Vdex Extractor

Command line tool to decompile and extract Android Dex bytecode from Vdex files that are generated along with Oat files when optimizing bytecode from dex2oat ART runtime compiler. Vdex file format has been introduced in the Oreo (API-26) build. More information is available [here][vdex-cr]. It should be noted that Oat files are no longer storing the matching Dex files inside their .rodata section. Instead they're always paired with a matching Vdex container file.

Compile

• Clone this repository
• Install Android NDK if you want to cross-compile for Android devices
• Invoke make.sh bash script with desired build target
• $ ./make.sh - if CC not defined from env use gcc by default
• $ ./make.sh gcc - compile with gcc
• $ ./make.sh clang - compile with clang
• $ ./make.sh cross-android - cross-compile (armeabi-v7a, arm64-v8a, x86 & x86_64) for Android with NDK
• Executables are copied under the bin directory
• For debug builds use $ DEBUG=true ./make.sh

Dependencies

The following external libraries should be installed the in the host system:

1. zlib
   • macOS with homebrew: brew install zlib-devel
   • macOS with macports: port install zlib
   • Linux with apt: apt install libz-dev
   • Other Linux/Unix systems: Check available package manager or compile from sources
   • Windows with cygwin: Install zlib-devel from cygwin installer

Usage

$ bin/vdexExtractor -h
              vdexExtractor ver. 0.5.2
    Anestis Bechtsoudis <anestis@census-labs.com>
  Copyright 2017 - 2018 by CENSUS S.A. All Rights Reserved.

 -i, --input=<path>   : input dir (search recursively) or single file
 -o, --output=<path>  : output path (default is same as input)
 -f, --file-override  : allow output file override if already exists (default: false)
 --no-unquicken       : disable unquicken bytecode decompiler (don't de-odex)
 --deps               : dump verified dependencies information
 --dis                : enable bytecode disassembler
 --ignore-crc-error   : decompiled Dex CRC errors are ignored (see issue #3)
 --new-crc=<path>     : text file with extracted Apk or Dex file location checksum(s)
 --get-api             : get Android API level based on Vdex version (expects single Vdex file)
 -v, --debug=LEVEL    : log level (0 - FATAL ... 4 - DEBUG), default: '3' (INFO)
 -l, --log-file=<path>: save disassembler and/or verified dependencies output to log file (default is STDOUT)
 -h, --help           : this help

Bytecode Unquickening Decompiler

The Vdex file includes all quick_info data (old vtable) required to revert the dex-to-dex transformations applied during bytecode optimization. The idea here is to create a quick standalone tool capable to revert optimized bytecode, that does not require building the entire libart from AOSP.

The Vdex fully unquicken functionality has been also implemented as part of the AOSP oatdump libart tool. The upstream contribution is available [here][aosp-master]. If you want to use oatdump with Oreo release you can use the corresponding patch [here][oatdump-oreo] or fork and build (inside and AOSP_SRC_ROOT workspace) the oreo-release branch of the [oatdump++][oatdump-plus] tool. Google has released the contributed patches along with the Android Pie release of the ART runtime. However, the upstream oatdump is appending the entire de-duplicated shared data section at the end of each CompactDex file when exporting.

Verified Dependencies Iterator

When the Dex bytecode files are compiled (optimized) for the first time, dex2oat executes the verification dependencies collector as part of the MethodVerifier The verification dependencies collector class is used to record resolution outcomes and type assignability tests of classes/methods/fields defined in the classpath. The compilation driver initializes the class and registers all Dex files which are being compiled. Classes defined in Dex files outside of this set (or synthesized classes without associated Dex files) are considered being in the classpath. All recorded dependencies are stored in the generated Vdex file along with the corresponding Oat file from the OatWriter class.

vdexExtractor tool integrates a Vdex dependencies walker function that is capable to iterate all dependencies information and dump them in a human readable format. The following snippet demonstrates a dependencies dump example of a sample Vdex file.

$ bin/vdexExtractor -i /tmp/BasicDreams.vdex -o /tmp --deps -f
[INFO] Processing 1 file(s) from /tmp/BasicDreams.vdex
------- Vdex Deps Info -------
dex file #0
 extra strings: number_of_strings=2
  0000: 'Ljava/lang/Thread;'
  0001: 'Ljava/lang/Throwable;'
 assignable type sets: number_of_sets=8
  0000: 'Landroid/service/dreams/DreamService;' must be assignable to 'Landroid/content/Context;'
  0001: 'Landroid/view/TextureView;' must be assignable to 'Landroid/view/View;'
  0002: 'Ljava/nio/FloatBuffer;' must be assignable to 'Ljava/nio/Buffer;'
...
 unassignable type sets: number_of_sets=0
 class dependencies: number_of_classes=34
  0000: 'Landroid/graphics/Color;' 'must' be resolved with access flags '1'
  0001: 'Landroid/graphics/SurfaceTexture;' 'must' be resolved with access flags '1'
...
  0024: 'Ljavax/microedition/khronos/egl/EGL10;' 'must' be resolved with access flags '513'
...
 field dependencies: number_of_fields=4
  0000: 'Ljavax/microedition/khronos/egl/EGL10;'->'EGL_DEFAULT_DISPLAY':'Ljava/lang/Object;' is expected to be in class 'Ljavax/microedition/khronos/egl/EGL10;' and have the access flags '9'
  0001: 'Ljavax/microedition/khronos/egl/EGL10;'->'EGL_NO_CONTEXT':'Ljavax/microedition/khronos/egl/EGLContext;' is expected to be in class 'Ljavax/microedition/khronos/egl/EGL10;' and have the access flags '9'
  0002: 'Ljavax/microedition/khronos/egl/EGL10;'->'EGL_NO_DISPLAY':'Ljavax/microedition/khronos/egl/EGLDisplay;' is expected to be in class 'Ljavax/microedition/khronos/egl/EGL10;' and have the access flags '9'
  0003: 'Ljavax/microedition/khronos/egl/EGL10;'->'EGL_NO_SURFACE':'Ljavax/microedition/khronos/egl/EGLSurface;' is expected to be in class 'Ljavax/microedition/khronos/egl/EGL10;' and have the access flags '9'
 method dependencies: number_of_methods=84
  0000: 'Landroid/graphics/Color;'->'HSVToColor':'([F)I' is expected to be in class 'Landroid/graphics/Color;', have the access flags '9
  0001: 'Landroid/opengl/GLES20;'->'glAttachShader':'(II)V' is expected to be in class 'Landroid/opengl/GLES20;', have the access flags '9
  0002: 'Landroid/opengl/GLES20;'->'glClear':'(I)V' is expected to be in class 'Landroid/opengl/GLES20;', have the access flags '9
...
 unverified classes: number_of_classes=0
----- EOF Vdex Deps Info -----
[INFO] 1 out of 1 Vdex files have been processed
[INFO] 1 Dex files have been extracted in total
[INFO] Extracted Dex files are available in '/tmp'

Integrated Disassembler

To debug the decompiler and assist the Dex bytecode investigation tasks, a light disassembler has been implemented. The disassembler output is very similar to the one provided by the AOSP dexdump2 utility of the platform/art project. The disassembler can be used independently of the unquickening decompiler.

A sample output is illustrated in the following snippet. Lines prefixed with [new] illustrate the output of the decompiled instruction (previous line) located in that offset. Notice that all the quickened offsets and vtable references have been reverted back to original signatures and prototypes.

$ bin/vdexExtractor -i /tmp/Videos.vdex -o /tmp -f --dis -l /tmp/dis.log
[INFO] Processing 1 file(s) from /tmp/Videos.vdex
[INFO] 1 out of 1 Vdex files have been processed
[INFO] 2 Dex files have been extracted in total
[INFO] Extracted Dex files are available in '/tmp'
$ head -90 /tmp/dis.log
------ Dex Header Info ------
magic        : dex-035
checksum     : e14de163 (3779977571)
signature    : 9a91f8e5f2afe2c6b5c2b4853832d3c5ed01aef8
fileSize     : 8ca638 (9217592)
headerSize   : 70 (112)
endianTag    : 12345678 (305419896)
linkSize     : 0 (0)
linkOff      : 0 (0)
mapOff       : 8ca568 (9217384)
stringIdsSize: ef06 (61190)
stringIdsOff : 70 (112)
typeIdsSize  : 29f4 (10740)
typeIdsOff   : 3bc88 (244872)
protoIdsSize : 3df9 (15865)
protoIdsOff  : 46458 (287832)
fieldIdsSize : a79d (42909)
fieldIdsOff  : 74c04 (478212)
methodIdsSize: fed7 (65239)
methodIdsOff : c88ec (821484)
classDefsSize: 2288 (8840)
classDefsOff : 147fa4 (1343396)
dataSize     : 73d594 (7591316)
dataOff      : 18d0a4 (1626276)
-----------------------------
file #0: classDefsSize=8840
  class #0: a.a ('La$a;')
   access=0601 (PUBLIC INTERFACE ABSTRACT)
   source_file=SourceFile, class_data_off=851907 (8722695)
   static_fields=0, instance_fields=0, direct_methods=0, virtual_methods=2
   virtual_method #0: onMenuItemSelected (La;Landroid/view/MenuItem;)Z
    access=0401 (PUBLIC ABSTRACT)
    codeOff=0 (0)
   virtual_method #1: invokeItem (Landroid/support/v7/view/menu/MenuItemImpl;)Z
    access=0401 (PUBLIC ABSTRACT)
    codeOff=0 (0)
  class #1: a.b ('La$b;')
   access=0601 (PUBLIC INTERFACE ABSTRACT)
   source_file=SourceFile, class_data_off=851913 (8722707)
   static_fields=0, instance_fields=0, direct_methods=0, virtual_methods=1
   virtual_method #0: invokeItem (Landroid/support/v7/view/menu/MenuItemImpl;)Z
    access=0401 (PUBLIC ABSTRACT)
    codeOff=0 (0)
  class #2: SupportMenu ('Landroid/support/v4/internal/view/SupportMenu;')
   access=0601 (PUBLIC INTERFACE ABSTRACT)
   source_file=SourceFile, class_data_off=0 (0)
  class #3: a ('La;')
   access=0001 (PUBLIC)
   source_file=SourceFile, class_data_off=85191b (8722715)
   static_fields=1, instance_fields=25, direct_methods=12, virtual_methods=74
   direct_method #0: <clinit> ()V
    access=10008 (STATIC CONSTRUCTOR)
    codeOff=1abb50 (1751888)
    quickening_size=4 (4)
      1abb60: 1260                                   |0000: const/4 v0, #int 6 // #6
      1abb62: 2300 e426                              |0001: new-array v0, v0, [I // type@26e4
      1abb66: 2600 0700 0000                         |0003: fill-array-data v0, 0000000a // +00000000
      1abb6c: 6900 1900                              |0006: sput-object v0, La;.sCategoryToOrder:[I // field@0019
      1abb70: 7300                                   |0008: return-void-no-barrier
[new] 1abb70: 0e00                                   |0008: return-void
      1abb72: 0000                                   |0009: nop // spacer
      1abb74: 0003 0400 0600 0000 0100 0000 0400 ... |000a: array-data (16 units)
   direct_method #1: invokeItem (Landroid/support/v7/view/menu/MenuItemImpl;)Z
    access=10001 (PUBLIC CONSTRUCTOR)
    codeOff=1abb94 (1751956)
    quickening_size=22 (34)
      1abba4: 1211                                   |0000: const/4 v1, #int 1 // #1
      1abba6: 1200                                   |0001: const/4 v0, #int 0 // #0
      1abba8: 7010 dbf9 0200                         |0002: invoke-direct {v2}, Ljava/lang/Object;.<init>:()V // method@f9db
      1abbae: e620 4000                              |0005: iput-quick v0, v2, [obj+0040]
[new] 1abbae: 5920 0400                              |0005: iput v0, v2, La;.mDefaultShowAsAction:I // field@0004
      1abbb2: eb20 4a00                              |0007: iput-boolean-quick v0, v2, [obj+004a]
[new] 1abbb2: 5c20 1200                              |0007: iput-boolean v0, v2, La;.mPreventDispatchingItemsChanged:Z // field@0012
      1abbb6: eb20 4700                              |0009: iput-boolean-quick v0, v2, [obj+0047]
[new] 1abbb6: 5c20 0d00                              |0009: iput-boolean v0, v2, La;.mItemsChangedWhileDispatchPrevented:Z // field@000d
      1abbba: eb20 4d00                              |000b: iput-boolean-quick v0, v2, [obj+004d]
[new] 1abbba: 5c20 1600                              |000b: iput-boolean v0, v2, La;.mStructureChangedWhileDispatchPrevented:Z // field@0016
      1abbbe: eb20 4800                              |000d: iput-boolean-quick v0, v2, [obj+0048]
[new] 1abbbe: 5c20 0f00                              |000d: iput-boolean v0, v2, La;.mOptionalIconsVisible:Z // field@000f
      1abbc2: eb20 4500                              |000f: iput-boolean-quick v0, v2, [obj+0045]
[new] 1abbc2: 5c20 0a00                              |000f: iput-boolean v0, v2, La;.mIsClosing:Z // field@000a
      1abbc6: 2200 fe25                              |0011: new-instance v0, Ljava/util/ArrayList; // type@25fe
      1abbca: 7010 6bfb 0000                         |0013: invoke-direct {v0}, Ljava/util/ArrayList;.<init>:()V // method@fb6b
      1abbd0: e820 3800                              |0016: iput-object-quick v0, v2, [obj+0038]
[new] 1abbd0: 5b20 1700                              |0016: iput-object v0, v2, La;.mTempShortcutItemList:Ljava/util/ArrayList; // field@0017
      1abbd4: 2200 2c26                              |0018: new-instance v0, Ljava/util/concurrent/CopyOnWriteArrayList; // type@262c
      1abbd8: 7010 cdfc 0000                         |001a: invoke-direct {v0}, Ljava/util/concurrent/CopyOnWriteArrayList;.<init>:()V // method@fccd
      1abbde: e820 3000                              |001d: iput-object-quick v0, v2, [obj+0030]
[new] 1abbde: 5b20 1100                              |001d: iput-object v0, v2, La;.mPresenters:Ljava/util/concurrent/CopyOnWriteArrayList; // field@0011
      1abbe2: e823 1000                              |001f: iput-object-quick v3, v2, [obj+0010]

Compact Dex Converter

The Android 9 (Pie) release has introduced a new type of Dex file, the Compact Dex (Cdex). Cdex is an ART internal file format that is compacting various Dex data structs (e.g. method header) and deduplicates common data blobs (e.g. strings) in multi-dex files. The deduplicated data from the Dex files of an input application are stored in the shared section of the Vdex container.

Now since the Vdex containers are storing Cdex files instead of standar