LD_PRELOADING dlopen on android

Question

I was curios about which libraries and Syscalls are used by my app while its running.So I started to investigate my app with LD_PRELOAD and some "syscalls" like open, access and write.

But while I'm trying to preload dlopen, to find out which libraries are loaded, I got this error: Symbol not found:

void* dlopen(const char *file, int mode){
    static void* (*o_dlopen) ( const char *file, int mode )=0;
    printf( "dlopen was called\n" );
    o_dlopen = (void*(*)(const char *file, int mode))   
    dlsym(RTLD_NEXT,"dlopen");
    return (*o_dlopen)( file, mode );
}

It seems to be that dlsym is not able to find dlopen a second time. I compiled my preloaded *.so file with -ldl and the arm-gcc provided by android NDK. Using -rdynamic does not work either.

The preloading works fine but not for dlopen. Maybe you can help me...

Thanks in advance

Answer 1

Android dlopen is offered by the linker, therefore you need to use RTLD_DEFAULT when looking up the dlopen symbol from your preloaded library. See: bionic/libdl/libdl.c and bionic/linker/linker.cpp.