Compiling a library for Android

[raven-worx]

@vlada
This is a Java related error.
Caused by: java.lang.NoClassDefFoundError: org/mediainfo/android/MediaInfo

I don't know what happens in the code, but just from the error message your apk misses the java class org.mediainfo.android.MediaInfo

[vlada]

@raven-worx Yes, that is about all I understood too. The error message comes form the Java wrapper in QtCreator. But the library (libmediainfo.so) is there. Where does the library name org.mediainfo.android.MediaInfo comes from?

I use TagLib the same way without any problems.

[raven-worx]

@vlada
i don't know this library.
But it seems you also have to deploy a org.mediainfo.android.MediaInfo Java class in your apk

[vlada]

OK, now I see it. The source also contains a Java wrapper for the library. That is probably needed. But I found another library version from the same author.

This seems to work directly. Well at least the application now starts. But when I try to use the library, I get this error: "Unable to load libmediainfo.so.0"

Oh no again! I was fighting for many days to fix this error with TagLib. It is caused by the fact that Android doesn't know library versions but Linux on the other hand always creates hard links for these libraries and the programs link against them.

Where does the name (with .0 extension) come from? Isn't there any other way to solve it then to compile the library without any version? The project where I took the compiled library from is apparently able to use this library on Android.

[raven-worx]

@vlada said in Compiling a library for Android:

But when I try to use the library, I get this error: "Unable to load libmediainfo.so.0"

did you deploy this lib in the apk?

[vlada]

@raven-worx Yes, the library is included. But it's name is libmediainfo.so. I found it is referenced in the header file so I modified it to include Android specific library name:

#if defined(_WIN32) || defined(WIN32)
    #ifdef _UNICODE
        #define MEDIAINFODLL_NAME L"MediaInfo.dll"
    #else //_UNICODE
        #define MEDIAINFODLL_NAME "MediaInfo.dll"
    #endif //_UNICODE
#elif defined(__APPLE__) && defined(__MACH__)
    #define MEDIAINFODLL_NAME "libmediainfo.0.dylib"
    #define __stdcall
    #ifdef __cplusplus
        #include <new> //for size_t
    #else /* __cplusplus */
        #include <stddef.h> //for size_t
    #endif /* __cplusplus */
#elif defined(ANDROID) || defined(__ANDROID__)
    #define MEDIAINFODLL_NAME "libmediainfo.so"
    #define __stdcall
#else
    #define MEDIAINFODLL_NAME "libmediainfo.so.0"
    #define __stdcall
#endif //!defined(_WIN32) || defined(WIN32)

Here I added the lines regarding Android. Unfortunately it didn't help. During program execution I get this error:

D/dalvikvm( 3296): Trying to load lib /data/app-lib/org.qtproject.muzika-2/libmediainfo.so 0xb3d087b0
E/linker ( 3296): "libmediainfo.so": ignoring 2-entry DT_PREINIT_ARRAY in shared library!
D/dalvikvm( 3296): Added shared lib /data/app-lib/org.qtproject.muzika-2/libmediainfo.so 0xb3d087b0
D/dalvikvm( 3296): No JNI_OnLoad found in /data/app-lib/org.qtproject.muzika-2/libmediainfo.so 0xb3d087b0, skipping init

It seems the program can find the library. But when I actually try to use it, I get this error:
D/libMuzika.so( 3296): (null):0 ((null)): "Unable to load libmediainfo.so"

In the header file (MediaInfoDLL.h) the library is then loaded with this command(s):

        if (!MediaInfo_Module)
            MediaInfo_Module = dlopen(MEDIAINFODLL_NAME, RTLD_LAZY);
        if (!MediaInfo_Module)
            MediaInfo_Module = dlopen("./" MEDIAINFODLL_NAME, RTLD_LAZY);

Do you have any idea what the problem could be now?

[raven-worx]

@vlada
seems like Android has issues loading versioned libs.

[vlada]

Yes, I know about the problem with versioned libraries in Android. I spend many days before I made TagLib working in my application because of this. But in this case the problem is elsewhere.

I did some more tests and debugging with my limited skills and found out that the library is in fact loaded. The command

MediaInfo_Module = dlopen(MEDIAINFODLL_NAME, RTLD_LAZY);

returns a valid handle. But next in the header file are assigned functions of the library and this is where it fails. The code looks like this:

MediaInfo_Inform=(MEDIAINFO_Inform)dlsym(MediaInfo_Module, "MediaInfoA_Inform");

If I call

qDebug() << dlerror();

I get following error: "undefined symbol: MediaInfo_Inform". What should I try to find out what is the problem? Is it possible to find out what functions does the library provide? Thank you.

[jsulm]

@vlada You can use nm tool to list all symbols:

nm MY_LIB.so

[vlada]

Thank you for the tip. So it seems it is not the correct library. This is the output I got from objdump (I found it when trying to find how to use nm):

DYNAMIC SYMBOL TABLE:
00000000      DF *UND*  00000000 __libc_init
00000000      DF *UND*  00000000 __cxa_atexit
00000000      DF *UND*  00000000 strcmp
00000000      DF *UND*  00000000 __errno
00000000      DF *UND*  00000000 lstat
00000000      DF *UND*  00000000 __stack_chk_fail
00000000      DO *UND*  00000000 __stack_chk_guard
00000000      DF *UND*  00000000 stat
00000000      DF *UND*  00000000 realloc
00000000      DF *UND*  00000000 malloc
00000000      DF *UND*  00000000 free
00000000      DF *UND*  00000000 strcpy
00000000      DF *UND*  00000000 opendir
00000000      DF *UND*  00000000 mbrtowc
00000000      DF *UND*  00000000 closedir
00000000      DF *UND*  00000000 readdir
00000000      DF *UND*  00000000 issetugid
00000000      DF *UND*  00000000 getlogin
00000000      DF *UND*  00000000 getenv
00000000      DF *UND*  00000000 getpwnam
00000000      DF *UND*  00000000 getuid
00000000      DF *UND*  00000000 getpwuid
00000000      DF *UND*  00000000 qsort
001deba9 g    DF .text  00000068 operator new(unsigned int)
00000000      DF *UND*  00000000 pthread_mutex_init
00000000      DF *UND*  00000000 pthread_mutex_destroy
001deffd g    DF .text  00000008 operator delete(void*)
00000000      DF *UND*  00000000 pthread_mutex_lock
00000000      DF *UND*  00000000 pthread_mutex_unlock
00000000      DF *UND*  00000000 mkdir
00000000      DF *UND*  00000000 truncate
00000000      DF *UND*  00000000 unlink
00000000      DF *UND*  00000000 rename
00000000      DF *UND*  00000000 wmemcmp
00000000      DF *UND*  00000000 memset
00000000      DF *UND*  00000000 fmodf
00000000      DF *UND*  00000000 fmod
00000000      DF *UND*  00000000 strlen
00000000      DF *UND*  00000000 pthread_attr_init
00000000      DF *UND*  00000000 pthread_attr_setdetachstate
00000000      DF *UND*  00000000 pthread_create
00000000      DF *UND*  00000000 sched_yield
000162a5  w   DF .text  00000018 tolower
00000000      DO *UND*  00000000 _tolower_tab_
000162bd  w   DF .text  00000018 toupper
00000000      DO *UND*  00000000 _toupper_tab_
001df1f5 g    DF .text  00000014 operator new[](unsigned int)
001dee45 g    DF .text  00000004 operator delete[](void*)
00000000      DF *UND*  00000000 wcslen
00000000      DF *UND*  00000000 wcsncpy
00000000      DF *UND*  00000000 strncpy
00000000      DF *UND*  00000000 memcpy
00000000      DF *UND*  00000000 gmtime
00000000      DF *UND*  00000000 localtime
001de4a9 g    DF .text  00000004 operator delete(void*, std::nothrow_t const&)
002f3fc0 g    DO .rodata        00000001 std::nothrow
001df449 g    DF .text  00000050 operator new(unsigned int, std::nothrow_t const
&)
00000000      DF *UND*  00000000 strftime
00000000      DF *UND*  00000000 time
00000000      DF *UND*  00000000 memmove
00000000      DF *UND*  00000000 pow
00000000      DF *UND*  00000000 powf
00000000      DF *UND*  00000000 ceil
001df3f5 g    DF .text  00000018 __cxa_pure_virtual
001de38d g    DF .text  0000009a __cxa_guard_acquire
001de469 g    DF .text  0000003e __cxa_guard_release
001de429 g    DF .text  00000040 __cxa_guard_abort
00000000      DF *UND*  00000000 logf
00000000      DF *UND*  00000000 log
00000000      DF *UND*  00000000 log10
00000000      DF *UND*  00000000 log10f
00000000      DF *UND*  00000000 floorf
00000000      DF *UND*  00000000 memcmp
00000000      DF *UND*  00000000 strtod
00000000      DF *UND*  00000000 strchr
00000000      DF *UND*  00000000 atoi
00000000      DF *UND*  00000000 uncompress
00000000      DF *UND*  00000000 compress2
00000000      DF *UND*  00000000 atan2f
00000000      DF *UND*  00000000 ceilf
00000000      DF *UND*  00000000 setlocale
001d5d0d  w   DF .text  00000024 isspace
00000000      DO *UND*  00000000 _ctype_
00000000      DF *UND*  00000000 strncmp
00000000      DF *UND*  00000000 snprintf
00000000      DF *UND*  00000000 sscanf
00000000      DF *UND*  00000000 fseek
00000000      DF *UND*  00000000 fgetc
00000000      DF *UND*  00000000 ferror
00000000      DF *UND*  00000000 ftell
00000000      DF *UND*  00000000 fread
00000000      DF *UND*  00000000 fopen
00000000      DF *UND*  00000000 fclose
00000000      DF *UND*  00000000 printf
00000000      DO *UND*  00000000 __sF
00000000      DF *UND*  00000000 vfprintf
00000000      DF *UND*  00000000 vsnprintf
00000000      DF *UND*  00000000 __android_log_print
00000000      DF *UND*  00000000 syscall
00000000      DF *UND*  00000000 abort
00000000      DF *UND*  00000000 pthread_key_delete
00000000      DF *UND*  00000000 pthread_getspecific
00000000      DF *UND*  00000000 pthread_setspecific
00000000      DF *UND*  00000000 pthread_key_create
00000000      DF *UND*  00000000 write
00000000      DF *UND*  00000000 acos
00000000      DF *UND*  00000000 asin
00000000      DF *UND*  00000000 atan
00000000      DF *UND*  00000000 atan2
00000000      DF *UND*  00000000 cos
00000000      DF *UND*  00000000 cosh
00000000      DF *UND*  00000000 exp
00000000      DF *UND*  00000000 frexp
00000000      DF *UND*  00000000 sqrt
00000000      DF *UND*  00000000 modf
00000000      DF *UND*  00000000 sin
00000000      DF *UND*  00000000 sinh
00000000      DF *UND*  00000000 tan
00000000      DF *UND*  00000000 tanh
00000000      DF *UND*  00000000 wmemcpy
00000000      DF *UND*  00000000 vsprintf
00000000      DF *UND*  00000000 memchr
00000000      DF *UND*  00000000 wcsftime
00000000      DF *UND*  00000000 pthread_once
00000000      DF *UND*  00000000 fflush
00000000      DF *UND*  00000000 fdopen
00000000      DF *UND*  00000000 setvbuf
00000000      DF *UND*  00000000 read
00000000      DF *UND*  00000000 writev
00000000      DF *UND*  00000000 lseek
00000000      DF *UND*  00000000 ioctl
00000000      DF *UND*  00000000 poll
00000000      DF *UND*  00000000 fstat
00000000      DF *UND*  00000000 wmemchr
00000000      DF *UND*  00000000 strcoll
00000000      DF *UND*  00000000 strxfrm
00000000      DF *UND*  00000000 wcscoll
00000000      DF *UND*  00000000 wcsxfrm
00000000      DF *UND*  00000000 fwrite
00000000      DF *UND*  00000000 getwc
00000000      DF *UND*  00000000 putwc
00000000      DF *UND*  00000000 getc
00000000      DF *UND*  00000000 ungetc
00000000      DF *UND*  00000000 ungetwc
00000000      DF *UND*  00000000 putc
00000000      DF *UND*  00000000 wmemset
00000000      DF *UND*  00000000 wmemmove
00000000      DF *UND*  00000000 wctype
00000000      DF *UND*  00000000 towupper
00000000      DF *UND*  00000000 towlower
00000000      DF *UND*  00000000 iswctype
00000000      DF *UND*  00000000 wctob
00000000      DF *UND*  00000000 btowc
00000000      DF *UND*  00000000 pthread_cond_destroy
00000000      DF *UND*  00000000 pthread_cond_wait
00000000      DF *UND*  00000000 pthread_cond_signal
00000000      DF *UND*  00000000 pthread_cond_broadcast
00000000      DF *UND*  00000000 strerror
00000000      DF *UND*  00000000 fputs
00000000      DF *UND*  00000000 fputc
00000000      DF *UND*  00000000 sprintf
00304458 g    D  *ABS*  00000000 _edata
00304458 g    D  *ABS*  00000000 __bss_start
0030a329 g    D  *ABS*  00000000 _end
00000000  w   DF *UND*  00000000 __gnu_Unwind_Find_exidx
00000000      DF *UND*  00000000 raise

It is clear the functions I'm trying to use are simply not there. So I have probably no other option then to compile the library myself.

[jsulm]

@vlada Are you sure you called objdump on that library? That list looks like a dump from a C standard library.

[vlada]

Yes, I'm pretty sure I called it on the correct library. Or at least I thought it is the correct library. I found it here.

I hope I will have some time over the weekend to try to compile it myself.