Dynamic C/C++ lib for Android 2.2: error Symbol not found

问题

I have two projects. One of them is Android app with native code, which just loads dynamically library android_lib.so.

Another project is that library (android_lib.so). Code of this library is simple just for learning how things are going. It has only one function. Here is it:

int calculate (int x, int y)
{
  return (x*x+y*y);
}

In Makefile I use cross-platform compilator from Android 2.2 toolchains (/usr/local/android-ndk-r8/toolchains/arm-linux-androideabi4.4.3/prebuilt/linux-x86/bin/arm-linux-androideabi-gcc):

NDK_DIR=/usr/local/android-ndk-r8/toolchains/arm-linux-androideabi-4.4.3/prebuilt/linux-x86/bin
ANDROID_GCC=$(NDK_DIR)/arm-linux-androideabi-gcc
NDK_ROOT=/usr/local/android-ndk-r8

CPPFLAGS = $(NDK_ROOT)/platforms/android-8/arch-arm/usr/include
CFLAGS =-nostdlib
LDFLAGS = -Wl,-rpath-link=$(NDK_ROOT)/platforms/android-8/arch-arm/usr/lib/ -L$(NDK_ROOT)/platforms/android-8/arch-arm/usr/lib/
LIBS=-lc

android_lib.so: calculate.o
    $(ANDROID_GCC) $(CFLAGS)  -shared -o android_lib.so calculate.o 

calculate.o: calculate.c
    $(ANDROID_GCC) $(CPPFLAGS) $(CFLAGS) -c -fPIC calculate.c
clean:
    rm -f *.o *.so

So I type make and get android_lib.so. In native part of android project (it is mixed Java/C++ Eclipse project) I call dlopen()

dl_handle = dlopen( lib, RTLD_LAZY );
  if (!dl_handle) {
      error = (char *) dlerror();
      if (error != NULL) {
          __android_log_print(ANDROID_LOG_INFO,"nativeCode",error);
          return -1;
      }
      else {
          sprintf(sError,"%s is not found",lib);
          __android_log_print(ANDROID_LOG_INFO,"nativeCode",sError);
          return -2;
      }
  }

It succesfully loads android_lib.so. But if I am trying to call function calculate() I get error.

func = (int (*)(int, int)) dlsym( dl_handle, "calculate" );
  error = (char *) dlerror();
  if (error != NULL) {
      __android_log_print(ANDROID_LOG_INFO,"nativeCode",error);
      return -3;
  }

Function returns -3 and in LogCat of Eclipse I can see

01-01 07:00:44.624: I/nativeCode(8696): Symbol not found:

Please help me to solve this issue.

Update:

$ cd /usr/local/android-ndk-r8/toolchains/arm-linux-androideabi-4.4.3/prebuilt/linux-x86/bin 
$ sudo ./arm-linux-androideabi-objdump -T /home/chet/workspace/dinLib/android_lib.so

/home/chet/workspace/dinLib/android_lib.so:     file format elf32-littlearm

DYNAMIC SYMBOL TABLE:
00000234 l    d  .text  00000000 .text
00000274 g    D  *ABS*  00000000 __exidx_end
000012e0 g    D  *ABS*  00000000 _bss_end__
00000234 g    DF .text  00000040 calculate
000012e0 g    D  *ABS*  00000000 __bss_start__
00000274 g    D  *ABS*  00000000 __exidx_start
000012e0 g    D  *ABS*  00000000 __bss_end__
000012e0 g    D  *ABS*  00000000 __bss_start
000012e0 g    D  *ABS*  00000000 __end__
000012e0 g    D  *ABS*  00000000 _edata
000012e0 g    D  *ABS*  00000000 _end
000012e0 g    D  .got   00000000 __data_start

回答1:

Some important rules:

you should use ndk-build instead directly arm-linux-androideabi-gcc
in Android.mk of library type next options: LOCAL_LDFLAGS += -Wl,--export-dynamic
if dlerror() returns error it doesn't mean that dlsym() failed. Check if dlsym() really returns NULL. Because it may return a valid address but dlerror() may return error "Symbol not found" at the same time %)) I had this stupid mistake!!! See code.
You do not need call System.LoadLibrary(your_lib.so). Only dlopen("your_lib.so") from native code with RTLD_NOW or RTLD_LAZY no matter!

Be sure that your_lib.so is situated in /data/data/app_name/libs

func = (int (*)(int, int)) dlsym( dl_handle, "calculate" );
error = (char *) dlerror();
if (error != NULL) { //replace it with if ((func == NULL)&& (error != NULL))
  __android_log_print(ANDROID_LOG_INFO,"nativeCode",error);
  return -3; 
}

That's all :)

来源：https://stackoverflow.com/questions/10785740/dynamic-c-c-lib-for-android-2-2-error-symbol-not-found

标签

android

dynamic

makefile

android-ndk