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.
This commit is contained in:
guy
parent
c547cb1649
commit
750519deb0
81
gencode.c
81
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 1.269 2006-09-13 06:54:15 guy Exp $ (LBL)";
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"@(#) $Header: /tcpdump/master/libpcap/gencode.c,v 1.270 2006-09-13 07:35:42 guy Exp $ (LBL)";
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#endif
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#ifdef HAVE_CONFIG_H
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@ -1270,10 +1270,22 @@ gen_load_llrel(offset, size)
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* header is "off_ll".
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*/
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if (s != NULL) {
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/*
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* There's a variable-length prefix preceding the
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* link-layer header. "s" points to a list of statements
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* that put the length of that prefix into the X register.
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* do an indirect load, to use the X register as an offset.
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*/
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s2 = new_stmt(BPF_LD|BPF_IND|size);
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s2->s.k = offset;
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sappend(s, s2);
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} else {
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/*
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* There is no variable-length header preceding the
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* link-layer header; add in off_ll, which, if there's
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* a fixed-length header preceding the link-layer header,
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* is the length of that header.
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*/
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s = new_stmt(BPF_LD|BPF_ABS|size);
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s->s.k = offset + off_ll;
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}
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@ -1311,17 +1323,24 @@ gen_load_a(offrel, offset, size)
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case OR_TRAN_IPV4:
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/*
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* Load the X register with the length of the IPv4 header,
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* in bytes.
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* Load the X register with the length of the IPv4 header
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* (plus the offset of the link-layer header, if it's
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* preceded by a variable-length header such as a radio
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* header), in bytes.
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*/
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s = gen_loadx_iphdrlen();
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/*
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* Load the item at {length of the link-layer header} +
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* {length of the IPv4 header} + {specified offset}.
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* Load the item at {offset of the link-layer header} +
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* {offset, relative to the start of the link-layer
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* header, of the IPv4 header} + {length of the IPv4 header} +
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* {specified offset}.
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*
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* (If the link-layer is variable-length, it's included
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* in the value in the X register, and off_ll is 0.)
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*/
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s2 = new_stmt(BPF_LD|BPF_IND|size);
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s2->s.k = off_nl + offset;
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s2->s.k = off_ll + off_nl + offset;
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sappend(s, s2);
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break;
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@ -1379,12 +1398,12 @@ gen_loadx_iphdrlen()
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} else {
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/*
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* There is no variable-length header preceding the
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* link-layer header; if there's a fixed-length
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* header preceding it, its length is included in
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* the off_ variables, so it doesn't need to be added.
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* link-layer header; add in off_ll, which, if there's
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* a fixed-length header preceding the link-layer header,
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* is the length of that header.
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*/
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s = new_stmt(BPF_LDX|BPF_MSH|BPF_B);
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s->s.k = off_nl;
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s->s.k = off_ll + off_nl;
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}
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return s;
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}
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@ -4243,11 +4262,11 @@ gen_protochain(v, proto, dir)
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/* A = ip->ip_p */
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s[i] = new_stmt(BPF_LD|BPF_ABS|BPF_B);
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s[i]->s.k = off_nl + 9;
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s[i]->s.k = off_ll + off_nl + 9;
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i++;
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/* X = ip->ip_hl << 2 */
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s[i] = new_stmt(BPF_LDX|BPF_MSH|BPF_B);
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s[i]->s.k = off_nl;
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s[i]->s.k = off_ll + off_nl;
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i++;
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break;
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#ifdef INET6
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@ -4256,7 +4275,7 @@ gen_protochain(v, proto, dir)
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/* A = ip6->ip_nxt */
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s[i] = new_stmt(BPF_LD|BPF_ABS|BPF_B);
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s[i]->s.k = off_nl + 6;
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s[i]->s.k = off_ll + off_nl + 6;
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i++;
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/* X = sizeof(struct ip6_hdr) */
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s[i] = new_stmt(BPF_LDX|BPF_IMM);
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@ -4336,7 +4355,7 @@ gen_protochain(v, proto, dir)
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i++;
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/* A = P[X + packet head] */
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s[i] = new_stmt(BPF_LD|BPF_IND|BPF_B);
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s[i]->s.k = off_nl;
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s[i]->s.k = off_ll + off_nl;
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i++;
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/* MEM[reg2] = A */
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s[i] = new_stmt(BPF_ST);
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@ -4354,7 +4373,7 @@ gen_protochain(v, proto, dir)
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i++;
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/* A = P[X + packet head]; */
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s[i] = new_stmt(BPF_LD|BPF_IND|BPF_B);
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s[i]->s.k = off_nl;
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s[i]->s.k = off_ll + off_nl;
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i++;
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/* A += 1 */
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s[i] = new_stmt(BPF_ALU|BPF_ADD|BPF_K);
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@ -4413,7 +4432,7 @@ gen_protochain(v, proto, dir)
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i++;
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/* A = P[X + packet head]; */
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s[i] = new_stmt(BPF_LD|BPF_IND|BPF_B);
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s[i]->s.k = off_nl;
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s[i]->s.k = off_ll + off_nl;
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i++;
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/* MEM[reg2] = A */
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s[i] = new_stmt(BPF_ST);
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@ -4431,7 +4450,7 @@ gen_protochain(v, proto, dir)
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i++;
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/* A = P[X + packet head] */
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s[i] = new_stmt(BPF_LD|BPF_IND|BPF_B);
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s[i]->s.k = off_nl;
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s[i]->s.k = off_ll + off_nl;
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i++;
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/* A += 2 */
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s[i] = new_stmt(BPF_ALU|BPF_ADD|BPF_K);
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@ -5465,11 +5484,14 @@ gen_load(proto, index, size)
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/*
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* Load the item at the sum of the offset we've put in the
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* X register and the offset of the start of the network
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* layer header.
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* X register, the offset of the start of the network
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* layer header, and the offset of the start of the link
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* layer header (which is 0 if the radio header is
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* variable-length; that header length is what we put
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* into the X register and then added to the index).
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*/
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tmp = new_stmt(BPF_LD|BPF_IND|size);
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tmp->s.k = off_nl;
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tmp->s.k = off_ll + off_nl;
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sappend(s, tmp);
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sappend(index->s, s);
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@ -5494,6 +5516,11 @@ gen_load(proto, index, size)
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/*
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* The offset is relative to the beginning of
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* the transport-layer header.
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*
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* Load the X register with the length of the IPv4 header
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* (plus the offset of the link-layer header, if it's
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* a variable-length header), in bytes.
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*
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* XXX - are there any cases where we want
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* off_nl_nosnap?
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* XXX - we should, if we're built with
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@ -5503,22 +5530,24 @@ gen_load(proto, index, size)
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s = gen_loadx_iphdrlen();
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/*
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* The X register now contains the sum of the offset
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* of the beginning of the link-layer header and
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* the length of the network-layer header. Load
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* into the A register the offset relative to
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* The X register now contains the sum of the length
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* of any variable-length header preceding the link-layer
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* header and the length of the network-layer header.
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* Load into the A register the offset relative to
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* the beginning of the transport layer header,
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* add the X register to that, move that to the
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* X register, and load with an offset from the
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* X register equal to the offset of the network
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* layer header relative to the beginning of
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* the link-layer header.
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* the link-layer header plus the length of any
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* fixed-length header preceding the link-layer
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* header.
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*/
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sappend(s, xfer_to_a(index));
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sappend(s, new_stmt(BPF_ALU|BPF_ADD|BPF_X));
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sappend(s, new_stmt(BPF_MISC|BPF_TAX));
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sappend(s, tmp = new_stmt(BPF_LD|BPF_IND|size));
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tmp->s.k = off_nl;
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tmp->s.k = off_ll + off_nl;
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sappend(index->s, s);
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/*
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