ddb(4)
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DDB(4) NetBSD Programmer's 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
DESCRIPTION
ddb is the in-kernel debugger. It may be entered at any time via a spe-
cial 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.
amiga <LAlt>-<LAmiga>-<F10>
atari <Alt>-<LeftShift>-<F9>
hp300 <Shift>-<Reset>
i386 <Ctrl>-<Alt>-<Esc>
mac68k <Command>-<Power>, or the Interrupt switch.
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.
sun3 <L1>-A, or <Stop>-A on a Sun keyboard.
<Break> on serial console.
sun3x <L1>-A, or <Stop>-A on a Sun keyboard.
<Break> on serial console.
x68k Interrupt switch on the body.
In addition, ddb may be explicitly activated by the debugging code in the
kernel if DDB is configured.
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 examined or the last location modified, and set next to the
next location to be examined or modified. 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 a
count of 1 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.
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 dis-
plays ``--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 in-
put mode.
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 manipulated 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:
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 long-words (32 bits).
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 charac-
ters 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 alterna-
tive formats depending upon the machine:
alpha print register operands
m68k use Motorola syntax
pc532 print instruction bytes in hex
vax don't assume that each external label is a
procedure entry mask
x[/modifier] address[,count]
A synonym for examine.
xf Examine forward. xf re-executes the most recent execute command
with the same parameters except that address is set to next.
xb Examine backward. xb re-executes the most recent execute command
with the same parameters, except that address is set to the last
start address minus its size.
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
write[/bhl] address expression [expression ...]
Write the expressions at succeeding locations. The unit size is
specified with a modifier character, as per examine. Valid modi-
fiers are: /b, /h, and /l. If no modifier is specified, /l is
used.
Warning: since there is no delimiter between expressions, strange
things may occur. It's best to enclose each expression in paren-
theses.
set $variable [=] expression
Set the named variable or register to the value of expression.
Valid variable names are described in VARIABLES.
break[/u] address[,count]
Set a breakpoint at address. If count is supplied, continues
(count-1) times before stopping at the breakpoint. If the break-
point is set, a breakpoint number is printed with `#'. This num-
ber 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 mes-
sage 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 debug-
ger, user-space breakpoints may not work correctly. Setting a
breakpoint at the low-level code paths may also cause strange be-
havior.
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 `#'.
step[/p] [,count]
Single-step count times. If /p is specified, print each instruc-
tion 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.
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.
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. Otherwise, only print when the matching
return is hit.
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.
match[/p]
A synonym for next.
trace[/u] [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 omitted, all frames are printed.
Warning: user-space stack trace is valid only if the machine de-
pendent code supports it.
trace/t [pid][,count]
Stack trace by ``thread'' (process, on NetBSD) rather than by
stack frame address. Note that pid is interpreted using the cur-
rent radix, whilst ps displays pids in decimal; prefix pid with
`0t' to force it to be interpreted as decimal (see VARIABLES sec-
tion for radix)
Warning: trace by pid is valid only if the machine dependent code
supports it.
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 limits the search.
reboot [flags]
Reboot, using the optionally supplied boot flags.
Note: Limitations of the command line interface preclude specifi-
cation of a boot string.
show all procs[/a][/n][/w]
Display all process information. Valid modifiers:
/n show process information in a ps(1) style format (this is the
default). Information printed includes: process ID, parent
process ID, process group, UID, process status, process
flags, process command name, and process wait channel mes-
sage.
/a show the kernel virtual addresses of each process' proc
structure, u-are, and vmspace structure. The vmspace address
is also the address of the process' vm_map structure, and can
be used in the show map command.
/w show each process' PID, command, system call emulation, wait
channel address, and wait channel message.
ps[/a][/n][/w]
A synonym for show all procs.
show registers[/u]
Display the register set. If /u is specified, display user regis-
ters instead of kernel registers or the currently save one.
Warning: support for /u is machine dependent. If not supported,
incorrect information will be displayed.
show map[/f] address
Print the vm_map at address. If /f is specified the complete map
is printed.
show object[/f] address
Print the vm_object at address. If /f is specified the complete
object is printed.
show watches
Display all watchpoints.
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 unre-
coverable error in some systems such as i386. Watchpoints on user
addresses work the best.
dwatch address
Delete the watchpoint at address that was previously set with
watch command.
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.
call address[(expression[,...])]
Call the function specified by address with the argument(s) list-
ed in parentheses. Parentheses may be omitted if the function
takes no arguments. The number of arguments is currently limited
to 10.
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:
ALPHA
halt Call the PROM monitor to halt the CPU.
reboot Call the PROM monitor to reboot the CPU.
ARM32
vmstat Equivalent to vmstat(8) output with "-s" option (statistics).
vnode Print out a description of a vnode.
intrchain Print the list of IRQ handlers.
panic Print the current "panic" string.
frame Given a trap frame address, print out the trap frame.
MIPS
halt Call the PROM monitor to halt the CPU.
tlb Print out the Translation Lookaside Buffer (TLB).
trapdump Print out the Trap Log. Only works in NetBSD kernels compiled
with DEBUG option.
SPARC
prom Exit to the Sun PROM monitor.
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).
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 indi-
cate user register (e.g., $eax:u).
Built-in variables currently supported are:
lines The number of lines. This is used by the more feature.
maxoff Addresses are printed as 'symbol'+offset unless offset is
greater than maxoff.
maxwidth The width of the displayed line.
onpanic If non-zero (the default), ddb will be invoked when the
kernel panics. If the kernel configuration option
options DDB_ONPANIC=0
is used, onpanic will be initialised to off.
radix Input and output radix.
tabstops Tab stop width.
workxx Temporary work variable. `xx' is between 0 and 31.
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 identifi-
er. If supported by an object format dependent rou-
tine, [filename:]function[:linenumber], [file-
name:]variable, and filename[:linenumber], can be ac-
cepted 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 charac-
ters: `0x' - hex, `0o' - octal, `0t' - decimal, other-
wise 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 multiple of right-hand side.
*expr expression indirection. It may be followed by a `:'
and modifiers as described above.
HISTORY
The ddb kernel debugger was written as part of the MACH project at
Carnegie-Mellon University.
SEE ALSO
options(4), sysctl(8)
NetBSD 1.4 November 17, 1997 8
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