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JNI Analyzer


A simple tool to help finding JNI calls in a x86/ARM disassembly listing.

Originally presented in this article archived here, the script has been modified in order to support both x86 syntaxes as well as ARM.

Thus, it can be used for debugging/reverse engineering Android native libraries using JNI.


  • Support of x86 AT&T and Intel syntaxes
  • Support of ARM


Pass the ARM or x86 (AT&T or Intel syntax) disassembly listing via stdin.
This was particulary designed for the objdump output.
The processed text can be collected at stdout.

x86 AT&T syntax

$ objdump -d | python -a x86

x86 Intel syntax

$ objdump -M intel -d | python -a x86


$ tools/arm-linux-androideabi-objdump -d | python -a arm


You can find some compiled libraries coming from different projects, and their source code in the examples folder.

hello-jni: sample from android-ndk-r8b

$ objdump -M intel -d examples/hello-jni/libs/x86/ | python -a x86
00000500 <Java_com_example_hellojni_HelloJni_stringFromJNI>:
 500:   53                      push   ebx
 501:   83 ec 18                sub    esp,0x18
 504:   e8 e8 ff ff ff          call   4f1 <__cxa_atexit@plt+0x101>
 509:   81 c3 cf 1a 00 00       add    ebx,0x1acf
 50f:   8b 44 24 20             mov    eax,DWORD PTR [esp+0x20]
 513:   8b 00                   mov    eax,DWORD PTR [eax]
 515:   8b 90 9c 02 00 00       mov    edx,DWORD PTR [eax+0x29c]
 51b:   8d 83 5c e5 ff ff       lea    eax,[ebx-0x1aa4]
 521:   89 44 24 04             mov    DWORD PTR [esp+0x4],eax
 525:   8b 44 24 20             mov    eax,DWORD PTR [esp+0x20]
 529:   89 04 24                mov    DWORD PTR [esp],eax
 52c:   ff d2                   call   edx      ;jnicall: NewStringUTF
 52e:   83 c4 18                add    esp,0x18
 531:   5b                      pop    ebx
 532:   c3                      ret    
 533:   90                      nop
$ tools/arm-linux-androideabi-objdump -d examples/hello-jni/libs/armeabi/ | python -a arm
00000c24 <Java_com_example_hellojni_HelloJni_stringFromJNI>:
     c24:       b500            push    {lr}
     c26:       b083            sub     sp, #12
     c28:       9001            str     r0, [sp, #4]
     c2a:       9100            str     r1, [sp, #0]
     c2c:       9b01            ldr     r3, [sp, #4]
     c2e:       681a            ldr     r2, [r3, #0]
     c30:       23a7            movs    r3, #167      ;0xa7
     c32:       009b            lsls    r3, r3, #2              ;jnicall: NewStringUTF
     c34:       58d2            ldr     r2, [r2, r3]
     c36:       9901            ldr     r1, [sp, #4]
     c38:       4b04            ldr     r3, [pc, #16] ;(c4c <Java_com_example_hellojni_HelloJni_stringFromJNI+0x28>)
     c3a:       447b            add     r3, pc
     c3c:       1c08            adds    r0, r1, #0
     c3e:       1c19            adds    r1, r3, #0
     c40:       4790            blx     r2

secretcode: example 'ex03' from that article

$ objdump -d examples/secretcode/ | python -a x86 | grep jnicall
 4be:   ff 90 a4 02 00 00       call   *0x2a4(%eax)     ;jnicall: GetStringUTFChars
 4d9:   ff 90 a0 02 00 00       call   *0x2a0(%eax)     ;jnicall: GetStringUTFLength
 550:   ff 90 9c 02 00 00       call   *0x29c(%eax)     ;jnicall: NewStringUTF
 571:   ff 90 a8 02 00 00       call   *0x2a8(%eax)     ;jnicall: ReleaseStringUTFChars

Copyright and license

JNI Analyzer is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

JNI Analyzer is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with JNI Analyzer. If not, see


  • Paulo Matias < thotypous [at] gmail [dot] com >, author of the original JNI Analyzer
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