587 lines
15 KiB
Groff
587 lines
15 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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.Dd January 16, 1996
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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 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 DDB_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 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 DDB_UNATTENDED
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option is specified.
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.Pp
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The current location is called `dot'. The `dot' is displayed with
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a hexadecimal format at a prompt.
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Examine and write commands update `dot' to the address of the last line
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examined or the last location modified, and set `next' to the address of
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the next location to be examined or changed.
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Other commands don't change `dot', and set `next' to be the same as `dot'.
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.Pp
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The general command syntax is:
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.Cm 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 `next' with
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count 1 and no modifiers. Specifying
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.Ar address
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sets `dot' to the
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address. Omitting
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.Ar address
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uses `dot'. 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 feature like the
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.Xr more 1
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command
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for the output. If an output line exceeds the number set in the
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.Li \&$lines
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variable, it displays
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.Dq Em --db_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 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 emacs-style command line editing capabilities. In addition to
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the emacs control keys, the usual ANSI 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 -ohang
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.It Cm examine
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.It Cm 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 formats 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 Li b
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look at by bytes (8 bits)
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.It Li h
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look at by half words (16 bits)
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.It Li l
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look at by long words (32 bits)
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.It Li a
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print the location being displayed
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.It Li A
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print the location with a line number if possible
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.It Li x
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display in unsigned hex
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.It Li z
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display in signed hex
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.It Li o
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display in unsigned octal
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.It Li d
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display in signed decimal
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.It Li u
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display in unsigned decimal
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.It Li r
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display in current radix, signed
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.It Li 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., `\e000').
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.It Li 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 Li 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 Li i
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display as an instruction
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.It Li 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 MIPS -compact
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.It Tn VAX
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don't assume that each external label is a procedure entry mask
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.It Tn i386
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don't round to the next long word boundary
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.It Tn MIPS
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print register contents
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.El
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.El
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.It Cm xf
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Examine forward:
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Execute an examine 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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.It Cm xb
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Examine backward:
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Execute an examine 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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.It Cm print Ns Op 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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.Li examine ) .
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Valid formats are:
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.Li a ,
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.Li x ,
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.Li z ,
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.Li o ,
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.Li d ,
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.Li u ,
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.Li r ,
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and
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.Li c .
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If no modifier is specified, the last one specified to it is used.
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.Ar addr
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can be a string, in which case it is printed as it is. 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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.It Xo
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.Cm write Ns Op Cm /bhl
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.Ar addr Ar 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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.Li b
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(byte),
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.Li h
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(half word) or
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.Li l
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(long word) respectively. 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's best to enclose each expression in parentheses.
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.It Xo
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.Cm set
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.Li \&$ Ns Ar variable
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.Op Li =
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.Ar expr
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.Xc
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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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.It Cm break Ns Op 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. If the break point is set, a break point number is
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printed with
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.Sq Li \&# .
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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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.Li u
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modifier is specified, this command sets a break point in user space
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address. Without the
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.Li 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. Setting a break
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point at the low-level code paths may also cause strange behavior.
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.It Cm delete Ar addr
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.It Cm delete Li \&# Ns Ar number
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Delete the break point. The target break point can be specified by a
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break point number with
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.Li # ,
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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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.Cm break
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command.
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.It Cm step Ns Op 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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.Li 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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.It Cm continue Ns Op Cm /c
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Continue execution until a breakpoint or watchpoint.
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If the
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.Li 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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.It Cm until Ns Op Cm /p
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Stop at the next call or return instruction.
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If the
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.Li 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. Otherwise,
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only print when the matching return is hit.
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.It Cm next Ns Op Cm /p
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.It Cm match Ns Op Cm /p
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Stop at the matching return instruction.
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If the
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.Li 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. Otherwise,
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only print when the matching return is hit.
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.It Xo
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.Cm trace Ns Op Cm /u
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.Op Ar frame
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.Op , Ns Ar count
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.Xc
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Stack trace. The
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.Li u
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option traces user space; if omitted,
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.Cm trace
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only traces
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kernel space.
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.Ar count
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is the number of frames to be traced.
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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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.It Xo
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.Cm search Ns Op 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 , Ns Ar count
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.Xc
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Search memory for
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.Ar value .
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This command might fail in interesting
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ways if it doesn't find the searched-for value. This is because
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ddb doesn't 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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.It Cm show all procs Ns Op Cm /m
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.It Cm ps Ns Op Cm /m
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Display all process information.
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The process information may not be shown if it is not
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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.
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The
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.Li m
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modifier will alter the display to show VM map
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addresses for the process and not show other info.
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.It Cm show registers Ns Op Cm /u
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Display the register set.
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If the
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.Li u
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option is specified, it displays user registers instead of
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kernel or currently saved one.
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.Pp
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.Sy Warning :
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The support of the
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.Li u
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modifier depends on the machine. If
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not supported, incorrect information will be displayed.
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.It Xo
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.Cm show map Ns Op Cm /f
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.Ar addr
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.Xc
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Prints the VM map at
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.Ar addr .
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If the
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.Li f
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modifier is specified the
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complete map is printed.
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.It Xo
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.Cm show object Ns Op Cm /f
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.Ar addr
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.Xc
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Prints the VM object at
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.Ar addr .
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If the
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.Li f
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option is specified the
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complete object is printed.
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.It Cm "show watches"
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Displays all watchpoints.
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.It Xo
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.Cm watch
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.Ar addr Ns Li \&, Ns Ar size
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.Xc
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Set a watchpoint for a region. Execution stops
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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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.It Xo
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.Cm hwatch
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.Ar addr Ns Li \&, Ns Ar size
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.Xc
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Set a hardware watchpoint for a region if supported by the
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architecture. Execution stops when an attempt to modify the region
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occurs. 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 seperate
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address spaces like the watch command does. Use
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.Cm 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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.It Xo
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.Cm dhwatch
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.Ar addr Ns Li \&, Ns Ar size
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.Xc
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Delete specified hardware watchpoint.
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.It Cm gdb
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Toggles between remote GDB and DDB mode. In remote GDB mode, another
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machine is required that runs
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.Xr gdb 1
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using the remote debug feature, with a connection to the serial
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|
console port on the target machine. Currently only available on the
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.Em i386
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and
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.Em Alpha
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architectures.
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.It Cm help
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|
Print a short summary of the available commands and command
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abbreviations.
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.El
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.Sh VARIABLES
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The debugger accesses registers and variables as
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.Li \&$ Ns Em name .
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Register names are as in the
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.Dq Cm show registers
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command.
|
|
Some variables are suffixed with numbers, and may have some modifier
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following a colon immediately after the variable name.
|
|
For example, register variables can have a
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.Li u
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modifier to indicate user register (e.g.,
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.Li $eax:u ) .
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.Pp
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|
Built-in variables currently supported are:
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.Bl -tag -width tabstops -compact
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.It Li radix
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Input and output radix
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.It Li maxoff
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|
Addresses are printed as 'symbol'+offset unless offset is greater than maxoff.
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.It Li maxwidth
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The width of the displayed line.
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.It Li lines
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The number of lines. It is used by "more" feature.
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.It Li tabstops
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|
Tab stop width.
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.It Li work Ns Ar xx
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Work variable.
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.Ar xx
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can be 0 to 31.
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.El
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.Sh EXPRESSIONS
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|
Almost all expression operators in C are supported except
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.Sq Li \&~ ,
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.Sq Li \&^ ,
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and unary
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.Sq Li \&& .
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|
Special rules in
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.Nm
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are:
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.Bl -tag -width Identifiers
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.It Em Identifiers
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|
The name of a symbol is translated to the value of the symbol, which
|
|
is the address of the corresponding object.
|
|
.Sq Li \&.
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and
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.Sq Li \&:
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can be used in the identifier.
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|
If supported by an object format dependent routine,
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.Sm off
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.Oo Em filename : Oc Em func : lineno ,
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.Sm on
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.Oo Em filename : Oc Ns Em variable ,
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and
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.Oo Em filename : Oc Ns Em lineno
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|
can be accepted as a symbol.
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|
.It Em Numbers
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|
Radix is determined by the first two letters:
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.Li 0x :
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hex,
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.Li 0o :
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octal,
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.Li 0t :
|
|
decimal; otherwise, follow current radix.
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|
.It Li \&.
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`dot'
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.It Li \&+
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`next'
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|
.It Li \&..
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|
address of the start of the last line examined.
|
|
Unlike `dot' or `next', this is only changed by
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.Dq Li examine
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|
or
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.Dq Li write
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|
command.
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.It Li \&'
|
|
last address explicitly specified.
|
|
.It Li \&$ Ns Em variable
|
|
Translated to the value of the specified variable.
|
|
It may be followed by a
|
|
.Li :
|
|
and modifiers as described above.
|
|
.It Em a Ns Li \&# Ns Em b
|
|
a binary operator which rounds up the left hand side to the next
|
|
multiple of right hand side.
|
|
.It Li \&* Ns Em expr
|
|
indirection. It may be followed by a
|
|
.Sq Li :
|
|
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
|
|
.Fl man
|
|
macros by Garrett Wollman.
|