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dbx(1) [osf1 man page]

dbx(1)							      General Commands Manual							    dbx(1)

NAME
dbx - source level debugger SYNOPSIS
dbx [-I dir] [-c file] [-k] [-i] [-r] [-pid xxx] [object [core]] OPTIONS
The dbx debugger accepts the following options: Selects a command file other than Invokes dbx in interactive mode. This option causes the debugger to not treat source lines beginning with number signs (#) as comments. Adds dir to the list of directories that dbx searches for source files. By default, dbx searches the current directory and the directory where object is located. You can specify multiple directo- ries by using multiple -I options. Maps memory addresses. This option is useful for kernel debugging. For information on kernel debug- ging, see the Kernel Debugging manual. Specifies the directory path where dbx should search for shared libraries (or loadable kernel mod- ules). This option is useful if, for example, you are debugging a core dump (or a kernel crash dump) and the version of a shared library (or module) that was running when the dump occurred has been moved to a different location. Using this option automatically sets the $mod- ule_path dbx variable to the specified path. If dbx cannot find a file in the specified directory, it looks in the directory where that file was originally, as recorded in the dump. See also the DBX_MODULE_PATH environment variable. For information on kernel debugging, see the Kernel Debugging manual. Causes dbx to print the path of shared libraries (or loadable kernel modules, if debugging a kernel) as they are being loaded. By default, dbx does not print the path. Using this option automatically sets the $module_verbose dbx variable to the value 1. See also the DBX_MODULE_VERBOSE environment variable. For information on kernel debugging, see the Kernel Debugging manual. Exe- cutes the object file immediately. If program execution terminates with an error, dbx displays the message that describes the error. You can then either invoke the debugger or let the program continue exiting. The dbx debugger reads from /dev/tty when you specify the -r option and standard input is not a terminal. If the program executes successfully, dbx prompts you for input. For use in debugging ker- nels. (Refer to the Kernel Debugging manual for information on kernel debugging. For information on debugging a running kernel using breakpoints, refer to kdbx(8).) Outputs file and line number information in a format compatible with the emacs function gdb. Attaches dbx to a currently running process specified by process id xxx. dbx Commands The debugger supplies a number of commands that you can issue at the dbx prompt. Multiple commands can be specified on the same command line by separating them with a semicolon (;). You can repeat dbx commands by pressing carriage return. Pressing carriage return repeats the last command issued to dbx. (This feature can be turned off by setting the $repeatmode variable to 0.) The following sections describe the commands supported by dbx. Controlling the Monitor Use the following commands to control the dbx monitor: Executes a command from the history list. You can specify the command name in the string argument. If you specify an integer, dbx executes the command having that number in the history list. If you specify -integer, the debugger executes the command that you issued integer commands ago. For example, if you specify -3, the debugger issues the command you issued three commands ago. The debugger echoes the command on standard output before executing it. With no argument, displays a list of topics for which help information is available. If you name a topic, the debugger displays help information on that topic. Displays a list of the previous commands you issued. By default, the debugger displays the previous 20 commands. You can change the number of commands dbx keeps in the history list by using the set command to modify the $lines debugger variable. Predefined alias for history command: h Exit dbx. Predefined alias for quit command: q Controlling dbx Use the following commands to control the operation of the dbx debugger. Lists all existing aliases or defines an alias. If you omit all arguments to the alias command, dbx displays a list of the existing aliases. You can supply arguments to define a new alias. If you specify a dbx command for string, the debugger assigns name as an alias for that command. For example, to define an alias rr for the command rerun, issue the following command: (dbx) alias rr "rerun" If you specify parameters in the alias command, the debugger substitutes the values you supply on the command line when it executes the command. For example, to define halt as an alias that sets a stop at a particular line, issue the following command: (dbx) alias halt(x) "stop at x" Once you issue this command, dbx interprets the following commands as the same: (dbx) halt(12) (dbx) stop at 12 Both commands set a breakpoint at source line 12. To remove an alias, use the unalias command, as shown: (dbx) unalias halt Deletes the specified breakpoint, trace event, or record event from the status list. The argument all and the argument * delete all events from the status list. Predefined alias for delete command: d Displays the names of the objects that have been loaded by dbx. These objects include the main program and all of the shared libraries that are used in the application. Replays commands that were saved with the record input command in a text file. If you omit file, the debugger reads commands from the temporary file it creates by default when you issue the record input command. Predefined alias for playback input command: pi or source. Replays debugger output that was saved with the record output command. If you omit file, the debugger displays output stored in a temporary file it creates by default when you issue the record output command. Predefined alias for playback output command: po Records all commands you enter at the dbx prompt. If you omit file, the debugger creates a temporary file that it deletes when you exit from the debugger. The debugger associates an event number with each record command you issue. You use the event number to turn off recording, as described with the delete command. Predefined alias for record input command: ri Records all dbx output. If you omit file, the debugger creates a temporary file that it deletes when you exit from the debugger. To record input and output to the same file, set the $rimode debugger variable. The debugger associates an event number with each record command you issue. You use the event number to turn off recording, as described with the delete command. Predefined alias for record output command: ro Executes the dbx commands from the specified file. This command is an alias for the playback input command. Lists current breakpoints, record events, and trace events. Predefined alias for status command: j Lists existing debugger variables and their values or defines a value for the named debugger variable. Some debugger variables contain either a zero or nonzero value that controls dbx behavior. For example, when set to a nonzero value, the $hexstrings variable causes the debugger to display all strings in hexadecimal format. When set to zero, this variable causes the debugger to display strings in character format. You can set a variable like $hexstrings to a nonzero value as shown: (dbx) set $hexstrings = 1 You can disable the variable using the unset command, as shown: (dbx) unset $hexstrings You can create a debugger variable using a name of your own. A debugger variable name you create must not conflict with the name of any variable in the program you are debugging, and it must not begin with a dollar sign ($). For information on existing debugger variables, see Predefined dbx Variables. (Use the assign command to change the value of variables in your program. See the section Preparing for Program Execution for information on the assign command.) Sets the environment variable name to string by changing the value of an existing environment variable or creating a new one. To reset the environment variable, specify a null string. The following example shows how to reset the EDITOR environment variable: (dbx) setenv EDITOR "" Calls a shell from dbx or executes the specified shell command. The sh command cannot be used in the action list of the when and wheni dbx commands. Returns the value of tagname, where tagname is a tag that marks a function or type defini- tion in your program. If the tag extends to more than one line or if it contains arguments, the debugger issues an error message. You can use tagvalue in commands where you specify a procedure or function name. For example, if a tag getline is associated with a function, the following command is valid: (dbx) call tagvalue(getline) () This command causes execution to begin at the location associated with the getline tag. You create tags using the ctags command. See ctags(1) for information. The debugger uses the file named in the $tagfile variable when resolving references to tags. Removes the specified alias. Removes the setting of a specified debugger variable. Examining Source Code The following commands allow you to examine your source files during a debugging session: Searches forward or backward in the source code for the regular expression. Invokes an editor on file or the current source file if none is specified. By default, dbx invokes the vi editor. You can override the default setting by modifying the EDITOR environment variable. Changes the current file to file, or, if you omit file, displays the name of the current file. Predefined alias for file command: e Changes the current procedure or function to the one you specify. If you omit expression and procedure, the debugger displays the name of the current procedure or function. Changing the current function implicitly changes the current source file to the one that contains the procedure or function; it also changes the current scope used for name resolution. Predefined alias for func command: f Lists the lines in the current source file. If you specify a source line number and an integer, dbx lists beginning from source-line-number and continuing for integer number of lines. If you omit integer, the debugger displays 10 lines by default. If you specify two source line numbers separated by a comma, the debugger begins the display at the first source line number and continues through the second source line number. If you omit the second source line number, the debugger displays 10 lines by default. If you specify a procedure or function name, the debugger displays lines in that procedure or function. The debugger displays 10 lines by default. If you omit all arguments, the debugger begins the display at the current line and displays 10 lines by default. The $listwindow debugger variable controls how many lines the debugger displays. The default value for $listwindow is 10. Predefined aliases for list command: The next 10 lines of source code. The next 10 machine instructions after the current machine instruction. The previous 10 lines of source code. The five lines before and after the current line. The 10 lines before and after the current line. The five machine instructions before and after the current one. Sets the current source file or source line to the location specified by tagname. You create tags using the ctags command. See ctags(1) for more information. The debugger uses the tag file named in the $tagfile debugger variable to resolve references to tags. Displays or sets the list of directories that dbx uses when searching for source files. If you issue the use command without arguments, the debugger displays the list of directories it searches for source files. To change the directory list, specify the names of the directories you want on the list as arguments to the use command. The direc- tories you specify replace any existing directory list. Give absolute or relative pathnames; ~ is not supported. The use command looks first for source files in the path consisting of the complete source path used when the file was compiled appended to the directory specified in the use command. If the use command cannot find the source file with that path, it takes the directory specified by the use command and only the filename part of the compilation source path. For example, when you built the program, the sources were in /usr/src/project. For some reason, perhaps because of different NFS mounting, when you run it, the sources are in /project. You enter: (dbx) use /project The use command looks for /project/../../src/project/filename.c and cannot find it. If you enter the following command, the use command can find the source file: (dbx) use /project/filename.c Displays the type declaration for variable. (If variable is a dbx keyword, it must be enclosed within parentheses.) Displays the fully qualified name of each occurrence of variable. The order in which the debugger displays the quali- fied names is not meaningful. (If variable is a dbx keyword, it must be enclosed within parentheses.) Displays the fully qualified name of variable. (If variable is a dbx keyword, it must be enclosed within parentheses.) Preparing for Program Execution Before you execute your program under dbx control, you might want to perform setup tasks, such as changing the value of debugger variables, specifying what signals your program should recognize or ignore, and setting breakpoints. The following commands allow you to perform these tasks: Loads a shared library and reads in the library's symbol table. If you specify an absolute or relative path (path) for the library, dbx looks only in the specified location. If you specify only the library file name (file), dbx first looks for that file in the directory specified by the $module_path variable, if set. If $module_path is not set or if dbx cannot find the file in the specified directory, it looks in the directory where that file was originally, as recorded in the object (or in the dump, if debugging a core dump). Use this command only for debugging applications that load in their own shared libraries instead of using the dynamic loader. For applications that do not load their own shared libraries, dbx will obtain the names of the shared libraries from the dynamic loader. Limitation: dbx will not work correctly when a shared library is added with the addobj command and the library is loaded at an address that differs from the address at which it was linked. You can also use the addobj command to load loadable modules when debugging a kernel. In general, the basic considerations described above for shared libraries also apply to loadable modules. For complete information on kernel debugging, see the Kernel Debugging manual. Assigns the value of the specified expression to the specified program variable. The program must be running for the assign command to work. (If variable is a dbx keyword, it must be enclosed within parentheses.) Use the set command to set the value of debugger variables. Predefined alias for assign command: a Lists all signals that dbx catches or, if you supply an argument, causes dbx to catch that signal. The signal you specify is added to the list of signals dbx catches, so the debugger continues to catch any signals that were already on its list. Some signals cannot be caught by any process. For a list of signals and information on which signals can be caught, see signal(4) for more information. Lists all signals that dbx ignores. If you specify a signal, this command adds the signal to the list of signals the debugger ignores. Some signals cannot be ignored by any process. For a list of signals and information on which signals can be ignored, see signal(4) for more information. Patches executable disk files to correct bad data or instructions. The text, initialized data, or read-only data areas can be patched. The bss segment cannot be patched because it does not exist in disk files. Examples: patch &main = 0 patch foo = 20 or patch &foo = 20 patch 0xnnnnn = 0xnnnnn Stops execution when the specified variable changes value, the specified source line is reached, the specified procedure or function is called, or the specified condition is true. The condi- tion must be a Boolean expression. (If variable is a dbx keyword, it must be enclosed within parentheses.) If you specify variable with a source line number, the debugger stops execution when the source line number is reached and the vari- able changes value. If you specify variable with in procedure, the debugger stops execution when it is executing in the named proce- dure or function and the named variable changes value. With if condition, the debugger stops execution when the condition is met and the variable changes value. If you specify a condition with at source-line or in procedure, the debugger stops only if the condition is true. The debugger associates an event number with each stop command you issue. You use the event number to remove the breakpoint, as described with the delete command. Predefined aliases for stop command: Sets a breakpoint at a specified line. Stops in a specified procedure. Displays tracing information during program execution. The dbx debugger associates an event number with each trace command you issue. You use the event number to turn off tracing, as described with the delete command. (If variable is a dbx keyword, it must be enclosed within parentheses.) The first argument to the trace command specifies what the debugger is to trace. You can specify a source line number, a procedure name, or a variable name. If you specify a source line number, dbx displays the source line immediately prior to executing it. You can specify a source line number in a source file that is not the current one. To do so, precede the source line number with the source file name in quota- tion marks (" ") followed by a colon (:), as shown in the following example: (dbx) trace at "source_file.c":17 The example specifies tracing line 17 in source_file.c. Specifying a procedure or function name causes dbx to display the name of the calling routine, the source line that contains the call, and the parameters that are passed to the called routine. In addition, dbx notes the return of the named procedure or func- tion and displays the return value, if any. The debugger displays this information each time the procedure or function is called. Specifying a variable name causes dbx to display the name and value of the variable each time it changes. Program execution is sub- stantially slower during this form of tracing. If you specify the in procedure clause, dbx displays tracing information only while executing the specified procedure or function. The condition is a Boolean expression that dbx evaluates prior to displaying any tracing information. The debugger displays tracing information only if the condition is true. Predefined alias for trace command: tr Executes the specified dbx command list. You can separate the commands by commas (,) or semi-colons (;). If you specify variable, the debugger executes the command list when the value of the variable changes. Specify at line or in pro- cedure to control which occurrence of the variable causes the debugger to execute the command list. (If variable is a dbx keyword, it must be enclosed within parentheses.) Initiating Program Execution The following commands allow you to control program execution: Executes the object code associated with the named procedure or function. This command passes the specified parameters to the procedure or function. The print and call commands treat values returned by called procedures differently: the print command displays them and the call command does not. Continues execution from where it stopped. If you specify an integer n, the debugger ignores that number of stops after it resumes program execution. If you specify signal, the process continues as though it received the signal. If you specify to source-line, the debugger continues execution until it reaches the specified source line. If you specify in procedure, the debugger continues until the specified procedure after receiving the specified signal. Predefined alias for cont command: c Branches to the specified source line. Execution continues from that point when you issue a cont command. Predefined alias for goto command: g Executes up to the next source line. The next command does not step into procedures of functions; execution stops at the source line that follows the call. If you spec- ify integer, the debugger performs the specified number of next commands. Predefined alias for next command: n Reruns the program, using the same arguments that were specified with the run command. If you specify new arguments, rerun uses those arguments. You can use angle brackets (< or >) to redirect input or output in the usual manner. Predefined alias for rerun command: r Runs the program, passing it the specified arguments. Arguments containing brackets ([]), asterisks (*), or other special characters must be enclosed in quotes or escaped to avoid parsing errors. You can use angle brackets (< or >) to redirect input or output in the usual manner. Executes until a return to procedure is exe- cuted or until the current procedure or function returns if you omit procedure. Executes one source line. If the source line con- tains a call to a procedure or function, the step command stops at the first line of the procedure or function. (The debugger does not stop at the first line of a procedure or function if you compiled your program without using the -g option.) If you specify integer, the debugger performs the specified number of step commands. Predefined alias for step command: s Examining Program State Use the following commands to determine the state of your program: Displays variable information about the named procedure or function, or the current procedure or function if you do not specify one. If you specify dot (.), the debugger displays information on all procedures or functions in the stack and their variables. Moves the current function down in the stack (based on the number of activation levels that you specify). The default is one level. Moves the current function up in the stack (based on the number of activation levels that you specify). The default is one level. Displays the value of the specified expression. (If a specified expression contains the name of a variable that is also a dbx keyword, the variable name must be enclosed within parentheses.) Predefined alias for print command: p Formats an expression as specified. You use the same format specifiers for this command as for the printf subroutine. For information on specifying the format, see printf(3). (The %s conversion specification is not sup- ported.) Predefined aliases for printf command print the following values: The specified expression or variable in decimal. The specified expression or variable in octal. The specified expression or variable in hexadecimal. Displays all register values. Predefined alias for printregs command: pr Displays a list of the active procedures and functions. If you specify n, the debugger displays only procedures and functions in the top n levels of the stack. Predefined alias for where command: t Attaching to a Running Process The dbx debugger supports /proc debugging. The major advantage of this is that it allows attaching to a running process and this can be used to attach to a child process. In order to do this, the /proc filesystem must be mounted. The following commands are available to attach to, and detach from, a running process: Use this command to attach to a running process, where xxx is the proc id of the process you want to attach to. This command checks to see if /proc is mounted. If it is mounted, dbx will then look for the proc id in /proc. If the proc id is present, dbx will attempt to open the process, issue a stop command, report the current position, and issue the dbx> prompt. Use this command to detach from a running process, where the optional xxx is the proc id of the process you want to detach from. Use this command to switch from one process to another, where xxx is the proc id of the process you want to switch to. You must already have attached to the target process using the attach command. Use this command to display a list of active processes and their status. The debugger indicates the current process with a marker: --> Debugging at the Machine Code Level You can use machine level commands to debug any program, regardless of whether the program object file contains extended symbol table information. You can specify symbolic addresses by preceding the name with an ampersand (&). You denote registers by $rN, where N is the number of the register. Addresses may be expressions made up of other addresses and the operators plus (+), minus (-), and indirection (unary asterisk, *). Use the following commands to debug programs at the machine code level: Searches forward (or backward, if you specify ?) and displays the contents of address or disassembles the code for the instruction address. The count argument specifies the number of items that the debug- ger displays at the specified address. The mode determines how dbx displays memory; if you omit it, the debugger uses the previous mode. The initial mode is X. You can specify the following modes: Displays a byte in octal. Displays a byte as a character. Displays a 16-bit value in decimal. Displays a 32-bit value in decimal. Displays a 64-bit value in decimal. Displays a single precision real number. Dis- plays a double precision real number. Displays machine instructions. Displays data in typed format. Displays a 16-bit value in octal. Displays a 32-bit value in octal. Displays a 64-bit value in octal. Displays a string of characters that ends in a null. Displays a 16-bit value in hexadecimal. Displays a 32-bit value in hexadecimal. Displays a 64-bit value in hexadecimal. The debugger maintains the next address to be displayed in dot (.). To display the next address, you can use the following command: (dbx) ./ The debugger will display the next count locations in the mode specified in the previous command. Searches for a 64-bit word that satisfies the mask. The debugger starts searching at the specified address. The count argument specifies the number of words the debugger processes during the search. You type the M to specify a match. The debugger masks the word stored at address using the value specified in mask. If the masked value equals value, the debugger dis- plays the address of the masked value. Otherwise, the debugger increments address and continues to search. Continues execution of assembly code from where it stopped. If you specify an integer n, the debugger ignores that number of stops after it resumes pro- gram execution. If you specify signal, the process continues as though it received the signal. If you specify to address, the debugger continues execution until it reaches the specified address. If you specify in procedure, the debugger resumes execution in the named procedure or function. Executes up to the next machine instruction. The nexti command does not step into procedures or functions; execution stops at the machine instruction that follows the call. If you specify an integer, the debugger performs integer nexti instructions. Predefined alias for nexti command: ni Executes the specified number of machine instructions. If one of the machine instructions contains a call to a procedure or function, the debugger stops at the first instruction of the procedure or function. The default is to execute one instruction. Predefined alias for stepi command: si Stops when the specified variable changes value, the specified address is reached, the speci- fied condition is true, or the specified procedure or function is reached. (If variable is a dbx keyword, it must be enclosed within parentheses.) By combining the arguments, you can cause the debugger to stop, for example, only when the occurrence of variable at the specified address changes value and condition is true. Traces the value of variable or the execution of a particular address. (If variable is a dbx keyword, it must be enclosed within parentheses.) When you trace the value of a variable, you can use at address, in procedure, and if condition to control the specific variable that is traced. You can specify a condition when you trace the execution of an address. The debugger displays tracing information only when the condition is true. Executes the specified dbx machine command list. You can separate the commands by commas (,) or semi-colons (;). If you specify variable, the debugger executes the command list when the value of the variable changes. Specify at address or in procedure to control which occurrence of the variable causes the debugger to execute the command list. (If variable is a dbx key- word, it must be enclosed within parentheses.) Predefined dbx Variables The debugger contains variables that control certain aspects of its operations. Some debugger variables are used internally by dbx. You must not change the value of those variables. The debugger allows you to change the values of other variables using the set and unset com- mands. The following list describes the debugger variables you can control: Specifies the format for addresses. You can set this variable to any format that you can use with the printf function, except %s because the %s conversion specification is not supported by dbx. See printf(3) reference page for information on valid formats. By default, this variable is set to 0x%x, which specifies hexadecimal format. When set to a positive nonzero value, indicates that dbx is in asynchronous mode. When 0 (zero) or negative, indicates that asynchronous debugging is disabled. Incremented by 1 when a new process is attached and decremented by 1 when a process terminates or is detached. The default value is 0. To prevent dbx from entering asynchronous mode, set $asynch_interface to a negative value. When set to a nonzero value, specifies that uppercase and lowercase letters be treated as different characters during a search. When $casesense is set to zero, dbx ignores the case of letters. The default is zero. The $casesense variable has no effect on the interpretation of eight-bit charac- ters; thus, for example, A-acute-accent and a-acute-accent are always treated as different characters. Caches information from the data space so that dbx must access the data space only once. If this variable is set to zero, the debugger does not cache data space. If your program contains any data declared as volatile, you may want to set this variable to zero. To debug the operating system, set this vari- able to zero; otherwise, set it to a nonzero value. The default is a nonzero value. Causes the debugger to be in the correct mode to debug pixie code. When set to zero, the debugger displays machine code while debugging. When set to a nonzero value, the debugger displays pixie code. The default is zero. When set to a nonzero value, causes the debugger to display characters in hexadecimal format. When set to a nonzero value, causes the debugger to interpret input constants as hexadecimal. When set, this variable overrides the $octin vari- able. When set to a nonzero value, changes the default output constants to hexadecimal. When set, this variable overrides the $octints variable. When set to a nonzero value, causes the debugger to display all strings in hexadecimal format. When set to zero, causes the debugger to display strings in character format. Stores the current history line. Determines how many lines the debugger stores in its history list. The default is 20 lines. Specifies how many lines the list command displays. The default is 10 lines. Specifies the name of the procedure or function that dbx begins when running the process. The debugger can begin a process at any procedure or function. By default, the debugger begins a process at a procedure named main. Specifies how many characters of a string dbx displays for pointers to strings. The default is 128 characters. Specifies the directory path where dbx should search for shared libraries (or loadable kernel modules). This variable is useful if, for example, you are debugging a core dump (or a kernel crash dump) and the version of a shared library (or module) that was running when the dump occurred has been moved to a different location. Setting this variable with the set com- mand affects only any files that are loaded after the variable is set. To affect files that are loaded at dbx startup, use the -module_path option or the DBX_MODULE_PATH environment variable. See also the addobj command. For information on kernel debugging see the Kernel Debug- ging manual. When set to a nonzero value, causes dbx to print the location of shared libraries (or loadable kernel modules, if debugging a kernel) as they are being loaded. By default, or when this variable is set to zero, dbx does not print the location. See also the -mod- ule_verbose option and the DBX_MODULE_VERBOSE environment variable. For information on kernel debugging, see the Kernel Debugging manual. When set to a nonzero value, changes the default input constants to octal. When set, the $hexin variable overrides this variable. When set to a nonzero value, causes dbx to display integers in octal format. When set, the $hexints variable overrides this variable. Speci- fies whether to page long information. A nonzero value turns on paging; a zero turns it off. The default is one. Specifies how many lines the debugger displays when information runs longer than one screen. You can change this variable to match the number of lines on any ter- minal. If set to zero, this variable assumes one line. The default is 65. This variable affects only C++ modules. It specifies whether to print function parameters from C++ modules when displaying a stack trace (as from a where command). A nonzero value enables this fea- ture. A value of zero (the default) disables it -- that is, a C++ parameter list is shown empty in the stack trace (for example, my_rou- tine()). The default was chosen because dbx does not support complex C++ types beyond those supported for C, and a segmentation fault will occur if dbx tries to print function parameters of complex C++ types in a stack trace. (However, dbx then regains control and dis- plays its prompt.) If you are debugging C++ modules that have only simple (C) function-parameter types, setting $printcplusparams to 1 will enable dbx to print these parameters in a stack trace. Determines whether the debugger displays source lines or instructions when executing the step[n] and stepi[n] commands. When set to a nonzero value, causes dbx to display all n lines or instructions. When set to zero, causes dbx to display only the last line or instruction. The default is zero. Displays input when used with the playback input command. The default is zero. When set to a nonzero value, causes the debugger to display the contents of registers next to each instruction it displays. The debugger displays the registers used by the instruction. The default is zero. When set to a nonzero value, causes the debugger to display the contents of variables in a horizontal format. The default is zero. Sets the prompt for dbx. When set to a nonzero value, causes dbx to read instructions from the object file rather than the process. This variable should always be set to zero when the process being debugged copies in code during the debugging process. The default is a nonzero value. When set to a nonzero value, causes the debugger to display registers during disassembly in their normal r format (r0,r1,...,r31). When set to zero, causes the debugger to display registers in a special format (zero, at, v0, v1,...), which is commonly used in debugging programs written in assembly language. The default is a nonzero value. Setting this variable does not affect how the debugger displays the names of registers when you issue the printregs command. This variable affects the debugger's machine level commands. When set to a nonzero value, causes dbx to repeat the previous command if you press the Return key at the dbx prompt. The default is a nonzero value. When set to a nonzero value, causes the debugger to record input while recording output. The default is zero. Tells dbx the name of the code called by the system to invoke user sig- nal handlers. This variable is set to sigaction on Tru64 UNIX systems. Meaningful only when $stop_on_fork is set. If set to 1, dbx stops every time a new image is forked. If set to 0, dbx ignores most forks arising from system and library calls. The default is 0. When set to 1, *Ldbx detects calls to execl and execv and stops the newly executed images at the first line of executable code. The default is 1. If set to 1, specifies that dbx should stop when a new image is forked. If set to 0, instructs dbx to continue into the new image without stopping. The default is 1. Names the file that contains tags for the current program. The tag and tagvalue commands search the named file to resolve references to tags. For more information on using tag files, see ctags(1). Specifies the number of times dbx can ignore a SIGTRAP without being interrupted by another signal or breakpoint type. This variable helps avoid the infinite loop that can occur when you set a breakpoint in a SIGTRAP signal handler function. The default number for this variable is 3. DESCRIPTION
The dbx command invokes a source-level debugger. You can use dbx to debug programs written in C, Fortran, Pascal, assembly language, and machine code. Languages other than these are not supported by dbx. After invoking the dbx debugger, you issue dbx commands that allow you to examine source files, control program execution, display the state of the program, and debug at the machine level. You can use command options to modify some steps that dbx performs during startup. (For information on the available options, see the OPTIONS section.) Unless you specify the -r option, dbx prompts you for a command before it begins executing your program. The dbx prompt appears as follows: (dbx) To leave dbx, issue the quit command. See the Guide to DECthreads for information on how to debug multithreaded applications. Arguments On the command line, the object argument names the object file that you want dbx to read as input. For complete dbx support, the object file must contain extended symbol table information. The supported compilers each have a -g option that produces the symbol table informa- tion in the object file. The extended symbol table contains the names of all the source files translated by the compiler to create the object file. This information allows you to look at all of the source code that went into creating an object file during your debugging session. (The extended symbol table also contains other information.) If your object file does not contain the extended symbol table information, use the commands described in the Debugging at the Machine Code Level section to debug your program. If you omit the object argument, dbx prompts you for the name of an object file. If you press the Return key, dbx attempts to read a file named a.out from the current directory. If no a.out file exists, dbx exits. The core argument names a core dump file. You can examine the core dump file to determine the state of the program when it failed. Initialization File During its startup, dbx reads and executes the commands in an initialization file (if present). By default, dbx searches for the initial- ization file in the current directory. If no file exists in the current directory, dbx searches your home directory for the file. You can use the initialization file to issue setup commands automatically when you begin a dbx session. (See the section Predefined dbx Variables for information on the debugger variables that you can control in the initialization file.) Debugger Expressions You specify dbx expressions using the C syntax for expressions. The debugger supports a subset of the expression syntax. For example, you can denote indirection using either an asterisk (*) as a prefix or a circumflex (^) as a suffix. You can use the field reference operator (.) with pointers as well as with records or structures, making the C operator (->) unnecessary (although it is supported). You must enclose array expressions in brackets ([ ]). You can also specify a register name in an expression. You denote registers by $rN where N is the number of the register. The debugger supports symbol names and string literals containing displayable characters in the eight-bit ISO Latin-1 character set. Debugger Name Resolution The debugger resolves names by searching for the name in the static scope of the current function. If no name is defined in the static scope, the debugger searches the dynamic scope. If neither scope yields a defined name, the debugger chooses an arbitrary symbol and dis- plays the following message: [usingqualified.name] The debugger substitutes the qualified name of the arbitrary symbol for qualified.name in the message. You can override this name resolution procedure by qualifying identifiers with a block name, as in module.variable. For the C language, the debugger treats a source file as a module named from the filename without the suffix. Command Line Editing The dbx monitor provides commands that permit command-line editing. These commands allow you to correct mistakes without re-entering an entire command. There are two line-editing modes, vi mode and emacs mode. To enable a mode similar to the Korn shell's vi mode, set the EDITOR or EDITMODE environment variable to a path ending in vi before start- ing dbx. In vi mode, the following editing keys are recognized: $ + - 0 A B C D E F I R S W X ^ a b c d e f h i j k l r s w x ~ Ctrl/D Ctrl/H Ctrl/J Ctrl/L Ctrl/M Ctrl/C See ksh(1) for more information. To enable a mode similar to the Korn shell's emacs mode, set the LINEEDIT environment variable to any value, or set EDITOR or EDITMODE to a path ending in emacs, before starting dbx. The debugger treats ^K differently depending on whether the mode is enabled by LINEEDIT or by EDITOR or EDITMODE. In emacs mode, the following editing keys are recognized: Move the cursor to the beginning of the command line. Move the cursor back one character. Clear the line. Delete the character at the cursor. Move the cursor to the end of the line. Move the cursor ahead one character. Delete the character immediately preceding the cursor. Execute the line. (When enabled by LINEEDIT) Delete characters until the cursor rests on the next occurrence of char. (When enabled by EDITOR or EDITMODE) Delete from the cursor to the end of the line. If preceded by a numerical parameter whose value is less than the current cursor position, delete from given position up to the cursor. If preceded by a numerical parameter whose value is greater than the current cursor position, delete from cursor up to given position. Redisplay the current line. Execute the line. Move to the next line in the history list. Move to the previous line in the history list. Search back in the current line for the specified character. Interchange the two characters immediately preceding the cur- sor. Repeat the next character four times. Delete the entire line. Insert immediately before the cursor any text cut with ^K. Try to complete a file or symbol name. Try to complete a file or symbol name. Move to the next line in the history list. Move to the previous line in the history list. Move the cursor back one character. Move the cursor ahead one character. Note The notation ^ represents the CTRL key. For example, ^A indicates that the CTRL and A keys should be pressed simultaneously. RESTRICTIONS
The printf debugger command does not support the %s conversion specification. ENVIRONMENT VARIABLES
Specifies the directory path where dbx should search for shared libraries (or loadable kernel modules). This environment variable is useful if, for example, you are debugging a core dump (or a kernel crash dump) and the version of a shared library (or module) that was running when the dump occurred has been moved to a different location. Setting this environment variable automatically sets the $module_path dbx variable to the specified path. If dbx cannot find a file in the specified directory, it looks in the directory where that file was origi- nally, as recorded in the dump. See also the -module_path option. For information on kernel debugging see the Kernel Debugging manual. When set to any value, causes dbx to print the path of shared libraries (or loadable kernel modules, if debugging a kernel) as they are being loaded. By default, dbx does not print the path. Setting this environment variable to any value automatically sets the $module_ver- bose dbx variable to the value 1. See also the -module_verbose option. For information on kernel debugging, see the Kernel Debugging man- ual. FILES
Object file Core dump file Initialization file SEE ALSO
Commands: as(1), cc(1), ctags(1), pixie(5), vi(1) Routines: printf(3), signal(4), kdbx(8) Kernel Debugging Programmer's Guide Guide to DECthreads dbx(1)

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