715 lines
17 KiB
Groff
715 lines
17 KiB
Groff
.\"
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.\" Mach Operating System
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.\" Copyright (c) 1991,1990 Carnegie Mellon University
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.\" All Rights Reserved.
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.\"
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.\" Permission to use, copy, modify and distribute this software and its
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.\" documentation is hereby granted, provided that both the copyright
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.\" notice and this permission notice appear in all copies of the
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.\" software, derivative works or modified versions, and any portions
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.\" thereof, and that both notices appear in supporting documentation.
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.\"
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.\" CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
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.\" CONDITION. CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND FOR
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.\" ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
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.\"
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.\" Carnegie Mellon requests users of this software to return to
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.\"
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.\" Software Distribution Coordinator or Software.Distribution@CS.CMU.EDU
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.\" School of Computer Science
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.\" Carnegie Mellon University
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.\" Pittsburgh PA 15213-3890
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.\"
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.\" any improvements or extensions that they make and grant Carnegie Mellon
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.\" the rights to redistribute these changes.
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.\"
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.\" changed a \# to #, since groff choked on it.
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.\"
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.\" HISTORY
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.\" ddb.4,v
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.\" Revision 1.1 1993/07/15 18:41:02 brezak
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.\" Man page for DDB
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.\"
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.\" Revision 2.6 92/04/08 08:52:57 rpd
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.\" Changes from OSF.
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.\" [92/01/17 14:19:22 jsb]
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.\" Changes for OSF debugger modifications.
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.\" [91/12/12 tak]
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.\"
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.\" Revision 2.5 91/06/25 13:50:22 rpd
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.\" Added some watchpoint explanation.
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.\" [91/06/25 rpd]
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.\"
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.\" Revision 2.4 91/06/17 15:47:31 jsb
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.\" Added documentation for continue/c, match, search, and watchpoints.
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.\" I've not actually explained what a watchpoint is; maybe Rich can
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.\" do that (hint, hint).
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.\" [91/06/17 10:58:08 jsb]
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.\"
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.\" Revision 2.3 91/05/14 17:04:23 mrt
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.\" Correcting copyright
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.\"
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.\" Revision 2.2 91/02/14 14:10:06 mrt
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.\" Changed to new Mach copyright
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.\" [91/02/12 18:10:12 mrt]
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.\"
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.\" Revision 2.2 90/08/30 14:23:15 dbg
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.\" Created.
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.\" [90/08/30 dbg]
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.\"
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.\" $FreeBSD$
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.\"
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.Dd October 27, 2006
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.Dt DDB 4
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.Os
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.Sh NAME
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.Nm ddb
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.Nd interactive kernel debugger
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.Sh SYNOPSIS
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.Cd options KDB
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.Cd options DDB
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.Pp
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To prevent activation of the debugger on kernel
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.Xr panic 9 :
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.Cd options KDB_UNATTENDED
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.Sh DESCRIPTION
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The
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.Nm
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kernel debugger has most of the features of the old
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.Nm kdb ,
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but with a more rational syntax
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inspired by
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.Xr gdb 1 .
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If linked into the running kernel,
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it can be invoked locally with the
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.Ql debug
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.Xr keymap 5
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action.
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The debugger is also invoked on kernel
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.Xr panic 9
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if the
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.Va debug.debugger_on_panic
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.Xr sysctl 8
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MIB variable is set non-zero,
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which is the default
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unless the
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.Dv KDB_UNATTENDED
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option is specified.
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.Pp
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The current location is called
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.Va dot .
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The
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.Va dot
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is displayed with
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a hexadecimal format at a prompt.
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The commands
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.Ic examine
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and
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.Ic write
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update
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.Va dot
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to the address of the last line
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examined or the last location modified, and set
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.Va next
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to the address of
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the next location to be examined or changed.
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Other commands do not change
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.Va dot ,
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and set
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.Va next
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to be the same as
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.Va dot .
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.Pp
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The general command syntax is:
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.Ar command Ns Op Li / Ns Ar modifier
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.Ar address Ns Op Li , Ns Ar count
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.Pp
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A blank line repeats the previous command from the address
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.Va next
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with
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count 1 and no modifiers.
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Specifying
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.Ar address
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sets
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.Va dot
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to the address.
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Omitting
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.Ar address
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uses
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.Va dot .
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A missing
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.Ar count
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is taken
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to be 1 for printing commands or infinity for stack traces.
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.Pp
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The
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.Nm
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debugger has a pager feature (like the
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.Xr more 1
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command)
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for the output.
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If an output line exceeds the number set in the
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.Va lines
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variable, it displays
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.Dq Li --More--
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and waits for a response.
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The valid responses for it are:
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.Pp
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.Bl -tag -compact -width ".Li SPC"
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.It Li SPC
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one more page
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.It Li RET
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one more line
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.It Li q
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abort the current command, and return to the command input mode
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.El
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.Pp
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Finally,
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.Nm
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provides a small (currently 10 items) command history, and offers
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simple
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.Nm emacs Ns -style
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command line editing capabilities.
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In addition to
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the
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.Nm emacs
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control keys, the usual
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.Tn ANSI
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arrow keys might be used to
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browse through the history buffer, and move the cursor within the
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current line.
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.Sh COMMANDS
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.Bl -tag -width indent -compact
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.It Ic examine
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.It Ic x
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Display the addressed locations according to the formats in the modifier.
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Multiple modifier formats display multiple locations.
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If no format is specified, the last format specified for this command
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is used.
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.Pp
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The format characters are:
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.Bl -tag -compact -width indent
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.It Cm b
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look at by bytes (8 bits)
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.It Cm h
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look at by half words (16 bits)
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.It Cm l
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look at by long words (32 bits)
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.It Cm a
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print the location being displayed
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.It Cm A
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print the location with a line number if possible
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.It Cm x
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display in unsigned hex
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.It Cm z
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display in signed hex
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.It Cm o
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display in unsigned octal
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.It Cm d
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display in signed decimal
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.It Cm u
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display in unsigned decimal
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.It Cm r
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display in current radix, signed
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.It Cm c
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display low 8 bits as a character.
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Non-printing characters are displayed as an octal escape code (e.g.,
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.Ql \e000 ) .
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.It Cm s
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display the null-terminated string at the location.
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Non-printing characters are displayed as octal escapes.
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.It Cm m
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display in unsigned hex with character dump at the end of each line.
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The location is also displayed in hex at the beginning of each line.
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.It Cm i
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display as an instruction
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.It Cm I
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display as an instruction with possible alternate formats depending on the
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machine:
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.Bl -tag -width ".Tn powerpc" -compact
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.It Tn alpha
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Show the registers of the instruction.
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.It Tn amd64
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No alternate format.
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.It Tn i386
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No alternate format.
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.It Tn ia64
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No alternate format.
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.It Tn powerpc
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No alternate format.
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.It Tn sparc64
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No alternate format.
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.El
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.El
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.Pp
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.It Ic xf
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Examine forward:
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execute an
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.Ic examine
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command with the last specified parameters to it
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except that the next address displayed by it is used as the start address.
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.Pp
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.It Ic xb
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Examine backward:
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execute an
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.Ic examine
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command with the last specified parameters to it
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except that the last start address subtracted by the size displayed by it
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is used as the start address.
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.Pp
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.It Ic print Ns Op Li / Ns Cm acdoruxz
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.It Ic p Ns Op Li / Ns Cm acdoruxz
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Print
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.Ar addr Ns s
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according to the modifier character (as described above for
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.Cm examine ) .
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Valid formats are:
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.Cm a , x , z , o , d , u , r ,
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and
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.Cm c .
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If no modifier is specified, the last one specified to it is used.
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The argument
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.Ar addr
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can be a string, in which case it is printed as it is.
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For example:
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.Bd -literal -offset indent
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print/x "eax = " $eax "\enecx = " $ecx "\en"
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.Ed
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.Pp
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will print like:
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.Bd -literal -offset indent
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eax = xxxxxx
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ecx = yyyyyy
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.Ed
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.Pp
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.It Xo
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.Ic write Ns Op Li / Ns Cm bhl
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.Ar addr expr1 Op Ar expr2 ...
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.Xc
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.It Xo
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.Ic w Ns Op Li / Ns Cm bhl
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.Ar addr expr1 Op Ar expr2 ...
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.Xc
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Write the expressions specified after
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.Ar addr
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on the command line at succeeding locations starting with
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.Ar addr .
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The write unit size can be specified in the modifier with a letter
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.Cm b
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(byte),
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.Cm h
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(half word) or
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.Cm l
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(long word) respectively.
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If omitted,
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long word is assumed.
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.Pp
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.Sy Warning :
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since there is no delimiter between expressions, strange
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things may happen.
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It is best to enclose each expression in parentheses.
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.Pp
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.It Ic set Li $ Ns Ar variable Oo Li = Oc Ar expr
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Set the named variable or register with the value of
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.Ar expr .
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Valid variable names are described below.
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.Pp
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.It Ic break Ns Op Li / Ns Cm u
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.It Ic b Ns Op Li / Ns Cm u
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Set a break point at
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.Ar addr .
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If
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.Ar count
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is supplied, continues
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.Ar count
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\- 1 times before stopping at the
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break point.
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If the break point is set, a break point number is
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printed with
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.Ql # .
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This number can be used in deleting the break point
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or adding conditions to it.
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.Pp
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If the
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.Cm u
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modifier is specified, this command sets a break point in user space
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address.
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Without the
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.Cm u
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option, the address is considered in the kernel
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space, and wrong space address is rejected with an error message.
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This modifier can be used only if it is supported by machine dependent
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routines.
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.Pp
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.Sy Warning :
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If a user text is shadowed by a normal user space debugger,
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user space break points may not work correctly.
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Setting a break
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point at the low-level code paths may also cause strange behavior.
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.Pp
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.It Ic delete Ar addr
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.It Ic d Ar addr
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.It Ic delete Li # Ns Ar number
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.It Ic d Li # Ns Ar number
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Delete the break point.
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The target break point can be specified by a
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break point number with
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.Ql # ,
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or by using the same
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.Ar addr
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specified in the original
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.Ic break
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command.
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.Pp
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.It Ic watch Ar addr Ns Li , Ns Ar size
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Set a watchpoint for a region.
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Execution stops when an attempt to modify the region occurs.
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The
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.Ar size
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argument defaults to 4.
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If you specify a wrong space address, the request is rejected
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with an error message.
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.Pp
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.Sy Warning :
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Attempts to watch wired kernel memory
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may cause unrecoverable error in some systems such as i386.
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Watchpoints on user addresses work best.
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.Pp
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.It Ic hwatch Ar addr Ns Li , Ns Ar size
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Set a hardware watchpoint for a region if supported by the
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architecture.
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Execution stops when an attempt to modify the region occurs.
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The
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.Ar size
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argument defaults to 4.
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.Pp
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.Sy Warning :
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The hardware debug facilities do not have a concept of separate
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address spaces like the watch command does.
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Use
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.Ic hwatch
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for setting watchpoints on kernel address locations only, and avoid
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its use on user mode address spaces.
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.Pp
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.It Ic dhwatch Ar addr Ns Li , Ns Ar size
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Delete specified hardware watchpoint.
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.Pp
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.It Ic step Ns Op Li / Ns Cm p
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.It Ic s Ns Op Li / Ns Cm p
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Single step
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.Ar count
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times (the comma is a mandatory part of the syntax).
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If the
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.Cm p
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modifier is specified, print each instruction at each step.
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Otherwise, only print the last instruction.
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.Pp
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.Sy Warning :
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depending on machine type, it may not be possible to
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single-step through some low-level code paths or user space code.
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On machines with software-emulated single-stepping (e.g., pmax),
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stepping through code executed by interrupt handlers will probably
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do the wrong thing.
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.Pp
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.It Ic continue Ns Op Li / Ns Cm c
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.It Ic c Ns Op Li / Ns Cm c
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Continue execution until a breakpoint or watchpoint.
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If the
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.Cm c
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modifier is specified, count instructions while executing.
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Some machines (e.g., pmax) also count loads and stores.
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.Pp
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.Sy Warning :
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when counting, the debugger is really silently single-stepping.
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This means that single-stepping on low-level code may cause strange
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behavior.
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.Pp
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.It Ic until Ns Op Li / Ns Cm p
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Stop at the next call or return instruction.
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If the
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.Cm p
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modifier is specified, print the call nesting depth and the
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cumulative instruction count at each call or return.
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Otherwise,
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only print when the matching return is hit.
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.Pp
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.It Ic next Ns Op Li / Ns Cm p
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.It Ic match Ns Op Li / Ns Cm p
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Stop at the matching return instruction.
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If the
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.Cm p
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modifier is specified, print the call nesting depth and the
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cumulative instruction count at each call or return.
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Otherwise, only print when the matching return is hit.
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.Pp
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.It Xo
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.Ic trace Ns Op Li / Ns Cm u
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.Op Ar pid | tid
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.Op Li , Ns Ar count
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.Xc
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.It Xo
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.Ic t Ns Op Li / Ns Cm u
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.Op Ar pid | tid
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.Op Li , Ns Ar count
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.Xc
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.It Xo
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.Ic where Ns Op Li / Ns Cm u
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.Op Ar pid | tid
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.Op Li , Ns Ar count
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.Xc
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.It Xo
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.Ic bt Ns Op Li / Ns Cm u
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.Op Ar pid | tid
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.Op Li , Ns Ar count
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.Xc
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Stack trace.
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The
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.Cm u
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option traces user space; if omitted,
|
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.Ic trace
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only traces
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kernel space.
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The optional argument
|
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.Ar count
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|
is the number of frames to be traced.
|
|
If
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.Ar count
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is omitted, all frames are printed.
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.Pp
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.Sy Warning :
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User space stack trace is valid
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only if the machine dependent code supports it.
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.Pp
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.It Xo
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.Ic search Ns Op Li / Ns Cm bhl
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.Ar addr
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.Ar value
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.Op Ar mask
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.Op Li , Ns Ar count
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.Xc
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|
Search memory for
|
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.Ar value .
|
|
This command might fail in interesting
|
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ways if it does not find the searched-for value.
|
|
This is because
|
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.Nm
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|
does not always recover from touching bad memory.
|
|
The optional
|
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.Ar count
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argument limits the search.
|
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.Pp
|
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.It Ic show Cm all procs Ns Op Li / Ns Cm m
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.It Ic ps Ns Op Li / Ns Cm m
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|
Display all process information.
|
|
The process information may not be shown if it is not
|
|
supported in the machine, or the bottom of the stack of the
|
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target process is not in the main memory at that time.
|
|
The
|
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.Cm m
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modifier will alter the display to show VM map
|
|
addresses for the process and not show other info.
|
|
.Pp
|
|
.It Ic show Cm registers Ns Op Li / Ns Cm u
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|
Display the register set.
|
|
If the
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.Cm u
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modifier is specified, it displays user registers instead of
|
|
kernel or currently saved one.
|
|
.Pp
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|
.Sy Warning :
|
|
The support of the
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.Cm u
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modifier depends on the machine.
|
|
If not supported, incorrect information will be displayed.
|
|
.Pp
|
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.It Ic show Cm geom Op Ar addr
|
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If the
|
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.Ar addr
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|
argument is not given, displays the entire GEOM topology.
|
|
If the
|
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.Ar addr
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is given, displays details about the given GEOM object (class, geom, provider
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or consumer).
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|
.Pp
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|
.It Ic show Cm map Ns Oo Li / Ns Cm f Oc Ar addr
|
|
Prints the VM map at
|
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.Ar addr .
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|
If the
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.Cm f
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modifier is specified the
|
|
complete map is printed.
|
|
.Pp
|
|
.It Ic show Cm object Ns Oo Li / Ns Cm f Oc Ar addr
|
|
Prints the VM object at
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.Ar addr .
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|
If the
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.Cm f
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|
option is specified the
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|
complete object is printed.
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|
.Pp
|
|
.It Ic show Cm vnode Ar addr
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|
Displays details about the given vnode.
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|
.Pp
|
|
.It Ic show Cm watches
|
|
Displays all watchpoints.
|
|
.Pp
|
|
.It Ic gdb
|
|
Toggles between remote GDB and DDB mode.
|
|
In remote GDB mode, another machine is required that runs
|
|
.Xr gdb 1
|
|
using the remote debug feature, with a connection to the serial
|
|
console port on the target machine.
|
|
Currently only available on the
|
|
i386
|
|
architecture.
|
|
.Pp
|
|
.It Ic halt
|
|
Halt the system.
|
|
.Pp
|
|
.It Ic kill Ar sig pid
|
|
Send signal
|
|
.Ar sig
|
|
to process
|
|
.Ar pid .
|
|
The signal is acted on upon returning from the debugger.
|
|
This command can be used to kill a process causing resource contention
|
|
in the case of a hung system.
|
|
See
|
|
.Xr signal 3
|
|
for a list of signals.
|
|
Note that the arguments are reversed relative to
|
|
.Xr kill 2 .
|
|
.Pp
|
|
.It Ic reboot
|
|
.It Ic reset
|
|
Hard reset the system.
|
|
.Pp
|
|
.It Ic help
|
|
Print a short summary of the available commands and command
|
|
abbreviations.
|
|
.El
|
|
.Sh VARIABLES
|
|
The debugger accesses registers and variables as
|
|
.Li $ Ns Ar name .
|
|
Register names are as in the
|
|
.Dq Ic show Cm registers
|
|
command.
|
|
Some variables are suffixed with numbers, and may have some modifier
|
|
following a colon immediately after the variable name.
|
|
For example, register variables can have a
|
|
.Cm u
|
|
modifier to indicate user register (e.g.,
|
|
.Dq Li $eax:u ) .
|
|
.Pp
|
|
Built-in variables currently supported are:
|
|
.Pp
|
|
.Bl -tag -width ".Va tabstops" -compact
|
|
.It Va radix
|
|
Input and output radix.
|
|
.It Va maxoff
|
|
Addresses are printed as
|
|
.Dq Ar symbol Ns Li + Ns Ar offset
|
|
unless
|
|
.Ar offset
|
|
is greater than
|
|
.Va maxoff .
|
|
.It Va maxwidth
|
|
The width of the displayed line.
|
|
.It Va lines
|
|
The number of lines.
|
|
It is used by the built-in pager.
|
|
.It Va tabstops
|
|
Tab stop width.
|
|
.It Va work Ns Ar xx
|
|
Work variable;
|
|
.Ar xx
|
|
can take values from 0 to 31.
|
|
.El
|
|
.Sh EXPRESSIONS
|
|
Most expression operators in C are supported except
|
|
.Ql ~ ,
|
|
.Ql ^ ,
|
|
and unary
|
|
.Ql & .
|
|
Special rules in
|
|
.Nm
|
|
are:
|
|
.Bl -tag -width ".No Identifiers"
|
|
.It Identifiers
|
|
The name of a symbol is translated to the value of the symbol, which
|
|
is the address of the corresponding object.
|
|
.Ql \&.
|
|
and
|
|
.Ql \&:
|
|
can be used in the identifier.
|
|
If supported by an object format dependent routine,
|
|
.Sm off
|
|
.Oo Ar filename : Oc Ar func : lineno ,
|
|
.Sm on
|
|
.Oo Ar filename : Oc Ns Ar variable ,
|
|
and
|
|
.Oo Ar filename : Oc Ns Ar lineno
|
|
can be accepted as a symbol.
|
|
.It Numbers
|
|
Radix is determined by the first two letters:
|
|
.Ql 0x :
|
|
hex,
|
|
.Ql 0o :
|
|
octal,
|
|
.Ql 0t :
|
|
decimal; otherwise, follow current radix.
|
|
.It Li \&.
|
|
.Va dot
|
|
.It Li +
|
|
.Va next
|
|
.It Li ..
|
|
address of the start of the last line examined.
|
|
Unlike
|
|
.Va dot
|
|
or
|
|
.Va next ,
|
|
this is only changed by
|
|
.Ic examine
|
|
or
|
|
.Ic write
|
|
command.
|
|
.It Li '
|
|
last address explicitly specified.
|
|
.It Li $ Ns Ar variable
|
|
Translated to the value of the specified variable.
|
|
It may be followed by a
|
|
.Ql \&:
|
|
and modifiers as described above.
|
|
.It Ar a Ns Li # Ns Ar b
|
|
A binary operator which rounds up the left hand side to the next
|
|
multiple of right hand side.
|
|
.It Li * Ns Ar expr
|
|
Indirection.
|
|
It may be followed by a
|
|
.Ql \&:
|
|
and modifiers as described above.
|
|
.El
|
|
.Sh HINTS
|
|
On machines with an ISA expansion bus, a simple NMI generation card can be
|
|
constructed by connecting a push button between the A01 and B01 (CHCHK# and
|
|
GND) card fingers.
|
|
Momentarily shorting these two fingers together may cause the bridge chipset to
|
|
generate an NMI, which causes the kernel to pass control to
|
|
.Nm .
|
|
Some bridge chipsets do not generate a NMI on CHCHK#, so your mileage may vary.
|
|
The NMI allows one to break into the debugger on a wedged machine to
|
|
diagnose problems.
|
|
Other bus' bridge chipsets may be able to generate NMI using bus specific
|
|
methods.
|
|
.Sh SEE ALSO
|
|
.Xr gdb 1
|
|
.Sh HISTORY
|
|
The
|
|
.Nm
|
|
debugger was developed for Mach, and ported to
|
|
.Bx 386 0.1 .
|
|
This manual page translated from
|
|
.Xr man 7
|
|
macros by
|
|
.An Garrett Wollman .
|