libobjc2 runtime warning I don't understand why I get it

[Sebastian Reitenbach]

I get the following runtime warning from libobjc2 in debug mode:

Calling [SnifferController -handlePacket:] with incorrect signature.  Method 
has v12@0:4@8, selector has v12@0:4r*8

- handlePacket is defined in my libpcap wrapper GSPcap.h as a delegate 
protocol, the application has to implement:
@protocol GSPcapDelegate
-(void) handlePacket: (NSData *) _packet;
@end

and in GSPcap.m its called like this:

/*
 * callback function called from pcap_loop
 */
void
got_packet(u_char *args, const struct pcap_pkthdr *header, const u_char *packet)
{
  NSData *pData = [NSData dataWithBytes:packet length:header->len];
  if ([[(id)args delegate] conformsToProtocol:@protocol(GSPcapDelegate)])
    {
      [(id<GSPcapDelegate>)[(id)args delegate] handlePacket:pData];
    }
}

The SnifferController, part of my application implements the protocol

SnifferController.h:-(void)handlePacket: (NSData *)_packet;
SnifferController.m:-(void)handlePacket: (NSData *)_packet

and while compiling, I don't get any warnings.

Now, I don't understand why I get the warning from libobjc2, anything I do 
wrong?
Before I changed it to use NSData * as parameter, I just passed (const char *) 
to it,
and I did not got the warning when running the application.


Sebastian