C chars_ptr STORAGE_ERROR in Imported function

[Kim Rostgaard Christensen <krc@greenpc.dk>]

Hello there

I am in progress of binding the pcap c library to ada, it is a part of a
school project. And for that i need a funtion that modifies a parameter 
to a function like so:

char    *pcap_lookupdev(char *);

I have figured out this much:

  function pcap_lookupdev(errbuff : Interfaces.C.Strings.Chars_Ptr) 
return Interfaces.C.Strings.Chars_Ptr;
  pragma Import (C, pcap_lookupdev, "pcap_lookupdev");

This works in the sense that running it as root returns the device 
found, but when I run it as normal user I get

raised STORAGE_ERROR : stack overflow (or erroneous memory access)

Do I need to declare the buffer and then then pass its c pointer to the 
function?

It is declared like this in a c example:
char errbuf[PCAP_ERRBUF_SIZE];

Best
Kim Rostgaard Christensen