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87 lines
4.3 KiB
87 lines
4.3 KiB
11 years ago
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1. About the decompiler
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Fernflower is the first actually working analytical decompiler for Java and
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probably for a high-level programming language in general. Naturally it is still
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under development, please send your bug reports and improvement suggestions at
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fernflower.decompiler@gmail.com
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2. License
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See license_en.txt
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3. Running from the command line
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java -jar fernflower.jar [-<option>=<value>]* [<source>]+ <destination>
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* means 0 or more times
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+ means 1 or more times
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<source>: file or directory with files to be decompiled. Directories are recursively scanned. Allowed file extensions are class, zip and jar.
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Sources prefixed with -e= mean "library" files that won't be decompiled, but taken into account when analysing relationships between
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classes or methods. Especially renaming of identifiers (s. option 'ren') can benefit from information about external classes.
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<destination>: destination directory
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<option>,<value>: command line option with the corresponding value, see 4.
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Examples:
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java -jar fernflower.jar -hes=0 -hdc=0 c:\Temp\binary\ -e=c:\Java\rt.jar c:\Temp\source\
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java -jar fernflower.jar -dgs=1 c:\Temp\binary\library.jar c:\Temp\binary\Boot.class c:\Temp\source\
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4. Command line options
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With the exception of mpm and urc the value of 1 means the option is activated, 0 - deactivated. Default
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value, if any, is given between parentheses.
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Typically, the following options will be changed by user, if any: hes, hdc, dgs, mpm, ren, urc
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The rest of options can be left as they are: they are aimed at professional reverse engineers.
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rbr (1): hide bridge methods
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rsy (0): hide synthetic class members
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din (1): decompile inner classes
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dc4 (1): collapse 1.4 class references
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das (1): decompile assertions
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hes (1): hide empty super invocation
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hdc (1): hide empty default constructor
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dgs (0): decompile generic signatures
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occ (0): ouput copyright comment
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ner (1): assume return not throwing exceptions
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den (1): decompile enumerations
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rgn (1): remove getClass() invocation, when it is part of a qualified new statement
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bto (1): interpret int 1 as boolean true (workaround to a compiler bug)
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nns (1): allow for not set synthetic attribute (workaround to a compiler bug)
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uto (1): consider nameless types as java.lang.Object (workaround to a compiler architecture flaw)
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udv (1): reconstruct variable names from debug information, if present
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rer (1): remove empty exception ranges
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fdi (1): deinline finally structures
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asc (0): allow only ASCII characters in string literals. All other characters will be encoded using Unicode escapes (JLS 3.3). Default encoding is UTF8.
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mpm (0): maximum allowed processing time per decompiled method, in seconds. 0 means no upper limit.
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ren (0): rename ambiguous (resp. obfuscated) classes and class elements
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urc : full name of user-supplied class implementing IIdentifierRenamer. It is used to determine which
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class identifiers should be renamed and provides new identifier names. For more information
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s. section 5
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The default logging level is INFO. This value can be overwritten by setting the option 'log' as follows:
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log (INFO): possible values TRACE, INFO, WARN, ERROR
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5. Renaming identifiers
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Some obfuscators give classes and their member elements short, meaningless and above all ambiguous names. Recompiling of such
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code leads to a great number of conflicts. Therefore it is advisable to let the decompiler rename elements in its turn,
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ensuring uniqueness of each identifier.
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Option 'ren' (i.e. -ren=1) activates renaming functionality. Default renaming strategy goes as follows:
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- rename an element if its name is a reserved word or is shorter than 3 characters
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- new names are built according to a simple pattern: (class|method|field)_<consecutive unique number>
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You can overwrite this rules by providing your own implementation of the 4 key methods invoked by the decompiler while renaming. Simply
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pass a class that implements de.fernflower.main.extern.IIdentifierRenamer in the option 'urc' (e.g. -urc=com.mypackage.MyRenamer) to
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Fernflower. The class must be available on the application classpath.
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The meaning of each method should be clear from naming: toBeRenamed determine whether the element will be renamed, while the other three
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provide new names for classes, methods and fields respectively.
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