Ok, I think you are bit confused about the calls. A couple of posts ago, you wrote:

Now for the source of your problem (I think):

                XS(XS_Net__LibnetRaw_libnet_init_packet)
                [...]
                        u_char *        buf = (u_char *)SvPV(ST(1),PL_
+na);
                [...]
                        RETVAL = libnet_init_packet(p_size, &buf);
                        sv_setpv((SV*)ST(1), buf);
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This function seems to have used a different typemap for buf which is trying to extract the '\0'-terminated string that it is supposed to point to. I think all you need to do is fix this typemap to be like the other functions. I'm going to check some other things I noticed and I'll reply separately if I detect any problems. It seems that you are under the impression that libnet_init_packet() and functions like libnet_do_checksum() have the same prototype for buf. They don't. As per my original post, the prototype for libnet_init_packet() is<

int libnet_init_packet(size_t p_size, u_char **buf);
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This function asks for a pointer to a pointer. So the pointed-to pointer (confusing, I know...) is being altered. This is how the function gets the pointer returns from malloc() back to the program. The other functions are prototyped like this:

int libnet_build_ip([...], u_char *buf);
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The pointer itself is not being modified so the pointer to a pointer is unnecessasry. But the data being pointed to is. If I understand correctly, you thought that this was the way in wich libnet_init_packet() and libnet_destroy_packet() were also prototyped.

So my feeling is that, like a C program would using this library, the value stored in the top level of the program in $buf should be a pointer. In C, I usually do something like this:

u_char *buf;

libnet_init_packet(IP_H + TCP_H, &buf); /* This calls malloc() and set
+s buf as a pointer to that new memory */
[...]
libnet_build_ip([...], buf); /* The pointer value is the same, but dat
+a pointed to is altered */
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So essentially I am attempt to make the perl calls the same. I did try it some others ways, based on your suggestions and my own tinkering. In the past couple of days, I have tried a few things. Not being experience with XS, I am obviously confused on some issues. The unary & was one example.

For now, though, I don't have a lot of time to devote to contemplating this problem. I still have some ideas that I might attempt to bounce off this thread in the future.