After building and installing the modular X11R7 tree, I found that the Xorg   
server segfaults immediatly. Debugging the server I found that the getifaddrs()  
function returned entries with ifa_addr == NULL. The server tried to 
dereference the NULL pointer and crashed. The patch below fixes the problem. 
 
My system is running Linux (kernel 2.6.15, glibc-2.3.6). 
 
 
--- xorg-server-X11R7.0-1.0.1-orig/os/access.c	2005-11-08 07:33:30.000000000 
+0100 
+++ xorg-server-X11R7.0-1.0.1/os/access.c	2006-01-25 01:37:50.000000000 
+0100 
@@ -975,6 +975,8 @@ DefineSelf (int fd) 
 	return; 
     } 
     for (ifr = ifap; ifr != NULL; ifr = ifr->ifa_next) { 
+        if (!ifr->ifa_addr) 
+		continue; 
 #ifdef DNETCONN 
 	if (ifr->ifa_addr.sa_family == AF_DECnet)  
 	    continue;