can fishhook hook c function written by ourself?

[Zhengwei Yin]

myFunction is a c function written by me in my project, I want to hook it, but I tried this code failed.

int myFunction(int a){
    return a+1;
}

static int (*orig_myFunction)(int);

int hook_myFunction(int a){
    return a+2;
}

int main(int argc, char * argv[])
{
    @autoreleasepool {
        rebind_symbols((struct rebinding[1]){{"myFunction", hook_myFunction, (void *)&orig_myFunction}}, 1);
        printf("%d\n" , myFunction(1));
       return UIApplicationMain(argc, argv, nil, NSStringFromClass([AppDelegate class]));
    }
}

This means fishhook can only hook system api or how to hook c function written by ourself ?
Thanks.

[Fred Potter]

fishhook can only hook functions that exist in other libraries. It cannot
hook functions that exist in the same image (library or executable) as your
currently running code.

The reason for this is that there's no indirection that happens when you
call a function in your own executable. It's just a plain jump to another
code address in your executable.

That's very different from calling a function in an external library, where
your executable uses dyld to figure out the address of the function being
called before jumping to it.

On Sun, Mar 6, 2016 at 10:59 PM, Zhengwei Yin [e-mail]
wrote:

myFunction is a c function written by me in my project, I want to hook
it, but I tried this code failed.

int myFunction(int a){
return a+1;
}

static int (*orig_myFunction)(int);

int hook_myFunction(int a){
return a+2;
}

int main(int argc, char * argv[])
{
@autoreleasepool {
rebind_symbols((struct rebinding[1]){{"myFunction", hook_myFunction, (void *)&orig_myFunction}}, 1);
printf("%d\n" , myFunction(1));
return UIApplicationMain(argc, argv, nil, NSStringFromClass([AppDelegate class]));
}
}

This means fishhook can only hook system api or how to hook c function
written by ourself ?
Thanks.

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[Zhengwei Yin]

Thanks！