What are ODEX files in Android

Question

After some android apps installed  I found that it will change to odex file  not apk  in smartphone   How does it happens  Who can teach me  I am very interested about it

User · Answer

ART According to the docs  http   web archive org web 20170909233829 https   source android com devices tech dalvik configure an  odex file   contains AOT compiled code for methods in the APK   Furthermore  they appear to be regular shared libraries  since if you get any app  and check  file  data app com android appname-  oat arm64 base odex  it says  base odex  ELF shared object  64-bit LSB arm64  stripped  and aarch64-linux-gnu-objdump -d base odex seems to work and give some meaningful disassembly  but also some rubbish sections

User · Answer

This Blog article explains the internals of ODEX files      WHAT IS AN ODEX FILE       In Android file system  applications come in packages with the   extension  apk  These application packages  or APKs contain certain    odex files whose supposed function is to save space  These    odex      files are actually collections of parts of an application that are   optimized before booting  Doing so speeds up the boot process  as it   preloads part of an application  On the other hand  it also makes   hacking those applications difficult because a part of the coding has   already been extracted to another location before execution

User · Answer

The blog article is mostly right  but not complete  To have a full understanding of what an odex file does  you have to understand a little about how application files  APK  work  Applications are basically glorified ZIP archives  The java code is stored in a file called classes dex and this file is parsed by the Dalvik JVM and a cache of the processed classes dex file is stored in the phone s Dalvik cache  An odex is basically a pre-processed version of an application s classes dex that is execution-ready for Dalvik  When an application is odexed  the classes dex is removed from the APK archive and it does not write anything to the Dalvik cache  An application that is not odexed ends up with 2 copies of the classes dex file--the packaged one in the APK  and the processed one in the Dalvik cache  It also takes a little longer to launch the first time since Dalvik has to extract and process the classes dex file  If you are building a custom ROM  it s a really good idea to odex both your framework JAR files and the stock apps in order to maximize the internal storage space for user-installed apps  If you want to theme  then simply deodex - gt  apply your theme - gt  reodex - gt  release  To actually deodex  use small and baksmali  https   github com JesusFreke smali wiki DeodexInstructions

[android] What are ODEX files in Android?

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