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NetBSD 6.1.5 - man page for ddb (netbsd section 4)

DDB(4)				   BSD Kernel Interfaces Manual 			   DDB(4)

NAME
     ddb -- in-kernel debugger

SYNOPSIS
     options DDB

     To enable history editing:
     options DDB_HISTORY_SIZE=integer

     To disable entering ddb upon kernel panic:
     options DDB_ONPANIC=0

     To enable teeing all ddb output to the kernel msgbuf:
     options DDB_TEE_MSGBUF=1

     To specify commands which will be executed on each entry to ddb:
     options DDB_COMMANDONENTER="trace;show registers"
     In this case, "trace" and then "show registers" will be executed automatically.

     To enable extended online help:
     options DDB_VERBOSE_HELP.

DESCRIPTION
     ddb is the in-kernel debugger.  It may be entered at any time via a special key sequence,
     and optionally may be invoked when the kernel panics.

ENTERING THE DEBUGGER
     Unless DDB_ONPANIC is set to 0, ddb will be activated whenever the kernel would otherwise
     panic.

     ddb may also be activated from the console.  In general, sending a break on a serial console
     will activate ddb.  There are also key sequences for each port that will activate ddb from
     the keyboard:
	   alpha     <Ctrl>-<Alt>-<Esc> on PC style keyboards.
	   amd64     <Ctrl>-<Alt>-<Esc>
		     <Break> on serial console.
	   amiga     <LAlt>-<LAmiga>-<F10>
	   atari     <Alt>-<LeftShift>-<F9>
	   hp300     <Shift>-<Reset>
	   hp700     <Ctrl>-<Alt>-<Esc> on PC style keyboards.
		     +++++ (five plus signs) on PDC console
		     <Break> on serial console.
	   hpcarm    <Ctrl>-<Alt>-<Esc>
	   hpcmips   <Ctrl>-<Alt>-<Esc>
	   hpcsh     <Ctrl>-<Alt>-<Esc>
	   i386      <Ctrl>-<Alt>-<Esc>
		     <Break> on serial console.
	   mac68k    <Command>-<Power>, or the Interrupt switch.
	   macppc    Some models: <Command>-<Option>-<Power>
	   mvme68k   Abort switch on CPU card.
	   pmax      <Do> on LK-201 rcons console.
		     <Break> on serial console.
	   sparc     <L1>-A, or <Stop>-A on a Sun keyboard.
		     <Break> on serial console.
	   sparc64   <L1>-A, or <Stop>-A on a Sun keyboard.
		     <Break> on serial console.
	   sun3      <L1>-A, or <Stop>-A on a Sun keyboard.
		     <Break> on serial console.
	   vax	     <Esc>-<Shift>-D on serial console.
	   x68k      Interrupt switch on the body.
	   xen dom0  <Ctrl>-<Alt>-<Esc> on PC style keyboards.
		     +++++ (five plus signs) on serial console.
	   xen domU  +++++ (five plus signs) on serial console.
	   zaurus    <Ctrl>-<Alt>-<Esc>

     The key sequence to activate ddb can be changed by modifying ``hw.cnmagic'' with sysctl(8).
     If the console is not dedicated to ddb the sequence should not be easily typed by accident.
     In addition, ddb may be explicitly activated by the debugging code in the kernel if DDB is
     configured.

     Commands can be automatically run when ddb is entered by using options DDB_COMMANDONENTER or
     by setting ddb.commandonenter with sysctl(8).  Multiple commands can be separated by a semi-
     colon.

COMMAND SYNTAX
     The general command syntax is:

	   command[/modifier] address [,count]

     The current memory location being edited is referred to as dot, and the next location is
     next.  They are displayed as hexadecimal numbers.

     Commands that examine and/or modify memory update dot to the address of the last line exam-
     ined or the last location modified, and set next to the next location to be examined or mod-
     ified.  Other commands don't change dot, and set next to be the same as dot.

     A blank line repeats the previous command from the address next with the previous count and
     no modifiers.  Specifying address sets dot to the address.  If address is omitted, dot is
     used.  A missing count is taken to be 1 for printing commands, and infinity for stack
     traces.

     The syntax:

	   ,count

     repeats the previous command, just as a blank line does, but with the specified count.

     ddb has a more(1)-like functionality; if a number of lines in a command's output exceeds the
     number defined in the lines variable, then ddb displays ``--db more--'' and waits for a
     response, which may be one of:

	   <return>  one more line.

	   <space>   one more page.

	   q	     abort the current command, and return to the command input mode.

     You can set lines variable to zero to disable this feature.

     If ddb history editing is enabled (by defining the
	   options DDB_HISTORY_SIZE=num
     kernel option), then a history of the last num commands is kept.  The history can be manipu-
     lated with the following key sequences:

	   <Ctrl>-P  retrieve previous command in history (if any).

	   <Ctrl>-N  retrieve next command in history (if any).

COMMANDS
     ddb supports the following commands:

     !address[(expression[,...])]
	    A synonym for call.

     break[/u] address[,count]
	    Set a breakpoint at address.  If count is supplied, continues (count-1) times before
	    stopping at the breakpoint.  If the breakpoint is set, a breakpoint number is printed
	    with '#'.  This number can be used to delete the breakpoint, or to add conditions to
	    it.

	    If /u is specified, set a breakpoint at a user-space address.  Without /u, address is
	    considered to be in the kernel-space, and an address in the wrong space will be
	    rejected, and an error message will be emitted.  This modifier may only be used if it
	    is supported by machine dependent routines.

	    Warning: if a user text is shadowed by a normal user-space debugger, user-space
	    breakpoints may not work correctly.  Setting a breakpoint at the low-level code paths
	    may also cause strange behavior.

     bt[/ul] [frame-address][,count]
	    A synonym for trace.

     bt/t[/ul] [pid][,count]
	    A synonym for trace/t.

     bt/a[/ul] [lwpaddr][,count]
	    A synonym for trace/a.

     call address[(expression[,...])]
	    Call the function specified by address with the argument(s) listed in parentheses.
	    Parentheses may be omitted if the function takes no arguments.  The number of argu-
	    ments is currently limited to 10.

     continue[/c]
	    Continue execution until a breakpoint or watchpoint.  If /c is specified, count
	    instructions while executing.  Some machines (e.g., pmax) also count loads and
	    stores.

	    Warning: when counting, the debugger is really silently single-stepping.  This means
	    that single-stepping on low-level may cause strange behavior.

     delete address | #number
	    Delete a breakpoint.  The target breakpoint may be specified by address, as per
	    break, or by the breakpoint number returned by break if it's prefixed with '#'.

     dmesg [count]
	    Prints the contents of the kernel message buffer.  The optional count argument will
	    limit printing to at most the last count bytes of the message buffer.

     dwatch address
	    Delete the watchpoint at address that was previously set with watch command.

     examine[/modifier] address[,count]
	    Display the address locations according to the format in modifier.	Multiple modifier
	    formats display multiple locations.  If modifier isn't specified, the modifier from
	    the last use of examine is used.

	    The valid format characters for modifier are:
		  b   examine bytes (8 bits).
		  h   examine half-words (16 bits).
		  l   examine words (legacy ``long'', 32 bits).
		  L   examine long words (implementation dependent)
		  a   print the location being examined.
		  A   print the location with a line number if possible.
		  x   display in unsigned hex.
		  z   display in signed hex.
		  o   display in unsigned octal.
		  d   display in signed decimal.
		  u   display in unsigned decimal.
		  r   display in current radix, signed.
		  c   display low 8 bits as a character.  Non-printing characters as displayed as
		      an octal escape code (e.g., '\000').
		  s   display the NUL terminated string at the location.  Non-printing characters
		      are displayed as octal escapes.
		  m   display in unsigned hex with a character dump at the end of each line.  The
		      location is displayed as hex at the beginning of each line.
		  i   display as a machine instruction.
		  I   display as a machine instruction, with possible alternative formats depend-
		      ing upon the machine:
			    alpha  print register operands
			    m68k   use Motorola syntax
			    vax    don't assume that each external label is a procedure entry
				   mask

     kill pid[,signal_number]
	    Send a signal to the process specified by the pid.	Note that pid is interpreted
	    using the current radix (see trace/t command for details).	If signal_number isn't
	    specified, the SIGTERM signal is sent.

     match[/p]
	    A synonym for next.

     next[/p]
	    Stop at the matching return instruction.  If /p is specified, print the call nesting
	    depth and the cumulative instruction count at each call or return.	Otherwise, only
	    print when the matching return is hit.

     print[/axzodurc] address [address ...]
	    Print addresses address according to the modifier character, as per examine.  Valid
	    modifiers are: /a, /x, /z, /o, /d, /u, /r, and /c (as per examine).  If no modifier
	    is specified, the most recent one specified is used.  address may be a string, and is
	    printed ``as-is''.	For example:

		  print/x "eax = " $eax "\necx = " $ecx "\n"

	    will produce:

		  eax = xxxxxx
		  ecx = yyyyyy

     ps[/a][/n][/w][/l]
	    A synonym for show all procs.

     reboot [flags]
	    Reboot, using the optionally supplied boot flags, which is a bitmask supporting the
	    same values as for reboot(2).  Some of the more useful flags:

	    Value    Name	     Description
	    0x1      RB_ASKNAME      Ask for file name to reboot from
	    0x2      RB_SINGLE	     Reboot to single user mode
	    0x4      RB_NOSYNC	     Don't sync before reboot
	    0x8      RB_HALT	     Halt instead of reboot
	    0x40     RB_KDB	     Boot into kernel debugger
	    0x100    RB_DUMP	     Dump unconditionally before reboot
	    0x808    RB_POWERDOWN    Power off (or at least halt)

	    Note: Limitations of the command line interface preclude specification of a boot
	    string.

     search[/bhl] address value [mask] [,count]
	    Search memory from address for value.  The unit size is specified with a modifier
	    character, as per examine.	Valid modifiers are: /b, /h, and /l.  If no modifier is
	    specified, /l is used.

	    This command might fail in interesting ways if it doesn't find value.  This is
	    because ddb doesn't always recover from touching bad memory.  The optional count lim-
	    its the search.

     set $variable [=] expression
	    Set the named variable or register to the value of expression.  Valid variable names
	    are described in VARIABLES.

     show all callout
	    Display information about callouts in the system.  See callout(9) for more informa-
	    tion on callouts.

     show all pages
	    Display basic information about all physical pages managed by the VM system.  For
	    more detailed information about a single page, use show page.

     show all pools[/clp]
	    Display all pool information.  Modifiers are the same as show pool.

     show all procs[/a][/n][/w][/l]
	    Display all process information.  Valid modifiers:

	    /n	 show process information in a ps(1) style format.  Information printed includes:
		 process ID, parent process ID, process group, UID, process status, process
		 flags, number of LWPs, command name, and process wait channel message.

	    /a	 show each process ID, command name, kernel virtual addresses of each process'
		 proc structure, u-area, and vmspace structure.  The vmspace address is also the
		 address of the process' vm_map structure, and can be used in the show map com-
		 mand.

	    /w	 show each LWP ID, process ID, command name, system call emulation, priority,
		 wait channel message and wait channel address.  LWPs currently running on a CPU
		 are marked with the '>' sign.

	    /l	 show each LWP ID, process ID, process status, CPU ID the LWP runs on, process
		 flags, kernel virtual address of LWP structure, LWP name and wait channel mes-
		 sage.	LWPs currently running on a CPU are marked with the '>' sign.  This is
		 the default.

     show arptab
	    Dump the entire AF_INET routing table.  This command is available only on systems
	    which support inet and ARP.

     show breaks
	    Display all breakpoints.

     show buf[/f] address
	    Print the struct buf at address.  The /f does nothing at this time.

     show event[/f][/i][/m][/t]
	    Print all the non-zero evcnt(9) event counters.  Valid modifiers:

	    /f	 event counters with a count of zero are printed as well.

	    /i	 interrupted counters will be displayed.

	    /m	 misc counters will be displayed.

	    /t	 trap counters will be displayed.

	    If none of /i, /m or /t are specified, all are shown.  You can combine any of these.
	    For example, the modifier /itf will select both interrupt and trap events, including
	    those that are non-zero.

     show files address
	    Display information about the vnodes of the files that are currently open by the
	    process associated with the proc structure at address.  This address can be found
	    using the show all procs /a command.  If the kernel is compiled with options
	    LOCKDEBUG then details about the locking of the underlying uvm object will also be
	    displayed.

     show lock address
	    Display information about a lock at address.  This command is useful only if a kernel
	    is compiled with options LOCKDEBUG.

     show malloc address
	    If address is supplied, display the kernel memory allocator's idea on the allocation
	    status for it.  Also, print out global statistics for the memory allocator.  This
	    command is useful only if a kernel is compiled with options MALLOC_DEBUG.

     show map[/f] address
	    Print the vm_map at address.  If /f is specified, the complete map is printed.

     show mount[/f] address
	    Print the mount structure at address.  If /f is specified, the complete vnode list is
	    printed.

     show mbuf[/c] address
	    Print the mbuf structure at address.  If /c is specified, the mbufs in the chain are
	    followed.

     show ncache address
	    Dump the namecache list associated with vnode at address.

     show object[/f] address
	    Print the vm_object at address.  If /f is specified, the complete object is printed.

     show page[/f] address
	    Print the vm_page at address.  If /f is specified, the complete page is printed.

     show pool[/clp] address
	    Print the pool at address.	Valid modifiers:
	    /c	  Print the cachelist and its statistics for this pool.
	    /l	  Print the log entries for this pool.
	    /p	  Print the pagelist for this pool.

     show proc[/ap] address | pid
	    Show information about a process and its LWPs.  LWPs currently running on a CPU are
	    marked with the '>' sign.
	    /a	  The argument passed is the kernel virtual address of LWP structure.
	    /p	  The argument passed is a PID.  Note that pid is interpreted using the current
		  radix (see trace/t command for details).  This is the default.

     show registers[/u]
	    Display the register set.  If /u is specified, display user registers instead of ker-
	    nel registers or the currently save one.

	    Warning: support for /u is machine dependent.  If not supported, incorrect informa-
	    tion will be displayed.

     show sched_qs
	    Print the state of the scheduler's run queues.  For each run queue that has an LWP,
	    the run queue index and the list of LWPs will be shown.  If the run queue has LWPs,
	    but the sched_whichqs bit is not set for that queue, the queue index will be prefixed
	    with a '!'.

     show uvmexp
	    Print a selection of UVM counters and statistics.

     show uvmhist
	    Dumps the UVM histories.  This command is available only if a kernel is compiled with
	    options UVMHIST.

     show vnode[/f] address
	    Print the vnode at address.  If /f is specified, the complete vnode is printed.

     show watches
	    Display all watchpoints.

     sifting[/F] string
	    Search the symbol tables for all symbols of which string is a substring, and display
	    them.  If /F is specified, a character is displayed immediately after each symbol
	    name indicating the type of symbol.

	    For a.out(5)-format symbol tables, absolute symbols display @, text segment symbols
	    display *, data segment symbols display +, BSS segment symbols display -, and file-
	    name symbols display /.  For ELF-format symbol tables, object symbols display +,
	    function symbols display *, section symbols display &, and file symbols display /.

	    To sift for a string beginning with a number, escape the first character with a back-
	    slash as:

		  sifting \386

     step[/p] [,count]
	    Single-step count times.  If /p is specified, print each instruction at each step.
	    Otherwise, only print the last instruction.

	    Warning: depending on the machine type, it may not be possible to single-step through
	    some low-level code paths or user-space code.  On machines with software-emulated
	    single-stepping (e.g., pmax), stepping through code executed by interrupt handlers
	    will probably do the wrong thing.

     sync   Force a crash dump, and then reboot.

     trace[/u[l]] [frame-address][,count]
	    Stack trace from frame-address.  If /u is specified, trace user-space, otherwise
	    trace kernel-space.  count is the number of frames to be traced.  If count is omit-
	    ted, all frames are printed.  If /l is specified, the trace is printed and also
	    stored in the kernel message buffer.

	    Warning: user-space stack trace is valid only if the machine dependent code supports
	    it.

     trace/t[l] [pid][,count]
	    Stack trace by ``thread'' (process, on NetBSD) rather than by stack frame address.
	    Note that pid is interpreted using the current radix, whilst ps displays pids in dec-
	    imal; prefix pid with '0t' to force it to be interpreted as decimal (see VARIABLES
	    section for radix).  If /l is specified, the trace is printed and also stored in the
	    kernel message buffer.

	    Warning: trace by pid is valid only if the machine dependent code supports it.

     trace/a[l] [lwpaddr][,count]
	    Stack trace by light weight process (LWP) address rather than by stack frame address.
	    If /l is specified, the trace is printed and also stored in the kernel message buf-
	    fer.

	    Warning: trace by LWP address is valid only if the machine dependent code supports
	    it.

     until[/p]
	    Stop at the next call or return instruction.  If /p is specified, print the call
	    nesting depth and the cumulative instruction count at each call or return.	Other-
	    wise, only print when the matching return is hit.

     watch address[,size]
	    Set a watchpoint for a region.  Execution stops when an attempt to modify the region
	    occurs.  size defaults to 4.

	    If you specify a wrong space address, the request is rejected with an error message.

	    Warning: attempts to watch wired kernel memory may cause an unrecoverable error in
	    some systems such as i386.	Watchpoints on user addresses work the best.

     whatis address
	    Describe what an address is.

     write[/bhlBHL] address expression [expression ...]
	    Write the expressions at succeeding locations.  The unit size is specified with a
	    modifier character, as per examine.  Valid modifiers are: /b, /h, and /l.  If no mod-
	    ifier is specified, /l is used.

	    Specifying the modifiers in upper case, /B, /H, /L, will prevent ddb from reading the
	    memory location first, which is useful for avoiding side effects when writing to I/O
	    memory regions.

	    Warning: since there is no delimiter between expressions, strange things may occur.
	    It's best to enclose each expression in parentheses.

     x[/modifier] address[,count]
	    A synonym for examine.

MACHINE-SPECIFIC COMMANDS
     The "glue" code that hooks ddb into the NetBSD kernel for any given port can also add
     machine specific commands to the ddb command parser.  All of these commands are preceded by
     the command word machine to indicate that they are part of the machine-specific command set
     (e.g.  machine reboot).  Some of these commands are:

   ACORN26
     bsw	Writes one or two bytes to the IObus.  Takes an address and a value.  Use the
		``b'' modifier to write a single byte and the ``h'' modifier to write two bytes.
     frame	Given a trap frame address, print out the trap frame.
     irqstat	Display the IRQ statistics
     panic	Print the current "panic" string.

   ALPHA
     cpu	Switch to another cpu.

   AMD64
     cpu	Switch to another cpu.

   ARM32
     frame	Given a trap frame address, print out the trap frame.
     panic	Print the current "panic" string.

   HP700
     frame	Without an address the default trap frame is printed.  Otherwise, the trap frame
		address can be given, or, when the ``l'' modifier is used, an LWP address.

   I386
     cpu	Switch to another cpu.

   IA64
     vector	Without a vector, information about all 256 vectors is shown.  Otherwise, the
		given vector is shown.

   MIPS
     cp0	Dump CP0 (coprocessor 0) register values.
     kvtop	Print the physical address for a given kernel virtual address.
     tlb	Print out the Translation Lookaside Buffer (TLB).  Only works in NetBSD kernels
		compiled with DEBUG option.

   POWERPC 4xx
     ctx	Print process MMU context information.
     pv 	Print PA->VA mapping information.
     reset	Reset the system.
     tf 	Display the contents of the trapframe.
     tlb	Display instruction translation storage buffer information.
     dcr	Set the DCR register.  Must be between 0x00 and 0x3ff.
     user	Display user memory.  Use the ``i'' modifier to get instruction decoding.

   POWERPC OEA
     bat	Print BAT registers and translations.
     mmu	Print MMU registers.

   SH3
     tlb	Print TLB entries.
     cache	Print cache entries.
     frame	Print switch frame and trap frames.
     stack	Print kernel stack usage.  Only works in NetBSD kernels compiled with the
		KSTACK_DEBUG option.

   SPARC
     cpu	Switch to another cpu.
     prom	Enter the Sun PROM monitor.
     proc	Display some information about the LWP pointed to, or curlwp.
     pcb	Display information about the ``struct pcb'' listed.
     page	Display the pointer to the ``struct vm_page'' for this physical address.

   SPARC64
     ctx	Print process context information.
     cpu	Switch to another cpu.
     dtlb	Print data translation look-aside buffer context information.
     dtsb	Display data translation storage buffer information.
     kmap	Display information about the listed mapping in the kernel pmap.  Use the ``f''
		modifier to get a full listing.
     extract	Extract the physical address for a given virtual address from the kernel pmap.
     fpstate	Dump the FPU state.
     itlb	Print instruction translation look-aside buffer context information.
     itsb	Display instruction translation storage buffer information.
     lwp	Display a struct lwp
     pcb	Display information about the ``struct pcb'' listed.
     pctx	Attempt to change process context.
     page	Display the pointer to the ``struct vm_page'' for this physical address.
     phys	Display physical memory.
     pmap	Display the pmap.  Use the ``f'' modifier to get a fuller listing.
     proc	Display some information about the process pointed to, or curproc.
     prom	Enter the OFW PROM.
     pv 	Display the ``struct pv_entry'' pointed to.
     sir	Reset the machine and enter prom (do a Software Initiated Reset).
     stack	Dump the window stack.	Use the ``u'' modifier to get userland information.
     tf 	Display full trap frame state.	This is most useful for inclusion with bug
		reports.
     ts 	Display trap state.
     traptrace	Display or set trap trace information.	Use the ``r'' and ``f'' modifiers to get
		reversed and full information, respectively.
     watch	Set or clear a physical or virtual hardware watchpoint.  Pass the address to be
		watched, or ``0'' (or omit the address) to clear the watchpoint.  Optional modi-
		fiers are ``p'' for physical address, ``r'' for trap on read access (default:
		trap on write access only), ``b'' for 8 bit width, ``h'' for 16 bit, ``l'' for 32
		bit or ``L'' for 64 bit.
     window	Print register window information.  Argument is a stack frame number (0 is top of
		stack, which is used when no index is given).

   SUN2, SUN3 and SUN3X
     abort	Drop into monitor via abort (allows continue).
     halt	Exit to Sun PROM monitor as in halt(8).
     reboot	Reboot the machine as in reboot(8).
     pgmap	Given an address, print the address, segment map, page map, and Page Table Entry
		(PTE).

   VAX
     cpu	Switch to another cpu.

VARIABLES
     ddb accesses registers and variables as $name.  Register names are as per the show registers
     command.  Some variables are suffixed with numbers, and may have a modifier following a
     colon immediately after the variable name.  For example, register variables may have a 'u'
     modifier to indicate user register (e.g., $eax:u).

     Built-in variables currently supported are:
	   lines     The number of lines.  This is used by the more feature.  When this variable
		     is set to zero the more feature is disabled.
	   maxoff    Addresses are printed as 'symbol'+offset unless offset is greater than
		     maxoff.
	   maxwidth  The width of the displayed line.  ddb wraps the current line by printing new
		     line when maxwidth column is reached.  When this variable is set to zero ddb
		     doesn't perform any wrapping.
	   onpanic   If greater than zero (the default is 1), ddb will be invoked when the kernel
		     panics.  If the kernel configuration option
			   options DDB_ONPANIC=0
		     is used, onpanic will be initialized to off, causing a stack trace to be
		     printed and the system to be rebooted instead of ddb being entered.  Other
		     useful settings are -1, which suppresses the stack trace before reboot, and
		     2, which causes a stack trace to be printed and ddb to be entered.
	   fromconsole
		     If non-zero (the default), the kernel allows to enter ddb from the console
		     (by break signal or special key sequence).  If the kernel configuration
		     option
			   options DDB_FROMCONSOLE=0
		     is used, fromconsole will be initialized to off.
	   radix     Input and output radix.
	   tabstops  Tab stop width.
	   tee_msgbuf
		     If explicitly set to non zero (zero is the default) all ddb output will not
		     only be displayed on screen but also be fed to the msgbuf.  The default of
		     the variable can be set using the kernel configuration option
			   options DDB_TEE_MSGBUF=1
		     which will initialize tee_msgbuf to be 1.	This option is especially handy
		     for poor souls who don't have a serial console but want to recall ddb output
		     from a crash investigation.  This option is more generic than the /l command
		     modifier possible for selected commands as discussed above to log the out-
		     put.  Mixing both /l and this setting can give double loggings.

     All built-in variables are accessible via sysctl(3).

EXPRESSIONS
     Almost all expression operators in C are supported, except '~', '^', and unary '&'.  Special
     rules in ddb are:

	   identifier  name of a symbol.  It is translated to the address (or value) of it.  '.'
		       and ':' can be used in the identifier.  If supported by an object format
		       dependent routine, [filename:]function[:line number], [filename:]variable,
		       and filename[:line number], can be accepted as a symbol.  The symbol may
		       be prefixed with symbol_table_name:: (e.g., emulator::mach_msg_trap) to
		       specify other than kernel symbols.

	   number      number.	Radix is determined by the first two characters: '0x' - hex, '0o'
		       - octal, '0t' - decimal, otherwise follow current radix.

	   .	       dot

	   +	       next

	   ..	       address of the start of the last line examined.	Unlike dot or next, this
		       is only changed by the examine or write commands.

	   "	       last address explicitly specified.

	   $name       register name or variable.  It is translated to the value of it.  It may
		       be followed by a ':' and modifiers as described above.

	   #	       a binary operator which rounds up the left hand side to the next multiple
		       of right hand side.

	   *expr       expression indirection.	It may be followed by a ':' and modifiers as
		       described above.

SEE ALSO
     reboot(2), options(4), crash(8), reboot(8), sysctl(8), cnmagic(9)

HISTORY
     The ddb kernel debugger was written as part of the MACH project at Carnegie-Mellon Univer-
     sity.

BSD					February 12, 2012				      BSD


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