2 .\" Mach Operating System
3 .\" Copyright (c) 1991,1990 Carnegie Mellon University
4 .\" All Rights Reserved.
6 .\" Permission to use, copy, modify and distribute this software and its
7 .\" documentation is hereby granted, provided that both the copyright
8 .\" notice and this permission notice appear in all copies of the
9 .\" software, derivative works or modified versions, and any portions
10 .\" thereof, and that both notices appear in supporting documentation.
12 .\" CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
13 .\" CONDITION. CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND FOR
14 .\" ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
16 .\" Carnegie Mellon requests users of this software to return to
18 .\" Software Distribution Coordinator or Software.Distribution@CS.CMU.EDU
19 .\" School of Computer Science
20 .\" Carnegie Mellon University
21 .\" Pittsburgh PA 15213-3890
23 .\" any improvements or extensions that they make and grant Carnegie Mellon
24 .\" the rights to redistribute these changes.
26 .\" changed a \# to #, since groff choked on it.
30 .\" Revision 1.1 1993/07/15 18:41:02 brezak
33 .\" Revision 2.6 92/04/08 08:52:57 rpd
35 .\" [92/01/17 14:19:22 jsb]
36 .\" Changes for OSF debugger modifications.
39 .\" Revision 2.5 91/06/25 13:50:22 rpd
40 .\" Added some watchpoint explanation.
43 .\" Revision 2.4 91/06/17 15:47:31 jsb
44 .\" Added documentation for continue/c, match, search, and watchpoints.
45 .\" I've not actually explained what a watchpoint is; maybe Rich can
46 .\" do that (hint, hint).
47 .\" [91/06/17 10:58:08 jsb]
49 .\" Revision 2.3 91/05/14 17:04:23 mrt
50 .\" Correcting copyright
52 .\" Revision 2.2 91/02/14 14:10:06 mrt
53 .\" Changed to new Mach copyright
54 .\" [91/02/12 18:10:12 mrt]
56 .\" Revision 2.2 90/08/30 14:23:15 dbg
66 .Nd interactive kernel debugger
70 To prevent activation of the debugger on kernel
72 .Cd options KDB_UNATTENDED
76 kernel debugger has most of the features of the old kdb,
77 but with a more rational syntax
80 If linked into the running kernel,
81 it can be invoked locally with the
85 The debugger is also invoked on kernel
88 .Va debug.debugger_on_panic
90 MIB variable is set non-zero,
96 The current location is called `dot'.
97 The `dot' is displayed with
98 a hexadecimal format at a prompt.
99 Examine and write commands update `dot' to the address of the last line
100 examined or the last location modified, and set `next' to the address of
101 the next location to be examined or changed.
102 Other commands do not change `dot', and set `next' to be the same as `dot'.
104 The general command syntax is:
105 .Cm command Ns Op Li \&/ Ns Ar modifier
106 .Ar address Ns Op Li , Ns Ar count
108 A blank line repeats the previous command from the address `next' with
109 count 1 and no modifiers.
120 to be 1 for printing commands or infinity for stack traces.
124 debugger has a feature like the
128 If an output line exceeds the number set in the
130 variable, it displays
132 and waits for a response.
133 The valid responses for it are:
135 .Bl -tag -compact -width ".Li SPC"
141 abort the current command, and return to the command input mode
146 provides a small (currently 10 items) command history, and offers
147 simple emacs-style command line editing capabilities.
149 the emacs control keys, the usual ANSI arrow keys might be used to
150 browse through the history buffer, and move the cursor within the
156 Display the addressed locations according to the formats in the modifier.
157 Multiple modifier formats display multiple locations.
158 If no format is specified, the last formats specified for this command
161 The format characters are:
162 .Bl -tag -compact -width indent
164 look at by bytes (8 bits)
166 look at by half words (16 bits)
168 look at by long words (32 bits)
170 print the location being displayed
172 print the location with a line number if possible
174 display in unsigned hex
176 display in signed hex
178 display in unsigned octal
180 display in signed decimal
182 display in unsigned decimal
184 display in current radix, signed
186 display low 8 bits as a character.
187 Non-printing characters are displayed as an octal escape code (e.g., `\e000').
189 display the null-terminated string at the location.
190 Non-printing characters are displayed as octal escapes.
192 display in unsigned hex with character dump at the end of each line.
193 The location is also displayed in hex at the beginning of each line.
195 display as an instruction
197 display as an instruction with possible alternate formats depending on the
199 .Bl -tag -width ".Tn powerpc" -compact
201 Show the registers of the instruction.
216 Execute an examine command with the last specified parameters to it
217 except that the next address displayed by it is used as the start address.
220 Execute an examine command with the last specified parameters to it
221 except that the last start address subtracted by the size displayed by it
222 is used as the start address.
223 .It Cm print Ns Op Cm /acdoruxz
226 according to the modifier character (as described above for
238 If no modifier is specified, the last one specified to it is used.
240 can be a string, in which case it is printed as it is.
242 .Bd -literal -offset indent
243 print/x \&"eax = \&" $eax \&"\enecx = \&" $ecx \&"\en\&"
247 .Bd -literal -offset indent
252 .Cm write Ns Op Cm /bhl
253 .Ar addr Ar expr1 Op Ar "expr2 ..."
255 Write the expressions specified after
257 on the command line at succeeding locations starting with
259 The write unit size can be specified in the modifier with a letter
265 (long word) respectively.
267 long word is assumed.
270 since there is no delimiter between expressions, strange
272 It is best to enclose each expression in parentheses.
275 .Li \&$ Ns Ar variable
279 Set the named variable or register with the value of
281 Valid variable names are described below.
282 .It Cm break Ns Op Cm /u
287 is supplied, continues
289 - 1 times before stopping at the
291 If the break point is set, a break point number is
294 This number can be used in deleting the break point
295 or adding conditions to it.
299 modifier is specified, this command sets a break point in user space
303 option, the address is considered in the kernel
304 space, and wrong space address is rejected with an error message.
305 This modifier can be used only if it is supported by machine dependent
309 If a user text is shadowed by a normal user space debugger,
310 user space break points may not work correctly.
312 point at the low-level code paths may also cause strange behavior.
313 .It Cm delete Ar addr
314 .It Cm delete Li \&# Ns Ar number
315 Delete the break point.
316 The target break point can be specified by a
317 break point number with
321 specified in the original
324 .It Cm step Ns Op Cm /p
327 times (the comma is a mandatory part of the syntax).
330 modifier is specified, print each instruction at each step.
331 Otherwise, only print the last instruction.
334 depending on machine type, it may not be possible to
335 single-step through some low-level code paths or user space code.
336 On machines with software-emulated single-stepping (e.g., pmax),
337 stepping through code executed by interrupt handlers will probably
339 .It Cm continue Ns Op Cm /c
340 Continue execution until a breakpoint or watchpoint.
343 modifier is specified, count instructions while executing.
344 Some machines (e.g., pmax) also count loads and stores.
347 when counting, the debugger is really silently single-stepping.
348 This means that single-stepping on low-level code may cause strange
350 .It Cm until Ns Op Cm /p
351 Stop at the next call or return instruction.
354 modifier is specified, print the call nesting depth and the
355 cumulative instruction count at each call or return.
357 only print when the matching return is hit.
358 .It Cm next Ns Op Cm /p
359 .It Cm match Ns Op Cm /p
360 Stop at the matching return instruction.
363 modifier is specified, print the call nesting depth and the
364 cumulative instruction count at each call or return.
365 Otherwise, only print when the matching return is hit.
367 .Cm trace Ns Op Cm /u
374 option traces user space; if omitted,
379 is the number of frames to be traced.
382 is omitted, all frames are printed.
385 User space stack trace is valid
386 only if the machine dependent code supports it.
388 .Cm search Ns Op Cm /bhl
396 This command might fail in interesting
397 ways if it does not find the searched-for value.
398 This is because ddb does not always recover from touching bad memory.
401 argument limits the search.
402 .It Cm show all procs Ns Op Cm /m
403 .It Cm ps Ns Op Cm /m
404 Display all process information.
405 The process information may not be shown if it is not
406 supported in the machine, or the bottom of the stack of the
407 target process is not in the main memory at that time.
410 modifier will alter the display to show VM map
411 addresses for the process and not show other info.
412 .It Cm show registers Ns Op Cm /u
413 Display the register set.
416 option is specified, it displays user registers instead of
417 kernel or currently saved one.
422 modifier depends on the machine.
423 If not supported, incorrect information will be displayed.
425 .Cm show map Ns Op Cm /f
432 modifier is specified the
433 complete map is printed.
435 .Cm show object Ns Op Cm /f
438 Prints the VM object at
442 option is specified the
443 complete object is printed.
444 .It Cm "show watches"
445 Displays all watchpoints.
447 Hard reset the system.
450 .Ar addr Ns Li \&, Ns Ar size
452 Set a watchpoint for a region.
453 Execution stops when an attempt to modify the region occurs.
456 argument defaults to 4.
457 If you specify a wrong space address, the request is rejected
458 with an error message.
461 Attempts to watch wired kernel memory
462 may cause unrecoverable error in some systems such as i386.
463 Watchpoints on user addresses work best.
466 .Ar addr Ns Li \&, Ns Ar size
468 Set a hardware watchpoint for a region if supported by the
470 Execution stops when an attempt to modify the region occurs.
473 argument defaults to 4.
476 The hardware debug facilities do not have a concept of separate
477 address spaces like the watch command does.
480 for setting watchpoints on kernel address locations only, and avoid
481 its use on user mode address spaces.
484 .Ar addr Ns Li \&, Ns Ar size
486 Delete specified hardware watchpoint.
488 Toggles between remote GDB and DDB mode.
489 In remote GDB mode, another machine is required that runs
491 using the remote debug feature, with a connection to the serial
492 console port on the target machine.
493 Currently only available on the
499 Print a short summary of the available commands and command
503 The debugger accesses registers and variables as
505 Register names are as in the
506 .Dq Cm show registers
508 Some variables are suffixed with numbers, and may have some modifier
509 following a colon immediately after the variable name.
510 For example, register variables can have a
512 modifier to indicate user register (e.g.,
515 Built-in variables currently supported are:
516 .Bl -tag -width ".Li tabstops" -compact
518 Input and output radix
520 Addresses are printed as 'symbol'+offset unless offset is greater than maxoff.
522 The width of the displayed line.
536 Almost all expression operators in C are supported except
544 .Bl -tag -width ".Em Identifiers"
546 The name of a symbol is translated to the value of the symbol, which
547 is the address of the corresponding object.
551 can be used in the identifier.
552 If supported by an object format dependent routine,
554 .Oo Em filename : Oc Em func : lineno ,
556 .Oo Em filename : Oc Ns Em variable ,
558 .Oo Em filename : Oc Ns Em lineno
559 can be accepted as a symbol.
561 Radix is determined by the first two letters:
567 decimal; otherwise, follow current radix.
573 address of the start of the last line examined.
574 Unlike `dot' or `next', this is only changed by
580 last address explicitly specified.
581 .It Li \&$ Ns Em variable
582 Translated to the value of the specified variable.
583 It may be followed by a
585 and modifiers as described above.
586 .It Em a Ns Li \&# Ns Em b
587 a binary operator which rounds up the left hand side to the next
588 multiple of right hand side.
589 .It Li \&* Ns Em expr
591 It may be followed by a
593 and modifiers as described above.
596 On machines with an ISA expansion bus, a simple NMI generation card can be
597 constructed by connecting a push button between the A01 and B01 (CHCHK# and
599 Momentarily shorting these two fingers together may cause the bridge chipset to
600 generate an NMI, which causes the kernel to pass control to
602 Some bridge chipsets do not generate a NMI on CHCHK#, so your mileage may vary.
603 The NMI allows one to break into the debugger on a wedged machine to
605 Other bus' bridge chipsets may be able to generate NMI using bus specific
612 debugger was developed for Mach, and ported to
614 This manual page translated from
616 macros by Garrett Wollman.