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.
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guy
parent
41995a4191
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85f4786ac2
91
gencode.c
91
gencode.c
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@ -21,7 +21,7 @@
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*/
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#ifndef lint
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static const char rcsid[] _U_ =
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"@(#) $Header: /tcpdump/master/libpcap/gencode.c,v 1.303 2007-11-26 21:17:49 gianluca Exp $ (LBL)";
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"@(#) $Header: /tcpdump/master/libpcap/gencode.c,v 1.304 2007-12-29 02:34:23 guy Exp $ (LBL)";
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#endif
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#ifdef HAVE_CONFIG_H
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@ -203,6 +203,7 @@ static struct block *gen_ether_linktype(int);
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static struct block *gen_linux_sll_linktype(int);
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static struct slist *gen_load_radiotap_llprefixlen(void);
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static struct slist *gen_load_ppi_llprefixlen(void);
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static struct slist *gen_load_avs_llprefixlen(void);
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static void insert_compute_vloffsets(struct block *);
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static struct slist *gen_llprefixlen(void);
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static struct slist *gen_off_macpl(void);
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@ -1075,16 +1076,10 @@ init_linktype(p)
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* the 802.11 header, containing a bunch of additional
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* information including radio-level information.
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*
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* The header is 64 bytes long, at least in its
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* current incarnation.
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*
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* XXX - same variable-length header problem, only
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* more so; this header is also variable-length,
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* with the length being the 32-bit big-endian
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* number at an offset of 4 from the beginning
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* of the radio header. We should handle that the
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* same way we handle the length at the beginning
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* of the radiotap header.
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* The radiotap header is variable length, and we
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* generate code to compute its length and store it
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* in a register. These offsets are relative to the
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* beginning of the 802.11 header.
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*
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* XXX - in Linux, do any drivers that supply an AVS
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* header supply a link-layer type other than
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@ -1095,7 +1090,6 @@ init_linktype(p)
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* have to check the header in the generated code to
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* determine whether it's Prism or AVS.
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*/
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off_ll = 64;
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off_linktype = 24;
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off_macpl = 0; /* link-layer header is variable-length */
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off_macpl_is_variable = 1;
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@ -2262,6 +2256,46 @@ gen_load_ppi_llprefixlen()
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return (NULL);
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}
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static struct slist *
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gen_load_avs_llprefixlen()
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{
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struct slist *s1, *s2;
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/*
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* Generate code to load the length of the AVS header into
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* the register assigned to hold that length, if one has been
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* assigned. (If one hasn't been assigned, no code we've
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* generated uses that prefix, so we don't need to generate any
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* code to load it.)
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*/
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if (reg_off_ll != -1) {
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/*
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* The 4 bytes at an offset of 4 from the beginning of
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* the AVS header are the length of the AVS header.
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* That field is big-endian.
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*/
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s1 = new_stmt(BPF_LD|BPF_W|BPF_ABS);
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s1->s.k = 4;
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/*
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* Now allocate a register to hold that value and store
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* it.
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*/
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s2 = new_stmt(BPF_ST);
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s2->s.k = reg_off_ll;
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sappend(s1, s2);
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/*
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* Now move it into the X register.
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*/
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s2 = new_stmt(BPF_MISC|BPF_TAX);
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sappend(s1, s2);
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return (s1);
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} else
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return (NULL);
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}
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/*
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* Load a value relative to the beginning of the link-layer header after the 802.11
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* header, i.e. LLC_SNAP.
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@ -2505,6 +2539,10 @@ insert_compute_vloffsets(b)
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s = gen_load_ppi_llprefixlen();
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break;
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case DLT_IEEE802_11_RADIO_AVS:
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s = gen_load_avs_llprefixlen();
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break;
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default:
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s = NULL;
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break;
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@ -2608,7 +2646,29 @@ gen_ppi_llprefixlen(void)
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}
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/*
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* Load the register containing the radiotap length
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* Load the register containing the PPI length
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* into the X register.
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*/
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s = new_stmt(BPF_LDX|BPF_MEM);
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s->s.k = reg_off_ll;
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return s;
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}
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static struct slist *
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gen_avs_llprefixlen(void)
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{
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struct slist *s;
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if (reg_off_ll == -1) {
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/*
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* We haven't yet assigned a register for the length
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* of the radiotap header; allocate one.
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*/
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reg_off_ll = alloc_reg();
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}
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/*
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* Load the register containing the AVS length
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* into the X register.
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*/
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s = new_stmt(BPF_LDX|BPF_MEM);
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@ -2629,10 +2689,13 @@ gen_llprefixlen(void)
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case DLT_PPI:
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return gen_ppi_llprefixlen();
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case DLT_IEEE802_11_RADIO:
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return gen_radiotap_llprefixlen();
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case DLT_IEEE802_11_RADIO_AVS:
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return gen_avs_llprefixlen();
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default:
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return NULL;
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}
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