Question

I’m actually porting a Linux app to Mac OS X. My problem is that I can access the variables but not the pointers.

I declared the variables in the main.h this way:

uint64_t test;
uint64_t *test2;

In the mylib.h:

extern uint64_t test;
extern uint64_t *test2;

and in mylib.c I access the variables this way:

printf("%llu\n",test);
printf("%llu\n",*test2);

The first printf() doesn’t have any problems but the second gives me this error:

Program received signal EXC_BAD_ACCESS, Could not access memory.
Reason: KERN_INVALID_ADDRESS at address: 0x0000000000000008

Does anybody know why this happened?

My ggc command line has the following flags:

gcc -Wall -g -fPIC -c main.c gcc -shared -Wl,-undefined,dynamic_lookup -o mylib.so mylib.o

Answer 1

Just for someone with a similar problem:

I decided to work with getter & setter because there wasn’t problems to access the function of the main program with a dynamic library just the variables.

in mylib.c :

test2 = getTest();

in main.c :

uint64_t* getTest(){
    return &test;
}

Update

I finally found a way around this getter & setter. The problem you are facing is that you’re defining your variable twice, in my case this happened during a misunderstanding of the extern keyword. To solve your problem you need to declare the variables as extern in your main.h e.g.:

extern uint64_t test;
extern uint64_t *test2;

Next step is to define the variables in your main.c e.g.:

int main(...) {
    test = 1;
    test2 = &test;
}

And finally remove the extern declaration from your mylib.h

The following SO post led to my solution: link