elfcopy: fail if debug link target is empty

[emaste]

Summary

An empty debug link target previously returned a confusing and incorrect error like "objcopy: fread failed: No error: 0".

GNU objcopy allows an empty file as the debug link target. However, that case is nonsensical so just return an explicit error.

head/contrib/elftoolchain/elfcopy/sections.c

 #include <net/vnet.h>
 
 #include <netinet/in_systm.h>
 #include <netinet/in.h>
 #include <netinet/ip6.h>
 #include <netinet/ip.h>
 #include <netinet/ip_var.h>
 #include <netinet/tcp.h>
+#include <netinet/tcp_seq.h>
 #include <netinet/tcp_lro.h>
 #include <netinet/tcp_var.h>
 
 #include <netinet6/ip6_var.h>
 
 #include <machine/in_cksum.h>
 
 static MALLOC_DEFINE(M_LRO, "LRO", "LRO control structures");
#endif
                 if (le->p_len > (lc->lro_length_lim - tcp_data_len)) {
                         tcp_lro_active_remove(le);
                         tcp_lro_flush(lc, le);
                         break;
                 }
 
                 /* Try to append the new segment. */
                 if (__predict_false(seq != le->next_seq ||
-                    (tcp_data_len == 0 && le->ack_seq == th->th_ack))) {
+                    (tcp_data_len == 0 &&
+                    le->ack_seq == th->th_ack &&
+                    le->window == th->th_win))) {
                         /* Out of order packet or duplicate ACK. */
                         tcp_lro_active_remove(le);
                         tcp_lro_flush(lc, le);
                         return (TCP_LRO_CANNOT);
                 }
 
                 if (l != 0) {
                         uint32_t tsval = ntohl(*(ts_ptr + 1));
                         /* Make sure timestamp values are increasing. */
                         /* XXX-BZ flip and use TSTMP_GEQ macro for this? */
                         if (__predict_false(le->tsval > tsval ||
                             *(ts_ptr + 2) == 0))
                                 return (TCP_LRO_CANNOT);
                         le->tsval = tsval;
                         le->tsecr = *(ts_ptr + 2);
                 }
-
+                if (tcp_data_len || SEQ_GT(ntohl(th->th_ack), ntohl(le->ack_seq))) {
                         le->next_seq += tcp_data_len;
                         le->ack_seq = th->th_ack;
                         le->window = th->th_win;
                         le->append_cnt++;
-
+                } else if (th->th_ack == le->ack_seq) {
+                        le->window = WIN_MAX(le->window, th->th_win);
+                        le->append_cnt++;
+                } else {
+                        /* no data and old ack */
+                        le->append_cnt++;
+                        m_freem(m);
+                        return (0);
+                }
 #ifdef TCP_LRO_UPDATE_CSUM
                 le->ulp_csum += tcp_lro_rx_csum_fixup(le, l3hdr, th,
                     tcp_data_len, ~csum);
 #endif
 
                 if (tcp_data_len == 0) {
                         m_freem(m);
                         /*