Using bpf_for_each_map_elem helper with BCC

Hi all,
I was trying to use the new `bpf_for_each_map_elem` helper within a BCC-based application.
I have modified the rewriter to support a new function so that the helper can be called in this way:

```
map.for_each_elem(callback_function, &data, 0);
```

However, I get the following error when trying to deploy the program (kernel 5.13rc1, LLVM10):
```
HINT: The 'unknown opcode' can happen if you reference a global or static variable, or data in read-only section.
```

I guess the problem is within the "callback_function", which is not correctly relocated.
Does anyone have an idea of how to solve this issue?