The AVS radio header is variable-length, and fields were added to it

recently, so it's not only variable-length in theory, it's
variable-length in practice.  Treat it as such.

diff --git a/gencode.c b/gencode.c
index aefe394e470fb5ee7118d9fb8f060cc82f3e2ac6..152825c18744038d1ab2ad9aef226a70fbda625d 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 1.290.2.13 2007-11-26 21:12:06 gianluca Exp $ (LBL)";
+    "@(#) $Header: /tcpdump/master/libpcap/gencode.c,v 1.290.2.14 2007-12-29 02:35:16 guy Exp $ (LBL)";
 #endif
 
 #ifdef HAVE_CONFIG_H
@@ -203,6 +203,7 @@ static struct block *gen_ether_linktype(int);
 static struct block *gen_linux_sll_linktype(int);
 static struct slist *gen_load_radiotap_llprefixlen(void);
 static struct slist *gen_load_ppi_llprefixlen(void);
+static struct slist *gen_load_avs_llprefixlen(void);
 static void insert_compute_vloffsets(struct block *);
 static struct slist *gen_llprefixlen(void);
 static struct slist *gen_off_macpl(void);
@@ -1075,16 +1076,10 @@ init_linktype(p)
                 * the 802.11 header, containing a bunch of additional
                 * information including radio-level information.
                 *
-                * The header is 64 bytes long, at least in its
-                * current incarnation.
-                *
-                * XXX - same variable-length header problem, only
-                * 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.  We should handle that the
-                * same way we handle the length at the beginning
-                * of the radiotap header.
+                * The radiotap header is variable length, and we
+                * generate code to compute its length and store it
+                * in a register.  These offsets are relative to the
+                * beginning of the 802.11 header.
                 *
                 * XXX - in Linux, do any drivers that supply an AVS
                 * header supply a link-layer type other than
@@ -1095,7 +1090,6 @@ init_linktype(p)
                 * have to check the header in the generated code to
                 * determine whether it's Prism or AVS.
                 */
-               off_ll = 64;
                off_linktype = 24;
                off_macpl = 0;          /* link-layer header is variable-length */
                off_macpl_is_variable = 1;
@@ -2262,6 +2256,46 @@ gen_load_ppi_llprefixlen()
                return (NULL);
 }
 
+static struct slist *
+gen_load_avs_llprefixlen()
+{
+       struct slist *s1, *s2;
+
+       /*
+        * Generate code to load the length of the AVS header into
+        * the register assigned to hold that length, if one has been
+        * assigned.  (If one hasn't been assigned, no code we've
+        * generated uses that prefix, so we don't need to generate any
+        * code to load it.)
+        */
+       if (reg_off_ll != -1) {
+               /*
+                * The 4 bytes at an offset of 4 from the beginning of
+                * the AVS header are the length of the AVS header.
+                * That field is big-endian.
+                */
+               s1 = new_stmt(BPF_LD|BPF_W|BPF_ABS);
+               s1->s.k = 4;
+
+               /*
+                * Now allocate a register to hold that value and store
+                * it.
+                */
+               s2 = new_stmt(BPF_ST);
+               s2->s.k = reg_off_ll;
+               sappend(s1, s2);
+
+               /*
+                * Now move it into the X register.
+                */
+               s2 = new_stmt(BPF_MISC|BPF_TAX);
+               sappend(s1, s2);
+
+               return (s1);
+       } else
+               return (NULL);
+}
+
 /*
  * Load a value relative to the beginning of the link-layer header after the 802.11
  * header, i.e. LLC_SNAP.
@@ -2505,6 +2539,10 @@ insert_compute_vloffsets(b)
                s = gen_load_ppi_llprefixlen();
                break;
 
+       case DLT_IEEE802_11_RADIO_AVS:
+               s = gen_load_avs_llprefixlen();
+               break;
+
        default:
                s = NULL;
                break;
@@ -2608,7 +2646,29 @@ gen_ppi_llprefixlen(void)
        }
 
        /*
-        * Load the register containing the radiotap length
+        * Load the register containing the PPI length
+        * into the X register.
+        */
+       s = new_stmt(BPF_LDX|BPF_MEM);
+       s->s.k = reg_off_ll;
+       return s;
+}
+
+static struct slist *
+gen_avs_llprefixlen(void)
+{
+       struct slist *s;
+
+       if (reg_off_ll == -1) {
+               /*
+                * We haven't yet assigned a register for the length
+                * of the radiotap header; allocate one.
+                */
+               reg_off_ll = alloc_reg();
+       }
+
+       /*
+        * Load the register containing the AVS length
         * into the X register.
         */
        s = new_stmt(BPF_LDX|BPF_MEM);
@@ -2629,10 +2689,13 @@ gen_llprefixlen(void)
 
        case DLT_PPI:
                return gen_ppi_llprefixlen();
-       
+
        case DLT_IEEE802_11_RADIO:
                return gen_radiotap_llprefixlen();
 
+       case DLT_IEEE802_11_RADIO_AVS:
+               return gen_avs_llprefixlen();
+
        default:
                return NULL;
        }