Make off_linktype, off_nl, and off_nl_nosnap *not* include off_ll.

Make gen_load_llrel() add in off_ll if there isn't a variable-length
radio header, so the offset passed to it is always relative to the
beginning of the link-layer header, not the beginning of the packet.
Don't add in off_ll when calling it.

Those changes centralize the addition of off_ll, so it's only done in
one place (rather than twice, where it was done before, meaning that the
offsets were wrong for the Prism and AVS headers as they had 2*off_ll
rather than just off_ll, as off_ll was added twice).

diff --git a/gencode.c b/gencode.c
index d1c039dbc351db1c11483f81c65c88ee798b66a3..1c4e2ddf46df206e14f913fddcbea116b36626a0 100644 (file)
--- a/gencode.c
+++ b/gencode.c
@@ -21,7 +21,7 @@
  */
 #ifndef lint
 static const char rcsid[] _U_ =
-    "@(#) $Header: /tcpdump/master/libpcap/gencode.c,v 1.221.2.39 2006-05-28 20:13:42 guy Exp $ (LBL)";
+    "@(#) $Header: /tcpdump/master/libpcap/gencode.c,v 1.221.2.40 2006-09-13 06:57:07 guy Exp $ (LBL)";
 #endif
 
 #ifdef HAVE_CONFIG_H
@@ -668,20 +668,26 @@ gen_ncmp(offrel, offset, size, mask, jtype, reverse, v)
 static int reg_ll_size;
 
 /*
- * This is the offset of the beginning of the link-layer header.
+ * This is the offset of the beginning of the link-layer header from
+ * the beginning of the raw packet data.
+ *
  * It's usually 0, except for 802.11 with a fixed-length radio header.
+ * (For 802.11 with a variable-length radio header, we have to generate
+ * code to compute that offset; off_ll is 0 in that case.)
  */
 static u_int off_ll;
 
 /*
  * This is the offset of the beginning of the MAC-layer header.
- * It's usually 0, except for ATM LANE.
+ * It's usually 0, except for ATM LANE, where it's the offset, relative
+ * to the beginning of the raw packet data, of the Ethernet header.
  */
 static u_int off_mac;
 
 /*
  * "off_linktype" is the offset to information in the link-layer header
- * giving the packet type.
+ * giving the packet type.  This offset is relative to the beginning
+ * of the link-layer header (i.e., it doesn't include off_ll).
  *
  * For Ethernet, it's the offset of the Ethernet type field.
  *
@@ -734,6 +740,8 @@ static u_int off_payload;
 
 /*
  * These are offsets to the beginning of the network-layer header.
+ * They are relative to the beginning of the link-layer header (i.e.,
+ * they don't include off_ll).
  *
  * If the link layer never uses 802.2 LLC:
  *
@@ -956,9 +964,9 @@ init_linktype(p)
                 * the Prism header is fixed-length.
                 */
                off_ll = 144;
-               off_linktype = 144+24;
-               off_nl = 144+32;        /* Prism+802.11+802.2+SNAP */
-               off_nl_nosnap = 144+27; /* Prism+802.11+802.2 */
+               off_linktype = 24;
+               off_nl = 32;    /* Prism+802.11+802.2+SNAP */
+               off_nl_nosnap = 27;     /* Prism+802.11+802.2 */
                return;
 
        case DLT_IEEE802_11_RADIO_AVS:
@@ -974,12 +982,23 @@ init_linktype(p)
                 * more so; this header is also variable-length,
                 * with the length being the 32-bit big-endian
                 * number at an offset of 4 from the beginning
-                * of the radio header.
+                * of the radio header.  We should handle that the
+                * same way we handle the length at the beginning
+                * of the radiotap header.
+                *
+                * XXX - in Linux, do any drivers that supply an AVS
+                * header supply a link-layer type other than
+                * ARPHRD_IEEE80211_PRISM?  If so, we should map that
+                * to DLT_IEEE802_11_RADIO_AVS; if not, or if there are
+                * any drivers that supply an AVS header but supply
+                * an ARPHRD value of ARPHRD_IEEE80211_PRISM, we'll
+                * have to check the header in the generated code to
+                * determine whether it's Prism or AVS.
                 */
                off_ll = 64;
-               off_linktype = 64+24;
-               off_nl = 64+32;         /* Radio+802.11+802.2+SNAP */
-               off_nl_nosnap = 64+27;  /* Radio+802.11+802.2 */
+               off_linktype = 24;
+               off_nl = 32;            /* Radio+802.11+802.2+SNAP */
+               off_nl_nosnap = 27;     /* Radio+802.11+802.2 */
                return;
 
        case DLT_IEEE802_11_RADIO:
@@ -1240,6 +1259,9 @@ gen_load_llrel(offset, size)
         * If "s" is non-null, it has code to arrange that the X register
         * contains the length of the prefix preceding the link-layer
         * header.
+        *
+        * Otherwise, the length of the prefix preceding the link-layer
+        * header is "off_ll".
         */
        if (s != NULL) {
                s2 = new_stmt(BPF_LD|BPF_IND|size);
@@ -1247,7 +1269,7 @@ gen_load_llrel(offset, size)
                sappend(s, s2);
        } else {
                s = new_stmt(BPF_LD|BPF_ABS|size);
-               s->s.k = offset;
+               s->s.k = offset + off_ll;
        }
        return s;
 }
@@ -1269,7 +1291,7 @@ gen_load_a(offrel, offset, size)
                break;
 
        case OR_LINK:
-               s = gen_load_llrel(off_ll + offset, size);
+               s = gen_load_llrel(offset, size);
                break;
 
        case OR_NET: