mdb(1) User Commands mdb(1)NAMEmdb - modular debugger
SYNOPSISmdb [-fkmuwyAFKMSUW] [±o option] [-p pid] [-s distance]
[-I path] [-L path] [-P prompt] [-R root]
[-V dis-version] [object [core] | core | suffix]
DESCRIPTION
Introduction
The mdb utility is an extensible utility for low-level debugging and
editing of the live operating system, operating system crash dumps,
user processes, user process core dumps, and object files. For a more
detailed description of mdb features, refer to the manual, .
Debugging is the process of analyzing the execution and state of a
software program in order to remove defects. Traditional debugging
tools provide facilities for execution control so that programmers can
re-execute programs in a controlled environment and display the current
state of program data or evaluate expressions in the source language
used to develop the program.
Unfortunately, these techniques are often inappropriate for debugging
complex software systems such as an operating system, where bugs might
not be reproducible and program state is massive and distributed, for
programs that are highly optimized, have had their debug information
removed, or are themselves low-level debugging tools, or for customer
situations where the developer can only access post-mortem information.
mdb provides a completely customizable environment for debugging these
programs and scenarios, including a dynamic module facility that pro‐
grammers can use to implement their own debugging commands to perform
program-specific analysis. Each mdb module can be used to examine the
program in several different contexts, including live and post-mortem.
Definitions
The target is the program being inspected by the debugger. mdb cur‐
rently provides support for the following types of targets: user pro‐
cesses, user process core files, the live operating system (via
/dev/kmem and /dev/ksyms), operating system crash dumps, user process
images recorded inside an operating system crash dump, ELF object
files, and raw binary files. Each target exports a standard set of
properties, including one or more address spaces, one or more symbol
tables, a set of load objects, and a set of threads that can be exam‐
ined using the debugger commands described below.
A debugger command, or dcmd (pronounced dee-command) in mdb terminol‐
ogy, is a routine in the debugger that can access any of the properties
of the current target. mdb parses commands from standard input, and
then executes the corresponding dcmds. Each dcmd can also accept a list
of string or numerical arguments, as shown in the syntax description
below. mdb contains a set of built-in dcmds, described below, that are
always available. You can also extend the capabilities of mdb itself by
writing your own dcmds, as described in the .
A walker is a set of routines that describe how to walk, or iterate,
through the elements of a particular program data structure. A walker
encapsulates the data structure's implementation from dcmds and from
mdb itself. You can use walkers interactively, or use them as a primi‐
tive to build other dcmds or walkers. As with dcmds, you can extend mdb
by implementing your own walkers as part of a debugger module.
A debugger module, or dmod (pronounced dee-mod), is a dynamically
loaded library containing a set of dcmds and walkers. During initial‐
ization, mdb attempts to load dmods corresponding to the load objects
present in the target. You can subsequently load or unload dmods at any
time while running mdb. mdb ships with a set of standard dmods for
debugging the Solaris kernel. The contains more information on devel‐
oping your own debugger modules.
A macro file is a text file containing a set of commands to execute.
Macro files are typically used to automate the process of displaying a
simple data structure. mdb provides complete backward compatibility for
the execution of macro files written for adb(1), and the Solaris
installation includes a set of macro files for debugging the Solaris
kernel that can be used with either tool.
Syntax
The debugger processes commands from standard input. If standard input
is a terminal, mdb provides terminal editing capabilities. mdb can also
process commands from macro files and from dcmd pipelines, described
below. The language syntax is designed around the concept of computing
the value of an expression (typically a memory address in the target),
and then applying a dcmd to that address. The current address location
is referred to as dot, and its value is referenced using ``.''.
A metacharacter is one of the following characters:
[ ] | ! / \ ? = > $ : ;
NEWLINE SPACE TAB
A blank is a TAB or a SPACE. A word is a sequence of characters sepa‐
rated by one or more non-quoted metacharacters. Some of the metacharac‐
ters only function as delimiters in certain contexts, as described
below. An identifier is a sequence of letters, digits, underscores,
periods, or backquotes beginning with a letter, underscore, or period.
Identifiers are used as the names of symbols, variables, dcmds, and
walkers. Commands are delimited by a NEWLINE or semicolon ( ; ).
A dcmd is denoted by one of the following words or metacharacters:
/ \ ? = > $character :character ::identifier
dcmds named by metacharacters or prefixed by a single $ or : are pro‐
vided as built-in operators, and implement complete compatibility with
the command set of the legacy adb(1) utility. Once a dcmd has been
parsed, the /, \, ?, =, >, $, and : characters are no longer recognized
as metacharacters until the termination of the argument list.
A simple-command is a dcmd followed by a sequence of zero or more
blank-separated words. The words are passed as arguments to the invoked
dcmd, except as specified under Quoting and Arithmetic Expansion below.
Each dcmd returns an exit status that indicates it was either success‐
ful, failed, or was invoked with invalid arguments.
A pipeline is a sequence of one or more simple commands separated by |.
Unlike the shell, dcmds in mdb pipelines are not executed as separate
processes. After the pipeline has been parsed, each dcmd is invoked in
order from left to right. Each dcmd's output is processed and stored as
described under dcmd Pipelines below. Once the left-hand dcmd is com‐
plete, its processed output is used as input for the next dcmd in the
pipeline. If any dcmd does not return a successful exit status, the
pipeline is aborted.
An expression is a sequence of words that is evaluated to compute a
64-bit unsigned integer value. The words are evaluated using the rules
described under Arithmetic Expansion below.
Commands
A command is one of the following:
pipeline [! word ...] [ ; ]
A simple-command or pipeline can be optionally suffixed with the !
character, indicating that the debugger should open a pipe(2) and
send the standard output of the last dcmd in the mdb pipeline to an
external process created by executing $SHELL -c followed by the
string formed by concatenating the words after the ! character. For
more details, refer to Shell Escapes below.
expression pipeline [! word ...] [ ; ]
A simple-command or pipeline can be prefixed with an expression.
Before execution of the pipeline, the value of dot (the variable
denoted by ``.'') is set to the value of the expression.
expression , expression pipeline [! word ...] [ ; ]
A simple-command or pipeline can be prefixed with two expressions.
The first is evaluated to determine the new value of dot, and the
second is evaluated to determine a repeat count for the first dcmd
in the pipeline. This dcmd is executed count times before the next
dcmd in the pipeline is executed. The repeat count only applies to
the first dcmd in the pipeline.
, expression pipeline [! word ...] [ ; ]
If the initial expression is omitted, dot is not modified but the
first dcmd in the pipeline is repeated according to the value of
the expression.
expression [! word ...] [ ; ]
A command can consist only of an arithmetic expression. The expres‐
sion is evaluated and the dot variable is set to its value, and
then the previous dcmd and arguments are executed using the new
value of dot.
expression, expression [! word ...] [ ; ]
A command can consist only of a dot expression and repeat count
expression. After dot is set to the value of the first expression,
the previous dcmd and arguments are repeatedly executed the number
of times specified by the value of the second expression.
, expression [! word ...] [ ; ]
If the initial expression is omitted, dot is not modified but the
previous dcmd and arguments are repeatedly executed the number of
times specified by the value of the count expression.
! word ... [ ; ]
If the command begins with the ! character, no dcmds are executed
and the debugger simply executes $SHELL -c followed by the string
formed by concatenating the words after the ! character.
Comments
A word beginning with // causes that word and all the subsequent char‐
acters up to a NEWLINE to be ignored.
Arithmetic Expansion
Arithmetic expansion is performed when an mdb command is preceded by an
optional expression representing a start address, or a start address
and a repeat count. Arithmetic expansion can also be performed to com‐
pute a numerical argument for a dcmd. An arithmetic expression can
appear in an argument list enclosed in square brackets preceded by a
dollar sign ($[ expression ]), and is replaced by the value of the
expression.
Expressions can contain any of the following special words:
integer
The specified integer value. Integer values can be prefixed with 0i
or 0I to indicate binary values, 0o or 0O to indicate octal values,
0t or 0T to indicate decimal values, and 0x or 0X to indicate hexa‐
decimal values (the default).
0[tT][0-9]+.[0-9]+
The specified decimal floating point value, converted to its IEEE
double-precision floating point representation.
'cccccccc'
The integer value computed by converting each character to a byte
equal to its ASCII value. Up to eight characters can be specified
in a character constant. Characters are packed into the integer in
reverse order (right-to-left) beginning at the least significant
byte.
<identifier
The value of the variable named by identifier.
identifier
The value of the symbol named by identifier.
(expression)
The value of expression.
.
The value of dot.
&
The most recent value of dot used to execute a dcmd.
+
The value of dot incremented by the current increment.
^
The value of dot decremented by the current increment.
The increment is a global variable that stores the total bytes read by
the last formatting dcmd. For more information on the increment, refer
to the discussion of Formatting dcmds below.
Unary operators are right associative and have higher precedence than
binary operators. The unary operators are:
#expression
Logical negation.
~expression
Bitwise complement.
-expression
Integer negation.
%expression
The value of a pointer-sized quantity at the object file location
corresponding to virtual address expression in the target's virtual
address space.
%/[csil]/expression
The value of a char, short, int, or long-sized quantity at the
object file location corresponding to virtual address expression in
the target's virtual address space.
%/[1248]/expression
The value of a one, two, four, or eight-byte quantity at the object
file location corresponding to virtual address expression in the
target's virtual address space.
*expression
The value of a pointer-sized quantity at virtual address expression
in the target's virtual address space.
*/[csil]/expression
The value of a char, short, int, or long-sized quantity at virtual
address expression in the target's virtual address space.
*/[1248]/expression
The value of a one, two, four, or eight-byte quantity at virtual
address expression in the target's virtual address space.
Binary operators are left associative and have lower precedence than
unary operators. The binary operators, in order of precedence from
highest to lowest, are:
*
Integer multiplication.
%
Integer division.
#
Left-hand side rounded up to next multiple of right-hand side.
+
Integer addition.
-
Integer subtraction.
<<
Bitwise shift left.
>>
Bitwise shift right.
==
Logical equality.
!=
Logical inequality.
&
Bitwise AND.
^
Bitwise exclusive OR.
|
Bitwise inclusive OR.
Quoting
Each metacharacter described above (see Syntax) terminates a word
unless quoted. Characters can be quoted (forcing mdb to interpret each
character as itself without any special significance) by enclosing them
in a pair of single (' ') or double (" ") quote marks. A single quote
cannot appear within single quotes. Inside double quotes, mdb recog‐
nizes the C programming language character escape sequences.
Shell Escapes
The ! character can be used to create a pipeline between an mdb command
and the user's shell. If the $SHELL environment variable is set, mdb
forks and execs this program for shell escapes; otherwise /bin/sh is
used. The shell is invoked with the -c option followed by a string
formed by concatenating the words after the ! character. The ! charac‐
ter takes precedence over all other metacharacters, except semicolon
(;) and NEWLINE. Once a shell escape is detected, the remaining charac‐
ters up to the next semicolon or NEWLINE are passed as is to the shell.
The output of shell commands can not be piped to mdb dcmds. Commands
executed by a shell escape have their output sent directly to the ter‐
minal, not to mdb.
Variables
A variable is a variable name, a corresponding integer value, and a set
of attributes. A variable name is a sequence of letters, digits, under‐
scores, or periods. A variable can be assigned a value using the > dcmd
or ::typeset dcmd, and its attributes can be manipulated using the
::typeset dcmd. Each variable's value is represented as a 64-bit
unsigned integer. A variable can have one or more of the following
attributes: read-only (cannot be modified by the user), persistent
(cannot be unset by the user), and tagged (user-defined indicator).
The following variables are defined as persistent:
0
The most recent value printed using the /, \, ?, or = dcmd.
9
The most recent count used with the $< dcmd.
b
The virtual address of the base of the data section.
d
The size of the data section in bytes.
e
The virtual address of the entry point.
m
The initial bytes (magic number) of the target's primary object
file, or zero if no object file has been read yet.
t
The size of the text section in bytes.
hits
The count of the number of times the matched software event speci‐
fier has been matched. See Event Callbacks, below.
thread
The thread identifier of the current representative thread. The
value of the identifier depends on the threading model used by the
current target. See Thread Support, below.
In addition, the mdb kernel and process targets export the current val‐
ues of the representative thread's register set as named variables. The
names of these variables depend on the target's platform and instruc‐
tion set architecture.
Symbol Name Resolution
As explained in the Syntax description above, a symbol identifier
present in an expression context evaluates to the value of this symbol.
The value typically denotes the virtual address of the storage associ‐
ated with the symbol in the target's virtual address space. A target
can support multiple symbol tables including, but not limited to, a
primary executable symbol table, a primary dynamic symbol table, a run-
time link-editor symbol table, and standard and dynamic symbol tables
for each of a number of load objects (such as shared libraries in a
user process, or kernel modules in the Solaris kernel). The target typ‐
ically searches the primary executable's symbol tables first, and then
one or more of the other symbol tables. Notice that ELF symbol tables
only contain entries for external, global, and static symbols; auto‐
matic symbols do not appear in the symbol tables processed by mdb.
Additionally, mdb provides a private user-defined symbol table that is
searched prior to any of the target symbol tables. The private symbol
table is initially empty, and can be manipulated using the ::nmadd and
::nmdel dcmds. The ::nm -P option can be used to display the contents
of the private symbol table. The private symbol table allows the user
to create symbol definitions for program functions or data that were
either missing from the original program or stripped out. These defini‐
tions are then used whenever mdb converts a symbolic name to an
address, or an address to the nearest symbol.
As targets contain multiple symbol tables, and each symbol table can
include symbols from multiple object files, different symbols with the
same name can exist. mdb uses the backquote (`) character as a symbol
name scoping operator to allow the programmer to obtain the value of
the desired symbol in this situation. The programmer can specify the
scope used to resolve a symbol name as either: object`name, or
file`name, or object`file`name. The object identifier refers to the
name of a load object. The file identifier refers to the basename of a
source file that has a symbol of type STT_FILE in the specified
object's symbol table. The object identifier's interpretation depends
on the target type.
The mdb kernel target expects object to specify the basename of a
loaded kernel module. For example, the symbol name
specfs`_init
evaluates to the value of the _init symbol in the specfs kernel module.
The mdb process target expects object to specify the name of the exe‐
cutable or of a loaded shared library. It can take any of the following
forms:
1. An exact match (that is, a full pathname):
/usr/lib/libc.so.1
2. An exact basename match: libc.so.1
3. An initial basename match up to a ``.'' suffix: libc.so or
libc
4. The literal string a.out is accepted as an alias for the
executable.
The process target also accepts any of the four forms described above
preceded by an optional link-map id (lmid). The lmid prefix is speci‐
fied by an initial "LM" followed by the link-map id in hexadecimal fol‐
lowed by an additional backquote. For example, the symbol name
LM0`libc.so.1`_init
evaluates to the value of the _init symbol in the libc.so.1 library
that is loaded on link-map 0 (LM_ID_BASE). The link-map specifier can
be necessary to resolve symbol naming conflicts in the event that the
same library is loaded on more than one link map. For more information
on link maps, refer to the and dlopen(3C). Link-map identifiers are
displayed when symbols are printed according to the setting of the
showlmid option, as described under OPTIONS.
In the case of a naming conflict between symbols and hexadecimal inte‐
ger values, mdb attempts to evaluate an ambiguous token as a symbol
first, before evaluating it as an integer value. For example, the token
f can either refer to the decimal integer value 15 specified in hexa‐
decimal (the default base), or to a global variable named f in the tar‐
get's symbol table. If a symbol with an ambiguous name is present, the
integer value can be specified by using an explicit 0x or 0X prefix.
dcmd and Walker Name Resolution
As described earlier, each mdb dmod provides a set of dcmds and walk‐
ers. dcmds and walkers are tracked in two distinct, global namespaces.
mdb also keeps track of a dcmd and walker namespace associated with
each dmod. Identically named dcmds or walkers within a given dmod are
not allowed: a dmod with this type of naming conflict fails to load.
Name conflicts between dcmds or walkers from different dmods are
allowed in the global namespace. In the case of a conflict, the first
dcmd or walker with that particular name to be loaded is given prece‐
dence in the global namespace. Alternate definitions are kept in a list
in load order. The backquote character (`) can be used in a dcmd or
walker name as a scoping operator to select an alternate definition.
For example, if dmods m1 and m2 each provide a dcmd d, and m1 is loaded
prior to m2, then:
::d
Executes m1's definition of d.
::m1`d
Executes m1's definition of d.
::m2`d
Executes m2's definition of d.
If module m1 were now unloaded, the next dcmd on the global definition
list (m2`d) would be promoted to global visibility. The current defini‐
tion of a dcmd or walker can be determined using the ::which dcmd,
described below. The global definition list can be displayed using the
::which -v option.
dcmd Pipelines
dcmds can be composed into a pipeline using the | operator. The purpose
of a pipeline is to pass a list of values, typically virtual addresses,
from one dcmd or walker to another. Pipeline stages might be used to
map a pointer from one type of data structure to a pointer to a corre‐
sponding data structure, to sort a list of addresses, or to select the
addresses of structures with certain properties.
mdb executes each dcmd in the pipeline in order from left to right. The
leftmost dcmd is executed using the current value of dot, or using the
value specified by an explicit expression at the start of the command.
When a | operator is encountered, mdb creates a pipe (a shared buffer)
between the output of the dcmd to its left and the mdb parser, and an
empty list of values. As the dcmd executes, its standard output is
placed in the pipe and then consumed and evaluated by the parser, as if
mdb were reading this data from standard input. Each line must consist
of an arithmetic expression terminated by a NEWLINE or semicolon (;).
The value of the expression is appended to the list of values associ‐
ated with the pipe. If a syntax error is detected, the pipeline is
aborted.
When the dcmd to the left of a | operator completes, the list of values
associated with the pipe is then used to invoke the dcmd to the right
of the | operator. For each value in the list, dot is set to this value
and the right-hand dcmd is executed. Only the rightmost dcmd in the
pipeline has its output printed to standard output. If any dcmd in the
pipeline produces output to standard error, these messages are printed
directly to standard error and are not processed as part of the pipe‐
line.
Signal Handling
The debugger ignores the PIPE and QUIT signals. The INT signal aborts
the command that is currently executing. The debugger intercepts and
provides special handling for the ILL, TRAP, EMT, FPE, BUS, and SEGV
signals. If any of these signals are generated asynchronously (that is,
delivered from another process using kill(2)), mdb restores the signal
to its default disposition and dump core. However, if any of these sig‐
nals are generated synchronously by the debugger process itself and a
dcmd from an externally loaded dmod is currently executing, and stan‐
dard input is a terminal, mdb provides a menu of choices allowing the
user to force a core dump, quit without producing a core dump, stop for
attach by a debugger, or attempt to resume. The resume option aborts
all active commands and unload the dmod whose dcmd was active at the
time the fault occurred. It can then be subsequently re-loaded by the
user. The resume option provides limited protection against buggy
dcmds. Refer to WARNINGS, Use of the Error Recovery Mechanism, below
for information about the risks associated with the resume option.
Command Re-entry
The text of the last HISTSIZE (default 128) commands entered from a
terminal device are saved in memory. The in-line editing facility,
described next, provides key mappings for searching and fetching ele‐
ments from the history list.
In-line Editing
If standard input is a terminal device, mdb provides some simple emacs-
style facilities for editing the command line. The search, previous,
and next commands in edit mode provide access to the history list. Only
strings, not patterns, are matched when searching. In the table below,
the notation for control characters is caret (^) followed by a charac‐
ter shown in upper case. The notation for escape sequences is M- fol‐
lowed by a character. For example, M-f (pronounced meta-eff) is entered
by depressing ESC followed by 'f', or by depressing Meta followed by
'f' on keyboards that support a Meta key. A command line is committed
and executed using RETURN or NEWLINE. The edit commands are:
^F
Move cursor forward (right) one character.
M-f
Move cursor forward one word.
^B
Move cursor backward (left) one character.
M-b
Move cursor backward one word.
^A
Move cursor to start of line.
^E
Move cursor to end of line.
^D
Delete current character, if the current line is not empty. If the
current line is empty, ^D denotes EOF and the debugger exits.
M-^H
(Meta-backspace) Delete previous word.
^K
Delete from the cursor to the end of the line.
^L
Clear the screen and reprint the current line.
^T
Transpose current character with next character.
^N
Fetch the next command from the history. Each time ^N is entered,
the next command forward in time is retrieved.
^P
Fetch the previous command from the history. Each time ^P is
entered, the next command backward in time is retrieved.
^R[string]
Search backward in the history for a previous command line contain‐
ing string. The string should be terminated by a RETURN or NEWLINE.
If string is omitted, the previous history element containing the
most recent string is retrieved.
The editing mode also interprets the following user-defined sequences
as editing commands. User defined sequences can be read or modified
using the stty(1) command.
erase
User defined erase character (usually ^H or ^?). Delete previous
character.
intr
User defined interrupt character (usually ^C). Abort the current
command and print a new prompt.
kill
User defined kill character (usually ^U). Kill the entire current
command line.
quit
User defined quit character (usually ^\). Quit the debugger.
suspend
User defined suspend character (usually ^Z). Suspend the debugger.
werase
User defined word erase character (usually ^W). Erase the preceding
word.
On keyboards that support an extended keypad with arrow keys, mdb
interprets these keystrokes as editing commands:
up-arrow
Fetch the previous command from the history (same as ^P).
down-arrow
Fetch the next command from the history (same as ^N).
left-arrow
Move cursor backward one character (same as ^B).
right-arrow
Move cursor forward one character (same as ^F).
Output Pager
mdb provides a built-in output pager. The output pager is enabled if
the debugger's standard output is a terminal device. Each time a com‐
mand is executed, mdb pauses after one screenful of output is produced
and displays a pager prompt:
>> More [<space>, <cr>, q, n, c, a] ?
The following key sequences are recognized by the pager:
SPACE
Display the next screenful of output.
a, A
Abort the current top-level command and return to the prompt.
c, C
Continue displaying output without pausing at each screenful until
the current top-level command is complete.
n, N, NEWLINE, RETURN
Display the next line of output.
q, Q, ^C, ^\
Quit (abort) the current dcmd only.
Formatting dcmds
The /, \, ?, and = metacharacters are used to denote the special output
formatting dcmds. Each of these dcmds accepts an argument list consist‐
ing of one or more format characters, repeat counts, or quoted strings.
A format character is one of the ASCII characters shown in the table
below. Format characters are used to read and format data from the tar‐
get. A repeat count is a positive integer preceding the format charac‐
ter that is always interpreted in base 10 (decimal). A repeat count can
also be specified as an expression enclosed in square brackets preceded
by a dollar sign ($[ ]). A string argument must be enclosed in double-
quotes (" "). No blanks are necessary between format arguments.
The formatting dcmds are:
/
Display data from the target's virtual address space starting at
the virtual address specified by dot.
\
Display data from the target's physical address space starting at
the physical address specified by dot.
?
Display data from the target's primary object file starting at the
object file location corresponding to the virtual address specified
by dot.
=
Display the value of dot itself in each of the specified data for‐
mats. The = dcmd is therefore useful for converting between bases
and performing arithmetic.
In addition to dot, mdb keeps track of another global value called the
increment. The increment represents the distance between dot and the
address following all the data read by the last formatting dcmd. For
example, if a formatting dcmd is executed with dot equal to address A,
and displays a 4-byte integer, then after this dcmd completes, dot is
still A, but the increment is set to 4. The + character (described
under Arithmetic Expansion above) would now evaluate to the value A +
4, and could be used to reset dot to the address of the next data
object for a subsequent dcmd.
Most format characters increase the value of the increment by the num‐
ber of bytes corresponding to the size of the data format, shown in the
table. The table of format characters can be displayed from within mdb
using the ::formats dcmd. The format characters are:
+ increment dot by the count (variable size)
- decrement dot by the count (variable size)
B hexadecimal int (1 byte)
C character using C character notation (1 byte)
D decimal signed int (4 bytes)
E decimal unsigned long long (8 bytes)
F double (8 bytes)
G octal unsigned long long (8 bytes)
H swap bytes and shorts (4 bytes)
I address and disassembled instruction (variable
size)
J hexadecimal long long (8 bytes)
K hexadecimal uintptr_t (4 or 8 bytes)
N newline
O octal unsigned int (4 bytes)
P symbol (4 or 8 bytes)
Q octal signed int (4 bytes)
R binary int (8 bytes)
S string using C string notation (variable size)
T horizontal tab
U decimal unsigned int (4 bytes)
V decimal unsigned int (1 byte)
W default radix unsigned int (4 bytes)
X hexadecimal int (4 bytes)
Y decoded time32_t (4 bytes)
Z hexadecimal long long (8 bytes)
^ decrement dot by increment * count (variable
size)
a dot as symbol+offset
b octal unsigned int (1 byte)
c character (1 byte)
d decimal signed short (2 bytes)
e decimal signed long long (8 bytes)
f float (4 bytes)
g octal signed long long (8 bytes)
h swap bytes (2 bytes)
i disassembled instruction (variable size)
n newline
o octal unsigned short (2 bytes)
p symbol (4 or 8 bytes)
q octal signed short (2 bytes)
r whitespace
s raw string (variable size)
t horizontal tab
u decimal unsigned short (2 bytes)
v decimal signed int (1 byte)
w default radix unsigned short (2 bytes)
x hexadecimal short (2 bytes)
y decoded time64_t (8 bytes)
The /, \, and ? formatting dcmds can also be used to write to the tar‐
get's virtual address space, physical address space, or object file by
specifying one of the following modifiers as the first format charac‐
ter, and then specifying a list of words that are either immediate val‐
ues or expressions enclosed in square brackets preceded by a dollar
sign ($[ ]).
The write modifiers are:
v
Write the lowest byte of the value of each expression to the target
beginning at the location specified by dot.
w
Write the lowest two bytes of the value of each expression to the
target beginning at the location specified by dot.
W
Write the lowest 4 bytes of the value of each expression to the
target beginning at the location specified by dot.
Z
Write the complete 8 bytes of the value of each expression to the
target beginning at the location specified by dot.
The /, \, and ? formatting dcmds can also be used to search for a par‐
ticular integer value in the target's virtual address space, physical
address space, and object file, respectively, by specifying one of the
following modifiers as the first format character, and then specifying
a value and optional mask. The value and mask are each specified as
either immediate values or expressions enclosed in square brackets pre‐
ceded by a dollar sign. If only a value is specified, mdb reads inte‐
gers of the appropriate size and stops at the address containing the
matching value. If a value V and mask M are specified, mdb reads inte‐
gers of the appropriate size and stops at the address containing a
value X where (X & M) == V. At the completion of the dcmd, dot is
updated to the address containing the match. If no match is found, dot
is left at the last address that was read.
The search modifiers are:
l Search for the specified 2-byte value.
L Search for the specified 4-byte value.
M Search for the specified 8-byte value.
Notice that for both user and kernel targets, an address space is typi‐
cally composed of a set of discontiguous segments. It is not legal to
read from an address that does not have a corresponding segment. If a
search reaches a segment boundary without finding a match, it aborts
when the read past the end of the segment boundary fails.
Execution Control
mdb provides facilities for controlling and tracing the execution of a
live running program. Currently, only the user process target provides
support for execution control. mdb provides a simple model of execution
control: a target process can be started from within the debugger using
::run, or mdb can attach to an existing process using :A, ::attach, or
the -p command-line option, as described below. A list of traced soft‐
ware events can be specified by the user. Each time a traced event
occurs in the target process, all threads in the target stop, the
thread that triggered the event is chosen as the representative thread,
and control returns to the debugger. Once the target program is set
running, control can be asynchronously returned to the debugger by typ‐
ing the user-defined interrupt character (typically ^C).
A software event is a state transition in the target program that is
observed by the debugger. For example, the debugger can observe the
transition of a program counter register to a value of interest (a
breakpoint) or the delivery of a particular signal.
A software event specifier is a description of a class of software
events that is used by the debugger to instrument the target program in
order to observe these events. The ::events dcmd is used to list the
software event specifiers. A set of standard properties is associated
with each event specifier, as described under ::events, below.
The debugger can observe a variety of different software events,
including breakpoints, watchpoints, signals, machine faults, and system
calls. New specifiers can be created using ::bp, ::fltbp, ::sigbp,
::sysbp, or ::wp. Each specifier has an associated callback (an mdb
command string to execute as if it had been typed at the command
prompt) and a set of properties, as described below. Any number of
specifiers for the same event can be created, each with different call‐
backs and properties. The current list of traced events and the proper‐
ties of the corresponding event specifiers can be displayed using the
::events dcmd. The event specifier properties are defined as part of
the description of the ::events and ::evset dcmds, below.
The execution control built-in dcmds, described below, are always
available, but issues an error message indicating they are not sup‐
ported if applied to a target that does not support execution control.
For more information about the interaction of exec, attach, release,
and job control with debugger execution control, refer to NOTES, below.
Event Callbacks
The ::evset dcmd and event tracing dcmds allow you to associate an
event callback (using the -c option) with each event specifier. The
event callbacks are strings that represent mdb commands to execute when
the corresponding event occurs in the target. These commands are exe‐
cuted as if they had been typed at the command prompt. Before executing
each callback, the dot variable is set to the value of the representa‐
tive thread's program counter and the "hits" variable is set to the
number of times this specifier has been matched, including the current
match.
If the event callbacks themselves contain one or more commands to con‐
tinue the target (for example, ::cont or ::step), these commands do not
immediately continue the target and wait for it to stop again. Instead,
inside of an event callback, the continue dcmds note that a continue
operation is now pending, and then return immediately. Therefore, if
multiple dcmds are included in an event callback, the step or continue
dcmd should be the last command specified. Following the execution of
all event callbacks, the target immediately resumes execution if all
matching event callbacks requested a continue. If conflicting continue
operations are requested, the operation with the highest precedence
determines what type of continue occurs. The order of precedence from
highest to lowest is: step, step-over (next), step-out, continue.
Thread Support
mdb provides facilities to examine the stacks and registers of each
thread associated with the target. The persistent "thread" variable
contains the current representative thread identifier. The format of
the thread identifier depends on the target. The ::regs and ::fpregs
dcmds can be used to examine the register set of the representative
thread, or of another thread if its register set is currently avail‐
able. In addition, the register set of the representative thread is
exported as a set of named variables. The user can modify the value of
one or more registers by applying the > dcmd to the corresponding named
variable.
The mdb kernel target exports the virtual address of the corresponding
internal thread structure as the identifier for a given thread. The
provides more information on debugging support for threads in the
Solaris kernel. The mdb process target provides proper support for
examination of multi-threaded user processes that use the native lwp_*
interfaces, /usr/lib/libthread.so or /usr/lib/lwp/libthread.so. When
debugging a live user process, mdb detects if a single threaded process
dlopens or closes libthread and automatically adjusts its view of the
threading model on-the-fly. The process target thread identifiers cor‐
responds to either the lwpid_t, thread_t, or pthread_t of the represen‐
tative, depending on the threading model used by the application.
If mdb is debugging a user process target and the target makes use of
compiler-supported thread-local storage, mdb automatically evaluates
symbol names referring to thread-local storage to the address of the
storage corresponding to the current representative thread. The ::tls
built-in dcmd can be used to display the value of the symbol for
threads other than the representative thread.
Built-in dcmds
mdb provides a set of built-in dcmds that are always defined. Some of
these dcmds are only applicable to certain targets: if a dcmd is not
applicable to the current target, it fails and prints a message indi‐
cating "command is not supported by current target". In many cases, mdb
provides a mnemonic equivalent (::identifier) for the legacy adb(1)
dcmd names. For example, ::quit is provided as the equivalent of $q.
Programmers who are experienced with adb(1) or who appreciate brevity
or arcana can prefer the $ or : forms of the built-ins. Programmers who
are new to mdb might prefer the more verbose :: form. The built-ins are
shown in alphabetical order. If a $ or : form has a ::identifier equiv‐
alent, it is shown underneath the ::identifier form. The built-in dcmds
are:
> variable-name
>/modifier/variable-name
Assign the value of dot to the specified named variable. Some vari‐
ables are read-only and can not be modified. If the > is followed
by a modifier character surrounded by / /, then the value is modi‐
fied as part of the assignment. The modifier characters are:
c
unsigned char quantity (1-byte)
s
unsigned short quantity (2-byte)
i
unsigned int quantity (4-byte)
l
unsigned long quantity (4-byte in 32-bit, 8-byte in 64-bit)
Notice that these operators do not perform a cast. Instead, they
fetch the specified number of low-order bytes (on little-endian
architectures) or high-order bytes (big-endian architectures). Mod‐
ifiers are provided for backwards compatibility; the mdb */modi‐
fier/ and %/modifier/ syntax should be used instead.
$< macro-name
Read and execute commands from the specified macro file. The file‐
name can be given as an absolute or relative path. If the filename
is a simple name (that is, if it does not contain a '/'), mdb
searches for it in the macro file include path. If another macro
file is currently being processed, this file is closed and replaced
with the new file.
$<< macro-name
Read and execute commands from the specified macro file (as with
$<), but do not close the current open macro file.
$?
Print the process-ID and current signal of the target if it is a
user process or core file, and then print the general register set
of the representative thread.
[ address ] $C [ count ]
Print a C stack backtrace, including stack frame pointer informa‐
tion. If the dcmd is preceded by an explicit address, a backtrace
beginning at this virtual memory address is displayed. Otherwise
the stack of the representative thread is displayed. If an optional
count value is given as an argument, no more than count arguments
are displayed for each stack frame in the output.
[ base ] $d
Get or set the default output radix. If the dcmd is preceded by an
explicit expression, the default output radix is set to the given
base; otherwise the current radix is printed in base 10 (decimal).
The default radix is base 16 (hexadecimal).
$e
Print a list of all known external (global) symbols of type object
or function, the value of the symbol, and the first 4 (32-bit mdb)
or 8 (64-bit mdb) bytes stored at this location in the target's
virtual address space. The ::nm dcmd provides more flexible options
for displaying symbol tables.
$P prompt-string
Set the prompt to the specified prompt-string. The default prompt
is '> '. The prompt can also be set using ::set -P or the -P com‐
mand-line option.
distance $s
Get or set the symbol matching distance for address-to-symbol-name
conversions. The symbol matching distance modes are discussed along
with the -s command-line option under OPTIONS. The symbol matching
distance can also be modified using the ::set -s option. If no dis‐
tance is specified, the current setting is displayed.
$v
Print a list of the named variables that have non-zero values. The
::vars dcmd provides other options for listing variables.
width $w
Set the output page width to the specified value. Typically, this
command is not necessary as mdb queries the terminal for its width
and handles resize events.
$W
Re-open the target for writing, as if mdb had been executed with
the -w option on the command line. Write mode can also be enabled
with the ::set -w option.
[ pid ] ::attach [ core | pid ]
[ pid ] :A [ core | pid ]
If the user process target is active, attach to and debug the spec‐
ified process-ID or core file. The core file pathname should be
specified as a string argument. The process-ID can be specified as
the string argument, or as the value of the expression preceding
the dcmd. Recall that the default base is hexadecimal, so decimal
PIDs obtained using pgrep(1) or ps(1) should be preceded with "0t"
when specified as expressions.
[address] ::bp [-/-dDesT] [-c cmd] [-n count] sym ...
address :b [cmd ...]
Set a breakpoint at the specified locations. The ::bp dcmd sets a
breakpoint at each address or symbol specified, including an
optional address specified by an explicit expression preceding the
dcmd, and each string or immediate value following the dcmd. The
arguments can either be symbol names or immediate values denoting a
particular virtual address of interest. If a symbol name is speci‐
fied, it can refer to a symbol that cannot yet be evaluated in the
target process. That is, it can consist of an object name and func‐
tion name in a load object that has not yet been opened. In this
case, the breakpoint is deferred and is not active in the target
until an object matching the given name is loaded. The breakpoint
is automatically enabled when the load object is opened. Break‐
points on symbols defined in a shared library should always be set
using a symbol name and not using an address expression, as the
address can refer to the corresponding Procedure Linkage Table
(PLT) entry instead of the actual symbol definition. Breakpoints
set on PLT entries can be overwritten by the run-time link-editor
when the PLT entry is subsequently resolved to the actual symbol
definition. The -d, -D, -e, -s, -t, -T, -c, and -n options have the
same meaning as they do for the ::evset dcmd, as described below.
If the :b form of the dcmd is used, a breakpoint is only set at the
virtual address specified by the expression preceding the dcmd. The
arguments following the :b dcmd are concatenated together to form
the callback string. If this string contains meta-characters, it
must be quoted.
::cat filename ...
Concatenate and display files. Each filename can be specified as a
relative or absolute pathname. The file contents are printed to
standard output, but are not passed to the output pager. This dcmd
is intended to be used with the | operator; the programmer can ini‐
tiate a pipeline using a list of addresses stored in an external
file.
::cont [ SIG ]
:c [ SIG ]
Suspend the debugger, continue the target program, and wait for it
to terminate or stop following a software event of interest. If the
target is already running because the debugger was attached to a
running program with the -o nostop option enabled, this dcmd simply
waits for the target to terminate or stop after an event of inter‐
est. If an optional signal name or number (see signal.h(3HEAD)) is
specified as an argument, the signal is immediately delivered to
the target as part of resuming its execution. If the SIGINT signal
is traced, control can be asynchronously returned to the debugger
by typing the user-defined interrupt character (usually ^C). This
SIGINT signal is automatically cleared and is not observed by the
target the next time it is continued. If no target program is cur‐
rently running, ::cont starts a new program running as if by ::run.
address ::context
address $p
Context switch to the specified process. A context switch operation
is only valid when using the kernel target. The process context is
specified using the address of its proc structure in the kernel's
virtual address space. The special context address "0" is used to
denote the context of the kernel itself. mdb can only perform a
context switch when examining a crash dump if the dump contains the
physical memory pages of the specified user process (as opposed to
just kernel pages). The kernel crash dump facility can be config‐
ured to dump all pages or the pages of the current user process
using dumpadm(1M). The ::status dcmd can be used to display the
contents of the current crash dump.
When the user requests a context switch from the kernel target, mdb
constructs a new target representing the specified user process.
Once the switch occurs, the new target interposes its dcmds at the
global level: thus the / dcmd now formats and displays data from
the virtual address space of the user process, the ::mappings dcmd
displays the mappings in the address space of the user process, and
so on. The kernel target can be restored by executing 0::context.
::dcmds
List the available dcmds and print a brief description for each
one.
[ address ] ::delete [ id | all ]
[ address ] :d [ id | all ]
Delete the event specifiers with the given id number. The id number
argument is interpreted in decimal by default. If an optional
address is specified preceding the dcmd, all event specifiers that
are associated with the given virtual address are deleted (for
example, all breakpoints or watchpoints affecting that address). If
the special argument "all" is given, all event specifiers are
deleted, except those that are marked sticky (T flag). The ::events
dcmd displays the current list of event specifiers.
[ address ] ::dis [ -fw ] [ -n count ] [ address ]
Disassemble starting at or around the address specified by the
final argument, or the current value of dot. If the address matches
the start of a known function, the entire function is disassembled.
Otherwise, a "window" of instructions before and after the speci‐
fied address is printed in order to provide context. By default,
instructions are read from the target's virtual address space. If
the -f option is present, instructions are read from the target's
object file instead. The -f option is enabled by default if the
debugger is not currently attached to a live process, core file, or
crash dump. The -w option can be used to force "window"-mode, even
if the address is the start of a known function. The size of the
window defaults to ten instructions; the number of instructions can
be specified explicitly using the -n option.
::disasms
List the available disassembler modes. When a target is initial‐
ized, mdb attempts to select the appropriate disassembler mode. The
user can change the mode to any of the modes listed using the
::dismode dcmd.
::dismode [ mode ]
$V [ mode ]
Get or set the disassembler mode. If no argument is specified,
print the current disassembler mode. If a mode argument is speci‐
fied, switch the disassembler to the specified mode. The list of
available disassemblers can be displayed using the ::disasms dcmd.
::dmods [ -l ] [ module-name ]
List the loaded debugger modules. If the -l option is specified,
the list of the dcmds and walkers associated with each dmod is
printed below its name. The output can be restricted to a particu‐
lar dmod by specifying its name as an additional argument.
[ address ] ::dump [ -eqrstu ] [ -f|-p ]
[ -g bytes ] [ -w paragraphs ]
Print a hexadecimal and ASCII memory dump of the 16-byte aligned
region of memory containing the address specified by dot. If a
repeat count is specified for ::dump, this is interpreted as a num‐
ber of bytes to dump rather than a number of iterations. The ::dump
dcmd also recognizes the following options:
-e
Adjusts for endian-ness. The -e option assumes 4-byte words.
The -g option can be used to change the default word size.
-f
Reads data from the object file location corresponding to the
given virtual address instead of from the target's virtual
address space. The -f option is enabled by default if the
debugger is not currently attached to a live process, core
file, or crash dump.
-g bytes
Displays bytes in groups of bytes. The default group size is 4
bytes. The group size must be a power of two that divides the
line width.
-p
Interprets address as a physical address location in the tar‐
get's address space instead of a virtual address.
-q
Does not print an ASCII decoding of the data.
-r
Numbers lines relative to the start address instead of with the
explicit address of each line. This option implies the -u
option.
-s
Elides repeated lines.
-t
Only reads from and displays the contents of the specified
addresses, instead of reading and printing entire lines.
-u
Unaligns output instead of aligning the output at a paragraph
boundary.
-w paragraphs
Displays paragraphs at 16-byte paragraphs per line. The default
number of paragraphs is one. The maximum value accepted for -w
is 16.
::echo [ string | value ...]
Print the arguments separated by blanks and terminated by a NEWLINE
to standard output. Expressions enclosed in $[ ] is evaluated to a
value and printed in the default base.
::eval command
Evaluate and execute the specified string as a command. If the com‐
mand contains metacharacters or whitespace, it should be enclosed
in double or single quotes.
::events [ -av ]
$b [ -av ]
Display the list of software event specifiers. Each event specifier
is assigned a unique ID number that can be used to delete or modify
it at a later time. The debugger can also have its own internal
events enabled for tracing. These events are only be displayed if
the -a option is present. If the -v option is present, a more ver‐
bose display, including the reason for any specifier inactivity,
are shown. Here is some sample output:
> ::events
ID S TA HT LM Description Action
----- - -- -- -- -------------------------------- ------
[ 1 ] - T 1 0 stop on SIGINT -
[ 2 ] - T 0 0 stop on SIGQUIT -
[ 3 ] - T 0 0 stop on SIGILL -
...
[ 11] - T 0 0 stop on SIGXCPU -
[ 12] - T 0 0 stop on SIGXFSZ -
[ 13] - 2 0 stop at libc`printf ::echo printf
>
The following table explains the meaning of each column. A summary
of this information is available using ::help events.
ID
The event specifier identifier. The identifier is shown in
square brackets [ ] if the specifier is enabled, in parentheses
( ) if the specifier is disabled, or in angle brackets < > if
the target program is currently stopped on an event that
matches the given specifier.
S
The event specifier state. The state is one of the following
symbols:
-
The event specifier is idle. When no target program is run‐
ning, all specifiers are idle. When the target program is
running, a specifier can be idle if it cannot be evaluated
(for example, a deferred breakpoint in a shared object that
is not yet loaded).
+
The event specifier is active. When the target is contin‐
ued, events of this type is detected by the debugger.
*
The event specifier is armed. This state means that the
target is currently running with instrumentation for this
type of event. This state is only visible if the debugger
is attached to a running program with the -o nostop option.
!
The event specifier was not armed due to an operating sys‐
tem error. The ::events -v option can be used to display
more information about the reason the instrumentation
failed.
TA
The Temporary, Sticky, and Automatic event specifier proper‐
ties. One or more of the following symbols can be shown:
t
The event specifier is temporary, and is deleted the next
time the target stops, regardless of whether it is matched.
T
The event specifier is sticky, and is not be deleted by
::delete all or :z. The specifier can be deleted by explic‐
itly specifying its id number to ::delete.
d
The event specifier is automatically disabled when the hit
count is equal to the hit limit.
D
The event specifier is automatically deleted when the hit
count is equal to the hit limit.
s
The target automatically stops when the hit count is equal
to the hit limit.
HT
The current hit count. This column displays the number of times
the corresponding software event has occurred in the target
since the creation of this event specifier.
LM
The current hit limit. This column displays the limit on the
hit count at which the auto-disable, auto-delete, or auto-stop
behavior takes effect. These behaviors can be configured using
the ::evset dcmd, described below.
Description
A description of the type of software event that is matched by
the given specifier.
Action
The callback string to execute when the corresponding software
event occurs. This callback is executed as if it had been typed
at the command prompt.
[id] ::evset [-/-dDestT] [-c cmd] [-n count] id ...
Modify the properties of one or more software event specifiers. The
properties are set for each specifier identified by the optional
expression preceding the dcmd and an optional list of arguments
following the dcmd. The argument list is interpreted as a list of
decimal integers, unless an explicit radix is specified. The
::evset dcmd recognizes the following options:
-d
Disables the event specifier when the hit count reaches the hit
limit. If the -d form of the option is given, this behavior is
disabled. Once an event specifier is disabled, the debugger
removes any corresponding instrumentation and ignores the cor‐
responding software events until the specifier is subsequently
re-enabled. If the -n option is not present, the specifier is
disabled immediately.
-D
Deletes the event specifier when the hit count reaches the hit
limit. If the -D form of the option is given, this behavior is
disabled. The -D option takes precedence over the -d option.
The hit limit can be configured using the -n option.
-e
Enables the event specifier. If the -e form of the option is
given, the specifier is disabled.
-s
Stops the target program when the hit count reaches the hit
limit. If the -s form of the option is given, this behavior is
disabled. The -s behavior tells the debugger to act as if the
::cont were issued following each execution of the specifier's
callback, except for the Nth execution, where N is the current
value of the specifier's hit limit. The -s option takes prece‐
dence over both the -D option and the -d option.
-t
Marks the event specifier as temporary. Temporary specifiers
are automatically deleted the next time the target stops,
regardless of whether it stopped as the result of a software
event corresponding to the given specifier. If the -t form of
the option is given, the temporary marker is removed. The -t
option takes precedence over the -T option.
-T
Marks the event specifier as sticky. Sticky specifiers are not
deleted by ::delete all or :z. They can be deleted by specify‐
ing the corresponding specifier ID as an explicit argument to
::delete. If the -T form of the option is given, the sticky
property is removed. The default set of event specifiers are
all initially marked sticky.
-c
Executes the specified cmd string each time the corresponding
software event occurs in the target program. The current call‐
back string can be displayed using ::events.
-n
Sets the current value of the hit limit to count. If no hit
limit is currently set and the -n option does not accompany -s
or D, the hit limit is set to one.
A summary of this information is available using ::help evset.
::files
$f
Print a list of the known source files (symbols of type STT_FILE
present in the various target symbol tables).
[flt] ::fltbp [-/-dDestT] [-c cmd] [-n count] flt ...
Trace the specified machine faults. The faults are identified using
an optional fault number preceding the dcmd, or a list of fault
names or numbers (see <sys/fault.h>) following the dcmd. The -d,
-D, -e, -s, -t, -T, -c, and -n options have the same meaning as
they do for the ::evset dcmd.
[ thread ] ::fpregs
[ thread ] $x, $X, $y, $Y
Print the floating-point register set of the representative thread.
If a thread is specified, the floating point registers of that
thread are displayed. The thread expression should be one of the
thread identifiers described under Thread Support, above.
::formats
List the available output format characters for use with the /, \,
?, and = formatting dcmds. The formats and their use is described
under Formatting dcmds, above.
::grep command
Evaluate the specified command string, and then print the old value
of dot if the new value of dot is non-zero. If the command contains
whitespace or metacharacters, it must be quoted. The ::grep dcmd
can be used in pipelines to filter a list of addresses.
::help [ dcmd-name ]
With no arguments, the ::help dcmd prints a brief overview of the
help facilities available in mdb. If a dcmd-name is specified, mdb
prints a usage summary for that dcmd.
signal :i
If the target is a live user process, ignore the specified signal
and allow it to be delivered transparently to the target. All event
specifiers that are tracing delivery of the specified signal is
deleted from the list of traced events. By default, the set of
ignored signals is initialized to the complement of the set of sig‐
nals that cause a process to dump core by default (see sig‐
nal.h(3HEAD)), except for SIGINT, which is traced by default.
$i
Display the list of signals that are ignored by the debugger and
that is handled directly by the target. More information on traced
signals can be obtained using the ::events dcmd.
::kill
:k
Forcibly terminate the target if it is a live user process. The
target is also forcibly terminated when the debugger exits if it
was created by the debugger using ::run.
$l
Print the LWPID of the representative thread, if the target is a
user process.
$L
Print the LWPIDs of each LWP in the target, if the target is a user
process.
[ address ] ::list type member [ variable-name ]
Walk through the elements of a linked list data structure and print
the address of each element in the list. The address of the first
element in the list can be specified using an optional address.
Otherwise, the list is assumed to start at the current value of
dot. The type parameter must name a C struct or union type and is
used to describe the type of the list elements so that mdb can read
in objects of the appropriate size. The member parameter is used to
name the member of type that contains a pointer to the next list
element. The ::list dcmd continues iterating until a NULL pointer
is encountered, the first element is reached again (a circular
list), or an error occurs while reading an element. If the optional
variable-name is specified, the specified variable is assigned the
value returned at each step of the walk when mdb invokes the next
stage of a pipeline. The ::list dcmd can only be used with objects
that contain symbolic debugging information designed for use with
mdb. Refer to NOTES, Symbolic Debugging Information, below for more
information.
::load [ -s ] module-name
Load the specified dmod. The module name can be given as an abso‐
lute or relative path. If module-name is a simple name (that is,
does not contain a '/'), mdb searches for it in the module library
path. Modules with conflicting names can not be loaded; the exist‐
ing module must be unloaded first. If the -s option is present, mdb
remains silent and not issue any error messages if the module is
not found or could not be loaded.
::log [ -d | [ -e ] filename ]
$> [ filename ]
Enable or disable the output log. mdb provides an interactive log‐
ging facility where both the input commands and standard output can
be logged to a file while still interacting with the user. The -e
option enables logging to the specified file, or re-enables logging
to the previous log file if no filename is given. The -d option
disables logging. If the $> dcmd is used, logging is enabled if a
filename argument is specified; otherwise, logging is disabled. If
the specified log file already exists, mdb appends any new log out‐
put to the file.
::map command
Map the value of dot to a corresponding value using the command
specified as a string argument, and then print the new value of
dot. If the command contains whitespace or metacharacters, it must
be quoted. The ::map dcmd can be used in pipelines to transform the
list of addresses into a new list of addresses.
[ address ] ::mappings [ name ]
[ address ] $m [ name ]
Print a list of each mapping in the target's virtual address space,
including the address, size, and description of each mapping. If
the dcmd is preceded by an address, mdb only shows the mapping that
contains the given address. If a string name argument is given, mdb
only shows the mapping matching that description.
::next [ SIG ]
:e [ SIG ]
Step the target program one instruction, but step over subroutine
calls. If an optional signal name or number (see signal.h(3HEAD))
is specified as an argument, the signal is immediately delivered to
the target as part of resuming its execution. If no target program
is currently running, ::next starts a new program running as if by
::run and stop at the first instruction.
[ address ] ::nm [ -DPdghnopuvx ] [ -t types ]
[ -f format ] [ object ]
Print the symbol tables associated with the current target. If an
optional address preceding the dcmd is specified, only the symbol
table entry for the symbol corresponding to address is displayed.
If an object is specified, only the symbol table for this load
object is displayed. The ::nm dcmd also recognizes the following
options:
-D
Prints .dynsym (dynamic symbol table) instead of .symtab.
-P
Prints the private symbol table instead of .symtab.
-d
Prints value and size fields in decimal.
-g
Prints only global symbols.
-h
Suppresses the header line.
-n
Sorts symbols by name.
-o
Prints value and size fields in octal.
-p
Prints symbols as a series of ::nmadd commands. This option can
be used with -P to produce a macro file that can be subse‐
quently read into the debugger with $<.
-u
Prints only undefined symbols.
-v
Sorts symbols by value.
-x
Prints value and size fields in hexadecimal.
-t type[,type ... ]
Prints only symbols of the specified type(s). The valid type
argument strings are:
noty
STT_NOTYPE
objt
STT_OBJECT
func
STT_FUNC
sect
STT_SECTION
file
STT_FILE
comm
STT_COMMON
tls
STT_TLS
regi
STT_SPARC_REGISTER
-f format[,format ... ]
Prints only the specified symbol information. The valid format
argument strings are:
ndx
symbol table index
val
symbol value
size
size in bytes
type
symbol type
bind
binding
oth
other
shndx
section index
name
symbol name
ctype
C type for symbol (if known)
obj
object which defines symbol
value ::nmadd [ -fo ] [ -e end ] [ -s size ] name
Add the specified symbol name to the private symbol table. mdb pro‐
vides a private, configurable symbol table that can be used to
interpose on the target's symbol table, as described under Symbol
Name Resolution above. The ::nmadd dcmd also recognizes the follow‐
ing options:
-e
Sets the size of the symbol to end - value.
-f
Sets the type of the symbol to STT_FUNC.
-o
Sets the type of the symbol to STT_OBJECT.
-s
Sets the size of the symbol to size.
::nmdel name
Delete the specified symbol name from the private symbol table.
::objects [ -v ]
Print a map of the target's virtual address space, showing only
those mappings that correspond to the primary mapping (usually the
text section) of each of the known load objects. The -v option dis‐
plays the version of each load object. Version information is not
available for all load objects. Load objects without version infor‐
mation is listed as having a version of "Unknown" in the output for
the -v option.
::offsetof type member
Print the offset of the specified member of the specified type. The
type should be the name of a C structure. The offset is printed in
bytes, unless the member is a bit-field, in which case the offset
can be printed in bits. The output is always suffixed with the
appropriate units for clarity. The type name can use the backquote
(`) scoping operator described under Symbol Name Resolution, above.
The ::offsetof dcmd can only be used with objects that contain sym‐
bolic debugging information designed for use with mdb. Refer to
NOTES, Symbolic Debugging Information, below for more information.
address ::print [ -aCdiLptx ] [ -c lim ]
[ -l lim ] [ type [ member ... ] ]
Print the data structure at the specified virtual address using the
given type information. The type parameter can name a C struct,
union, enum, fundamental integer type, or a pointer to any of these
types. If the type name contains whitespace (for example, "struct
foo"), it must be enclosed in single or double quotes. The type
name can use the backquote (`) scoping operator described under
Symbol Name Resolution, above. If the type is a structured type,
the ::print dcmd recursively prints each member of the struct or
union. If the type argument is not present and a static or global
STT_OBJECT symbol matches the address, ::print infers the appropri‐
ate type automatically. If the type argument is specified, it can
be followed by an optional list of member expressions, in which
case only those members and submembers of the specified type are
displayed. If type contains other structured types, each member
string can refer to a sub-structure element by forming a list of
member names separated by period ('.') delimiters. The ::print dcmd
can only be used with objects that contain symbolic debugging
information designed for use with mdb. Refer to NOTES, Symbolic
Debugging Information, below for more information. After displaying
the data structure, ::print increments dot by the size of type in
bytes.
If the -a option is present, the address of each member is dis‐
played. If the -p option is present, ::print interprets address as
a physical memory address instead of a virtual memory address. If
the -t option is present, the type of each member is displayed. If
the -d or -x options are present, all integers are displayed in
decimal (-d) or hexadecimal (-x). By default, a heuristic is used
to determine if the value should be displayed in decimal or hexa‐
decimal. The number of characters in a character array that is read
and displayed as a string can be limited with the -c option. If the
-C option is present, no limit is enforced. The number of elements
in a standard array that is read and displayed can be limited with
the -l option. If the -L option is present, no limit is enforced
and all array elements are shown. The default values for -c and -l
can be modified using ::set or the -o command-line option as
described under OPTIONS.
If the -i option is specified, the address value is interpreted as
an immediate value to be printed. You must give a type with which
to interpret the value. If the type is smaller than 64 bits, the
immediate value is interpreted as if it were the size of the type.
The -i option cannot be used in conjunction with the -p option. If
the -a option is given, the addresses shown are byte offsets start‐
ing at zero.
::quit
$q
Quit the debugger.
[ thread ] ::regs
[ thread ] $r
Print the general purpose register set of the representative
thread. If a thread is specified, the general purpose register set
of that thread is displayed. The thread expression should be one of
the thread identifiers described under Thread Support, above.
::release [ -a ]
:R [ -a ]
Release the previously attached process or core file. If the -a
option is present, the process is released and left stopped and
abandoned. It can subsequently be continued by prun(1) (see
proc(1)) or it can be resumed by applying mdb or another debugger.
By default, a released process is forcibly terminated if it was
created by mdb using ::run, or it is released and set running if it
was attached to by mdb using the -p option or using the ::attach or
:A dcmds.
::run [ args . . . ]
:r [ args . . . ]
Start a new target program running with the specified arguments and
attach to it. The arguments are not interpreted by the shell. If
the debugger is already examining a live running program, it first
detaches from this program as if by ::release.
::set [ -wF ] [ -/-o option ] [ -s distance ] [ -I path ]
[ -L path ] [ -P prompt ]
Get or set miscellaneous debugger properties. If no options are
specified, the current set of debugger properties is displayed. The
::set dcmd recognizes the following options:
-F
Forcibly takes over the next user process that ::attach is
applied to, as if mdb had been executed with the -F option on
the command line.
-I
Sets the default path for locating macro files. The path argu‐
ment can contain any of the special tokens described for the -I
command-line option under OPTIONS.
-L
Sets the default path for locating debugger modules. The path
argument can contain any of the special tokens described for
the -I command-line option under OPTIONS.
-o
Enables the specified debugger option. If the -o form is used,
the option is disabled. The option strings are described along
with the -o command-line option under OPTIONS.
-P
Sets the command prompt to the specified prompt string.
-s
Sets the symbol matching distance to the specified distance.
Refer to the description of the -s command-line option under
OPTIONS for more information.
-w
Re-opens the target for writing, as if mdb had been executed
with the -w option on the command line.
::showrev [ -pv ]
Display revision information for the hardware and software. With no
options specified, general system information is displayed. The -v
option displays version information for all load objects, whereas
the -p option displays the version information only for the load
objects that have been installed on the system as part of a patch.
Version information is not available for all load objects. Load
objects without version information is omitted from the output for
the -p option and is listed as having a version of "Unknown" in the
output for the -v option.
[signal] ::sigbp [-/-dDestT] [-c cmd] [-n count] SIG ...
[signal] :t [-/-dDestT] [-c cmd] [-n count] SIG ...
Trace delivery of the specified signals. The signals are identified
using an optional signal number preceding the dcmd, or a list of
signal names or numbers (see signal.h(3HEAD)) following the dcmd.
The -d, -D, -e, -s, -t, -T, -c, and -n options have the same mean‐
ing as they do for the ::evset dcmd. Initially, the set of signals
that cause the process to dump core by default (see sig‐
nal.h(3HEAD)) and SIGINT are traced.
::sizeof type
Print the size of the specified type in bytes. The type parameter
can name a C struct, union, enum, fundamental integer type, or a
pointer to any of these types. The type name can use the backquote
(`) scoping operator described under Symbol Name Resolution, above.
The ::sizeof dcmd can only be used with objects that contain sym‐
bolic debugging information designed for use with mdb. Refer to
NOTES, Symbolic Debugging Information, below for more information.
[ address ] ::stack [ count ]
[ address ] $c [ count ]
Print a C stack backtrace. If the dcmd is preceded by an explicit
address, a backtrace beginning at this virtual memory address is
displayed. Otherwise the stack of the representative thread is dis‐
played. If an optional count value is given as an argument, no more
than count arguments are displayed for each stack frame in the out‐
put.
::status
Print a summary of information related to the current target.
::step [ over | out ] [ SIG ]
:s [ SIG ]
:u [ SIG ]
Step the target program one instruction. If an optional signal name
or number (see signal.h(3HEAD)) is specified as an argument, the
signal is immediately delivered to the target as part of resuming
its execution. If the optional "over" argument is specified, ::step
steps over subroutine calls. The ::step over argument is the same
as the ::next dcmd. If the optional "out" argument is specified,
the target program continues until the representative thread
returns from the current function. If no target program is cur‐
rently running, ::step out starts a new program running as if by
::run and stop at the first instruction. The :s dcmd is the same as
::step. The :u dcmd is the same as ::step out.
[ syscall ] ::sysbp [ -/-dDestT ] [ -io ] [ -c cmd ]
[ -n count ] syscall...
Trace entry to or exit from the specified system calls. The system
calls are identified using an optional system call number preceding
the dcmd, or a list of system call names or numbers (see
<sys/syscall.h>) following the dcmd. If the -i option is specified
(the default), the event specifiers trigger on entry into the ker‐
nel for each system call. If the -o option is specified, the event
specifiers trigger on exit out from the kernel. The -d, -D, -e, -s,
-t, -T, -c, and -n options have the same meaning as they do for the
::evset dcmd.
thread ::tls symbol
Print the address of the storage for the specified thread-local
storage (TLS) symbol in the context of the specified thread. The
thread expression should be one of the thread identifiers described
under Thread Support, above. The symbol name can use any of the
scoping operators described under Symbol Name Resolution, above.
::typeset [ -/-t] variable-name . . .
Set attributes for named variables. If one or more variable names
are specified, they are defined and set to the value of dot. If the
-t option is present, the user-defined tag associated with each
variable is set. If the -t option is present, the tag is cleared.
If no variable names are specified, the list of variables and their
values is printed.
::unload module-name
Unload the specified dmod. The list of active dmods can be printed
using the ::dmods dcmd. Built-in modules can not be unloaded. Mod‐
ules that are busy (that is, provide dcmds that are currently exe‐
cuting) can not be unloaded.
::unset variable-name . . .
Unset (remove) the specified variable(s) from the list of defined
variables. Some variables exported by mdb are marked as persistent,
and can not be unset by the user.
::vars [-npt]
Print a listing of named variables. If the -n option is present,
the output is restricted to variables that currently have non-zero
values. If the -p option is present, the variables are printed in a
form suitable for re-processing by the debugger using the $< dcmd.
This option can be used to record the variables to a macro file and
then restore these values later. If the -t option is present, only
the tagged variables are printed. Variables can be tagged using the
-t option of the ::typeset dcmd.
::version
Print the debugger version number.
address ::vtop [-a as]
Print the physical address mapping for the specified virtual
address, if possible. The ::vtop dcmd is only available when exam‐
ining a kernel target, or when examining a user process inside a
kernel crash dump (after a ::context dcmd has been issued).
When examining a kernel target from the kernel context, the -a
option can be used to specify the address (as) of an alternate
address space structure that should be used for the virtual to
physical translation. By default, the kernel's address space is
used for translation. This option is available for active address
spaces even when the dump content only contains kernel pages.
[ address ] ::walk walker-name [ variable-name ]
Walk through the elements of a data structure using the specified
walker. The available walkers can be listed using the ::walkers
dcmd. Some walkers operate on a global data structure and do not
require a starting address. For example, walk the list of proc
structures in the kernel. Other walkers operate on a specific data
structure whose address must be specified explicitly. For example,
given a pointer to an address space, walk the list of segments.
When used interactively, the ::walk dcmd prints the address of each
element of the data structure in the default base. The dcmd can
also be used to provide a list of addresses for a pipeline. The
walker name can use the backquote (`) scoping operator described
under dcmd and Walker Name Resolution, above. If the optional vari‐
able-name is specified, the specified variable is assigned the
value returned at each step of the walk when mdb invokes the next
stage of the pipeline.
::walkers
List the available walkers and print a brief description for each
one.
::whence [ -v ] name . . .
::which [ -v ] name ...
Print the dmod that exports the specified dcmds and walkers. These
dcmds can be used to determine which dmod is currently providing
the global definition of the given dcmd or walker. Refer to the
section on dcmd and Walker Name Resolution above for more informa‐
tion on global name resolution. The -v option causes the dcmd to
print the alternate definitions of each dcmd and walker in order of
precedence.
addr [ ,len ]::wp [ -/-dDestT ] [ -rwx ] [ -c cmd ]
[ -n count ]
addr [ ,len ] :a [ cmd . . . ]
addr [ ,len ] :p [ cmd . . . ]
addr [ ,len ] :w [ cmd . . . ]
Set a watchpoint at the specified address. The length in bytes of
the watched region can be set by specifying an optional repeat
count preceding the dcmd. If no length is explicitly set, the
default is one byte. The ::wp dcmd allows the watchpoint to be con‐
figured to trigger on any combination of read (-r option), write
(-w option), or execute (-x option) access. The -d, -D, -e, -s, -t,
-T, -c, and -n options have the same meaning as they do for the
::evset dcmd. The :a dcmd sets a read access watchpoint at the
specified address. The :p dcmd sets an execute access watchpoint at
the specified address. The :w dcmd sets a write access watchpoint
at the specified address. The arguments following the :a, :p, and
:w dcmds are concatenated together to form the callback string. If
this string contains meta-characters, it must be quoted.
::xdata
List the external data buffers exported by the current target.
External data buffers represent information associated with the
target that can not be accessed through standard target facilities
(that is, an address space, symbol table, or register set). These
buffers can be consumed by dcmds; for more information, refer to
the .
:z
Delete all event specifiers from the list of traced software
events. Event specifiers can also be deleted using ::delete.
OPTIONS
The following options are supported:
-A
Disables automatic loading of mdb modules. By default, mdb attempts
to load debugger modules corresponding to the active shared
libraries in a user process or core file, or to the loaded kernel
modules in the live operating system or an operating system crash
dump.
-f
Forces raw file debugging mode. By default, mdb attempts to infer
whether the object and core file operands refer to a user exe‐
cutable and core dump or to a pair of operating system crash dump
files. If the file type cannot be inferred, the debugger defaults
to examining the files as plain binary data. The -f option forces
mdb to interpret the arguments as a set of raw files to examine.
-F
Forcibly takes over the specified user process, if necessary. By
default, mdb refuses to attach to a user process that is already
under the control of another debugging tool, such as truss(1). With
the -F option, mdb attaches to these processes anyway. This can
produce unexpected interactions between mdb and the other tools
attempting to control the process.
-I path
Sets default path for locating macro files. Macro files are read
using the $< or $<< dcmds. The path is a sequence of directory
names delimited by colon (:) characters. The -I include path and -L
library path (see below) can also contain any of the following
tokens:
%i
Expands to the current instruction set architecture (ISA) name
('sparc', 'sparcv9', or 'i386').
%o
Expands to the old value of the path being modified. This is
useful for appending or prepending directories to an existing
path.
%p
Expands to the current platform string (either uname -i or the
platform string stored in the process core file or crash dump).
%r
Expands to the pathname of the root directory. An alternate
root directory can be specified using the -R option. If no -R
option is present, the root directory is derived dynamically
from the path to the mdb executable itself. For example, if
/bin/mdb is executed, the root directory is /. If /net/host‐
name/bin/mdb were executed, the root directory would be derived
as /net/hostname.
%t
Expands to the name of the current target. This is either be
the literal string 'proc' (a user process or user process core
file), 'kvm' (a kernel crash dump or the live operating sys‐
tem), or 'raw' (a raw file).
The default include path for 32-bit mdb is:
%r/usr/platform/%p/lib/adb:%r/usr/lib/adb
The default include path for 64-bit mdb is:
%r/usr/platform/%p/lib/adb/%i:%r/usr/lib/adb/%i
-k
Forces kernel debugging mode. By default, mdb attempts to infer
whether the object and core file operands refer to a user exe‐
cutable and core dump, or to a pair of operating system crash dump
files. The -k option forces mdb to assume these files are operating
system crash dump files. If no object or core operand is specified,
but the -k option is specified, mdb defaults to an object file of
/dev/ksyms and a core file of /dev/kmem. Read access to /dev/kmem
is restricted to group sys. Write access requires ALL privileges.
-K
Load kmdb, stop the live running operating system kernel, and pro‐
ceed to the kmdb debugger prompt. This option should only be used
on the system console, as the subsequent kmdb prompt appears on the
system console.
-L path
Sets default path for locating debugger modules. Modules are loaded
automatically on startup or using the ::load dcmd. The path is a
sequence of directory names delimited by colon (:) characters. The
-L library path can also contain any of the tokens shown for -I
above.
-m
Disables demand-loading of kernel module symbols. By default, mdb
processes the list of loaded kernel modules and performs demand
loading of per-module symbol tables. If the -m option is specified,
mdb does not attempt to process the kernel module list or provide
per-module symbol tables. As a result, mdb modules corresponding to
active kernel modules are not loaded on startup.
-M
Preloads all kernel module symbols. By default, mdb performs
demand-loading for kernel module symbols: the complete symbol table
for a module is read when an address is that module's text or data
section is referenced. With the -M option, mdb loads the complete
symbol table of all kernel modules during startup.
-o option
Enables the specified debugger option. If the -o form of the option
is used, the specified option is disabled. Unless noted below, each
option is off by default. mdb recognizes the following option argu‐
ments:
adb
Enables stricter adb(1) compatibility. The prompt is set to the
empty string and many mdb features, such as the output pager,
is disabled.
array_mem_limit=limit
Sets the default limit on the number of array members that
::print displays. If limit is the special token none, all array
members are displayed by default.
array_str_limit=limit
Sets the default limit on the number of characters that ::print
attempts to display as an ASCII string when printing a char
array. If limit is the special token none, the entire char
array is displayed as a string by default.
follow_exec_mode=mode
Sets the debugger behavior for following an exec(2) system
call. The mode should be one of the following named constants:
ask
If stdout is a terminal device, the debugger stops after
the exec(2) system call has returned and then prompts the
user to decide whether to follow the exec or stop. If std‐
out is not a terminal device, the ask mode defaults to
stop.
follow
The debugger follows the exec by automatically continuing
the target process and resetting all of its mappings and
symbol tables based on the new executable. The follow
behavior is discussed in more detail under NOTES, Interac‐
tion with Exec, below.
stop
The debugger stops following return from the exec system
call. The stop behavior is discussed in more detail under
NOTES, Interaction with Exec, below.
follow_fork_mode=mode
Sets the debugger behavior for following a fork(2), fork1(2),
or vfork(2) system call. The mode should be one of the follow‐
ing named constants:
ask
If stdout is a terminal device, the debugger stops after
the fork(2) system call has returned and then prompts the
user to decide whether to follow the parent or child. If
stdout is not a terminal device, the ask mode defaults to
parent.
parent
The debugger follows the parent process, and detaches from
the child process and sets it running.
child
The debugger follows the child process, and detaches from
the parent process and sets it running.
ignoreeof
The debugger does not exit when an EOF sequence (^D) is entered
at the terminal. The ::quit dcmd must be used to quit.
nostop
Does not stop a user process when attaching to it when the -p
option is specified or when the ::attach or :A dcmds are
applied. The nostop behavior is described in more detail under
NOTES, Process Attach and Release, below.
pager
Enables the output pager (default).
repeatlast
If a NEWLINE is entered as the complete command at the termi‐
nal, mdb repeats the previous command with the current value of
dot. This option is implied by -o adb.
showlmid
mdb provides support for symbol naming and identification in
user applications that make use of link maps other than
LM_ID_BASE and LM_ID_LDSO, as described in Symbol Name Resolu‐
tion, above. Symbols on link maps other than LM_ID_BASE or
LM_ID_LDSO is shown as LMlmid`library`symbol, where lmid is the
link-map ID in the default output radix (16). The user can
optionally configure mdb to show the link-map ID scope of all
symbols and objects, including those associated with LM_ID_BASE
and LM_ID_LDSO, by enabling the showlmid option. Built-in dcmds
that deal with object file names displays link-map IDs accord‐
ing to the value of showlmid above, including ::nm, ::mappings,
$m, and ::objects.
-p pid
Attaches to and stops the specified process-id. mdb uses the
/proc/pid/object/a.out file as the executable file pathname.
-P prompt
Sets the command prompt. The default prompt is '> '.
-R root
Sets root directory for pathname expansion. By default, the root
directory is derived from the pathname of the mdb executable
itself. The root directory is substituted in place of the %r token
during pathname expansion.
-s distance
Sets the symbol matching distance for address-to-symbol-name con‐
versions to the specified distance. By default, mdb sets the dis‐
tance to zero, which enables a smart-matching mode. Each ELF symbol
table entry includes a value V and size S, representing the size of
the function or data object in bytes. In smart mode, mdb matches an
address A with the given symbol if A is in the range [ V, V + S ).
If any non-zero distance is specified, the same algorithm is used,
but S in the expression above is always the specified absolute dis‐
tance and the symbol size is ignored.
-S
Suppresses processing of the user's ~/.mdbrc file. By default, mdb
reads and processes the macro file .mdbrc if one is present in the
user's home directory, as defined by $HOME. If the -S option is
present, this file is not read.
-u
Forces user debugging mode. By default, mdb attempts to infer
whether the object and core file operands refer to a user exe‐
cutable and core dump, or to a pair of operating system crash dump
files. The -u option forces mdb to assume these files are not oper‐
ating system crash dump files.
-U
Unload kmdb if it is loaded. You should unload kmdb when it is not
in use to release the memory used by the kernel debugger back to
the free memory available to the operating system.
-V version
Sets disassembler version. By default, mdb attempts to infer the
appropriate disassembler version for the debug target. The disas‐
sembler can be set explicitly using the -V option. The ::disasms
dcmd lists the available disassembler versions.
-w
Opens the specified object and core files for writing.
-W
Permit access to memory addresses that are mapped to I/O devices.
By default, mdb does not allow such access because many devices do
not provide hardware protection against invalid software manipula‐
tions. Use this option only when debugging device drivers and with
caution.
-y
Sends explicit terminal initialization sequences for tty mode. Some
terminals, such as cmdtool(1), require explicit initialization
sequences to switch into a tty mode. Without this initialization
sequence, terminal features such as standout mode can not be avail‐
able to mdb.
OPERANDS
The following operands are supported:
object
Specifies an ELF format object file to examine. mdb provides the
ability to examine and edit ELF format executables (ET_EXEC), ELF
dynamic library files (ET_DYN), ELF relocatable object files
(ET_REL), and operating system unix.X symbol table files.
core
Specifies an ELF process core file (ET_CORE), or an operating sys‐
tem crash dump vmcore.X file. If an ELF core file operand is pro‐
vided without a corresponding object file, mdb attempts to infer
the name of the executable file that produced the core using sev‐
eral different algorithms. If no executable is found, mdb still
executes, but some symbol information can be unavailable.
suffix
Specifies the numerical suffix representing a pair of operating
system crash dump files. For example, if the suffix is '3', mdb
infers that it should examine the files 'unix.3' and 'vmcore.3'. If
these files do not exist, but 'vmdump.3' does exist, then a message
is printed indicating that savecore -f vmdump.3 must be run first
in order to uncompress the dump file. The string of digits are not
interpreted as a suffix if an actual file of the same name is
present in the current directory.
USAGEmdb processes all input files (including scripts, object files, core
files, and raw data files) in a large file aware fashion. See large‐
file(5) for more information about the processing of large files, which
are files greater than or equal to 2 Gbytes (2^31 bytes).
EXIT STATUS
The following exit values are returned:
0
Debugger completed execution successfully.
1
A fatal error occurred.
2
Invalid command line options were specified.
ENVIRONMENT VARIABLES
HISTSIZE
This variable is used to determine the maximum length of the com‐
mand history list. If this variable is not present, the default
length is 128.
HOME
This variable is used to determine the pathname of the user's home
directory, where a .mdbrc file can reside. If this variable is not
present, no .mdbrc processing occurs.
SHELL
This variable is used to determine the pathname of the shell used
to process shell escapes requested using the ! meta-character. If
this variable is not present, /bin/sh is used.
FILES
$HOME/.mdbrc
User mdb initialization file. The .mdbrc file, if present, is pro‐
cessed after the debug target has been initialized, but before mod‐
ule auto-loading is performed or any commands have been read from
standard input.
/dev/kmem
Kernel virtual memory image device. This device special file is
used as the core file when examining the live operating system.
/dev/ksyms
Kernel symbol table device. This device special file is used as the
object file when examining the live operating system.
/proc/pid/*
Process information files that are read when examining and control‐
ling user processes.
/usr/lib/adb
/usr/platform/platform-name/lib/adb
Default directories for macro files that are read with the $< and
$<< dcmds. platform-name is the name of the platform, derived
either from information in a core file or crash dump, or from the
current machine as if by uname -i (see uname(1)).
/usr/lib/mdb
/usr/platform/platform-name/lib/mdb
Default directories for debugger modules that are loaded using the
::load dcmd. platform-name is the name of the platform, derived
either from information in a core file or crash dump, or from the
current machine as if by uname -i (see uname(1)).
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
┌─────────────────────────────┬─────────────────────────────┐
│ ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
├─────────────────────────────┼─────────────────────────────┤
│Availability │developer/debug/mdb │
├─────────────────────────────┼─────────────────────────────┤
│Interface Stability │Committed │
└─────────────────────────────┴─────────────────────────────┘
SEE ALSOadb(1), cmdtool(1), gcore(1), proc(1), pgrep(1), ps(1), stty(1),
truss(1), uname(1), coreadm(1M), dumpadm(1M), largefile(5),
savecore(1M), exec(2), fork(2), _lwp_self(2), pipe(2), vfork(2),
dlopen(3C), elf(3ELF), libc_db(3LIB), libkvm(3LIB), libthread(3LIB),
signal(3C), signal.h(3HEAD), thr_self(3C), core(4), proc(4),
attributes(5), largefile(5), threads(5), ksyms(7D), mem(7D)WARNINGS
Use of the Error Recovery Mechanism
The debugger and its dmods execute in the same address space, and thus
it is quite possible that a buggy dmod can cause mdb to dump core or
otherwise misbehave. The mdb resume capability, described above under
Signal Handling, provides a limited recovery mechanism for these situa‐
tions. However, it is not possible for mdb to know definitively whether
the dmod in question has corrupted only its own state, or the debug‐
ger's global state. Therefore a resume operation cannot be guaranteed
to be safe, or to prevent a subsequent crash of the debugger. The
safest course of action following a resume is to save any important
debug information, and then quit and restart the debugger.
Use of the Debugger to Modify the Live Operating System
The use of the debugger to modify (that is, write to) the address space
of live running operating system is extremely dangerous, and can result
in a system panic in the event the user damages a kernel data struc‐
ture.
NOTES
Limitations on Examining Process Core Files
mdb does not provide support for examining process core files that were
generated by a release of Solaris preceding Solaris 2.6. When debugging
core files generated by a release of Solaris 9 or an earlier release,
symbol information might not be available. Since the text section and
read-only data is not present in those core files, the symbol informa‐
tion might not match the data present in the process at the time it
dumped core. In releases later than Solaris 9, text sections and read-
only data are included in core files by default. Users can configure
their processes to exclude that information from core files using core‐
adm(1M). Thus, the information presented by mdb for those core files
can not match the data that was present at the time the process dumped
core. Core files from Solaris x86 systems can not be examined on
Solaris SPARC systems, and vice-versa.
Limitations on Examining Crash Dump Files
Crash dumps from Solaris 7 and earlier releases can only be examined
with the aid of the libkvm from the corresponding operating system
release. If a crash dump from one operating system release is examined
using the dmods from a different operating system release, changes in
the kernel implementation can prevent some dcmds or walkers from work‐
ing properly. mdb issues a warning message if it detects this condi‐
tion. Crash dumps from Solaris x86 systems can not be examined on
Solaris SPARC systems, and vice-versa.
Relationship Between 32-bit and 64-bit Debugger
mdb provides support for debugging both 32-bit and 64-bit programs.
Once it has examined the target and determined its data model, mdb
automatically re-executes the mdb binary that has the same data model
as the target, if necessary. This approach simplifies the task of writ‐
ing debugger modules, because the modules that are loaded use the same
data model as the primary target. Only the 64-bit debugger can be used
to debug 64-bit target programs. The 64-bit debugger can only be used
on a system that is running the 64-bit operating environment.
The debugger can also need to re-execute itself when debugging a 32-bit
process that execs a 64-bit process, or vice-versa. The handling of
this situation is discussed in more detail under Interaction with Exec,
below.
Interaction with Exec
When a controlled process performs a successful exec(2), the behavior
of the debugger is controlled by the ::set -o follow_exec_mode option,
as described above. If the debugger and victim process have the same
data model, then the "stop" and "follow" modes determine whether mdb
automatically continues the target or returns to the debugger prompt
following the exec. If the debugger and victim process have a different
data model, then the "follow" behavior causes mdb to automatically re-
exec the mdb binary with the appropriate data model and to re-attach to
the process, still stopped on return from the exec. Not all debugger
state is preserved across this re-exec.
If a 32-bit victim process execs a 64-bit program, then "stop" returns
to the command prompt, but the debugger is no longer able to examine
the process because it is now using the 64-bit data model. To resume
debugging, execute the ::release -a dcmd, quit mdb, and then execute
mdb-p pid to re-attach the 64-bit debugger to the process.
If a 64-bit victim process execs a 32-bit program, then "stop" returns
to the command prompt, but the debugger only provides limited capabili‐
ties for examining the new process. All built-in dcmds work as adver‐
tised, but loadable dcmds do not since they do not perform data model
conversion of structures. The user should release and re-attach the
debugger to the process as described above in order to restore full
debugging capabilities.
Interaction with Job Control
If the debugger is attached to a process that is stopped by job control
(that is, it stopped in response to SIGTSTP, SIGTTIN, or SIGTTOU), the
process can not be able to be set running again when it is continued by
a continue dcmd. If the victim process is a member of the same session
(that is, it shares the same controlling terminal as mdb), mdb attempts
to bring the associated process group to the foreground and to continue
the process with SIGCONT to resume it from job control stop. When mdb
is detached from such a process, it restores the process group to the
background before exiting. If the victim process is not a member of the
same session, mdb cannot safely bring the process group to the fore‐
ground, so it continues the process with respect to the debugger, but
the process remains stopped by job control. mdb prints a warning in
this case, and the user must issue an "fg" command from the appropriate
shell in order to resume the process.
Process Attach and Release
When mdb attaches to a running process, the process is stopped and
remains stopped until one of the continue dcmds is applied, or the
debugger quits. If the -o nostop option is enabled prior to attaching
the debugger to a process with -p, or prior to issuing an ::attach or
:A command, mdb attaches to the process but does not stop it. While the
process is still running, it can be inspected as usual (albeit with
inconsistent results) and breakpoints or other tracing flags might be
enabled. If the :c or ::cont dcmds are executed while the process is
running, the debugger waits for the process to stop. If no traced soft‐
ware events occur, the user can send an interrupt (^C) after :c or
::cont to force the process to stop and return control to the debugger.
mdb releases the current running process (if any) when the :R,
::release, :r, ::run, $q, or ::quit dcmds are executed, or when the
debugger terminates as the result of an EOF or signal. If the process
was originally created by the debugger using :r or ::run, it is
forcibly terminated as if by SIGKILL when it is released. If the
process was already running prior to attaching mdb to it, it is set
running again when it is released. A process can be released and left
stopped and abandoned using the ::release -a option.
Symbolic Debugging Information
The ::list, ::offsetof, ::print, and ::sizeof dcmds require that one or
more load objects contain compressed symbolic debugging information
suitable for use with mdb. This information is currently only available
for certain Solaris kernel modules.
Developer Information
The provides a more detailed description of mdb features, as well as
information for debugger module developers.
The header file <sys/mdb_modapi.h> contains prototypes for the func‐
tions in the MDB Module API, and the SUNWmdbdm package provides source
code for an example module in the directory /usr/demo/mdb.
SunOS 5.10 14 Aug 2009 mdb(1)
