Add off_ll to off_nl in cases where that's required and that we missed

in earlier checkins, now that off_nl no longer includes off_ll.

Add in more comments explaining what we're doing.

diff --git a/gencode.c b/gencode.c
index 3f864fdba1b6655007e5ef84b708bf4fd941bf6c..214a1a05fa092e5308238fdb41ae5fdfa57f000a 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 1.221.2.42 2006-09-13 07:04:07 guy Exp $ (LBL)";
+    "@(#) $Header: /tcpdump/master/libpcap/gencode.c,v 1.221.2.43 2006-09-13 07:36:19 guy Exp $ (LBL)";
 #endif
 
 #ifdef HAVE_CONFIG_H
@@ -1264,10 +1264,22 @@ gen_load_llrel(offset, size)
         * header is "off_ll".
         */
        if (s != NULL) {
+               /*
+                * There's a variable-length prefix preceding the
+                * link-layer header.  "s" points to a list of statements
+                * that put the length of that prefix into the X register.
+                * do an indirect load, to use the X register as an offset.
+                */
                s2 = new_stmt(BPF_LD|BPF_IND|size);
                s2->s.k = offset;
                sappend(s, s2);
        } else {
+               /*
+                * There is no variable-length header preceding the
+                * link-layer header; add in off_ll, which, if there's
+                * a fixed-length header preceding the link-layer header,
+                * is the length of that header.
+                */
                s = new_stmt(BPF_LD|BPF_ABS|size);
                s->s.k = offset + off_ll;
        }
@@ -1305,17 +1317,24 @@ gen_load_a(offrel, offset, size)
 
        case OR_TRAN_IPV4:
                /*
-                * Load the X register with the length of the IPv4 header,
-                * in bytes.
+                * Load the X register with the length of the IPv4 header
+                * (plus the offset of the link-layer header, if it's
+                * preceded by a variable-length header such as a radio
+                * header), in bytes.
                 */
                s = gen_loadx_iphdrlen();
 
                /*
-                * Load the item at {length of the link-layer header} +
-                * {length of the IPv4 header} + {specified offset}.
+                * Load the item at {offset of the link-layer header} +
+                * {offset, relative to the start of the link-layer
+                * header, of the IPv4 header} + {length of the IPv4 header} +
+                * {specified offset}.
+                *
+                * (If the link-layer is variable-length, it's included
+                * in the value in the X register, and off_ll is 0.)
                 */
                s2 = new_stmt(BPF_LD|BPF_IND|size);
-               s2->s.k = off_nl + offset;
+               s2->s.k = off_ll + off_nl + offset;
                sappend(s, s2);
                break;
 
@@ -1373,12 +1392,12 @@ gen_loadx_iphdrlen()
        } else {
                /*
                 * There is no variable-length header preceding the
-                * link-layer header; if there's a fixed-length
-                * header preceding it, its length is included in
-                * the off_ variables, so it doesn't need to be added.
+                * link-layer header; add in off_ll, which, if there's
+                * a fixed-length header preceding the link-layer header,
+                * is the length of that header.
                 */
                s = new_stmt(BPF_LDX|BPF_MSH|BPF_B);
-               s->s.k = off_nl;
+               s->s.k = off_ll + off_nl;
        }
        return s;
 }
@@ -4236,11 +4255,11 @@ gen_protochain(v, proto, dir)
 
                /* A = ip->ip_p */
                s[i] = new_stmt(BPF_LD|BPF_ABS|BPF_B);
-               s[i]->s.k = off_nl + 9;
+               s[i]->s.k = off_ll + off_nl + 9;
                i++;
                /* X = ip->ip_hl << 2 */
                s[i] = new_stmt(BPF_LDX|BPF_MSH|BPF_B);
-               s[i]->s.k = off_nl;
+               s[i]->s.k = off_ll + off_nl;
                i++;
                break;
 #ifdef INET6
@@ -4249,7 +4268,7 @@ gen_protochain(v, proto, dir)
 
                /* A = ip6->ip_nxt */
                s[i] = new_stmt(BPF_LD|BPF_ABS|BPF_B);
-               s[i]->s.k = off_nl + 6;
+               s[i]->s.k = off_ll + off_nl + 6;
                i++;
                /* X = sizeof(struct ip6_hdr) */
                s[i] = new_stmt(BPF_LDX|BPF_IMM);
@@ -4329,7 +4348,7 @@ gen_protochain(v, proto, dir)
                i++;
                /* A = P[X + packet head] */
                s[i] = new_stmt(BPF_LD|BPF_IND|BPF_B);
-               s[i]->s.k = off_nl;
+               s[i]->s.k = off_ll + off_nl;
                i++;
                /* MEM[reg2] = A */
                s[i] = new_stmt(BPF_ST);
@@ -4347,7 +4366,7 @@ gen_protochain(v, proto, dir)
                i++;
                /* A = P[X + packet head]; */
                s[i] = new_stmt(BPF_LD|BPF_IND|BPF_B);
-               s[i]->s.k = off_nl;
+               s[i]->s.k = off_ll + off_nl;
                i++;
                /* A += 1 */
                s[i] = new_stmt(BPF_ALU|BPF_ADD|BPF_K);
@@ -4406,7 +4425,7 @@ gen_protochain(v, proto, dir)
        i++;
        /* A = P[X + packet head]; */
        s[i] = new_stmt(BPF_LD|BPF_IND|BPF_B);
-       s[i]->s.k = off_nl;
+       s[i]->s.k = off_ll + off_nl;
        i++;
        /* MEM[reg2] = A */
        s[i] = new_stmt(BPF_ST);
@@ -4424,7 +4443,7 @@ gen_protochain(v, proto, dir)
        i++;
        /* A = P[X + packet head] */
        s[i] = new_stmt(BPF_LD|BPF_IND|BPF_B);
-       s[i]->s.k = off_nl;
+       s[i]->s.k = off_ll + off_nl;
        i++;
        /* A += 2 */
        s[i] = new_stmt(BPF_ALU|BPF_ADD|BPF_K);
@@ -5458,11 +5477,14 @@ gen_load(proto, index, size)
 
                /*
                 * Load the item at the sum of the offset we've put in the
-                * X register and the offset of the start of the network
-                * layer header.
+                * X register, the offset of the start of the network
+                * layer header, and the offset of the start of the link
+                * layer header (which is 0 if the radio header is
+                * variable-length; that header length is what we put
+                * into the X register and then added to the index).
                 */
                tmp = new_stmt(BPF_LD|BPF_IND|size);
-               tmp->s.k = off_nl;
+               tmp->s.k = off_ll + off_nl;
                sappend(s, tmp);
                sappend(index->s, s);
 
@@ -5487,6 +5509,11 @@ gen_load(proto, index, size)
                /*
                 * The offset is relative to the beginning of
                 * the transport-layer header.
+                *
+                * Load the X register with the length of the IPv4 header
+                * (plus the offset of the link-layer header, if it's
+                * a variable-length header), in bytes.
+                *
                 * XXX - are there any cases where we want
                 * off_nl_nosnap?
                 * XXX - we should, if we're built with
@@ -5496,22 +5523,24 @@ gen_load(proto, index, size)
                s = gen_loadx_iphdrlen();
 
                /*
-                * The X register now contains the sum of the offset
-                * of the beginning of the link-layer header and
-                * the length of the network-layer header.  Load
-                * into the A register the offset relative to
+                * The X register now contains the sum of the length
+                * of any variable-length header preceding the link-layer
+                * header and the length of the network-layer header.
+                * Load into the A register the offset relative to
                 * the beginning of the transport layer header,
                 * add the X register to that, move that to the
                 * X register, and load with an offset from the
                 * X register equal to the offset of the network
                 * layer header relative to the beginning of
-                * the link-layer header.
+                * the link-layer header plus the length of any
+                * fixed-length header preceding the link-layer
+                * header.
                 */
                sappend(s, xfer_to_a(index));
                sappend(s, new_stmt(BPF_ALU|BPF_ADD|BPF_X));
                sappend(s, new_stmt(BPF_MISC|BPF_TAX));
                sappend(s, tmp = new_stmt(BPF_LD|BPF_IND|size));
-               tmp->s.k = off_nl;
+               tmp->s.k = off_ll + off_nl;
                sappend(index->s, s);
 
                /*