Some machines (e.g., pmax) also count loads and stores.
.Pp
Warning: when counting, the debugger is really silently
single-stepping.
This means that single-stepping on low-level may cause strange
behavior.
.It Ic until Ns Op Cm /p
Stop at the next call or return instruction.
If
.Cm /p
is specified, print the call nesting depth and the
cumulative instruction count at each call or return.
Otherwise, only print when the matching return is hit.
.It Ic next Ns Op Cm /p
Stop at the matching return instruction.
If
.Cm /p
is specified, print the call nesting depth and the
cumulative instruction count at each call or return.
Otherwise, only print when the matching return is hit.
.It Ic match Ns Op Cm /p
A synonym for
.Ic next .
.It Xo
.Cm trace Ns Op Cm /u
.Sm off
.Op Ar frame-address
.Op Cm , Ar count
.Sm on
.Xc
Stack trace from
.Ar frame-address .
If
.Cm /u
is specified, trace user-space, otherwise trace kernel-space.
.Ar count
is the number of frames to be traced.
If
.Ar count
is omitted, all frames are printed.
.Pp
Warning: user-space stack trace is valid only if the machine dependent
code supports it.
.It Xo
.Cm trace/t
.Sm off
.Op Ar pid
.Op Cm , Ar count
.Sm on
.Xc
Stack trace by
.Dq thread
(process, on NetBSD) rather than by stack frame address.
Note that
.Ar pid
is interpreted using the current radix, whilst
.Ic ps
displays pids in decimal; prefix
.Ar pid
with
.Sq 0t
to force it to be interpreted as decimal.
.Pp
Warning: trace by pid is valid only if the machine dependent code
supports it.
.It Xo
.Ic search Ns Op Cm /bhl
.Ar address
.Ar value
.Op Ar mask
.Op Cm , Ns Ar count
.Xc
Search memory from
.Ar address
for
.Ar value .
The unit size is specified with a modifier character, as per
.Ic examine .
Valid modifiers are:
.Cm /b ,
.Cm /h ,
and
.Cm /l .
If no modifier is specified,
.Cm /l
is used.
.Pp
This command might fail in interesting ways if it doesn't find
.Ar value .
This is because
.Nm
doesn't always recover from touching bad memory.
The optional
.Ar count
limits the search.
.It Ic reboot Op Ar flags
Reboot, using the optionally supplied boot
.Ar flags .
.Pp
Note: Limitations of the command line interface preclude
specification of a boot string.
.It Xo
.Sm off
.Ic "show\ all\ procs"
.Op Cm /a
.Op Cm /n
.Op Cm /w
.Sm on
.Xc
Display all process information.
Valid modifiers:
.Bl -tag -width 3n
.It Cm /n
show process information in a
.Xr ps 1
style format (this is the default).
Information printed includes: process ID, parent process ID,
process group, UID, process status, process flags, process
command name, and process wait channel message.
.It Cm /a
show the kernel virtual addresses of each process'
proc structure, u-are, and vmspace structure.
The vmspace address is also the address of the process'
vm_map structure, and can be used in the
.Ic "show map"
command.
.It Cm /w
show each process' PID, command, system call emulation, wait channel
address, and wait channel message.
.El
.It Xo
.Sm off
.Ic ps
.Op Cm /a
.Op Cm /n
.Op Cm /w
.Sm on
.Xc
A synonym for
.Ic "show all procs" .
.It Ic "show registers" Ns Op Cm /u
Display the register set.
If
.Cm /u
is specified, display user registers instead of kernel registers
or the currently save one.
.Pp
Warning: support for
.Cm /u
is machine dependent.
If not supported, incorrect information will be displayed.
.It Xo
.Ic "show map" Ns Op Cm /f
.Ar address
.Xc 
Print the vm_map at
.Ar address .
If
.Cm /f
is specified the complete map is printed.
.It Xo
.Ic "show object" Ns Op Cm /f
.Ar address
.Xc 
Print the vm_object at
.Ar address .
If
.Cm /f
is specified the complete object is printed.
.It Ic "show watches"
Display all watchpoints.
.It Xo
.Ic watch
.Sm off
.Ar address
.Op Cm , Ar size
.Sm on
.Xc
Set a watchpoint for a region.
Execution stops when an attempt to modify the region occurs.
.Ar size
defaults to 4.
.Pp
If you specify a wrong space address, the request is
rejected with an error message.
.Pp
Warning: attempts to watch wired kernel memory may cause
an unrecoverable error in some systems such as i386.
Watchpoints on user addresses work the best.
.El
.Sh VARIABLES
.Nm
accesses registers and variables as
.Cm $ Ns Ar name .
Register names are as per the
.Ic "show registers"
command.
Some variables are suffixed with numbers, and may have a modifier
following a colon immediately after the variable name.
For example, register variables may have a
.Sq u
modifier to indicate user register
(e.g.,
.Li "$eax:u" ) .
.Pp
Built-in variables currently supported are:
.Bl -tag -offset indent -width "maxwidth"
.It Va lines
The number of lines.
This is used by the
.Ic more
feature.
.It Va maxoff
Addresses are printed as
.Li 'symbol'+offset
unless
.Li offset
is greater than
.Va maxoff .
.It Va maxwidth
The width of the displayed line.
.It Va onpanic
If non-zero (the default),
.Nm
will be invoked when the kernel panics.
If the kernel configuration option
.D1 Cd options DDB_ONPANIC=0
is used,
.Va onpanic
will be initialised to off.
.It Va radix
Input and output radix.
.It Va tabstops
Tab stop width.
.It Va work Ns Sy xx
Temporary work variable.
.Sq Sy xx
is between 0 and 31.
.El
.Pp
All built-in variables are accessible via
.Xr sysctl 3 .
.Sh EXPRESSIONS
Almost all expression operators in C are supported, except
.Sq ~ ,
.Sq ^ ,
and unary
.Sq & .
Special rules in
.Nm
are:
.Bl -tag -offset indent -width "identifier"
.It Ar identifier
name of a symbol.
It is translated to the address (or value) of it.
.Sq .
and
.Sq :
can be used in the identifier.
If supported by an object format dependent routine,
.Sm off
.Xo
.Oo Ar filename : Oc
.Ar function
.Oo : Ar "line number" Oc ,
.Xc
.Xo
.Oo Ar filename : Oc
.Ar variable ,
.Xc
and
.Xo
.Ar filename
.Oo : Ar "line number" Oc ,
.Xc
.Sm on
can be accepted as a symbol.
The symbol may be prefixed with
.Ar "symbol_table_name" Ns ::
(e.g.,
.Li emulator::mach_msg_trap )
to specify other than kernel symbols.
.It Ar number
number.
Radix is determined by the first two characters:
.Sq 0x
- hex,
.Sq 0o
- octal,
.Sq 0t
- decimal,
otherwise follow current radix.
.It Cm .
.Ar dot
.It Cm +
.Ar next
.It Cm ..
address of the start of the last line examined.
Unlike
.Ar dot
or
.Ar next ,
this is only changed by the
.Ic examine
or
.Ic write
commands.
.It Cm ,
last address explicitly specified.
.It Cm $ Ns Ar name
register name or variable.
It is translated to the value of it.
It may be followed by a
.Sq :
and modifiers as described above.
.It Cm a
multiple of right-hand side.
.It Cm * Ns Ar expr
expression indirection.
It may be followed by a
.Sq :
and modifiers as described above.
.El
.Sh ENTERING THE DEBUGGER
Unless
.Va onpanic
is set to 0,
.Nm
will be activated whenever the kernel would otherwise panic.
.Pp
.Nm
may also be activated from the console.
In general, sending a break on a serial console will activate
.Nm "" .
There are also key sequences for each port that will activate
.Nm
from the keyboard:
.Bl -tag -offset indent -width "mac68k"
.It amiga
<LAlt>-<LAmiga>-<F10>
.It hp300
<Shift>-<Reset>
.It i386
<Ctrl>-<Alt>-<Esc>
.It mac68k
<Command>-<Power>, or the Interrupt switch.
.It sparc
<L1>-A, or <Stop>-A
.El
.Pp
In addition,
.Nm
may be explicitly activated by the debugging code in the kernel
if
.Cm DDB
is configured.
.Sh SEE ALSO
.Xr options 4 ,
.Xr sysctl 8