NetBSD/share/man/man4/ddb.4

.\" -*- nroff -*-
.\" 
.\"	$NetBSD: ddb.4,v 1.9 1997/03/08 13:54:26 mouse Exp $
.\"
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.\" Copyright (c) 1991,1990 Carnegie Mellon University
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.\" any improvements or extensions that they make and grant Carnegie Mellon
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.\" 
.TH DDB 4
.SH NAME
ddb \- kernel debugger
.de XX
.sp
.ti -4n
\\$1
.br
.sp
..
.de XS
.nr )R +\\$1
..
.de XE
.nr )R -\\$1
..
.SH SYNOPSIS
.B "options DDB"
.SH DESCRIPTION
.br
.sp
The kernel debugger has most of the features of the old kdb,
but with a more rational (gdb-like) syntax.
.sp
The current location is called 'dot'.  The 'dot' is displayed with
a hexadecimal format at a prompt.
Examine and write commands update 'dot' to the address of the last line
examined or the last location modified, and set 'next' to the address of
the next location to be examined or changed.
Other commands don't change 'dot', and set 'next' to be the same as 'dot'.
.sp
The general command syntax is:
.sp
.ti +4n
\fIcommand[/modifier] address [,count]\fR
.sp
A blank line repeats from the address 'next' with count 1 and no modifiers.
Specifying 'address' sets 'dot' to the address.
Omitting 'address' uses 'dot'.
A missing 'count' is taken to be 1 for printing commands or infinity
for stack traces.
.sp
"\fBddb\fR" has a feature like a command "\fBmore\fR"
for the output.  If an output line exceeds the number set in the $lines
variable, it displays "\fI--db_more--\fR"
and waits for a response.
The valid responses for it are:
.XS 4n
.IP \fI\<space>\fR 10n
one more page
.IP \fI\<return>\fR 10n
one more line
.IP \fB\q\fR 10n
abort the current command, and return to the command input mode.
.LP
.sp
.XE 4n
.LP
.B COMMANDS
.sp
.XS 4n
.LP
.XX "\fBexamine(x) \fI[/<modifier>] <addr>[,<count>]\fR"
Display the addressed locations according to the formats in the modifier.
Multiple modifier formats display multiple locations.
If no format is specified, the last formats specified for this command
is used.
.br
The format characters are
.sp
.LP
.XS 2n
.IP b 5n
look at by bytes(8 bits)
.IP h 5n
look at by half words(16 bits)
.IP l 5n
look at by long words(32 bits)
.IP a 5n
print the location being displayed
.IP A 5n
print the location with a line number if possible
.IP x 5n
display in unsigned hex
.IP z 5n
display in signed hex
.IP o 5n
display in unsigned octal
.IP d 5n
display in signed decimal
.IP u 5n
display in unsigned decimal
.IP r 5n
display in current radix, signed
.IP c 5n
display low 8 bits as a character.
Non-printing characters are displayed as an octal escape code (e.g. '\\000').
.IP s 5n
display the null-terminated string at the location.
Non-printing characters are displayed as octal escapes.
.IP m 5n
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.
.IP i 5n
display as an instruction
.IP I 5n
display as an instruction with possible alternative formats depending on the
machine:
.XE 2n
.LP
.XS 5n
.LP
.IP vax 6n
don't assume that each external label is a procedure entry mask
.IP i386 6n
don't round to the next long word boundary
.IP mips 6n
print register contents
.LP
.XE 5n
.LP
.XX xf
Examine forward.
It executes an examine command with the last specified parameters to it
except that the next address displayed by it is used as the start address.
.XX xb
Examine backward.
It executes an 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.
.XX "\fBprint[/axzodurc] \fI<addr1> [ <addr2> ... ]\fR"
Print 'addr's according to the modifier character.
Valid formats are: a x z o d u r c.
If no modifier is specified, the last one specified to it is used.  'addr'
can be a string, and it is printed as it is.  For example,
.br
.sp
.ti +4n
print/x "eax = " $eax "\\necx = " $ecx "\\n"
.br
.sp
will print like
.sp
.in +4n
eax = xxxxxx
.br
ecx = yyyyyy
.in -4n
.sp
.br
.XX "\fBwrite[/bhl] \fI<addr> <expr1> [ <expr2> ... ]\fR"
Write the expressions at succeeding locations.
The write unit size can be specified in the modifier with a letter
b (byte), h (half word) or l(long word) respectively.  If omitted,
long word is assumed.
.br
Warning: since there is no delimiter between expressions, strange
things may happen.
It's best to enclose each expression in parentheses.
.XX "\fBset \fI$<variable> [=] <expr>\fR"
Set the named variable or register with the value of 'expr'.
Valid variable names are described below.
.XX "\fBbreak[/u] \fI<addr>[,<count>]\fR"
Set a break point at 'addr'.
If count is supplied, continues (count-1) times before stopping at the
break point.  If the break point is set, a break point number is
printed with '#'.  This number can be used in deleting the break point
or adding conditions to it.
.LP
.XS 2n
.IP u 5n
Set a break point in user space address. Without 'u' option,
the address is considered in the kernel space, and wrong space address
is rejected with an error message.
This option can be used only if it is supported by machine dependent
routines.
.LP
.XE 2n
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.
.XX "\fBdelete \fI<addr>|#<number>\fR"
Delete the break point.  The target break point can be specified by a
break point number with '#', or by 'addr' like specified in 'break'
command.
.XX "\fBstep[/p] \fI[,<count>]\fR"
Single step 'count' times.
If 'p' option is specified, print each instruction at each step.
Otherwise, only print the last instruction.
.br
.sp
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.
.XX "\fBcontinue[/c]\fR"
Continue execution until a breakpoint or watchpoint.
If /c, count instructions while executing.
Some machines (e.g., pmax) also count loads and stores.
.br
.sp
Warning: when counting, the debugger is really silently single-stepping.
This means that single-stepping on low-level code may cause strange
behavior.
.XX "\fBuntil[/p]\fR"
Stop at the next call or return instruction.
If 'p' option 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.
.XX "\fBnext[/p]\fR"
Stop at the matching return instruction.
If 'p' option 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.
.XX "\fBmatch[/p]\fR"
A synonym for 'next'.
.XX "\fBtrace[/u] \fI[ <frame_addr> ][,<count>]\fR"
Stack trace.  'u' option traces user space; if omitted, only traces
kernel space. 'count' is the number of frames to be traced. 
If the 'count' is omitted, all frames are printed.
.br
.sp
Warning: User space stack trace is valid
only if the machine dependent code supports it.
.XX "\fBsearch[/bhl] \fI<addr> <value> [<mask>] [,<count>]\fR"
Search memory for a value. This command might fail in interesting
ways if it doesn't find the searched-for value.  This is because
ddb doesn't always recover from touching bad memory.  The optional
count argument limits the search.
.XX "\fBshow all procs[/m]\fR"
Display all process information.
This version of "\fBddb\fR"
prints more information than previous one.
It shows UNIX process information like "ps".
The UNIX 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 'm' options will alter the 'ps' display to show vm_map
addresses for the process and not show other info.
.br
.XX "\fBps[/m]\fR"
A synonym for 'show all procs'.
.XX "\fBshow registers\fR"
Display the register set.
If 'u' option is specified, it displays user registers instead of
kernel or currently saved one.
.br
.sp
Warning: The support of 'u' option depends on the machine.  If
not supported, incorrect information will be displayed.
.XX "\fBshow map[/f] \fI<addr>\fR"
Prints the vm_map at 'addr'. If the 'f' option is specified the
complete map is printed.
.XX "\fBshow object[/f]  \fI<addr>\fR"
Prints the vm_object at 'addr'. If the 'f' option is specified the
complete object is printed.
.XX "\fBshow watches\fR"
Displays all watchpoints.
.XX "\fBwatch \fI<addr>,<size>\fR"
Set a watchpoint for a region.  Execution stops
when an attempt to modify the region occurs.
The 'size' argument defaults to 4.
.br
If you specify a wrong space address, the request is rejected
with an error message.
.br
.sp
Warning: Attempts to watch wired kernel memory
may cause unrecoverable error in some systems such as i386.
Watchpoints on user addresses work best.
.br
.LP
.XE 4n
.LP
.sp
.B VARIABLES
.sp
The debugger accesses registers and variables as
.I $<name>.
Register names are as in the "\fBshow registers\fR"
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 'u' modifier to indicate
user register (e.g. $eax:u).
.br
.sp
Built-in variables currently supported are:
.sp
.IP radix 12n
Input and output radix
.IP maxoff 12n
Addresses are printed as 'symbol'+offset unless offset is greater than maxoff.
.IP maxwidth 12n
The width of the displayed line.
.IP lines 12n
The number of lines.  It is used by "more" feature.
.IP tabstops 12n
Tab stop width.
.IP onpanic 12n
If non-zero, the debugger will be called when the kernel panics.  Default
is "on", and may be initialzed at build time with the "DDB_ONPANIC=0"
option set in the kernel configuration file.
.IP work\fIxx\fR
Work variable.
.I 'xx'
can be 0 to 31.
.LP
All built-in variables are accessible via sysctl(3).
.LP
.sp
.B EXPRESSIONS
.sp
Almost all expression operators in C are supported except '~', '^',
and unary '&'.
Special rules in "\fBddb\fR"
are:
.br
.IP "<identifier>" 15n
name of a symbol.  It is translated to the address(or value) of it.  '.'
and ':' can be used in the identifier.  If supported by an object format
dependent routine,
[\fI<file_name>\fR:]\fI<func>\fR[:\fI<line_number>\fR]
[\fI<file_name>\fR:]\fI<variable>\fR, and
\fI<file_name>\fR[:\fI<line_number>\fR]
can be accepted as a symbol.
The symbol may be prefixed with '\fI<symbol_table_name>\fR::'
like 'emulator::mach_msg_trap' to specify other than kernel symbols.
.IP "<number>" 15n
radix is determined by the first two letters:
0x: hex, 0o: octal, 0t: decimal, otherwise, follow current radix.
.IP \. 15n
\'dot'
.IP \+ 15n
\'next'
.IP \.. 15n
address of the start of the last line examined.
Unlike 'dot' or 'next', this is only changed by "examine" or
"write" command.
.IP \' 15n
last address explicitly specified.
.IP "$<variable>" 15n
register name or variable.  It is translated to the value of it.
It may be followed by a ':' and modifiers as described above.
.IP \# 15n
a binary operator which rounds up the left hand side to the next
multiple of right hand side.
.IP "*<expr>" 15n
indirection.  It may be followed by a ':' and  modifiers as described above.