#JDECOMPILER CODE#
#JDECOMPILER SERIES#

The resulting expression is more like high level language, and has also eliminated the use of the machine register eax. Mov eax, add eax, sub, eaxД¬ould result in the following IR after expression propagation: In particular, expression propagation combines the semantics of several instructions into more complex expressions. Various program analyses can be applied to the IR. Some languages also have extensive support for strings or long integers. It is particularly important to recognize the compiler idioms for subroutine calls, exception handling, and switch statements. Later phases group instruction expressions into more complex expressions, and modify them into a canonical (standardized) form, making it more likely that even the altered idiom will match a higher level pattern later in the decompilation. A pattern matching process in the disassembly phase would probably not recognize the altered pattern. For example, the instruction scheduling phase of a compiler may insert other instructions into an idiomatic sequence, or change the ordering of instructions in the sequence. In general, it is best to delay detection of idiomatic sequences if possible, to later stages that are less affected by instruction ordering. This can be implemented with a machine independent simplification rule, such as a = 0. For example, xor eax, eax clears the eax register (sets it to zero). Some idiomatic sequences are machine independent some involve only one instruction. For example, the Pentium machine instructionД¬dq eax edx is set to the sign-extensionв‰ edi,edi +(tex)push xor eax, edx sub eax, edx

#JDECOMPILER CODE#

The next logical phase is the disassembly of machine code instructions into a machine independent intermediate representation (IR). If it can determine the compiler or compilers used it may provide useful information in identifying code idioms. The front end may be able to identify the libraries used even if they are linked with the code, this will provide library interfaces. If available the symbol tables and debug data are also loaded. This excludes the runtime initialization code, which should not be decompiled if possible. In many cases, it should be able to find the equivalent of the main function of a C program, which is the start of the user written code. It should be able to discover basic facts about the input program, such as the architecture (Pentium, PowerPC, etc.) and the entry point. The first decompilation phase loads and parses the input machine code or intermediate language program's binary file format.

#JDECOMPILER SERIES#

Design Дecompilers can be thought of as composed of a series of phases each of which contributes specific aspects of the overall decompilation process. While decompilers are normally used to (re-)create source code from binary executables, there are also decompilers to turn specific binary data files into human-readable and editable sources. This is done to make it more difficult to reverse engineer the executable. Some compilers and post-compilation tools produce obfuscated code (that is, they attempt to produce output that is very difficult to decompile, or that decompiles to confusing output).

Machine language without such metadata or debug data is much harder to decompile. debug-symbols, may enable to reproduce the original names of variables and structures and even the line numbers.

NET Framework Common Language Runtime) often include extensive metadata and high-level features that make decompilation quite feasible. The bytecode formats used by many virtual machines (such as the Java Virtual Machine or the. The success of decompilation depends on the amount of information present in the code being decompiled and the sophistication of the analysis performed on it. It can be used for the recovery of lost source code, and is also useful in some cases for computer security, interoperability and error correction. By comparison, a disassembler translates an executable program into assembly language (and an assembler could be used for assembling it back into an executable program).Дecompilation is the act of using a decompiler, although the term can also refer to the output of a decompiler. The term decompiler is most commonly applied to a program which translates executable programs (the output from a compiler) into source code in a (relatively) high level language which, when compiled, will produce an executable whose behavior is the same as the original executable program.

JDecompiler