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AIX Version 4.3 Commands Reference, Volume 2

dbx Command

Purpose

Provides an environment to debug and run programs under the operating system.

Syntax

dbx [ -a ProcessID ] [ -c CommandFile ] [ -d NestingDepth ] [ -I Directory ] [ -E DebugEnvironment ] [ -k ] [ -u ] [ -F ] [ -r ] [ -x ] [ ObjectFile [ CoreFile ] ]

Description

The dbx command provides a symbolic debug program for C, C++, Pascal, and FORTRAN programs, allowing you to carry out operations such as the following:

The ObjectFile parameter is an object (executable) file produced by a compiler. Use the -g (generate symbol table) flag when compiling your program to produce the information the dbx command needs.

Note: The -g flag of the cc command should be used when the object file is compiled. If the -g flag is not used or if symbol references are removed from the xcoff file with the strip command, the symbolic capabilities of the dbx command are limited.

If the -c flag is not specified, the dbx command checks for a .dbxinit file in the user's $HOME directory. It then checks for a .dbxinit file in the user's current directory. If a .dbxinit file exists in the current directory, that file overrides the .dbxinit file in the user's $HOME directory. If a .dbxinit file exists in the user's $HOME directory or current directory, that file's subcommands run at the beginning of the debug session. Use an editor to create a .dbxinit file.

If ObjectFile is not specified, then dbx asks for the name of the object file to be examined. The default is a.out. If the core file exists in the current directory or a CoreFile parameter is specified, then dbx reports the location where the program faulted. Variables, registers, and memory held in the core image may be examined until execution of ObjectFile begins. At that point the dbx debug program prompts for commands.

Expression Handling

The dbx program can display a wide range of expressions. You can specify expressions in the dbx debug program with a common subset of C and Pascal syntax, with some FORTRAN extensions.

The following operators are valid in the debug program:

* (asterisk) or ^ (caret) Denotes indirection or pointer dereferencing.
[ ] (brackets) or ( ) (parentheses) Denotes subscript array expressions.
. (period) Use this field reference operator with pointers and structures. This makes the C operator -> (arrow) unnecessary, although it is allowed.
& (ampersand) Gets the address of a variable.
.. (two periods) Separates the upper and lower bounds when specifying a subsection of an array. For example: n[1..4].

The following types of operations are valid in expressions in the debug program:

Algebraic =, -, *, / (floating division), div (integral division), mod, exp (exponentiation)
Bitwise -, I, bitand, xor, ~. <<, >>
Logical or, and, not, II, &&
Comparison <, >, <=, >=, < > or !=, = or ==
Other (typename),sizeof

Logical and comparison expressions are allowed as conditions in stop and trace.

Expression types are checked. You override an expression type by using a renaming or casting operator. The three forms of type renaming are Typename(Expression), Expression|Typename, and (Typename) Expression. The following is an example where the x variable is an integer with value 97:

(dbx) print x
97
(dbx) print char (x), x \ char, (char) x, x
'a' 'a' 'a' 97

Command Line Editing

The dbx commands provides a command line editing feature similar to those provide by Korn Shell. vi mode provides vi-like editing features, while emacs mode gives you controls similar to emacs.

These features can be turned on by using dbx subcommand set -o or set edit. To turn on vi-style command-line editing, you would type the subcommand set edit vi or set -o vi.

You can also use the EDITOR environment variable to set the editing mode.

The dbx command saves commands entered to a history file .dbxhistory. If the DBXHISTFILE environment variable is not set, the history file used is $HOME/.dbxhistory.

By default, dbx saves the text of the last 128 commands entered. The DBXHISTSIZE environment variable can be used to increase this limit.

Flags

-a ProcessID Attaches the debug program to a process that is running. To attach the debug program, you need authority to use the kill command on this process. Use the ps command to determine the process ID. If you have permission, the dbx program interrupts the process, determines the full name of the object file, reads in the symbolic information, and prompts for commands.
-c CommandFile Runs the dbx subcommands in the file before reading from standard input. The specified file in the $HOME directory is processed first; then the file in the current directory is processed. The command file in the current directory overrides the command file in the $HOME directory. If the specified file does not exist in either the $HOME directory or the current directory, a warning message is displayed. The source subcommand can be used once the dbx program is started.
-d NestingDepth Sets the limit for the nesting of program blocks. The default nesting depth limit is 25.
-F Can be used to turn off the lazy read mode and make the dbx command read all symbols at startup time. By default, lazy reading mode is on: it reads only required symbol table information on initiation of dbx session. In this mode, dbx will not read local variables and types whose symbolic information has not been read. Therefore, commands such as whereis i may not list all instances of the local variable i in every function.
-I Directory (Uppercase i) Includes directory specified by the Directory variable in the list of directories searched for source files. The default is to look for source files in the following directories:
  • The directory the source file was located in when it was compiled. This directory is searched only if the compiler placed the source path in the object.
  • The current directory.
  • The directory where the program is currently located.
-E DebugEnvironment Specifies the environment variable for the debug program.
-k Maps memory addresses; this is useful for kernel debugging.
-r Runs the object file immediately. If it terminates successfully, the dbx debug program is exited. Otherwise, the debug program is entered and the reason for termination is reported.
Note: Unless -r is specified, the dbx command prompts the user and waits for a command.
-u Causes the dbx command to prefix file name symbols with an @ (at sign). This flag reduces the possibility of ambiguous symbol names.
-x Prevents the dbx command from stripping _ (trailing underscore ) characters from symbols originating in FORTRAN source code. This flag allows dbx to distinguish between symbols which are identical except for an underscore character, such as xxx and xxx_ .

Examples

  1. The following example explains how to start the dbx debug program simultaneously with a process. The example uses a program called samp.c. This C program is first compiled with the -g flag to produce an object file that includes symbolic table references. In this case, the program is named samp: 
    $ cc -g samp.c -o samp
    When the program samp is run, the operating system reports a bus error and writes a core image to your current working directory as follows: 
    $ samp
Bus Error - core dumped
    To determine the location where the error occurred, enter: 
    $ dbx samp
    The system returns the following message: 
    dbx version 3.1
Type 'help' for help.
reading symbolic information . . . [
using memory image in core]
  25   x[i] = 0;
(dbx) quit
  2. This example explains how to attach dbx to a process. This example uses the following program, looper.c: 
    main()
{
      int i,x[10];
       
      for (i = 0; i < 10;);
}
    The program will never terminate because i is never incremented. Compile looper.c with the -g flag to get symbolic debugging capability: 
    $ cc -g looper.c -o looper
    Run looper from the command line and perform the following steps to attach dbx to the program while it is running:

    1. To attach dbx to looper, you must determine the process ID. If you did not run looper as a background process, you must have another Xwindow open. From this Xwindow , enter: 
      ps -u UserID
      where UserID is your login ID. All active processes that belong to you are displayed as follows: 
      PID     TTY      TIME    COMMAND
68      console   0:04    sh
467     lft3     10:48    looper

      In this example the process ID associated with looper is 467 .

    2. To attach dbx to looper, enter: 
      $ dbx -a 467

      The system returns the following message:

      Waiting to attach to process 467 . . .
Successfully attached to /tmp/looper.
dbx is initializing
Type 'help' for help.
reading symbolic information . . .
 
attached in main at line 5
5     for (i = 0; i < 10;);
(dbx)

      You can now query and debug the process as if it had been originally started with dbx.

  3. To add directories to the list of directories to be searched for the source file of an executable file objefile, you can enter: 
    $dbx -I /home/user/src -I /home/group/src 
objfile

    The use subcommand may be used for this function once dbx is started. The use command resets the list of directories, whereas the -I flag adds a directory to the list.

  4. To use the -r flag, enter: 
    $ dbx -r samp
    The system returns the following message: 
    Entering debug program . . .
dbx version 3.1
Type 'help' for help.
reading symbolic information . . .
bus error in main at line 25
  25   x[i] = 0;
(dbx) quit

    The -r flag allows you to examine the state of your process in memory even though a core image is not taken.

  5. To specify the environment variables for the debug program, enter: 
    dbx -E LIBPATH=/home/user/lib -E LANG=Ja_JP objfile

dbx Subcommands

Note: The subcommands can only be used while running the dbx debug program.
/ Searches forward in the current source file for a pattern.
? Searches backward in the current source file for a pattern.
alias Creates aliases for dbx subcommands.
assign Assigns a value to a variable.
attribute Displays information about all or selected attributes objects.
call Runs the object code associated with the named procedure or function.
case Changes how the dbx debug program interprets symbols.
catch Starts trapping a signal before that signal is sent to the application program.
clear Removes all stops at a given source line.
cleari Removes all breakpoints at an address.
condition Displays information about all or selected condition variables.
cont Continues application program execution from the current stopping point until the program finishes or another breakpoint is encountered.
delete Removes the traces and stops corresponding to the specified event numbers.
detach Continues execution of application and exits the debug program.
display memory Displays the contents of memory.
down Moves the current function down the stack.
dump Displays the names and values of variables in the specified procedure.
edit Starts an editor on the specified file.
file Changes the current source file to the specified file.
func Changes the current function to the specified procedure or function.
goto Causes the specified source line to be the next line run.
gotoi Changes the program counter address.
help Displays help information for dbx subcommands or topics.
ignore Stops trapping a signal before that signal is sent to the application program.
list Displays lines of the current source file.
listi Lists instructions from the application program.
map Displays information about load characteristics of the application.
move Changes the next line to be displayed.
multproc Enables or disables multiprocess debugging.
mutex Displays information about all or selected mutexes.
next Runs the application program up to the next source line.
nexti Runs the application program up to the next machine instruction.
print Prints the value of an expression or runs a procedure and prints the return code of that procedure.
prompt Changes the dbx command prompt.
quit Stops the dbx debug program.
registers Displays the values of all general-purpose registers, system-control registers, floating-point registers, and the current instruction register.
rerun Begins execution of an application with the previous arguments.
return Continues running the application program until a return to the specified procedure is reached.
rwlock Displays information about the rwlocks.
run Begins running an application.
screen Opens an Xwindow for dbx command interaction.
set Defines a value for a dbx debug program variable.
sh Passes a command to the shell to be run.
skip Continues running the application program from the current stopping point.
source Reads dbx subcommands from a file.
status Displays the active trace and stop subcommands.
step Runs one source line.
stepi Runs one machine instruction.
stop Stops running of the application program.
stopi Sets a stop at a specified location.
thread Displays and controls threads.
trace Prints tracing information.
tracei Turns on tracing.
unalias Removes an alias.
unset Deletes a variable.
up Moves the current function up the stack.
use Sets the list of directories to be searched when looking for source files.
whatis Displays the declaration of application program components.
where Displays a list of active procedures and functions.
whereis Displays the full qualifications of all the symbols whose names match the specified identifier.
which Displays the full qualification of the given identifier.

/ Subcommand

/ [ RegularExpression [ / ] ]

The / subcommand searches forward in the current source file for the pattern specified by the RegularExpression parameter. Entering the / subcommand with no arguments causes dbx to search forward for the previous regular expression. The search wraps around the end of the file.

Examples
  1. To search forward in the current source file for the number 12, enter: 
    / 12
  2. To repeat the previous search, enter: 
    /

See the ? (search) subcommand and the regcmp subroutine.

? Subcommand

? [ RegularExpression [ ? ] ]

The ? subcommand searches backward in the current source file for the pattern specified by the RegularExpression parameter. Entering the ? subcommand with no arguments causes the dbx command to search backwards for the previous regular expression. The search wraps around the end of the file.

Examples
  1. To search backward in the current source file for the letter z , enter: 
    ?z
  2. To repeat the previous search, enter: 
    ?

See the / (search) subcommand and the regcmp subroutine.

alias Subcommand

alias [ Name [ [ (Arglist) ] String | Subcommand ] ]

The alias subcommand creates aliases for dbx subcommands. The Name parameter is the alias being created. The String parameter is a series of dbx subcommands that, after the execution of this subcommand, can be referred to by Name. If the alias subcommand is used without parameters, it displays all current aliases.

Examples
  1. To substitute rr for rerun , enter: 
    alias rr rerun
  2. To run the two subcommands print n and step whenever printandstep is typed at the command line, enter: 
    alias printandstep "print n; step"
  3. The alias subcommand can also be used as a limited macro facility. For example: 
    (dbx) alias px(n) "set $hexints; print n; unset $hexints"
(dbx) alias a(x,y) "print symname[x]->
symvalue._n_n.name.Id[y]"
(dbx) px(126)
0x7e

    In this example, the alias px prints a value in hexadecimal without permanently affecting the debugging environment.

assign Subcommand

assign Variable=Expression

The assign subcommand assigns the value specified by the Expression parameter to the variable specified by the Variable parameter.

Examples
  1. To assign a value of 5 to the x variable, enter: 
    assign x = 5
  2. To assign the value of the y variable to the x variable, enter: 
    assign x =  y
  3. To assign the character value 'z' to the z variable, enter: 
    assign  z  =  'z'
  4. To assign the boolean value false to the logical type variable B , enter: 
    assign  B  =  false
  5. To assign the "Hello World" string to a character pointer Y , enter: 
    assign  Y  =  "Hello  World"
  6. To disable type checking, set the dbx debug program variable $unsafeassign by entering: 
    set $unsafeassign

See Displaying and Modifying Variables.

attribute Subcommand

attribute [ AttributeNumber ... ]

The attribute subcommand displays information about the user thread, mutex, or condition attributes objects defined by the AttributeNumber parameters. If no parameters are specified, all attributes objects are listed.

For each attributes object listed, the following information is displayed:

attr Indicates the symbolic name of the attributes object, in the form $a AttributeNumber.
obj_addr Indicates the address of the attributes object.
type Indicates the type of the attributes object; this can be thr , mutex , or cond for user threads, mutexes, and condition variables respectively.
state Indicates the state of the attributes object. This can be valid or inval .
stack Indicates the stacksize attribute of a thread attributes object.
scope Indicates the scope attribute of a thread attributes object. This determines the contention scope of the thread, and defines the set of threads with which it must contend for processing resources. The value can be sys or pro for system or process contention scope.
prio Indicates the priority attribute of a thread attributes object.
sched Indicates the schedpolicy attribute of a thread attributes object. This attribute controls scheduling policy, and can be fifo , rr (round robin), or other .
p-shar Indicates the process-shared attribute of a mutex or condition attribute object. A mutex or condition is process-shared if it can be accessed by threads belonging to different processes. The value can be yes or no .
protocol Indicates the protocol attribute of a mutex. This attribute determines the effect of holding the mutex on a thread's priority. The value can be no_prio , prio , or protect .
Notes:
  1. The print subcommand of the dbx debug program recognizes symbolic attribute names, and can be used to display the status of the corresponding object.
  2. The available attributes depend on the implementation of POSIX options.
Examples
  1. To list information about all attributes, enter: 
    attribute
    The output is similar to: 
    attr   obj_addr   type  state  stack   scope    prio 
sched p-shar
$a1   0x200035c8  mutex valid                                no 
$a2   0x20003628  cond  valid                                no
$a3   0x200037c8  thr   valid  57344    sys      126 other
$a4   0x200050f8  thr   valid  57344    pro      126 other
  2. To list information about attributes 1 and 3, enter: 
    attribute 1 3
    The output is similar to: 
    attr   obj_addr   type  state  stack   scope    prio 
sched p-shar
$a1   0x200035c8  mutex valid                                no 
$a3   0x200037c8  thr   valid  57344    sys      126 other

See the condition subcommand, mutex subcommand, print subcommand, and thread subcommand for the dbx command.

Also, see Creating Threads, Using Mutexes, and Using Condition Variables in AIX Version 4.3 General Programming Concepts: Writing and Debugging Programs .

call Subcommand

call Procedure ( [ Parameters ] )

The call subcommand runs the procedure specified by the Procedure parameter. The return code is not printed. If any parameters are specified, they are passed to the procedure being run.

Example

To call a command while running dbx , enter:

(dbx) call printf("hello")
hello

printf returns successfully.

case Subcommand

case [ default | mixed | lower | upper ]

The case subcommand changes how the dbx debug program interprets symbols. The default handling of symbols is based on the current language. If the current language is C, C++, or undefined, the symbols are not folded; if the current language is FORTRAN or Pascal, the symbols are folded to lowercase. Use this subcommand if a symbol needs to be interpreted in a way not consistent with the current language.

Entering the case subcommand with no parameters displays the current case mode.

Flags
default Varies with the current language.
mixed Causes symbols to be interpreted as they actually appear.
lower Causes symbols to be interpreted as lowercase.
upper Causes symbols to be interpreted as uppercase.
Examples
  1. To display the current case mode, enter: 
    case
  2. To instruct dbx to interpret symbols as they actually appear, enter: 
    case mixed
  3. To instruct dbx to interpret symbols as uppercase, enter: 
    case upper

See Folding Variables to Lowercase and Uppercase.

catch Subcommand

catch [ SignalNumber | SignalName ]

The catch subcommand starts the trapping of a specified signal before that signal is sent to the application program. This subcommand is useful when the application program being debugged handles signals such as interrupts. The signal to be trapped can be specified by number or by name using either the SignalNumber or the SignalName parameter, respectively. Signal names are case insensitive, and the SIG prefix is optional. If neither the SignalNumber nor the SignalName parameter is specified, all signals are trapped by default except the SIGHUP, SIGCLD, SIGALARM, and SIGKILL signals. If no arguments are specified, the current list of signals to be caught is displayed.

Examples
  1. To display a current list of signals to be caught by dbx, enter: 
    catch
  2. To trap signal SIGALARM , enter: 
    catch SIGALARM

See the ignore subcommand and Handling Signals.

clear Subcommand

clear SourceLine

The clear subcommand removes all stops at a given source line. The SourceLine parameter can be specified in two formats:

Examples

To remove breakpoints set at line 19 , enter:

clear 19

The cleari subcommand and delete subcommand. Also, see Setting and Deleting Breakpoints in in AIX General Programming Concepts: Writing and Debugging Programs.

cleari Subcommand

cleari Address

The cleari subcommand clears all the breakpoints at the address specified by the Address parameter.

Examples
  1. To remove a breakpoint set at address 0x100001b4 , enter: 
    cleari 0x100001b4
  2. To remove a breakpoint set at the main() procedure address, enter: 
    cleari &main

See the clear subcommand, the delete subcommand, and Setting and Deleting Breakpoints in in AIX General Programming Concepts: Writing and Debugging Programs.

condition Subcommand

condition [ wait | nowait | ConditionNumber ... ]

The condition subcommand displays information about one or more condition variables. If one or more ConditionNumber parameters are given, the condition subcommand displays information about the specified condition variables. If no flags or parameters are specified, the condition subcommand lists all condition variables.

The information listed for each condition is as follows:

cv Indicates the symbolic name of the condition variable, in the form $c ConditionNumber.
obj_addr Indicates the memory address of the condition variable.
num_wait Indicates the number of threads waiting on the condition variable.
waiters Lists the user threads which are waiting on the condition variable.
Note: The print subcommand of the dbx debug program recognizes symbolic condition variable names, and can be used to display the status of the corresponding object.
Flags
wait Displays condition variables which have waiting threads.
nowait Displays condition variables which have no waiting threads.
Examples
  1. To display information about all condition variables, enter: 
    condition
  2. To display information about all condition variables which have waiting threads, enter: 
    condition wait
  3. To display information about the condition variable 3, enter: 
    condition 3
    The output is similar to: 
     cv      obj_addr     num_wait  waiters
 $c3     0x20003290         0

See the attribute subcommand, mutex subcommand, print subcommand, and thread subcommand.

Also, see Using Condition Variables in AIX Version 4.3 General Programming Concepts: Writing and Debugging Programs:.

{ Address,Address/ | Address/ [ Count ] } [ Mode ] [ >File ]

The display memory subcommand, which does not have a keyword to initiate the command, displays a portion of memory controlled by the following factors:

The range of memory displayed is controlled by specifying either:

Specify symbolic addresses by preceding the name with an & (ampersand). Addresses can be expressions made up of other addresses and the operators + (plus sign), - (minus sign), and * (indirection). Any expression enclosed in parentheses is interpreted as an address.

b Prints a byte in octal.
c Prints a byte as a character.
d Prints a short word in decimal.
D Prints a long word in decimal.
f Prints a single-precision real number.
g Prints a double-precision real number.
h Prints a byte in hexadecimal.
i Prints the machine instruction.
lld Prints an 8-byte signed decimal number.
llu Prints an 8-byte unsigned decimal number.
llx Prints an 8-byte unsigned hexadecimal number.
llo Prints an 8-byte unsigned octal number.
o Prints a short word in octal
O Prints a long word in octal.
q Prints an extended-precision floating-point number.
s Prints a string of characters terminated by a null byte.
x Prints a short word in hexadecimal.
X Prints a long word in hexadecimal.
Flag
>File Redirects output to the specified file.
Examples
  1. To display one long word of memory content in hexadecimal starting at the address 0x3fffe460 , enter: 
    0x3fffe460 / X
  2. To display two bytes of memory content as characters starting at the variable y address, enter: 
    &y / 2c
  3. To display the sixth through the eighth elements of the FORTRAN character string a_string, enter: 
    &a_string + 5, &a_string + 7/c

See Examining Memory Addresses in in AIX General Programming Concepts: Writing and Debugging Programs.

down Subcommand

down [ Count ]

The down subcommand moves the current function down the stack Count number of levels. The current function is used for resolving names. The default for the Count parameter is one.

Examples
  1. To move one level down the stack, enter: 
    down
  2. To move three levels down the stack, enter: 
    down 3

See the up subcommand, the where subcommand, and Displaying a Stack Trace in in AIX General Programming Concepts: Writing and Debugging Programs.

dump Subcommand

dump [ Procedure ] [ >File ]

The dump subcommand displays the names and values of all variables in the specified procedure. If the Procedure parameter is . (period), then all active variables are displayed. If the Procedure parameter is not specified, the current procedure is used. If the >File flag is used, the output is redirected to the specified file.

Flags
>File Redirects output to the specified file.
Examples
  1. To display names and values of variables in the current procedure, enter: 
    dump
  2. To display names and values of variables in the add_count procedure, enter: 
    dump add_count
  3. To redirect names and values of variables in the current procedure to the var.list file, enter: 
    dump > var.list

See Displaying and Modifying Variables in in AIX General Programming Concepts: Writing and Debugging Programs.

edit Subcommand

edit [ Procedure | File ]

The edit subcommand invokes an editor on the specified file. The file may be specified through the File parameter or by specifying the Procedure parameter, where the editor is invoked on the file containing that procedure. If no file is specified, the editor is invoked on the current source file. The default is the vi editor. Override the default by resetting the EDITOR environment variable to the name of the desired editor.

Examples
  1. To start an editor on the current source file, enter: 
    edit
  2. To start an editor on the main.c file, enter: 
    edit main.c
  3. To start an editor on the file containing the do_count() procedure, enter: 
    edit do_count

See the list subcommand, the vi or vedit command. Also, see Changing the Current File or Procedure and Displaying the Current File in in AIX General Programming Concepts: Writing and Debugging Programs.

file Subcommand

file [ File ]

The file subcommand changes the current source file to the file specified by the File parameter; it does not write to that file. The File parameter can specify a full path name to the file. If the File parameter does not specify a path, the dbx program tries to find the file by searching the use path. If the File parameter is not specified, the file subcommand displays the name of the current source file. The file subcommand also displays the full or relative path name of the file if the path is known.

Examples
  1. To change the current source file to the main.c file, enter: 
    file main.c
  2. To display the name of the current source file, enter: 
    file

See the func subcommand. Also, see Changing the Current File or Procedure and Displaying the Current File in in AIX General Programming Concepts: Writing and Debugging Programs.

func Subcommand

func [ Procedure ]

The func subcommand changes the current function to the procedure or function specified by the Procedure parameter. If the Procedure parameter is not specified, the default current function is displayed. Changing the current function implicitly changes the current source file to the file containing the new function; the current scope used for name resolution is also changed.

Examples
  1. To change the current function to the do_count procedure, enter: 
    func do_count
  2. To display the name of the current function, enter: 
    func

See the file subcommand. Also, see Changing the Current File or Procedure in in AIX General Programming Concepts: Writing and Debugging Programs.

goto Subcommand

goto SourceLine

The goto subcommand causes the specified source line to be run next. Normally, the source line must be in the same function as the current source line. To override this restriction, use the set subcommand with the $unsafegoto flag.

Example

To change the next line to be executed to line 6, enter:

goto 6

See the cont subcommand, the gotoi subcommand, and the set subcommand.

gotoi Subcommand

gotoi Address

The gotoi subcommand changes the program counter address to the address specified by the Address parameter.

Example

To change the program counter address to address 0x100002b4 , enter:

gotoi 0x100002b4

See the goto subcommand.

help Subcommand

help [ Subcommand | Topic ]

The help subcommand displays help information for dbx subcommands or topics, depending upon the parameter you specify. Entering the help subcommand with the Subcommand parameter displays the syntax statement and description of the specified subcommand. Entering the help subcommand with the Topic parameter displays a detailed description of the specified topic. The following topics are available:

startup Lists dbx startup options.
execution Lists dbx subcommands related to program execution.
breakpoints Lists dbx subcommands related to breakpoints and traces.
files Lists dbx subcommands for accessing source files.
data Lists dbx subcommands for accessing program variables and data.
machine Lists descriptions of dbx subcommands for machine-level debugging.
environment Lists dbx subcommands for setting dbx configuration and environment.
threads Lists dbx subcommands for accessing thread-related objects.
expressions Describes dbx expression syntax and operators.
scope Describes how dbx resolves names from different scopes.
set_variables Lists dbx debug variables with a usage description.
usage Lists common dbx subcommands with brief descriptions.
Examples
  1. To list all available dbx subcommands and topics, enter: 
    help
  2. To display the description of the dbx subcommand list, enter: 
    help list
  3. To display the description of the dbx topic set_variables, enter: 
    help set_variables

ignore Subcommand

ignore [ SignalNumber | SignalName ]

The ignore subcommand stops the trapping of a specified signal before that signal is sent to the application program. This subcommand is useful when the application program being debugged handles signals such as interrupts.

The signal to be trapped can be specified by:

Signal names are not case sensitive. The SIG prefix is optional.

If neither the SignalNumber nor the SignalName parameter is specified, all signals except the SIGHUP, SIGCLD, SIGALRM, and SIGKILL signals are trapped by default. The dbx debug program cannot ignore the SIGTRAP signal if it comes from a process outside of the debugee. If no arguments are specified, the list of currently ignored signals will be displayed.

Example

To cause dbx to ignore alarm clock time-out signals sent to the application program, enter:

ignore alrm

See the catch subcommand. Also, see Handling Signals in in AIX General Programming Concepts: Writing and Debugging Programs.

list Subcommand

list [ Procedure | SourceLine-Expression [ ,SourceLine-Expression ] ]

The list subcommand displays a specified number of lines of the source file. The number of lines displayed are specified in one of two ways:

In this case, the list subcommand displays lines starting a few lines before the beginning of the specified procedure and until the list window is filled.

The SourceLine-Expression parameter should consist of a valid line number followed by an optional + (plus sign), or - (minus sign), and an integer. In addition, a SourceLine of $ (dollar sign) may be used to denote the current line number; a SourceLine of @ (at sign) may be used to denote the next line number to be listed.

All lines from the first line number specified to the second line number specified, inclusive, are then displayed.

If the second source line is omitted, the first line is printed only.

If the list subcommand is used without parameters, the number of lines specified by $listwindow are printed, beginning with the current source line.

To change the number of lines to list by default, set the special debug program variable, $listwindow, to the number of lines you want. Initially, $listwindow is set to 10.

Examples
  1. To list the lines 1 through 10 in the current file, enter: 
    list 1,10
  2. To list 10 , or $listwindow , lines around the main procedure, enter: 
    list main
  3. To list 11 lines around the current line, enter: 
    list $-5,$+5
  4. You can use simple integer expressions involving addition and subtraction in SourceLineExpression expressions. For example: 
    (dbx) list $
4 {
    (dbx) list 5
5 char i = '4';
    (dbx) list sub
23 char *sub(s,a,k)
24 int a;
25 enum status k;  .  .  .  
    (dbx) move 
25
(dbx) list @ -2
23 char *sub(s,a,k)

See the edit subcommand, the listi subcommand, and the move subcommand. Also, see Displaying the Current File in in AIX General Programming Concepts: Writing and Debugging Programs.

listi Subcommand

listi [ Procedure | at SourceLine | Address [ , Address ] ]

The listi subcommand displays a specified set of instructions from the source file. The instructions displayed are specified by:

If the listi subcommand is used without flags or parameters, the next $listwindow instructions are displayed. To change the current size of the list window, use the set $listwindow=Value subcommand.

Disassembly Modes

The dbx program can disassemble instructions for either the POWER or PowerPC architecture. In the default mode, the dbx program displays the instructions for the architecture on which it is running.

The $instructionset and $mnemonics variables of the set subcommand for the dbx command allow you to override the default disassembly mode. For more information, see the set subcommand for the dbx command.

Flag
at SourceLine Specifies a starting source line for the listing.
Examples
  1. To list the next 10, or $listwindow , instructions, enter: 
    listi
  2. To list the machine instructions beginning at source line 10 , enter: 
    listi at 10
  3. To list the machine instructions beginning at source line 5 in file sample.c , enter: 
    listi at "sample.c":5
  4. To list the instructions between addresses 0x10000400 and 0x10000420 , enter: 
    listi 0x10000400, 0x10000420

See the list subcommand and the set subcommand. Also, see Debugging at the Machine Level with dbx in in AIX General Programming Concepts: Writing and Debugging Programs.

map Subcommand

map [ > File ]

The map subcommand displays characteristics for each loaded portion of the application. This information includes the name, text origin, text length, data origin, and data length for each loaded module.

Flag
> File Redirects output to the specified file.

See Debugging at the Machine Level with dbx in in AIX General Programming Concepts: Writing and Debugging Programs.

move Subcommand

move SourceLine

The move subcommand changes the next line to be displayed to the line specified by the SourceLine parameter. This subcommand changes the value of the @ (at sign) variable.

The SourceLine variable can be specified as an integer or as a file name string followed by a : (colon) and an integer.

Examples
  1. To change the next line to be listed to line 12 , enter: 
    move 12
  2. To change the next line to be listed to line 5 in file sample.c , enter: 
    move "sample.c":5

See the list subcommand. Also, see Displaying the Current File in in AIX General Programming Concepts: Writing and Debugging Programs.

multproc Subcommand

multproc [ on | parent | child | off ]

The multproc subcommand specifies the behavior of the dbx debug program when forked and execed processes are created. The on flag is used to specify that a new dbx session will be created to debug the child path of a fork. The original dbx will continue to debug the parent path. The parent and child flags are used to specify a single path of a fork to follow. All flags except off enable dbx to follow an execed process. The off flag disables multiprocess debugging. If no flags are specified, the multproc subcommand returns the current status of multiprocess debugging.

The dbx program uses Xwindows for multiprocess debugging. The dbx program opens as many windows as needed for multiprocessing. The title for each child window is the process ID (pid) of the child process. To switch between processes, use Xwindows handling techniques to activate the window where the dbx session is displayed. If the system does not have Xwindows support, a warning message is issued when the debuggee forks, and the dbx program continues debugging only the parent process. Multiprocess debugging can also be unsuccessful for the following reasons:

If $xdisplay is set to a remote display, the user may not be able to see the newly created Xwindow. If the $xdisplay setting is not correct, Xwindows or other system resources report the cause of the failure.

The dbx program does not distinguish between different types of failures, but the following message is sent when the subcommand is not successful:

Warning: dbx subcommand multiproc fails. dbx 
continued with multproc disabled.

The user-defined configuration of the newly created window can be defined under the dbx_term application name in the .Xdefaults file.

Flags
on Enables multiprocess debugging.
off Disables multiprocess debugging.
Examples
  1. To check the current status of multiprocess debugging, enter: 
    multproc
  2. To enable multiprocess debugging, enter: 
    multproc on
  3. To disable multiprocess debugging, enter: 
    multproc off

See the screen subcommand and the fork subroutine. Also, see Debugging Programs Involving Multiple Processes in in AIX General Programming Concepts: Writing and Debugging Programs.

mutex Subcommand

mutex [ lock | unlock | thnum | utid |  MutexNumber ... ]

The mutex subcommand displays information about mutexes. If the MutexNumber parameter is given, the mutex subcommand displays information about the specified mutexes. If no flags or parameters are specified, the mutex subcommand displays information about all mutexes.

The information listed for each mutex is as follows:

mutex Indicates the symbolic name of the mutex, in the form $m MutexNumber.
type Indicates the type of the mutex: non-rec (non recursive), recursi (recursive) or fast .
obj_addr Indicates the memory address of the mutex.
lock Indicates the lock state of the mutex: yes if the mutex is locked, no if not.
owner If the mutex is locked, indicates the symbolic name of the user thread which holds the mutex.
blockers List the user threads which are blocked on this mutex variable.
Note: The print subcommand of the dbx debug program recognizes symbolic mutex names, and can be used to display the status of the corresponding object.
Flags
lock Displays information about locked mutexes.
unlock Displays information about unlocked mutexes.
thnum Displays information about all the mutexes held by a particular thread.
utid Displays information about all the mutexes held by a user thread whose user thread id matches the given user thread id.
Examples
  1. To display information about all mutexes, enter: 
    mutex
  2. To display information about all locked mutexes, enter: 
    mutex lock
  3. To display information about mutexes number four, five and six enter: 
    mutex 4 5 6
    The output is similar to: 
    mutex   obj_addr         type     lock owner  blockers
$m4    0x20003274        non-rec   no
$m5    0x20003280        recursi   no
$m6    0x2000328a        fast      no
  4. To display information about all the mutexes held by thread 1, enter:
    mutex thnum 1
  5. To display information about all the mutexes held by a thread whose user thread id is 0x0001, enter: 
    mutex utid 0x0001

See the attribute subcommand, the condition subcommand, the print subcommand, and the thread subcommand.

Also, see. Using Mutexes in AIX Version 4.3 General Programming Concepts: Writing and Debugging Programs.

next Subcommand

next [ Number ]

The next subcommand runs the application program up to the next source line. The Number parameter specifies the number of times the next subcommand runs. If the Number parameter is not specified, next runs once only.

If you use the next subcommand in a multi-threaded application program, all the user threads run during the operation, but the program continues execution until the running thread reaches the specified source line. If you wish to step the running thread only, use the set subcommand to set the variable $hold_next. Setting this variable may result in deadlock since the running thread may wait for a lock held by one of the blocked threads.

Examples
  1. To continue execution up to the next source line, enter: 
    next
  2. To continue execution up to the third source line following the current source line, enter: 
    next 3

See the cont subcommand, goto subcommand, nexti subcommand, set subcommand, and the step subcommand.

nexti Subcommand

nexti [ Number ]

The nexti subcommand runs the application program up to the next instruction. The Number parameter specifies the number of times the nexti subcommand will run. If the Number parameter is not specified, nexti runs once only.

If you use the nexti subcommand in a multi-threaded application program, all the user threads run during the operation, but the program continues execution until the running thread reaches the specified machine instruction. If you wish to step the running thread only, use the set subcommand to set the variable $hold_next. Setting this variable may result in deadlock since the running thread may wait for a lock held by one of the blocked threads.

Examples
  1. To continue execution up to the next machine instruction, enter: 
    nexti
  2. To continue execution up to the third machine instruction following the current machine instruction, enter: 
    nexti 3

See the gotoi subcommand, next subcommand, set subcommand, and stepi subcommand. Also, see Running a Program at the Machine Level in in AIX General Programming Concepts: Writing and Debugging Programs.

print Subcommand

print Expression ...

print Procedure ( [ Parameters ] )

The print subcommand does either of the following:

Examples
  1. To display the value of x and the value of y shifted left two bits, enter: 
    print x, y << 2
  2. To display the value returned by calling the sbrk routine with an argument of 0, enter: 
    print sbrk(0)

See the assign subcommand, the call subcommand, and the set subcommand.

prompt Subcommand

prompt [ "String" ]

The prompt subcommand changes the dbx command prompt to the string specified by the String parameter.

Example

To change the prompt to dbx> , enter:

prompt "dbx>"

See Defining a New dbx Prompt in in AIX General Programming Concepts: Writing and Debugging Programs.

quit Subcommand

quit

The quit subcommand terminates all processes running in the dbx debugging session.

See the detach subcommand.

registers Subcommand

registers [ >File ]

The registers subcommand displays the values of general purpose registers, system control registers, floating-point registers, and the current instruction register.

Note: The registers subcommand cannot display registers if the current thread is in kernel mode.
Flag
>File Redirects output to the specified file.

See the set subcommand and the unset subcommand. Also, see Using Machine Registers in in AIX General Programming Concepts: Writing and Debugging Programs.

rerun Subcommand

rerun [ Arguments ] [ < File ] [ > File ] [ > > File ] [ 2> File ] [ 2> > File ] [ >& File ] [ > >& File ]

The rerun subcommand begins execution of the object file. The Arguments are passed as command line arguments. If the Arguments parameter is not specified, the arguments from the last run or rerun subcommand are reused.

Flags
<File Redirects input so that input is received from File.
>File Redirects output to File.
> >File Appends redirected output to File.
2>File Redirects standard error to File.
2> >File Appends redirected standard error to File.
>&File Redirects output and standard error to File.
> >&File Appends output and standard error to File.

See the run subcommand.

return Subcommand

return [ Procedure ]

The return subcommand causes the application program to execute until a return to the procedure specified by the Procedure parameter is reached. If the Procedure parameter is not specified, execution ceases when the current procedure returns.

Examples
  1. To continue execution to the calling routine, enter: 
    return
  2. To continue execution to the main procedure, enter: 
    return main

rwlock Subcommand

rwlock [read | write | RwlockNumber....]

The rwlock subcommand displays information about rwlocks. If the RwlockNumber parameter is given, the rwlock subcommand displays information about the specified rwlocks. If no flags or parameters are specified, the rwlock subcommand displays information about all rwlocks.

The information for each rwlock is as follows:

rwl Indicates the symbolic name of the rwlock, in the form $rw RwlockNumber.
flag_value Indicates the flag value.
owner Indicates the owner of the rwlock
status Indicates who is holding the rwlock. The values are read (if held by reader), write (if held by writer), free (if free).
wsleep[#] Indicates threads blocking in write. # indicates the total number of threads blocking in write.
rsleep[#] Indicates threads blocking in read. # indicates the total number of threads blocking in read.
Note: The print subcommand of the dbx debug program recognizes symbolic rwlock names, and can be used to display the status of the corresponding object
Flags
read Displays information about all rwlocks whose status is in read mode.
write Displays information about all rwlocks whose status is in write mode.
Examples
  1. To display information about all rwlocks, enter: 
    rwlock

    The output is similar to:

    rwl     flag_value    owner status
$rwl        1         $t1    write
        rsleeps[     0]:
        wsleeps[     0]:
  2. To display information about all rwlocks in write mode: 
    rwlock write

    The output is similar to:

    rwl     flag_value    owner status
$rwl        1         $t1    write
        rsleeps[     0]:
        wsleeps[     0]:

See the attribute subcommand, the condition subcommand, mutex subcommand, the print subcommand, and the thread subcommand

run Subcommand

run [ Arguments ] [ <File ] [ >File ] [ > >File ] [ 2>File ] [ 2> >File ] [ >&File ] [ > >&File ]

The run subcommand starts the object file. The Arguments are passed as command line arguments.

Flags
<File Redirects input so that input is received from File.
>File Redirects output to File.
2>File Redirects standard error to File.
> >File Appends redirected output to File.
2> >File Appends redirected standard error to File.
>&File Redirects output and standard error to File.
> >&File Appends output and standard error to File.
Example

To run the application with the arguments blue and 12 , enter:

run blue 12

See the rerun subcommand.

screen Subcommand

screen

The screen subcommand opens an Xwindow for the dbx command interaction. You continue to operate in the window in which the process originated.

The screen subcommand must be run while the dbx debug program is running in an Xwindows environment. If the screen subcommand is issued in a non-Xwindow environment, the dbx program displays a warning message and resumes debugging as if the screen subcommand had not been given. The screen subcommand can also be unsuccessful in the following situations:

The dbx program does not distinguish between different types of failures, but the program does send the following message:

Warning: dbx subcommand screen fails. dbx 
continues.

If $xdisplay is set to a remote display, the user may not be able to see the newly created Xwindow. If the $xdisplay setting is not correct, Xwindows or other system resources report the problem.

The user-defined configuration of the newly created window can be defined under the dbx_term application name in the .Xdefaults file.

Example

To open an Xwindow for dbx command interaction, enter:

screen

See Separating dbx Output From Program Output in in AIX General Programming Concepts: Writing and Debugging Programs and AIXwindows Overview, in AIX Version 4 AIXwindows Programming Guide.

set Subcommand

set [ Variable=Expression ]

The set subcommand defines a value for the dbx debug program variable. The value is specified by the Expression parameter; the program variable is specified by the Variable parameter. The name of the variable should not conflict with names in the program being debugged. A variable is expanded to the corresponding expression within other commands. If the set subcommand is used without arguments, the variables currently set are displayed.

The following variables are set with the set subcommand:

$catchbp Catches breakpoints during the execution of the next command.
$expandunions Displays values for each part of variant records or unions.
$frame Uses the stack frame pointed to by the address designated by the value of $frame for doing stack traces and accessing local variables.
$hexchars Prints characters as hexadecimal values.
$hexin Interprets addresses in hexadecimal.
$hexints Prints integers as hexadecimal values.
$hexstrings Prints character pointers in hexadecimal.
$hold_next Holds all threads except the running thread during the cont, next, nexti, and step subcommands. Setting this variable may result in deadlock since the running thread may wait for a lock held by one of the blocked threads.
$ignoreload Does not stop when your program performs the load, unload, or loadbind subroutine.
$instructionset Overrides the default disassembly mode. The following list contains possible values for the Expression parameter:
"default" Specifies the architecture on which the dbx program is running.
"com" Specifies the instruction set for the common intersection mode of the PowerPC and POWER architectures. The dbx program defaults to PowerPC mnemonics.
"pwr" Specifies the instruction set and mnemonics for the POWER architecture.
"pwrx" Specifies the instruction set and mnemonics for the POWER2 implementation of the POWER architecture.
"601" Specifies the instruction set and mnemonics for the PowerPC 601 RISC Microprocessor.
"603" Specifies the instruction set and mnemonics for the PowerPC 603 RISC Microprocessor.
"604" Specifies the instruction set and mnemonics for the PowerPC 604 RISC Microprocessor.
"ppc" Specifies the instruction set and mnemonics defined in the PowerPC architecture, excluding the optional instructions. These instructions are available in all PowerPC implementations except the PowerPC 601 RISC Microprocessor.
"any" Specifies any valid PowerPC or POWER instruction. For instruction sets that overlap, the default is the PowerPC mnemonics.

If no value is set for the Expression parameter, the dbx program uses the default disassembly mode.

$listwindow Specifies the number of lines to list around a function and the number to list when the list subcommand is used without parameters. The default is 10 lines.
$mapaddrs Starts mapping addresses. Unsetting $mapaddrs stops address mapping.
$mnemonics Changes the set of mnemonics to be used by the dbx program when disassembling.
"default" Specifies the mnemonics that most closely match the specified instruction set.
"pwr" Specifies the mnemonics for the POWER architecture.
"ppc" Specifies the mnemonics defined in the PowerPC architecture book, excluding the optional instructions.

If no value is set for the Expression parameter, the dbx program will use the mnemonics that most closely match the specified instruction set.

$noargs Omits arguments from subcommands, such as where, up, down, and dump.
$noflregs Omits the display of floating-point registers from the registers subcommand.
$octin Interprets addresses in octal.
$octints Prints integers in octal.
$repeat Repeats the previous command if no command was entered.
$sigblock Blocks signals to your program.
$stepignore Controls how the dbx command behaves when the step subcommand runs on a source line that calls another routine for which no debugging information is available. This variable enables the step subcommand to step over large routines for which no debugging information is available. The following list contains possible values for the Expression parameter:
"function" Performs the function of the next subcommand for the dbx command. This is the default value.
"module" Performs the function of the next subcommand if the function is in a load module for which no debug information is available (such as a system library).
"none" Performs the function of the stepi subcommand for the dbx command in the background until it reaches an instruction for which source information is available. At that point dbx will display where execution has stopped.
$thcomp When $thcomp is set, the information displayed by the thread command th- is shown in a compressed format.
$unsafeassign Turns off strict type checking between the two sides of an assign statement. Even if the $unsafeassign variable is set, the two sides of an assign statement may not contain storage types of different sizes.
$unsafebounds Turns off subscript checking on arrays.
$unsafecall Turns off strict type checking for arguments to subroutines or function calls.
$unsafegoto Turns off the goto subcommand destination checking.
$vardim Specifies the dimension length to use when printing arrays with unknown bounds. The default value is 10.
$xdisplay Specifies the display name for Xwindows, for use with the multproc subcommand or the screen subcommand. The default is the value of the shell DISPLAY variable.

The $unsafe variables limit the usefulness of the dbx debug program in detecting errors.

Examples
  1. To change the default number of lines to be listed to 20 , enter: 
    set $listwindow=20
  2. To disable type checking on the assign subcommand, enter: 
    set $unsafeassign
  3. To disassemble machine instructions for the PowerPC 601 RISC Microprocessor, enter: 
    set $instructionset="601"

See the unset subcommand. Also, see Changing Print Output with Special Debug Program Variables in in AIX General Programming Concepts: Writing and Debugging Programs.

set edit [vi, emacs] or set -o [vi, emacs] Subcommand

The set subcommand with the -o or edit option may be used to turn on one of the line edit modes. If the set-o vi or set edit vi command is given, you are placed in the input mode of the vi line editor. If the set -o emacs or set edit emacs command is given, you are placed in the input mode of the emacs line editor.

Example
  1. To turn on the vi line editor, enter: 
    set-o vi

    or

    set edit vi

sh Subcommand

sh [ Command ]

The sh subcommand passes the command specified by the Command parameter to the shell for execution. The SHELL environment variable determines which shell is used. The default is the sh shell. If no argument is specified, control is transferred to the shell.

Examples
  1. To run the ls command, enter: 
    sh ls
  2. To escape to a shell, enter: 
    sh
  3. To use the SHELL environment variable, enter: 
    sh echo $SHELL

See Running Shell Commands from dbx in in AIX General Programming Concepts: Writing and Debugging Programs.

skip Subcommand

skip [ Number ]

The skip subcommand continues execution of the application program from the current stopping point. A number of breakpoints equal to the value of the Number parameter are skipped and execution then ceases when the next breakpoint is reached or when the program finishes. If the Number parameter is not specified, it defaults to a value of one.

Example

To continue execution until the second breakpoint is encountered, enter:

skip 1

Also see the cont subcommand.

source Subcommand

source File

The source subcommand reads dbx subcommands from the file specified by the File parameter.

Example

To read the dbx subcommands in the cmdfile file, enter:

source cmdfile

See Reading dbx Subcommands from a File in in AIX General Programming Concepts: Writing and Debugging Programs.

status Subcommand

status [ >File ]

The status subcommand displays the trace and stop subcommands currently active. The > flag sends the output of the status subcommand to a file specified in the File parameter.

Flag
>File Redirects output to File.

See the clear subcommand, the delete subcommand, the stop subcommand, and the trace subcommand for the dbx command.

Also, see Setting and Deleting Breakpoints in in AIX General Programming Concepts: Writing and Debugging Programs.

step Subcommand

step [ Number ]

The step subcommand runs source lines of the application program. Specify the number of lines to be executed with the Number parameter. If the Number parameter is omitted, it defaults to a value of 1.

If you use the step subcommand on a multi-threaded application program, all the user threads run during the operation, but the program continues execution until the running thread reaches the specified source line. If you wish to step the running thread only, use the set subcommand to set the variable $hold_next. Setting this variable may result in deadlock since the running thread may wait for a lock held by one of the blocked threads.

Note: Use the $stepignore variable of the set subcommand to control the behavior of the step subcommand. The $stepignore variable enables the step subcommand to step over large routines for which no debugging information is available.
Examples
  1. To continue execution for one source line, enter: 
    step
  2. To continue execution for five source lines, enter: 
    step 5
  3. To prevent the dbx program from single-stepping the printf function, as illustrated in the following example code: 
    60 printf ("hello world \n");

    enter:

    set $stepignore="function"; step

See the cont subcommand, the goto subcommand , the next subcommand, the set subcommand, and the stepi subcommand.

stepi Subcommand

stepi [ Number ]

The stepi subcommand runs instructions of the application program. Specify the number of instructions to be executed in the Number parameter. If the Number parameter is omitted, it defaults to one.

If used on a multi-threaded application program, the stepi subcommand steps the running thread only. All other user threads remain stopped.

Examples
  1. To continue execution for one machine instruction, enter: 
    stepi
  2. To continue execution for 5 machine instructions, enter: 
    stepi 5

See the gotoi subcommand, the nexti subcommand, and the step subcommand.

stop Subcommand

stop { [Variable] [at SourceLine | in Procedure ] [ if Condition ]}

The stop subcommand halts the application program when certain conditions are fulfilled. The program is stopped when:

After any of these commands, the dbx debug program responds with a message reporting the event it has built as a result of your command. The message includes the event ID associated with your breakpoint along with an interpretation of your command. The syntax of the interpretation might not be exactly the same as your command. For example:

stop in main
[1] stop in main
stop at 19 if x == 3
[2] stop at "hello.c":19 if x = 3

The numbers in brackets are the event identifiers associated with the breakpoints. The dbx debug program associates event numbers with each stop subcommand. When the program is halted as the result of one of the events, the event identifier is displayed along with the current line to show what event caused the program to stop. The events you create coexist with internal events created by dbx, so event numbers may not always be sequential.

Use the status subcommand to view these numbers. You can redirect output from status to a file. Use the delete or clear subcommand to turn the stop subcommand off.

In a multi-threaded application program, all user threads are halted when any user thread hits a breakpoint. A breakpoint set on a source line or function will be hit by any user thread which executes the line or function, unless you specify conditions as shown in example 9 below. The following aliases specify the conditions automatically:

ThreadNumber is the number part of the symbolic thread name as reported by the thread subcommand (for example, 5 is the ThreadNumber for the thread name $t5). These aliases are actually macros which produce the expanded subcommands shown below:

stopi at &Function    if ($running_thread == 
ThreadNumber)
stop at SourceLine  if ($running_thread == ThreadNumber)
Flags
at SourceLine Specifies the line number.
if Condition Specifies the condition, such as true.
in Procedure Specifies the procedure to be called.
Examples
  1. To stop execution at the first statement in the main procedure, enter: 
    stop in main
  2. To stop execution when the value of the x variable is changed on line 12 of the execution, enter: 
    stop x at 12
  3. To stop execution at line 5 in file sample.c , enter: 
    stop at "sample.c":5
  4. To check the value of x each time that dbx runs a subroutine within func1 , enter: 
    stop in func1 if x = 22
  5. To check the value of x each time that dbx begins to run func1 , enter: 
    stopi at &func1 if x = 22
  6. To stop the program when the value of Variable changes, enter: 
    stop Variable
  7. To stop the program whenever Condition evaluates to true, enter: 
    stop if (x > y) and (x < 2000)
  8. The following example shows how to display active events and remove them: 
    status
[1] stop in main
[2] stop at "hello.c":19 if x = 3
delete 1
status
[2] stop at "hello.c":19 if x = 3
clear 19
status
(dbx)
    The delete command eliminates events by event identifier. The clear command deletes breakpoints by line number.
  9. To place a breakpoint at the start of func1 only when executed by thread $t5 , enter one of the following equivalent commands: 
    stopi at &func1 if ($running_thread == 5)
    or 
    bfth(func1, 5)

See the clear subcommand, the delete subcommand, the stopi subcommand, and the trace subcommand. Also, see Setting and Deleting Breakpoints in in AIX General Programming Concepts: Writing and Debugging Programs.

stopi Subcommand

stopi { [Address] [at Address | in Procedure ] [ if Condition ]}

The stopi subcommand sets a stop at the specified location:

Flags
if Condition Specifies the condition, such as true.
in Procedure Specifies the procedure to be called.
at Address Specifies the machine instruction address.
Examples
  1. To stop execution at address 0x100020f0 , enter: 
    stopi at 0x100020f0
  2. To stop execution when the contents of address 0x100020f0 change, enter: 
    stopi 0x100020f0
  3. To stop execution when the contents of address 0x100020f0 are changed by thread $t1 , enter: 
    stopi 0x200020f0 if ($running_thread == 1)

See the stop subcommand . Also, see Debugging at the Machine Level with dbx in in AIX General Programming Concepts: Writing and Debugging Programs.

thread Subcommand

Display Selected Threads

thread { [ info ] [ - ] [ ThreadNumber ... ] } | current | run | susp | term | wait

Select an Individual Thread

thread current [ - ] ThreadNumber

Hold or Release Threads

thread { hold | unhold } [ - ] [ ThreadNumber ... ]

Help for the options displayed

thread {help}

The thread subcommand displays and controls user threads.

The first form of the thread subcommand can display information in two formats. If the thread subcommand is th, then the information displayed is in the first format. If the thread subcommand is th -, then the information displayed is in the second format. If no parameters are given, information about all user threads is displayed. If one or more ThreadNumber parameters are given, information about the corresponding user threads is displayed. When the thread subcommand displays threads, the current thread line is preceded by a >. If the running thread is not the same as the current thread, its line is preceded by a *. The information displayed by the thread subcommand in both the formats is described below.

The information displayed by the thread subcommand in the first format is as follows:

thread Indicates the symbolic name of the user thread, in the form $t ThreadNumber.
state-k Indicates the state of the kernel thread (if the user thread is attached to a kernel thread). This can be run , wait , susp , or term , for running, waiting, suspended, or terminated.
wchan Indicates the event on which the kernel thread is waiting or sleeping (if the user thread is attached to a kernel thread).
state-u Indicates the state of the user thread. Possible states are running , blocked , or terminated .
k-tid Indicates the kernel thread identifier (if the user thread is attached to a kernel thread).
mode Indicates the mode (kernel or user) in which the user thread is stopped (if the user thread is attached to a kernel thread).
held Indicates whether the user thread has been held.
scope Indicates the contention scope of the user thread; this can be sys or pro for system or process contention scope.
function Indicates the name of the user thread function.

The information displayed by the thread subcommand in the second format is given below. By default, for the thread subcommand th -, the information is displayed in the long form.

thread Indicates the symbolic name of the user thread, in the form $t ThreadNumber.

Kernel thread related information

tid Indicates the user thread identifier (if the user thread is attached to a kernel thread).
pri Indicates the priority of the kernel thread.
sched Indicates the scheduling policy of the kernel thread. This can be fif, oth, rr, for fifo, other, or round robin scheduling policies.
state Indicates the state of the kernel thread (if the user thread is attached to a kernel thread). This can be run, wait, susp, or zomb, for running, waiting, suspended, or zombie.

User thread related information

tid Indicates the user thread identifier.
pri Indicates the priority of the userl thread.
sched Indicates the scheduling policy of the user thread. This can be fif, oth, rr, for fifo, other, or round robin scheduling policies.
state Indicates the state of the user thread. This can be running, creating, suspended, blocked, runnable, or terminated.
state Indicates the user state in hex.
flags Indicates the values for pthread flags in hex.
wchan Indicates the event on which the kernel thread is waiting or sleeping (if the user thread is attached to a kernel thread).
mode Indicates the mode (kernel or user) in which the user thread is stopped (if the user thread is attached to a kernel thread).
held Indicates whether the user thread has been held.
scope Indicates the contention scope of the user thread; this can be sys or pro for system or process contention scope.
cancellation
pending Indicates if cancellation is pending or not.
state Indicates the mode and state of cancellation.

If the cancellation is not pending and the state and mode are enabled and deferred respectively, then it is represented by ed, if cancellation state and mode is enabled and asynchronous, then it is represented by ea, and if mode is not enabled, then it is represented by d.

If the cancellation is pending and the cancellation state and mode is enabled and deferred respectively, then it is represented by ED, if cancellation state and mode is enabled and asynchronous, then it is represented by EA, and if mode is not enabled, then it is represented by D.

joinable Indicates whether the thread is joinable or not.
boosted Indicates the boosted value of the thread.
function Indicates the name of the user thread function.
cursig Indicates the current signal value.

If the option set $thcomp is set, then the information is displayed in the compressed form as shown below. 

m           mode           (k)ernel (u)ser
k           k-state        (r)unning (w)aiting (s)uspended (z)ombie
u           u-state        (r)unning (R)unnable (s)uspended (t)erminated

                           (b)locked (c)reating
h           held           (yes) (n)o
s           scope          (s)ystem (p)rocess
c           cancellation   not pending:  (e)nabled & (d)eferred,
                                         (e)nabled & (a)sync, (d)isabled
                           pending    :  (E)nabled & (D)eferred,
                                         (E)nabled & (A)sync, (D)isabled
j           joinable       (yes) (n)o
b           boosted        value of boosted field in pthread structure
plk         kernel thread  (oth)er  (fif)o  (rr)-> round-robin
            policy
plu         user thread    (oth)er  (fif)o  (rr)-> round-robin
            policy
prk         kernel thread  hex number
            policy
pru         user thread    hex number
            policy
k-tid                      kernel thread id in hex
u-tid                      pthread id in hex
fl                         value of flags field in pthread structure in hex
sta                        value of state field in pthread structure in hex
cs                         value of the current signal
wchan                      event for which thread is waiting
function                   function name

The second form of the thread subcommand is used to select the current thread. The print, registers, and where subcommands of the dbx debug program all work in the context of the current thread. The registers subcommand cannot display registers if the current thread is in kernel mode.

The third form of the thread subcommand is used to control thread execution. Threads can be held using the hold flag, or released using the unhold flag. A held thread will not be resumed until it is released.

Note: The print subcommand of the dbx debug program recognizes symbolic thread names, and can be used to display the status of the corresponding object.
Flags
current If the ThreadNumber parameter is not given, displays the current thread. If the ThreadNumber parameter is given, selects the specified user thread as the current thread.
help Displays all the information about the thread options that are shown when th - command is used.
hold If the ThreadNumber parameter is not given, holds and displays all user threads. If one or more ThreadNumber parameters are given, holds and displays the specified user threads.
unhold If the ThreadNumber parameter is not given, releases and displays all previously held user threads. If one or more ThreadNumber parameters are given, releases and displays the specified user threads.
info If the ThreadNumber parameter is not given, displays a long format listing of all user threads. If one or more ThreadNumber parameters are given, displays a long format listing the specified user threads.

All the above flags take [-] option. If this option is given, then the thread information displayed is in the second format and in the long form unless the set $thcomp option is set.

run Displays threads which are in the run state.
susp Displays threads which are in the susp state.
term Displays threads which are in the term state.
wait Displays threads which are in the wait state.
Examples
  1. To display information about threads that are in the wait state, enter: 
    thread wait
    The output is similar to: 
    thread  state-k   wchan state-u   k-tid mode held scope function 
 $t1     wait            running   17381   u   no   pro  main
 $t3     wait            running    8169   u   no   pro  iothread
  2. To display information about several given threads, enter: 
    thread 1 3 4
    The output is similar to: 
    thread  state-k   wchan state-u   k-tid mode held scope function
 $t1     wait           running   17381   u   no   pro  main
 $t3     wait           running    8169   u   no   pro  iothread
>$t4     run            running    9669   u   no   pro  save_thr
  3. To make thread 4 the current thread, enter: 
    thread current 4
  4. To hold thread number 2, enter: 
    thread hold 2
  5. To display information about threads that are in the wait state, in the second format, enter: 
    thread wait -

    The output is similar to:

    thread m k u h s c  j b  kpl  upl  kpr upr k_tid   u_tid   fl  sta wchan  function
*$t1   u r w n p ed y 0  oth  oth  61   1  0043e5  000001  51  004        main
 $t3   u r w n p ed y 0  oth  oth  61   1  001fe9  000102  51  004        iothread
>$t4   u r r n p ed y 0  oth  oth  61   1  0025c5  000203  50  064        save_thr
  6. To display information about several given threads in the second format, enter: 
    thread - 1 2 3

    The output is similar to:

    thread m k u h s c  j b  kpl  upl  kpr upr k_tid   u_tid   fl  sta wchan function
*$t1   u r w n p ed y 0  oth  oth  61   1  0043e5  000001  51  004       main
 $t3   u r w n p ed y 0  oth  oth  61   1  00fe9   000102  51  004       iothread
>$t4   u r r n p ed y 0  oth  oth  61   1  0025c5  000203  50  064       save_thr

See the attribute subcommand, the condition subcommand, the mutex subcommand, the print subcommand, the registers subcommand, and the where subcommand.

Also, see Creating Threads in AIX Version 4.3 General Programming Concepts: Writing and Debugging Programs.

trace Subcommand

trace [ SourceLine | Expression at SourceLine | Procedure | [ Variable ] [ at SourceLine | in Procedure ] ] [ if Condition ]

The trace subcommand prints tracing information for the specified procedure, function, source line, expression, or variable when the program runs. The SourceLine variable can be specified as an integer or as a file name string followed by a : (colon) and an integer. A condition can be specified. The dbx debug program associates a number with each trace subcommand. Use the status subcommand to view these numbers. Use the delete subcommand to turn tracing off.

By default, tracing is process based. In order to make a thread based trace, specify the thread in a condition as shown in example 8 below.

Flags
at SourceLine Specifies the source line where the expression being traced is found.
if Condition Specifies a condition for the beginning of the trace. The trace begins only if Condition is true.
in Procedure Specifies the procedure to use to find the procedure or variable being traced.
Examples
  1. To trace each call to the printf procedure, enter: 
    trace printf
  2. To trace each execution of line 22 in the hello.c file, enter: 
    trace "hello.c":22
  3. To trace changes to the x variable within the main procedure, enter: 
    trace x in main
  4. To trace the data address 0x2004000, enter: 
    set $A=0x2004000
trace $A
    Note: The tracei subcommand is designed to trace addresses.
  5. You can restrict the printing of source lines to when the specified Procedure is active. You can also specify an optional Condition to control when trace information should be produced. For example: 
    (dbx) trace in sub2
[1] trace in sub2
(dbx) run
trace in hellosub.c:  8  printf("%s",s);
trace in hellosub.c:  9  i = '5';
trace in hellosub.c:  10  }
  6. You can display a message each time a procedure is called or returned. When a procedure is called, the information includes passed parameters and the name of the calling routine. On a return, the information includes the return value from Procedure. For example: 
    (dbx) trace sub
[1] trace sub
(dbx) run
calling sub(s = "hello", a = -1, k = delete) from function main
returning "hello" from sub
  7. You can print the value of Expression when the program reaches the specified source line. The lines number and file are printed, but the source line is not. For example: 
    (dbx) trace x*17 at "hellosub.c":8 if (x > 0)
[1] trace x*17 at "hellosub.c":8 if x > 0
(dbx) run
at line 8 in file "hellosub.c": x*17 = 51
 
(dbx) trace x
[1] trace x
initially (at line 4 in "hello.c"):  x = 0
after line 17 in "hello.c":  x = 3
  8. To trace changes to the x variable made by thread $t1 , enter: 
    (dbx) trace x if ($running_thread == 1)

Also, see the tracei subcommand.

tracei Subcommand

tracei [ [ Address ] [ at Address | in Procedure ] | Expression at Address ] [ if Condition ]

The tracei subcommand turns on tracing when:

Flags
at Address Specifies an address. Tracing is enabled when the instruction at this address is run.
if Condition Specifies a condition. Tracing is enabled when this condition is met.
in Procedure Specifies a procedure. Tracing is enabled when this procedure is active.
Examples
  1. To trace each instruction executed, enter: 
    tracei
  2. To trace each time the instruction at address 0x100020f0 is executed, enter: 
    tracei at 0x100020f0
  3. To trace each time the contents of memory location 0x20004020 change while the main procedure is active, enter: 
    tracei 0x20004020 in main
  4. To trace each time the instruction at address 0x100020f0 is executed by thread $t4, enter: 
    tracei at 0x100020f0 if ($running_thread == 4)

See the trace subcommand. Also, see Debugging at the Machine Level with dbx in in AIX General Programming Concepts: Writing and Debugging Programs.

unalias Subcommand

unalias Name

The unalias subcommand removes the alias specified by the Name parameter.

Example

To remove an alias named printx , enter:

unalias printx

See the alias subcommand. Also, see Creating Subcommand Aliases in in AIX General Programming Concepts: Writing and Debugging Programs.

unset Subcommand

unset Name

The unset subcommand deletes the dbx debug program variable associated with the name specified by the Name parameter.

Example

To delete the variable inhibiting the display of floating-point registers, enter:

unset $noflregs

See the set subcommand. Also, see Changing Print Output With Special Debugging Variables in in AIX General Programming Concepts: Writing and Debugging Programs.

up Subcommand

up [ Count ]

The up subcommand moves the current function up the stack Count number of levels. The current function is used for resolving names. The default for the Count parameter is one.

Examples
  1. To move the current function up the stack 2 levels, enter: 
    up 2
  2. To display the current function on the stack, enter: 
    up 0

See the down subcommand. Also, see Changing the Current File or Procedure, Displaying a Stack Trace in in AIX General Programming Concepts: Writing and Debugging Programs.

use Subcommand

use [ Directory ... ]

The use subcommand sets the list of directories to be searched when the dbx debug program looks for source files. If the use subcommand is specified without arguments, the current list of directories to be searched is displayed.

The @ (at-sign) is a special symbol that directs the dbx program to look at the full-path name information in the object file, if it exists. If you have a relative directory called @ to search, you should use ./@ in the search path.

The use subcommand uses the + (plus-sign) to add more directories to the list of directories to be searched. If you have a directory named +, specify the full-path name for the directory (for example, ./+ or /tmp/+).

Examples
  1. To change the list of directories to be searched to the current directory (.), the parent directory (..), and the /tmp directory, enter: 
    use . .. /tmp
  2. To change the list of directories to be searched to the current directory (.), the directory the source file was located in at compilation time (@), and the ../source directory, enter: 
    use . @ ../source
  3. To add the /tmp2 directory to the list of directories to be searched, enter: 
    use + /tmp2

Also, see the edit subcommand and the list subcommand.

whatis Subcommand

whatis Name

The whatis subcommand displays the declaration of Name, where the Name parameter designates a variable, procedure, or function name, optionally qualified with a block name.

Note: Use the whatis subcommand only while running the dbx debug program.
Examples
  1. To display the declaration of the x variable, enter: 
    whatis x
  2. To display the declaration of the main procedure, enter: 
    whatis main
  3. To display the declaration of the x variable within the main function, enter: 
    whatis main.x
  4. To print the declaration of an enumeration, structure, or union tag (or the equivalent in Pascal), use $$TagName : 
    (dbx) whatis $$status
enum $$status { run, create, delete, suspend };

where Subcommand

where [ >File ]

The where subcommand displays a list of active procedures and functions. By using the >File flag, the output of this subcommand can be redirected to the specified file.

Flag
>File Redirects output to the specified file.

See the up subcommand and the down subcommand. Also, see Displaying a Stack Trace in in AIX General Programming Concepts: Writing and Debugging Programs.

whereis Subcommand

whereis Identifier

The whereis subcommand displays the full qualifications of all the symbols whose names match the specified identifier. The order in which the symbols print is not significant.

Examples

To display the qualified names of all symbols named x , enter:

whereis x

Also, see the which subcommand.

which Subcommand

which Identifier

The which subcommand displays the full qualification of the given identifier. The full qualification consists of a list of the outer blocks with which the identifier is associated.

Examples

To display the full qualification of the x symbol, enter:

which x

See the whereis subcommand. Also. seeScoping of Names in in AIX General Programming Concepts: Writing and Debugging Programs.

Files

a.out Object file; contains object code.
core Contains core dump.
.dbxinit Contains initial commands.

Related Information

The adb command, cc command.

The a.out file, core file.

The dbx Symbolic Debug Program Overview and Using the dbx Debug Program in AIX General Programming Concepts: Writing and Debugging Programs.

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