Mach Operating System
Copyright (c) 1991,1990 Carnegie Mellon University
Copyright (c) 2007 Robert N. M. Watson
All Rights Reserved.
Permission to use, copy, modify and distribute this software and its
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CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
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ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
Carnegie Mellon requests users of this software to return to
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changed a \# to #, since groff choked on it.
HISTORY
ddb.4,v
Revision 1.1 1993/07/15 18:41:02 brezak
Man page for DDB
Revision 2.6 92/04/08 08:52:57 rpd
Changes from OSF.
[92/01/17 14:19:22 jsb]
Changes for OSF debugger modifications.
[91/12/12 tak]
Revision 2.5 91/06/25 13:50:22 rpd
Added some watchpoint explanation.
[91/06/25 rpd]
Revision 2.4 91/06/17 15:47:31 jsb
Added documentation for continue/c, match, search, and watchpoints.
I've not actually explained what a watchpoint is; maybe Rich can
do that (hint, hint).
[91/06/17 10:58:08 jsb]
Revision 2.3 91/05/14 17:04:23 mrt
Correcting copyright
Revision 2.2 91/02/14 14:10:06 mrt
Changed to new Mach copyright
[91/02/12 18:10:12 mrt]
Revision 2.2 90/08/30 14:23:15 dbg
Created.
[90/08/30 dbg]
$FreeBSD: head/share/man/man4/ddb.4 176915 2008-03-07 18:14:29Z rwatson $
.Dd December 26, 2007 .Dt DDB 4 .Os .Sh NAME .Nm ddb .Nd interactive kernel debugger .Sh SYNOPSIS .Cd options KDB .Cd options DDB
p To prevent activation of the debugger on kernel .Xr panic 9 : .Cd options KDB_UNATTENDED .Sh DESCRIPTION The .Nm kernel debugger has most of the features of the old .Nm kdb , but with a more rational syntax inspired by .Xr gdb 1 . If linked into the running kernel, it can be invoked locally with the .Ql debug .Xr keymap 5 action. The debugger is also invoked on kernel .Xr panic 9 if the .Va debug.debugger_on_panic .Xr sysctl 8 MIB variable is set non-zero, which is the default unless the .Dv KDB_UNATTENDED option is specified.
p The current location is called .Va dot . The .Va dot is displayed with a hexadecimal format at a prompt. The commands c examine and c write update .Va dot to the address of the last line examined or the last location modified, and set .Va next to the address of the next location to be examined or changed. Other commands do not change .Va dot , and set .Va next to be the same as .Va dot .
p The general command syntax is: .Ar command Ns Op Li / Ns Ar modifier .Ar address Ns Op Li , Ns Ar count
p A blank line repeats the previous command from the address .Va next with count 1 and no modifiers. Specifying .Ar address sets .Va dot to the address. Omitting .Ar address uses .Va dot . A missing .Ar count is taken to be 1 for printing commands or infinity for stack traces.
p The .Nm debugger has a pager feature (like the .Xr more 1 command) for the output. If an output line exceeds the number set in the .Va lines variable, it displays .Dq Li --More-- and waits for a response. The valid responses for it are:
p l -tag -compact -width ".Li SPC" t Li SPC one more page t Li RET one more line t Li q abort the current command, and return to the command input mode .El
p Finally, .Nm provides a small (currently 10 items) command history, and offers simple .Nm emacs Ns -style command line editing capabilities. In addition to the .Nm emacs control keys, the usual .Tn ANSI arrow keys might be used to browse through the history buffer, and move the cursor within the current line. .Sh COMMANDS l -tag -width indent -compact t Ic examine t Ic x Display the addressed locations according to the formats in the modifier. Multiple modifier formats display multiple locations. If no format is specified, the last format specified for this command is used.
p The format characters are: l -tag -compact -width indent t Cm b look at by bytes (8 bits) t Cm h look at by half words (16 bits) t Cm l look at by long words (32 bits) t Cm a print the location being displayed t Cm A print the location with a line number if possible t Cm x display in unsigned hex t Cm z display in signed hex t Cm o display in unsigned octal t Cm d display in signed decimal t Cm u display in unsigned decimal t Cm r display in current radix, signed t Cm c display low 8 bits as a character. Non-printing characters are displayed as an octal escape code (e.g., .Ql \e000 ) . t Cm s display the null-terminated string at the location. Non-printing characters are displayed as octal escapes. t Cm m display in unsigned hex with character dump at the end of each line. The location is also displayed in hex at the beginning of each line. t Cm i display as an instruction t Cm I display as an instruction with possible alternate formats depending on the machine: l -tag -width ".Tn powerpc" -compact t Tn alpha Show the registers of the instruction. t Tn amd64 No alternate format. t Tn i386 No alternate format. t Tn ia64 No alternate format. t Tn powerpc No alternate format. t Tn sparc64 No alternate format. .El t Cm S display a symbol name for the pointer stored at the address .El
p t Ic xf Examine forward: execute an c examine command with the last specified parameters to it except that the next address displayed by it is used as the start address.
p t Ic xb Examine backward: execute an c examine command with the last specified parameters to it except that the last start address subtracted by the size displayed by it is used as the start address.
p t Ic print Ns Op Li / Ns Cm acdoruxz t Ic p Ns Op Li / Ns Cm acdoruxz Print .Ar addr Ns s according to the modifier character (as described above for .Cm examine ) . Valid formats are: .Cm a , x , z , o , d , u , r , and .Cm c . If no modifier is specified, the last one specified to it is used. The argument .Ar addr can be a string, in which case it is printed as it is. For example: d -literal -offset indent print/x "eax = " $eax "\enecx = " $ecx "\en" .Ed
p will print like: d -literal -offset indent eax = xxxxxx ecx = yyyyyy .Ed
p t Xo c write Ns Op Li / Ns Cm bhl .Ar addr expr1 Op Ar expr2 ... .Xc t Xo c w Ns Op Li / Ns Cm bhl .Ar addr expr1 Op Ar expr2 ... .Xc Write the expressions specified after .Ar addr on the command line at succeeding locations starting with .Ar addr . The write unit size can be specified in the modifier with a letter .Cm b (byte), .Cm h (half word) or .Cm l (long word) respectively. If omitted, long word is assumed.
p .Sy Warning : since there is no delimiter between expressions, strange things may happen. It is best to enclose each expression in parentheses.
p t Ic set Li $ Ns Ar variable Oo Li = Oc Ar expr Set the named variable or register with the value of .Ar expr . Valid variable names are described below.
p t Ic break Ns Op Li / Ns Cm u t Ic b Ns Op Li / Ns Cm u Set a break point at .Ar addr . If .Ar count is supplied, continues .Ar count - 1 times before stopping at the break point. If the break point is set, a break point number is printed with .Ql # . This number can be used in deleting the break point or adding conditions to it.
p If the .Cm u modifier is specified, this command sets a break point in user space address. Without the .Cm u option, the address is considered in the kernel space, and wrong space address is rejected with an error message. This modifier can be used only if it is supported by machine dependent routines.
p .Sy Warning : If a user text is shadowed by a normal user space debugger, user space break points may not work correctly. Setting a break point at the low-level code paths may also cause strange behavior.
p t Ic delete Ar addr t Ic d Ar addr t Ic delete Li # Ns Ar number t Ic d Li # Ns Ar number Delete the break point. The target break point can be specified by a break point number with .Ql # , or by using the same .Ar addr specified in the original c break command.
p t Ic watch Ar addr Ns Li , Ns Ar size Set a watchpoint for a region. Execution stops when an attempt to modify the region occurs. The .Ar size argument defaults to 4. If you specify a wrong space address, the request is rejected with an error message.
p .Sy Warning : Attempts to watch wired kernel memory may cause unrecoverable error in some systems such as i386. Watchpoints on user addresses work best.
p t Ic hwatch Ar addr Ns Li , Ns Ar size Set a hardware watchpoint for a region if supported by the architecture. Execution stops when an attempt to modify the region occurs. The .Ar size argument defaults to 4.
p .Sy Warning : The hardware debug facilities do not have a concept of separate address spaces like the watch command does. Use c hwatch for setting watchpoints on kernel address locations only, and avoid its use on user mode address spaces.
p t Ic dhwatch Ar addr Ns Li , Ns Ar size Delete specified hardware watchpoint.
p t Ic step Ns Op Li / Ns Cm p t Ic s Ns Op Li / Ns Cm p Single step .Ar count times (the comma is a mandatory part of the syntax). If the .Cm p modifier is specified, print each instruction at each step. Otherwise, only print the last instruction.
p .Sy Warning : depending on machine type, it may not be possible to single-step through some low-level code paths or user space code. On machines with software-emulated single-stepping (e.g., pmax), stepping through code executed by interrupt handlers will probably do the wrong thing.
p t Ic continue Ns Op Li / Ns Cm c t Ic c Ns Op Li / Ns Cm c Continue execution until a breakpoint or watchpoint. If the .Cm c modifier is specified, count instructions while executing. Some machines (e.g., pmax) also count loads and stores.
p .Sy Warning : when counting, the debugger is really silently single-stepping. This means that single-stepping on low-level code may cause strange behavior.
p t Ic until Ns Op Li / Ns Cm p Stop at the next call or return instruction. If the .Cm p modifier is specified, print the call nesting depth and the cumulative instruction count at each call or return. Otherwise, only print when the matching return is hit.
p t Ic next Ns Op Li / Ns Cm p t Ic match Ns Op Li / Ns Cm p Stop at the matching return instruction. If the .Cm p modifier is specified, print the call nesting depth and the cumulative instruction count at each call or return. Otherwise, only print when the matching return is hit.
p t Xo c trace Ns Op Li / Ns Cm u .Op Ar pid | tid .Op Li , Ns Ar count .Xc t Xo c t Ns Op Li / Ns Cm u .Op Ar pid | tid .Op Li , Ns Ar count .Xc t Xo c where Ns Op Li / Ns Cm u .Op Ar pid | tid .Op Li , Ns Ar count .Xc t Xo c bt Ns Op Li / Ns Cm u .Op Ar pid | tid .Op Li , Ns Ar count .Xc Stack trace. The .Cm u option traces user space; if omitted, c trace only traces kernel space. The optional argument .Ar count is the number of frames to be traced. If .Ar count is omitted, all frames are printed.
p .Sy Warning : User space stack trace is valid only if the machine dependent code supports it.
p t Xo c search Ns Op Li / Ns Cm bhl .Ar addr .Ar value .Op Ar mask .Op Li , Ns Ar count .Xc Search memory for .Ar value . This command might fail in interesting ways if it does not find the searched-for value. This is because .Nm does not always recover from touching bad memory. The optional .Ar count argument limits the search.
p t Ic show Cm all procs Ns Op Li / Ns Cm m t Ic ps Ns Op Li / Ns Cm m 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 target process is not in the main memory at that time. The .Cm m modifier will alter the display to show VM map addresses for the process and not show other info.
p t Ic show Cm registers Ns Op Li / Ns Cm u Display the register set. If the .Cm u modifier is specified, it displays user registers instead of kernel or currently saved one.
p .Sy Warning : The support of the .Cm u modifier depends on the machine. If not supported, incorrect information will be displayed.
p t Ic show Cm sysregs Show system registers (e.g., .Li cr0-4 on i386.) Not present on some platforms.
p t Ic show Cm geom Op Ar addr If the .Ar addr argument is not given, displays the entire GEOM topology. If the .Ar addr is given, displays details about the given GEOM object (class, geom, provider or consumer).
p t Ic show Cm map Ns Oo Li / Ns Cm f Oc Ar addr Prints the VM map at .Ar addr . If the .Cm f modifier is specified the complete map is printed.
p t Ic show Cm object Ns Oo Li / Ns Cm f Oc Ar addr Prints the VM object at .Ar addr . If the .Cm f option is specified the complete object is printed.
p t Ic show Cm vnode Ar addr Displays details about the given vnode.
p t Ic show Cm watches Displays all watchpoints.
p t 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.
p t Ic halt Halt the system.
p t 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 .
p t Ic reboot t Ic reset Hard reset the system.
p t Ic help Print a short summary of the available commands and command abbreviations.
p t Ic capture on t Ic capture off t Ic capture reset t Ic capture status .Nm supports a basic output capture facility, which can be used to retrieve the results of debugging commands from userpsace using .Xr sysctl 2 . c capture on enables output capture; c capture off disables capture. c capture reset will clear the capture buffer and disable capture. c capture status will report current buffer use, buffer size, and disposition of output capture.
p Userspace processes may inspect and manage .Nm capture state using .Xr sysctl 8 :
p .Dv debug.ddb.capture.bufsize may be used to query or set the current capture buffer size.
p .Dv debug.ddb.capture.maxbufsize may be used to query the compile-time limit on the capture buffer size.
p .Dv debug.ddb.capture.bytes may be used to query the number of bytes of output currently in the capture buffer.
p .Dv debug.ddb.capture.data returns the contents of the buffer as a string to an appropriately privileged process.
p This facility is particularly useful in concert with the scripting and .Xr textdump 4 facilities, allowing scripted debugging output to be captured and committed to disk as part of a textdump for later analysis. The contents of the capture buffer may also be inspected in a kernel core dump using .Xr kgdb 1 .
p t Ic run t Ic script t Ic scripts t Ic unscript Run, define, list, and delete scripts. See the .Sx SCRIPTING section for more information on the scripting facility.
p t Ic textdump set t Ic textdump status t Ic textdump unset The c textdump set command may be used to force the next kernel core dump to be a textdump rather than a traditional memory dump or minidump. c textdump status reports whether a textdump has been scheduled. c textdump unset cancels a request to perform a textdump as the next kernel core dump. More information may be found in .Xr textdump 4 . .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 ) .
p Built-in variables currently supported are:
p l -tag -width ".Va tabstops" -compact t Va radix Input and output radix. t Va maxoff Addresses are printed as .Dq Ar symbol Ns Li + Ns Ar offset unless .Ar offset is greater than .Va maxoff . t Va maxwidth The width of the displayed line. t Va lines The number of lines. It is used by the built-in pager. t Va tabstops Tab stop width. t 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: l -tag -width ".No Identifiers" t 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. t Numbers Radix is determined by the first two letters: .Ql 0x : hex, .Ql 0o : octal, .Ql 0t : decimal; otherwise, follow current radix. t Li . .Va dot t Li + .Va next t Li .. address of the start of the last line examined. Unlike .Va dot or .Va next , this is only changed by c examine or c write command. t Li ' last address explicitly specified. t Li $ Ns Ar variable Translated to the value of the specified variable. It may be followed by a .Ql : and modifiers as described above. t 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. t Li * Ns Ar expr Indirection. It may be followed by a .Ql : and modifiers as described above. .El .Sh SCRIPTING .Nm supports a basic scripting facility to allow automating tasks or responses to specific events. Each script consists of a list of DDB commands to be executed sequentially, and is assigned a unique name. Certain script names have special meaning, and will be automatically run on various .Nm events if scripts by those names have been defined.
p The c script command may be used to define a script by name. Scripts consist of a series of .Nm commands separated with the c ; character. For example: d -literal -offset indent script kdb.enter.panic=bt; show pcpu script lockinfo=show alllocks; show lockedvnods .Ed
p The c scripts command lists currently defined scripts.
p The c run command execute a script by name. For example: d -literal -offset indent run lockinfo .Ed
p The c unscript command may be used to delete a script by name. For example: d -literal -offset indent unscript kdb.enter.panic .Ed
p These functions may also be performed from userspace using the .Xr ddb 8 command.
p Certain scripts are run automatically, if defined, for specific .Nm events. The follow scripts are run when various events occur: l -tag -width kdb.enter.powerfail t Dv kdb.enter.acpi The kernel debugger was entered as a result of an .Xr acpi 4 event. t Dv kdb.enter.bootflags The kernel debugger was entered at boot as a result of the debugger boot flag being set. t Dv kdb.enter.break The kernel debugger was entered as a result of a serial or console break. t Dv kdb.enter.cam The kernel debugger was entered as a result of a .Xr CAM 4 event. t Dv kdb.enter.mac The kernel debugger was entered as a result of an assertion failure in the .Xr mac_test 4 module of the TrustedBSD MAC Framework. t Dv kdb.enter.ndis The kernel debugger was entered as a result of an .Xr ndis 4 breakpoint event. t Dv kdb.enter.netgraph The kernel debugger was entered as a result of a .Xr netgraph 4 event. t Dv kdb.enter.panic .Xr panic 9 was called. t Dv kdb.enter.powerfail The kernel debugger was entered as a result of a powerfail NMI on the sparc64 platform. t Dv kdb.enter.powerpc The kernel debugger was entered as a result of an unimplemented interrupt type on the powerpc platform. t Dv kdb.enter.sysctl The kernel debugger was entered as a result of the .Dv debug.kdb.enter sysctl being set. t Dv kdb.enter.trapsig The kernel debugger was entered as a result of a trapsig event on the sparc64 or sun4v platform. t Dv kdb.enter.unionfs The kernel debugger was entered as a result of an assertion failure in the union file system. t Dv kdb.enter.unknown The kernel debugger was entered, but no reason has been set. t Dv kdb.enter.vfslock The kernel debugger was entered as a result of a VFS lock violation. t Dv kdb.enter.watchdog The kernel debugger was entered as a result of a watchdog firing. t Dv kdb.enter.witness The kernel debugger was entered as a result of a .Xr witness 4 violation. .El
p In the event that none of these scripts is found, .Nm will attempt to execute a default script: l -tag -width kdb.enter.powerfail t Dv kdb.enter.default The kernel debugger was entered, but a script exactly matching the reason for entering was not defined. This can be used as a catch-all to handle cases not specifically of interest; for example, .Dv kdb.enter.witness might be defined to have special handling, and .Dv kdb.enter.default might be defined to simply panic and reboot. .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 , .Xr kgdb 1 , .Xr acpi 4 , .Xr CAM 4 , .Xr mac_text 4 , .Xr ndis 4 , .Xr netgraph 4 , .Xr textdump 4 , .Xr witness 4 , .Xr ddb 8 , .Xr sysctl 8 , .Xr panic 9 .Sh HISTORY The .Nm debugger was developed for Mach, and ported to x 386 0.1 . This manual page translated from .Xr man 7 macros by .An Garrett Wollman .
p .An Robert N. M. Watson added support for .Nm output capture, .Xr textdump 4 and scripting in .Fx 8.0 .