The Squawk virtual machine is a small Java TM virtual machine (VM) written mostly in Java that runs without an operating system on a wireless sensor platform. Squawk translates standard class file into an internal pre-linked, position independent format that is compact and allows for efficient execution of bytecodes that have been placed into a read-only memory. In addition, Squawk implements an application isolation mechanism whereby applications are represented as object and are therefore treated as first class objects (i.e., they can be reified). Application isolation also enables Squawk to run multiple applications at once with all immutable state being shared between the applications. Mutable state is not shared. The combination of these features reduce the memory footprint of the VM, making it ideal for deployment on small devices.Squawk provides a wireless API that allows developers to write applications for wireless sensor networks (WSNs), this API is an extension of the generic connection framework (GCF). Authentication of deployed files on the wireless device and migration of applications between devices is also performed by the VM. This paper describes the design and implementation of the Squawk VM as applied to the Sun TM Small Programmable Object Technology (SPOT) wireless device; a device developed at Sun Microsystems Laboratories for experimentation with wireless sensor and actuator applications.

Figure 5. UQBT uses PAL to perform parameter analysis of (a) a sequence of Sparc RTLs, to produce (b) HRTL code. From the HRTL, UQBT can generate code for other processors.

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The structure of a decompiler is presented, along with a thorough description of the different modules that form part of a decompiler, and the type of analyses that are performed on the machine code to regenerate high‐level language code. The phases of the decompiler have been grouped into three main modules: front‐end, universal decompiling machine, and back‐end. The front‐end is a machine‐dependent module that performs the loading, parsing and semantic analysis of the input program, as well as generating an intermediate representation of the program. The universal decompiling machine is a machine‐ and language‐independent module that performs data and control flow analysis of the program based on the intermediate representation, and the program's control flow graph. The back‐end is a language‐dependent module that deals with the details of the target high‐level language. In order to increase the readability of the generated programs, a decompiling system has been implemented which integrates a decompiler, dcc, and an automatic signature generator, dccSign. Signatures for libraries and compilers are stored in a database that is read by the decompiler; thus, the generated programs can make use of known library names, such as WriteLn() and printf(). dcc is a decompiler for the Intel 80286 architecture and the DOS operating system. dec takes as input binary programs from a DOS environment and generates C programs as output. Sample code produced by this decompiler is given.