Data processing: software development – installation – and managem – Software program development tool – Testing or debugging
Reexamination Certificate
2001-05-16
2004-02-10
Nguyen-Ba, Anthony (Department: 2122)
Data processing: software development, installation, and managem
Software program development tool
Testing or debugging
C717S148000, C709S241000
Reexamination Certificate
active
06691303
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
This invention relates, in its most general aspects, to a computer system and to a method of operating that system, and to improvements in the performance of various operations within such a system. It also relates to a computer-readable storage medium. The computer system may be, may include, or may be part of, a virtual machine. The computer-readable storage medium may contain executable code or other instructions for programming the computer system/virtual machine. In particular, the invention relates to a method for automatic testing and verification of dynamically compiled code in a virtual machine.
2. Description of Related Art
In recent years, there have been developments in programming languages towards what is known as an object-oriented language. In these developments, concepts are regarded as ‘objects’, each carrying with it a set of data, or attributes, pertinent to that object, as well as information relating to so-called ‘methods’, that is functions or sub-routines, that can be performed on that object and its data. This is well known to those skilled in the art of computing and/or programming.
The advent and rapid advancement in the spread and availability of computers has led to the independent development of different types of systems, such as the IBM and IBM-compatible PC running IBM-DOS or MS-DOS or MS-Windows applications, the Apple Macintosh machines running their own Apple System operating system, or various Unix machines running their own Unix operating systems. This proliferation of independent systems has led to useful applications being available only in one format and not being capable of running on a machine for which the application was not designed.
Under such circumstances, programmers have devised software which ‘emulates’ the host computer's operating system so that a ‘foreign’ application can be made to run successfully in such a way that, as far as the user is concerned, the emulation is invisible. In other words, the user can perform all of the normal functions of say a Windows-based application on a Unix machine using a Unix-based operating system without noticing that he is doing so.
A particularly notable product of this type is that developed by Insignia Solutions of High Wycombe, GB and Santa Clara, Calif., USA and known under the name ‘SoftWindows 2.0 for Powermac’. This software enables a physical Macintosh computer to emulate a PC having an Intel 80486DX processor and 80487 maths co-processor plus memory, two hard disks, IBM-style keyboard, colour display and other features normally found on recent versions of the PC-type of computer.
Furthermore, there is an ever-increasing demand by the consumer for electronics gadgetry, communications and control systems which, like computers, have developed independently of one another and have led to incompatibility between operating systems and protocols. For example, remote-control devices for video players, tape players and CD players have similar functions, analogous to ‘play,’ ‘forward,’ ‘reverse,’ ‘pause,’ etc, but the codes for transmission between the remote control, or commander, operated by the user may not be compatible either between different types of equipment made by the same manufacturer or between the same types of equipment made by different manufacturers. There would be clear benefits of having software within the equipment which can produce for example the correct ‘play’ code based upon a ‘play’ command regardless of the specific hardware used in the equipment. Such software is commonly known as a ‘Virtual Machine.’
Other uses and applications are legion: for example, set-top boxes for decoding television transmissions, remote diagnostic equipment, in-car navigation systems and so-called ‘Personal Digital Assistants.’ Mobile telephones, for instance, can have a system upgrade downloaded to them from any service provider.
Emulation software packages tend to have certain features in common, notably that they are not general purpose but are dedicated. They are of most benefit in rapid development areas and have a distinct advantage in enabling manufacturers to cut costs. In particular, they can divorce software from the physical machine, i.e., the effect of the software in the physical machine can be altered by the emulating software without having to go into the machine's native software to implement those changes.
The specific object-oriented language used in some of the implementations described later is that known as Java (registered trade mark to Sun Microsystems Corporation). Some of the following implementations will enable Java to be used in smaller devices than is currently possible because of the improved performance and/or reduced memory footprint. Future uses projected for embedded software (virtual machines) include computers worn on the body, office equipment, household appliances, and intelligent houses and cars.
While it is recognised that there are clear advantages in the use of virtual machines. especially those using object-oriented languages, there are naturally areas where it is important and/or beneficial for some of the operations that are carried out within the system to be optimised. These may include reducing the memory requirement, increasing the speed of operation, and improving the ‘transparency’ of the system when embedded in another system. One of the principal aims of the inventions described herein is to provide a Virtual Machine which is optimised to work as quickly as possible within a memory constraint of, for example, less than 10, 5, 2 or even 1 Mbyte. Such a constraint is likely to be applicable, for example, to electronics gadgetry and other equipment where cost (or size) is a major constraint.
Errors in dynamically compiled code frequently manifest themselves a long time after the error actually occurred, making it difficult to identify the true cause. An error may appear benign when it occurs (for example an incorrect calculation which is not immediately used), but its effects may be disastrous at some future time or event (for example, when the incorrect value is used).
When changing and/or adding optimisations to a dynamic compiler, it is difficult to demonstrate that the code produced as a result is correct. The invention is therefore concerned with testing for such errors.
In one known technique, testing as such was not conducted in a forward-looking sense. Instead, when an error was noted, the process would be investigated backwards to locate the origin of the error. This technique was clearly open to the risk of potentially disastrous errors occurring unnoticed until too late.
In another known technique which is an improvement over the previous one just mentioned, two execution engines are used within the same process and their results are compared. One execution engine is the trusted implementation (the master) and the other is the implementation under test (the slave). This test process is limited to a singly-threaded application and can be both cumbersome and time-consuming, since the execution engines must be run in series. The process is to save the initial state (state
1
), run part of the master, save the final state of the master (state
2
), restore state
1
, run part of the slave, then check the final state of the slave against the saved state
2
to detect discrepancies.
The testing technique implemented in Softwindows (by Insignia) was of such a type as just outlined. While effective for its purpose it would be fair to say that it was limited in that it was only applicable to single threaded environments and, when applied to a CPU emulator, had an executable that was simply enormous. The executables for the master and slave were in the same executable so testing had to be done in series. Moreover, the testing technique could itself introduce bugs and dissimilarities between master and slave. The points at which comparisons of state would have been carried out were largely only at transfers of control.
Techniques for identifying the cause of errors once ident
Charnell William Thomas
Darnell Stephen
Dias Blaise Abel Alec
Guthrie Philippa Joy
Kramskoy Jeremy Paul
Caesar Rivise Bernstein Cohen & Pokotilow Ltd.
Esmertec AG
Nguyen-Ba Anthony
LandOfFree
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