Debugger protocol generator

A method for automatically generating front-end code and back-end code that are both compatible with a specification, such as the JDWP communication protocol. First, a detailed protocol specification is written that contains a description of a communication protocol between the front-end code and the back-end code. The detailed specification is then input into a code generator that parses the specification. The front-end code is then automatically generated from the formal specification, and may be written in a first computer language such as the Java™ programming language. The code generator then generates the back-end code, which may be written in a second computer language such as C.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to the field of computer software, and more particularly to protocol generating software for generating software components from a formal specification.

2. Description of the Problem to be Solved

The Java™ Debug Wire Protocol (JDWP) (Java™ and related marks are trademarks of Sun Microsystems, Inc.) is a protocol for communicating between a debugger application and a Java Virtual Machine (target VM). By implementing the JDWP, a debugger can either work in a different process on the same computer, or on a remote computer. Since Java™ programming applications may be implemented across a wide variety of different hardware platforms and operating systems, the JDWP facilitates remote debugging across a multi-platform system. In contrast, many prior art debugging systems are designed to run on a single platform and must generally debug only applications running on the same or similar platform.

Typically, a debugger application is written in the Java programming language and the target side is written in native code. In a reference implementation of JDWP, a front-end debugger component is written in Java and a back-end reference implementation for the target VM is written in C. Both pieces of code need to be compliant with a detailed protocol specification, or the reference system will fail. What is needed is some mechanism to assure that both the front-end and back-end code portions are truly compatible with the protocol specification and with each other.

Languages exist for the specification of inter-process/object communication, such as the Interface Definition Language (IDL) which is part of the Common Object Request Broker Architecture (CORBA), developed by the Object Management Group (OMG). These languages are compiled (i.e. by an IDL compiler) to produce stubs for the client side of communication and skeletons for the server side. However, such languages are not directed to the problems associated with generating protocol compliant debugger code.

Therefore, it would be desirable to have a method for generating both the front-end code and the back-end code for a debugger directly from a detailed specification.

SUMMARY OF THE INVENTION

The present invention provides a method for automatically generating front-end code and back-end code that are both compatible with an interface specification, such as the JDWP communications protocol. First, a detailed protocol specification is written that contains a description of a communications protocol between the front-end and the back-end. The detailed specification is then input into a code generator that parses the specification. The front-end code is then automatically generated from the formal specification, and may be written in a first computer language such as the Java programming language. The code generator then generates the back-end code, which may be written in a second computer language such as C.

The present invention may further generate HTML code containing a human-readable description of the protocol specification.

DETAILED DESCRIPTION OF THE INVENTION

The following description is provided to enable any person skilled in the art to make and use the invention and sets forth the best modes contemplated by the inventor for carrying out the invention. Various modifications, however, will remain readily apparent to those skilled in the art, since the basic principles of the present invention have been defined herein specifically to provide a method for assuring compatibility between a front-end debugger program running on a first virtual machine and a back-end debugger agent program running on a second virtual machine, wherein a communications protocol between the front-end program and the back-end program is defined by a formal specification.

The present invention employs various computer-implemented operations involving data stored in computer systems. These operations include, but are not limited to, those requiring physical manipulation of physical quantities. Usually, though not necessarily, these quantities take the form of electrical or magnetic signals capable of being stored, transferred, combined, compared, and otherwise manipulated. The operations described herein that form part of the invention are useful machine operations. The manipulations performed are often referred to in terms, such as, producing, identifying, running, determining, comparing, executing, downloading, or detecting. It is sometimes convenient, principally for reasons of common usage, to refer to these electrical or magnetic signals as bits, values, elements, variables, characters, data, or the like. It should remembered, however, that all of these and similar terms are to be associated with the appropriate physical quantities and are merely convenient labels applied to these quantities.

The present invention also relates to a device, system or apparatus for performing the aforementioned operations. The system may be specially constructed for the required purposes, or it may be a general purpose computer selectively activated or configured by a computer program stored in the computer. The processes presented above are not inherently related to any particular computer or other computing apparatus. In particular, various general-purpose computers may be used with programs written in accordance with the teachings herein, or, alternatively, it may be more convenient to construct a more specialized computer system to perform the required operations.

FIG. 1is a block diagram of a general purpose computer system100suitable for carrying out the processing in accordance with one embodiment of the present invention.FIG. 1illustrates one embodiment of a general purpose computer system. Other computer system architectures and configurations can be used for carrying out the processing of the present invention. Computer system100, made up of various subsystems described below, includes at least one microprocessor subsystem (also referred to as a central processing unit, or CPU)102. That is, CPU102can be implemented by a single-chip processor or by multiple processors. It should be noted that in re-configurable computing systems, CPU102can be distributed amongst a group of programmable logic devices. In such a system, the programmable logic devices can be reconfigured as needed to control the operation of computer system100. In this way, the manipulation of input data is distributed amongst the group of programmable logic devices. CPU102is a general purpose digital processor which controls the operation of the computer system100. Using instructions retrieved from memory, the CPU102controls the reception and manipulation of input data, and the output and display of data on output devices.

CPU102is coupled bi-directionally with a first primary storage104, typically a random access memory (RAM), and uni-directionally with a second primary storage area106, typically a read-only memory (ROM), via a memory bus108. As is well known in the art, primary storage104can be used as a general storage area and as scratch-pad memory, and can also be used to store input data and processed data. It can also store programming instructions and data, in the form of data objects, in addition to other data and instructions for processes operating on CPU102, and is used typically used for fast transfer of data and instructions in a bi-directional manner over the memory bus108. Also as well known in the art, primary storage106typically includes basic operating instructions, program code, data and objects used by the CPU102to perform its functions. Primary storage devices104and106may include any suitable computer-readable storage media, described below, depending on whether, for example, data access needs to be bi-directional or uni-directional. CPU102can also directly and very rapidly retrieve and store frequently needed data in a cache memory110.

A removable mass storage device112provides additional data storage capacity for the computer system100, and is coupled either bi-directionally or uni-directionally to CPU102via a peripheral bus114. For example, a specific removable mass storage device commonly known as a CD-ROM typically passes data uni-directionally to the CPU102, whereas a floppy disk can pass data bi-directionally to the CPU102. Storage112may also include computer-readable media such as magnetic tape, flash memory, signals embodied on a carrier wave, PC-CARDS, portable mass storage devices, holographic storage devices, and other storage devices. A fixed mass storage116also provides additional data storage capacity and is coupled bi-directionally to CPU102via peripheral bus114. The most common example of mass storage116is a hard disk drive. Generally, access to these media is slower than access to primary storages104and106.

Mass storage112and116generally store additional programming instructions, data, and the like that typically are not in active use by the CPU102. It will be appreciated that the information retained within mass storage112and116may be incorporated, if needed, in standard fashion as part of primary storage104(e.g. RAM) as virtual memory.

In addition to providing CPU102access to storage subsystems, the peripheral bus114is used to provide access other subsystems and devices as well. In the described embodiment, these include a display monitor118and adapter120, a printer device122, a network interface124, an auxiliary input/output device interface126, a sound card128and speakers130, and other subsystems as needed.

The network interface124allows CPU102to be coupled to another computer, computer network, or telecommunications network using a network connection as shown. Through the network interface124, it is contemplated that the CPU102might receive information, e.g., data objects or program instructions, from another network, or might output information to another network in the course of performing the above-described method steps. Information, often represented as a sequence of instructions to be executed on a CPU, may be received from and outputted to another network, for example, in the form of a computer data signal embodied in a carrier wave. An interface card or similar device and appropriate software implemented by CPU102can be used to connect the computer system100to an external network and transfer data according to standard protocols. That is, method embodiments of the present invention may execute solely upon CPU102, or may be performed across a network such as the Internet, intranet networks, or local area networks, in conjunction with a remote CPU that shares a portion of the processing. Additional mass storage devices (not shown) may also be connected to CPU102through network interface124.

Auxiliary I/O device interface126represents general and customized interfaces that allow the CPU102to send and, more typically, receive data from other devices such as microphones, touch-sensitive displays, transducer card readers, tape readers, voice or handwriting recognizers, biometrics readers, cameras, portable mass storage devices, and other computers.

Also coupled to the CPU102is a keyboard controller132via a local bus134for receiving input from a keyboard136or a pointer device138, and sending decoded symbols from the keyboard136or pointer device138to the CPU102. The pointer device may be a mouse, stylus, track ball, or tablet, and is useful for interacting with a graphical user interface.

In addition, embodiments of the present invention further relate to computer storage products with a computer readable medium that contain program code for performing various computer-implemented operations. The computer-readable medium is any data storage device that can store data which can thereafter be read by a computer system. The media and program code may be those specially designed and constructed for the purposes of the present invention, or they may be of the kind well known to those of ordinary skill in the computer software arts. Examples of computer-readable media include, but are not limited to, all the media mentioned above: magnetic media such as hard disks, floppy disks, and magnetic tape; optical media such as CD-ROM disks; magneto-optical media such as floptical disks; and specially configured hardware devices such as application-specific integrated circuits (ASICs), programmable logic devices (PLDs), and ROM and RAM devices. The computer-readable medium can also be distributed as a data signal embodied in a carrier wave over a network of coupled computer systems so that the computer-readable code is stored and executed in a distributed fashion. Examples of program code include both machine code, as produced, for example, by a compiler, or files containing higher level code that may be executed using an interpreter.

It will be appreciated by those skilled in the art that the above described hardware and software elements are of standard design and construction. Other computer systems suitable for use with the invention may include additional or fewer subsystems. In addition, memory bus108, peripheral bus114, and local bus134are illustrative of any interconnection scheme serving to link the subsystems. For example, a local bus could be used to connect the CPU to fixed mass storage116and display adapter120. The computer system shown inFIG. 1is but an example of a computer system suitable for use with the invention. Other computer architectures having different configurations of subsystems may also be utilized.

In a described embodiment of the present invention, the invention is generally applicable to and described in terms of computer systems implementing a Java Platform based distributed architecture. However, as will be seen in the following description, the concepts and methodologies of the present invention should not be construed to be limited to a Java Platform based distributed architecture. Such an architecture is used only to describe a preferred embodiment. A distributed Java platform implementation may have many different types of hardware, operating systems, and even Java Virtual Machines (VMs). Therefore it may be necessary to debug a program running on a remote system, having completely different architecture. Also, in many instances it is preferable to actually load a main debugger program on a separate computer system so that the target system can be debugged in a state as close to possible to its “original” state. As shown inFIG. 2a, the Java Platform Debugger Architecture (JPDA) supports local and remote debugging by defining three separate interfaces. The Java Platform Debugger Architecture defines a set of interfaces used in the creation of debugger applications. It consists of the Java Debug Interface (JDI), the Java Debug Wire Protocol (JDWP), and the Java Virtual Machine Debug Interface (JVMDI). The JPDA provides a solution to the general connection problems encountered by debugger applications.

In the described embodiment, on a first computer system (debugger), a Java debugger application program runs on a first (debugger) Java Virtual Machine (VM). A Java VM suitable for use in the described embodiment of the present invention is shown and described inFIG. 4below. The debugger has a front-end component (hereinafter “front-end”) that implements a high-level Java Debug Interface (JDI). The Java debugger application program, which provides a user interface, is a client of the JDI. The debuggee (or debuggee process) is the process that is being debugged, and it consists of the application being debugged (debuggee application program), a second (debuggee) Java Virtual Machine (VM) running the application, and a “back-end” debugger agent (hereinafter “back-end”). The back-end is responsible for communicating requests from the debugger front-end to the debuggee (second) VM and for communicating the response to the requests back to the front-end. The back-end communicates with the front-end over a communications channel using the Java Debug Wire Protocol (JDWP). The back-end communicates with the debuggee VM using the Java Virtual Machine Debug Interface (JVMDI).

FIG. 2bis similar toFIG. 2abut shows two additional components needed to enable the present invention plus transport modules. The two additional logical components are a front-end JDWP processing module and a back-end JDWP processing module. One of the goals of the debugger protocol generator of the present invention is to generate front-end and back-end JDWP processing modules. The logical components shown inFIG. 2bare basic components for which vendors can provide their own implementations. The front-end and back-end transport modules implement a transport mechanism, such as shared memory, socket, or serial line.

Thus, as is shown inFIGS. 2aand2b, the Java Platform Debugger Architecture provides three separate and distinct interfaces for debugging. Third-party vendors can choose which interface level best suits their needs and write a debugger application accordingly. Specifically, the JDI is a 100% Java platform interface implemented by the front-end, which defines information and requests at a high level. For vendors who wish to concentrate on a graphical user interface for the JDPA, they only need to use this level.

The JVMDI interface is a native code interface implemented by the debuggee VM. It defines the services that a VM must provide for debugging and includes requests for information, actions, and notifications. Specifying the VM interface for a debugger allows any VM implementation to plug into the JPDA. The back-end may be written in non-native code, but experience has shown that debugger support code running sharing the same VM services as the debuggee can cause deadlocks and other undesired behavior.

The JDWP defines the format of information and requests transferred between the front-end and the back-end. It does not specify the transport mechanism used to physically transmit the formatted information, that is, the form of inter-process communication (IPC) is not specified. Different transport mechanisms may be used such as sockets, serial line, shared memory, etc. The specification of the communication protocol allows the debuggee and the debugger front-end to run under separate VM implementations and/or on separate platforms. Also, by defining an intermediate interface, the front-end may be written in a language other than the Java language, or the back-end in non-native code (i.e. Java language code). Note that due to the use of distributed interfaces, a VM vendor that does not wish to adhere to the JVMDI interface can still provide access via the JDWP.

By defining three separate interfaces, the Java Platform Debugger Architecture, JPDA overcomes many limitations associated with prior art debugger systems. The present invention addresses the problem of documenting the interface and of managing compatibility across multiple platforms and programming languages at the JDWP level. Because the JDI and JVMDI layers are conventional programming interfaces, the compatibility and documentation problems are less severe and more amenable to existing tools.

The compatibility and documentation problems are solved by generating compatible code and documentation from a single specification source. More specifically, this involves generating a front-end JDWP processing module (which becomes part of the front-end implementation in the Java language), a back-end JDWP processing module (which will become part of the back-end implementation in the C language), and HTML documentation of the protocol specification.

The tasks performed by the generated front-end JDWP processing module can be placed generally in two categories. One category relates to events generated in the debuggee VM, which must be sent to the front-end through the back-end. The front-end JDWP processing module: 1) reads and parses JDWP formatted events from the back-end; 2) converts the events into JDI events; and 3) queues the events. The other category relates to requests made through the JDI by the debugger application. The front-end JDWP processing module: 1) writes JDWP formatted requests to the wire, sending them to the back-end; 2) associates the appropriate reply to the request; 3) reads and parses the reply; and 4) delivers the reply to the requestor. The back-end JDWP processing module must handle the other end of the communication, so it too has two categories of processing. For event processing, the back-end JDWP processing module writes the event (which was generated through the JVMDI) to the wire, sending it to the front-end. For requesting processing, the back-end JDWP processing module: 1) reads and parses JDWP formatted requests from the front-end; 2) forwards the request to other back-end code, which will generate a reply; 3) writes the reply to the wire, sending it to the front-end.

Without a mechanically assured consistency between the JDWP specification, documentation and implementation code, it is unlikely that the Java Platform Debugger Architecture could evolve into a workable multi-vendor strategy. Thus, the present invention enforces a formal specification of the interface and thereby aids its evolution. The related art has not been designed to solve this problem in that it does not generate debugger implementation code and is not streamlined to the problems of debuggers.

As shown inFIG. 3, a JDWPGen program parses a formal specification of the JDWP (JDWP.spec), and from the specification generates: 1) the protocol documentation (JDWPdetails.html), the front-end JDWP processing module (JDWPjava), and a C language “include” file (JDWPConstants.h) which controls the behavior of the back-end JDWP processing module (which is presently manually written). Since both the JDWPjava and JDWPConstants.h are generated from the same specification, it is much easier to “debug” the debugger code, and to produce new versions of the JDWP without having to re-write two separate programs.

In one embodiment of the present invention, a specification language is defined so that the JDWP specification can be precisely interpreted by JDWPGen. This purely declarative language is the JDWP specification language, and is described below. The syntax of the JDWP specification language primarily consists of parenthesized statements with the general form: open parenthesis, statement type, argument list and close parenthesis. The argument list often consists of statements. The exact nesting these statements may have is highly constrained and is defined precisely by the following grammar for the JDWP specification language:SPECIFICATIONNAME COMMENT SETLISTSETLISTSETSETLIST SETSET(CommandSet NAMEVALUE COMMANDLIST)(ConstantSet NAME CONSTANTLIST)COMMANDLISTCOMMANDCOMMANDLIST COMMANDCOMMAND(Command NAMEVALUE COMMENT COMMANDBODY)COMMANDBODY(Out STRUCTURE) (Reply STRUCTURE)(Event STRUCTURE)STRUCTUREELEMENTSTRUCTURE ELEMENTELEMENT(DATATYPE NAME COMMENT)(Group NAME STRUCTURE)(Repeat NAME COMMENT ELEMENT)(Select NAME SELECTOR ALTLIST)SELECTOR(INTEGRALDATATYPE NAME COMMENT)ALTLISTALTALTLIST ALTALT(Alt NAMEVALUE COMMENT STRUCTURE)DATATYPEINTEGRALDATATYPEbooleanobjectthreadObjectthreadGroupObjectarrayObjectstringObjectclassLoaderObjectclassObjectreferenceTypereferenceTypeIDclassTypeinterfaceTypearraytypemethodfieldframestringvaluelocationtagged-objectreferenceTypeIDtyped-sequenceuntagged-valueINTEGRALDATATYPEintlongbyteCONSTANTLISTCONSTANTCONSTANTLIST CONSTANTCONSTANT(Constant NAMEVALUE COMMENT)NAMEVALUENAME=NUMBERNAME=NAME
The symbols in all capital letters are non-terminals and all other symbols are terminals. Non-terminals are defined within the grammar except for the following:NAME a sequence of lettersNUMBER a sequence of digitsCOMMENT arbitrary text within double quotes or nothing
Semantics of Specification Language

A request command specifies a request for information made by the front-end where the Out section exactly specifies the format of the data that makes up the request and the Reply section exactly specifies the format of the data that will be returned by the back-end. An event command exactly specifies the format of data in an event emanating from the back-end. Constants specify specific values for use within commands.

In the present embodiment, JDWPGen employs a recursive descent parser to parse the JDWP specification, which is written in the JDWP specification language. Other parsing techniques could be used as well, such as a generated LALR(1) parser. The parser constructs an abstract syntax tree representation of the specification. Each node in the tree is an object that encapsulates the actions needed to generate the outputs for that node. The nodes correspond directly with statements in the input specification. All further processing is accomplished by “walking” this abstract syntax tree. Several passes are used to resolve names and check for errors. Finally, the tree is walked three more times to generate the outputs: once to generate the Java class which is used by the front-end to send and receive information across JDWP; once to generate the C include file containing the definitions used by the back-end to send and receive information across JDWP; and once to generate the published human-readable specification document in HTML.

FIG. 4is a diagrammatic representation of a virtual machine, such as a JVM, that can be supported by computer system100ofFIG. 1described above. Source code401is provided to a bytecode compiler403within a compile-time environment409. Bytecode compiler403translates source code401into bytecodes405. In general, source code401is translated into bytecodes405at the time source code401is created by a software developer.

Bytecodes405can generally be reproduced, downloaded, or otherwise distributed through a network, e.g., through network interface124ofFIG. 1, or stored on a storage device such as primary storage104ofFIG. 1. In the described embodiment, bytecodes405are platform independent. That is, bytecodes405may be executed on substantially any computer system that is running a suitable virtual machine. Native instructions formed by compiling bytecodes may be retained for later use by the JVM. In this way the cost of the translation are amortized over multiple executions to provide a speed advantage for native code over interpreted code. By way of example, in a Java™ environment, bytecodes405can be executed on a computer system that is running a JVM.

Bytecodes405are provided to a runtime environment413which includes a virtual machine411. Runtime environment413can generally be executed using a processor such as CPU102ofFIG. 1Virtual machine411includes a compiler415, an interpreter417, and a runtime system419. Bytecodes405can generally be provided either to compiler415or interpreter417.

When bytecodes405are provided to compiler415, methods contained in bytecodes405are compiled into native machine instructions (not shown). On the other hand, when bytecodes405are provided to interpreter417, bytecodes405are read into interpreter417one bytecode at a time. Interpreter417then performs the operation defined by each bytecode as each bytecode is read into interpreter417. In general, interpreter417processes bytecodes405and performs operations associated with bytecodes405substantially continuously.

When a method is called from an operating system421, if it is determined that the method is to be invoked as an interpreted method, runtime system419can obtain the method from interpreter417. If, on the other hand, it is determined that the method is to be invoked as a compiled method, runtime system419activates compiler415. Compiler415then generates native machine instructions from bytecodes405, and executes the machine-language instructions. In general, the machine-language instructions are discarded when virtual machine411terminates. The operation of virtual machines or, more particularly, Java™ virtual machines, is described in more detail inThe Java™ Virtual Machine Specificationby Tim Lindholm and Frank Yellin (ISBN 0-201-63452-X), which is incorporated herein by reference in its entirety.