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Sun Studio 12: Debugging a Program With dbx

Using dbx Commands in Java Mode

When you are using dbx to debug a mixture of Java and native code, dbx commands fall into several categories:

Any commands not included in one of these categories work only in native mode.

The Java Expression Evaluation in dbx Commands

The Java expression evaluator used in most dbx commands supports the following constructs:

The Java expression evaluator does not support the following constructs:

A particularly useful way of inspecting the state of your Java application is using the display facility in the dbx Debugger.

Depending on precise value semantics in expressions that do more than just inspect data is not recommended.

Static and Dynamic Information Used by dbx Commands

Much of the information about a Java application is normally available only after the JVM software has started, and is unavailable after the Java application has finished executing. However, when you debug a Java application with dbx, dbx gleans some of the information it needs from class files and JAR files that are part of the system class path and user class path before it starts the JVM software. This allows dbx to do better error checking on breakpoints before you run the application.

Some Java classes and their attributes might not be accessible through the class path. dbx can inspect and step through these classes, and the expression parser can access them, once they are loaded. However, the information it gathers is temporary and is no longer available after the JVM software terminates.

Some information that dbx needs to debug your Java application is not recorded anywhere so dbx skims Java source files to derive this information as it is debugging your code.

Commands With Identical Syntax and Functionality in Java Mode and Native Mode

The following dbx commands have the same syntax and perform the same operations in Java mode as in native mode.

Command  

Functionality  

attach

Attaches dbx to a running process, stopping execution and putting the program under debugging control

cont

Causes the process to continue execution 

dbxenv

List or set dbx environment variables

delete

Deletes breakpoints and other events 

down

Moves down the call stack (away from main)

dump

Prints all variables local to a procedure or method 

file

Lists or changes the current file 

frame

Lists or changes the current stack frame number 

handler

Modifies event handlers (breakpoints) 

import

Import commands from a dbx command library

line

Lists or changes the current line number 

list

Lists or changes the current line number 

next

Steps one source line (steps over calls) 

pathmap

Maps one path name to another for finding source files, etc. 

proc

Displays the status of the current process 

prog

Manages programs being debugged and their attributes 

quit

Exits dbx

rerun

Runs the program with no arguments 

runargs

Changes the arguments of the target process 

status

Lists the event handlers (breakpoints) 

step up

Steps up and out of the current function or method 

stepi

Steps one machine instruction (steps into calls) 

up

Moves up the call stack (toward main)

whereami

Displays the current source line 

Commands With Different Syntax in Java Mode

The following dbx commands have different syntax for Java debugging than for native code debugging, and operate differently in Java mode than in native mode.

Command  

Native Mode Functionality  

Java Mode Functionality  

assign

Assigns a new value to a program variable 

Assigns a new value to a local variable or parameter 

call

Calls a procedure 

Calls a method 

dbx

Starts dbx

Starts dbx

debug

Loads the specified application and begins debugging the application 

Loads the specified Java application, checks for the existence of the class file, and begins debugging the application 

detach

Releases the target process from dbx’s control

Releases the target process from dbx’s control

display

Evaluates and prints expressions at every stopping point. 

Evaluates and prints expressions, local variables, or parameters at every stopping point 

files

Lists file names that match a regular expression 

Lists all of the Java source files known to dbx

func

Lists or changes the current function 

Lists or changes the current method 

next

Steps one source line (stepping over calls) 

Steps one source line (stepping over calls) 

print

Prints the value of an expression 

Prints the value of an expression, local variable, or parameter. 

run

Runs the program with arguments 

Runs the program with arguments 

step

Steps one source line or statement (stepping into calls) 

Steps one source line or statement (stepping into calls) 

stop

Sets a source-level breakpoint 

Sets a source-level breakpoint 

thread

Lists or changes the current thread 

Lists or changes the current thread 

threads

Lists all threads 

Lists all threads 

trace

Shows executed source lines, function calls, or variable changes 

Shows executed source lines, function calls, or variable changes 

undisplay

Undoes display commands

Undoes display commands

whatis

Prints the type of expression or declaration of type 

Prints the declaration of an identifier 

when

Executes commands when a specified event occurs 

Executes commands when a specified event occurs 

where

Prints the call stack 

Prints the call stack 

Commands Valid Only in Java Mode

The following dbx commands are valid only in Java mode or JNI mode.

Command  

Functionality  

java

Used when dbx is in JNI mode to indicate that the Java version of a specified command is to be executed

javaclasses

Prints the names of all Java classes known to dbx when you give the command

joff

Switches dbx from Java mode or JNI mode to native mode

jon

Switches dbx from native mode to Java mode

jpkgs

Prints the names of all Java packages known to dbx when you give the command

native

Used when dbx is in Java mode to indicate that the native version of a specified command is to be executed