1 <!doctype html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> 2 <html> 3 <head> 4 <meta http-equiv="content-type" content="text/html; charset=iso-8859-1"> 5 <meta http-equiv="content-style-type" content="text/css"> 6 <link rel="stylesheet" type="text/css" href="style.css"> 7 <title>ProGuard FAQ</title> 8 <script type="text/javascript" language="JavaScript"> 9 <!-- 10 if (window.self==window.top) 11 window.top.location.replace("index.html#"+window.location.pathname+window.location.hash); 12 else { 13 var hash="#"+window.location.pathname.replace(window.top.location.pathname.replace("index.html", ""), ""); 14 if (window.top.location.hash!=hash) 15 window.top.location.hash=hash; 16 } 17 //--> 18 </script> 19 </head> 20 <body> 21 22 <h2>Frequently Asked Questions</h2> 23 24 <h3>Contents</h3> 25 26 <ol> 27 <li><a href="#shrinking">What is shrinking?</a></li> 28 <li><a href="#obfuscation">What is obfuscation?</a></li> 29 <li><a href="#preverification">What is preverification?</a></li> 30 <li><a href="#optimization">What kind of optimizations does <b>ProGuard</b> 31 support?</a></li> 32 <li><a href="#commercial">Can I use <b>ProGuard</b> to process my commercial 33 application?</a></li> 34 <li><a href="#jdk1.4">Does <b>ProGuard</b> work with Java 2? Java 5? Java 35 6?</a></li> 36 <li><a href="#jme">Does <b>ProGuard</b> work with Java Micro Edition?</a></li> 37 <li><a href="#android">Does <b>ProGuard</b> work for Google Android 38 code?</a></li> 39 <li><a href="#blackberry">Does <b>ProGuard</b> work for Blackberry 40 code?</a></li> 41 <li><a href="#ant">Does <b>ProGuard</b> have support for Ant?</a></li> 42 <li><a href="#gui">Does <b>ProGuard</b> come with a GUI?</a></li> 43 <li><a href="#forname">Does <b>ProGuard</b> handle <code>Class.forName</code> 44 calls?</a></li> 45 <li><a href="#resource">Does <b>ProGuard</b> handle resource files?</a></li> 46 <li><a href="#encrypt">Does <b>ProGuard</b> encrypt strings constants?</a></li> 47 <li><a href="#flow">Does <b>ProGuard</b> perform control flow 48 obfuscation?</a></li> 49 <li><a href="#incremental">Does <b>ProGuard</b> support incremental 50 obfuscation?</a></li> 51 <li><a href="#keywords">Can <b>ProGuard</b> obfuscate using reserved 52 keywords?</a></li> 53 <li><a href="#stacktrace">Can <b>ProGuard</b> reconstruct obfuscated stack 54 traces?</a></li> 55 </ol> 56 57 <h3><a name="shrinking">What is shrinking?</a></h3> 58 59 Java source code (.java files) is typically compiled to bytecode (.class 60 files). Bytecode is more compact than Java source code, but it may still 61 contain a lot of unused code, especially if it includes program libraries. 62 Shrinking programs such as <b>ProGuard</b> can analyze bytecode and remove 63 unused classes, fields, and methods. The program remains functionally 64 equivalent, including the information given in exception stack traces. 65 66 <h3><a name="obfuscation">What is obfuscation?</a></h3> 67 68 By default, compiled bytecode still contains a lot of debugging information: 69 source file names, line numbers, field names, method names, argument names, 70 variable names, etc. This information makes it straightforward to decompile 71 the bytecode and reverse-engineer entire programs. Sometimes, this is not 72 desirable. Obfuscators such as <b>ProGuard</b> can remove the debugging 73 information and replace all names by meaningless character sequences, making 74 it much harder to reverse-engineer the code. It further compacts the code as a 75 bonus. The program remains functionally equivalent, except for the class 76 names, method names, and line numbers given in exception stack traces. 77 78 <h3><a name="preverification">What is preverification?</a></h3> 79 80 When loading class files, the class loader performs some sophisticated 81 verification of the byte code. This analysis makes sure the code can't 82 accidentally or intentionally break out of the sandbox of the virtual machine. 83 Java Micro Edition and Java 6 introduced split verification. This means that 84 the JME preverifier and the Java 6 compiler add preverification information to 85 the class files (StackMap and StackMapTable attributes, respectively), in order 86 to simplify the actual verification step for the class loader. Class files can 87 then be loaded faster and in a more memory-efficient way. <b>ProGuard</b> can 88 perform the preverification step too, for instance allowing to retarget older 89 class files at Java 6. 90 91 <h3><a name="optimization">What kind of optimizations does <b>ProGuard</b> support?</a></h3> 92 93 Apart from removing unused classes, fields, and methods in the shrinking step, 94 <b>ProGuard</b> can also perform optimizations at the bytecode level, inside 95 and across methods. Thanks to techniques like control flow analysis, data flow 96 analysis, partial evaluation, static single assignment, global value numbering, 97 and liveness analysis, <b>ProGuard</b> can: 98 99 <ul> 100 <li>Evaluate constant expressions.</li> 101 <li>Remove unnecessary field accesses and method calls.</li> 102 <li>Remove unnecessary branches.</li> 103 <li>Remove unnecessary comparisons and instanceof tests.</li> 104 <li>Remove unused code blocks.</li> 105 <li>Merge identical code blocks.</li> 106 <li>Reduce variable allocation.</li> 107 <li>Remove write-only fields and unused method parameters.</li> 108 <li>Inline constant fields, method parameters, and return values.</li> 109 <li>Inline methods that are short or only called once.</li> 110 <li>Simplify tail recursion calls.</li> 111 <li>Merge classes and interfaces.</li> 112 <li>Make methods private, static, and final when possible.</li> 113 <li>Make classes static and final when possible.</li> 114 <li>Replace interfaces that have single implementations.</li> 115 <li>Perform over 200 peephole optimizations, like replacing ...*2 by 116 ...<<1.</li> 117 <li>Optionally remove logging code.</li> 118 </ul> 119 The positive effects of these optimizations will depend on your code and on 120 the virtual machine on which the code is executed. Simple virtual machines may 121 benefit more than advanced virtual machines with sophisticated JIT compilers. 122 At the very least, your bytecode may become a bit smaller. 123 <p> 124 Some notable optimizations that aren't supported yet: 125 <ul> 126 <li>Moving constant expressions out of loops.</li> 127 <li>Optimizations that require escape analysis.</li> 128 </ul> 129 130 <h3><a name="commercial">Can I use <b>ProGuard</b> to process my commercial application?</a></h3> 131 132 Yes, you can. <b>ProGuard</b> itself is distributed under the GPL, but this 133 doesn't affect the programs that you process. Your code remains yours, and 134 its license can remain the same. 135 136 <h3><a name="jdk1.4">Does <b>ProGuard</b> work with Java 2? Java 5? Java 6? Java 7?</a></h3> 137 138 Yes, <b>ProGuard</b> supports all JDKs from 1.1 up to and including 7.0. Java 2 139 introduced some small differences in the class file format. Java 5 added 140 attributes for generics and for annotations. Java 6 introduced optional 141 preverification attributes. Java 7 made preverification obligatory and 142 introduced support for dynamic languages. <b>ProGuard</b> handles all versions 143 correctly. 144 145 <h3><a name="jme">Does <b>ProGuard</b> work with Java Micro Edition?</a></h3> 146 147 Yes. <b>ProGuard</b> itself runs in Java Standard Edition, but you can freely 148 specify the run-time environment at which your programs are targeted, 149 including Java Micro Edition. <b>ProGuard</b> then also performs the required 150 preverification, producing more compact results than the traditional external 151 preverifier. 152 <p> 153 <b>ProGuard</b> also comes with an obfuscator plug-in for the JME Wireless 154 Toolkit. 155 156 <h3><a name="android">Does <b>ProGuard</b> work for Google Android code?</a></h3> 157 158 Yes. Google's <code>dx</code> compiler converts ordinary jar files into files 159 that run on Android devices. By preprocessing the original jar files, 160 <b>ProGuard</b> can significantly reduce the file sizes and boost the run-time 161 performance of the code. 162 163 <h3><a name="blackberry">Does <b>ProGuard</b> work for Blackberry code?</a></h3> 164 165 It should. RIM's proprietary <code>rapc</code> compiler converts ordinary JME 166 jar files into cod files that run on Blackberry devices. The compiler performs 167 quite a few optimizations, but preprocessing the jar files with 168 <b>ProGuard</b> can generally still reduce the final code size by a few 169 percent. However, the <code>rapc</code> compiler also seems to contain some 170 bugs. It sometimes fails on obfuscated code that is valid and accepted by other 171 JME tools and VMs. Your mileage may therefore vary. 172 173 <h3><a name="ant">Does <b>ProGuard</b> have support for Ant?</a></h3> 174 175 Yes. <b>ProGuard</b> provides an Ant task, so that it integrates seamlessly 176 into your Ant build processes. You can still use configurations in 177 <b>ProGuard</b>'s own readable format. Alternatively, if you prefer XML, you 178 can specify the equivalent XML configuration. 179 180 <h3><a name="gui">Does <b>ProGuard</b> come with a GUI?</a></h3> 181 182 Yes. First of all, <b>ProGuard</b> is perfectly usable as a command-line tool 183 that can easily be integrated into any automatic build process. For casual 184 users, there's also a graphical user interface that simplifies creating, 185 loading, editing, executing, and saving ProGuard configurations. 186 187 <h3><a name="forname">Does <b>ProGuard</b> handle <code>Class.forName</code> calls?</a></h3> 188 189 Yes. <b>ProGuard</b> automatically handles constructs like 190 <code>Class.forName("SomeClass")</code> and <code>SomeClass.class</code>. The 191 referenced classes are preserved in the shrinking phase, and the string 192 arguments are properly replaced in the obfuscation phase. 193 <p> 194 With variable string arguments, it's generally not possible to determine their 195 possible values. They might be read from a configuration file, for instance. 196 However, <b>ProGuard</b> will note a number of constructs like 197 "<code>(SomeClass)Class.forName(variable).newInstance()</code>". These might 198 be an indication that the class or interface <code>SomeClass</code> and/or its 199 implementations may need to be preserved. The user can adapt his configuration 200 accordingly. 201 202 <h3><a name="resource">Does <b>ProGuard</b> handle resource files?</a></h3> 203 204 Yes. <b>ProGuard</b> copies all non-class resource files, optionally adapting 205 their names and their contents to the obfuscation that has been applied. 206 207 <h3><a name="encrypt">Does <b>ProGuard</b> encrypt strings constants?</a></h3> 208 209 No. Storing encrypted string constants in program code is fairly futile, since 210 the encryption has to be perfectly reversible by definition. Moreover, the 211 decryption costs additional memory and computation at run-time. If this feature 212 is ever incorporated, I'll provide a tool to decrypt the strings as well. 213 214 <h3><a name="flow">Does <b>ProGuard</b> perform flow obfuscation?</a></h3> 215 216 Not explicitly. Control flow obfuscation injects additional branches into the 217 bytecode, in an attempt to fool decompilers. <b>ProGuard</b> does not do this, 218 in order to avoid any negative effects on performance and size. However, the 219 optimization step often already restructures the code to the point where most 220 decompilers get confused. 221 222 <h3><a name="incremental">Does <b>ProGuard</b> support incremental obfuscation?</a></h3> 223 224 Yes. This feature allows you to specify a previous obfuscation mapping file in 225 a new obfuscation step, in order to produce add-ons or patches for obfuscated 226 code. 227 228 <h3><a name="keywords">Can <b>ProGuard</b> obfuscate using reserved keywords?</a></h3> 229 230 Yes. You can specify your own obfuscation dictionary, such as a list of 231 reserved key words, identifiers with foreign characters, random source files, 232 or a text by Shakespeare. Note that this hardly improves the obfuscation. 233 Decent decompilers can automatically replace reserved keywords, and the effect 234 can be undone fairly easily, by obfuscating again with simpler names. 235 236 <h3><a name="stacktrace">Can <b>ProGuard</b> reconstruct obfuscated stack traces?</a></h3> 237 238 Yes. <b>ProGuard</b> comes with a companion tool, <b>ReTrace</b>, that can 239 'de-obfuscate' stack traces produced by obfuscated applications. The 240 reconstruction is based on the mapping file that <b>ProGuard</b> can write 241 out. If line numbers have been obfuscated away, a list of alternative method 242 names is presented for each obfuscated method name that has an ambiguous 243 reverse mapping. Please refer to the <a href="manual/index.html">ProGuard User 244 Manual</a> for more details. 245 246 <hr /> 247 <noscript><div><a target="_top" href="index.html" class="button">Show menu</a></div></noscript> 248 <address> 249 Copyright © 2002-2011 250 <a target="other" href="http://www.lafortune.eu/">Eric Lafortune</a>. 251 </address> 252 </body> 253 </html> 254
