filter: bpf_dbg: add minimal bpf debugger

This patch adds a minimal BPF debugger that "emulates" the kernel's
BPF engine (w/o extensions) and allows for single stepping (forwards
and backwards through BPF code) or running with >=1 breakpoints through
selected or all packets from a pcap file with a provided user filter
in order to facilitate verification of a BPF program. When a breakpoint
is being hit, it dumps all register contents, decoded instructions and
in case of branches both decoded branch targets as well as other useful
information.

Having this facility is in particular useful to verify BPF programs
against given test traffic *before* attaching to a live system.

With the general availability of cls_bpf, xt_bpf, socket filters,
team driver and e.g. PTP code, all BPF users, quite often a single
more complex BPF program is being used. Reasons for a more complex
BPF program are primarily to optimize execution time for making a
verdict when multiple simple BPF programs are combined into one in
order to prevent parsing same headers multiple times. In particular,
for cls_bpf that can have various return paths for encoding flowids,
and xt_bpf to come to a fw verdict this can be the case.

Therefore, as this can result in more complex and harder to debug
code, it would be very useful to have this minimal tool for testing
purposes. It can also be of help for BPF JIT developers as filters
are "test attached" to the kernel on a temporary socket thus
triggering a JIT image dump when enabled. The tool uses an interactive
libreadline shell with auto-completion and history support.

Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 1411 insertions, 2 deletions

diff --git a/tools/net/Makefile b/tools/net/Makefile
index b4444d5..0f30d92 100644
--- a/tools/net/Makefile
+++ b/tools/net/Makefile
@@ -2,14 +2,19 @@ prefix = /usr
 
 CC = gcc
 
-all : bpf_jit_disasm
+all : bpf_jit_disasm bpf_dbg
 
 bpf_jit_disasm : CFLAGS = -Wall -O2
 bpf_jit_disasm : LDLIBS = -lopcodes -lbfd -ldl
 bpf_jit_disasm : bpf_jit_disasm.o
 
+bpf_dbg : CFLAGS = -Wall -O2
+bpf_dbg : LDLIBS = -lreadline
+bpf_dbg : bpf_dbg.o
+
 clean :
-	rm -rf *.o bpf_jit_disasm
+	rm -rf *.o bpf_jit_disasm bpf_dbg
 
 install :
 	install bpf_jit_disasm $(prefix)/bin/bpf_jit_disasm
+	install bpf_dbg $(prefix)/bin/bpf_dbg
diff --git a/tools/net/bpf_dbg.c b/tools/net/bpf_dbg.c
new file mode 100644
index 0000000..0fdcb70
--- /dev/null
+++ b/tools/net/bpf_dbg.c
@@ -0,0 +1,1404 @@
+/*
+ * Minimal BPF debugger
+ *
+ * Minimal BPF debugger that mimics the kernel's engine (w/o extensions)
+ * and allows for single stepping through selected packets from a pcap
+ * with a provided user filter in order to facilitate verification of a
+ * BPF program. Besides others, this is useful to verify BPF programs
+ * before attaching to a live system, and can be used in socket filters,
+ * cls_bpf, xt_bpf, team driver and e.g. PTP code; in particular when a
+ * single more complex BPF program is being used. Reasons for a more
+ * complex BPF program are likely primarily to optimize execution time
+ * for making a verdict when multiple simple BPF programs are combined
+ * into one in order to prevent parsing same headers multiple times.
+ *
+ * More on how to debug BPF opcodes see Documentation/networking/filter.txt
+ * which is the main document on BPF. Mini howto for getting started:
+ *
+ *  1) `./bpf_dbg` to enter the shell (shell cmds denoted with '>'):
+ *  2) > load bpf 6,40 0 0 12,21 0 3 20... (output from `bpf_asm` or
+ *     `tcpdump -iem1 -ddd port 22 | tr '\n' ','` to load as filter)
+ *  3) > load pcap foo.pcap
+ *  4) > run <n>/disassemble/dump/quit (self-explanatory)
+ *  5) > breakpoint 2 (sets bp at loaded BPF insns 2, do `run` then;
+ *       multiple bps can be set, of course, a call to `breakpoint`
+ *       w/o args shows currently loaded bps, `breakpoint reset` for
+ *       resetting all breakpoints)
+ *  6) > select 3 (`run` etc will start from the 3rd packet in the pcap)
+ *  7) > step [-<n>, +<n>] (performs single stepping through the BPF)
+ *
+ * Copyright 2013 Daniel Borkmann <borkmann@redhat.com>
+ * Licensed under the GNU General Public License, version 2.0 (GPLv2)
+ */
+
+#include <stdio.h>
+#include <unistd.h>
+#include <stdlib.h>
+#include <ctype.h>
+#include <stdbool.h>
+#include <stdarg.h>
+#include <setjmp.h>
+#include <linux/filter.h>
+#include <linux/if_packet.h>
+#include <readline/readline.h>
+#include <readline/history.h>
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <sys/stat.h>
+#include <sys/mman.h>
+#include <fcntl.h>
+#include <errno.h>
+#include <signal.h>
+#include <arpa/inet.h>
+#include <net/ethernet.h>
+
+#define TCPDUMP_MAGIC	0xa1b2c3d4
+
+#define BPF_LDX_B	(BPF_LDX | BPF_B)
+#define BPF_LDX_W	(BPF_LDX | BPF_W)
+#define BPF_JMP_JA	(BPF_JMP | BPF_JA)
+#define BPF_JMP_JEQ	(BPF_JMP | BPF_JEQ)
+#define BPF_JMP_JGT	(BPF_JMP | BPF_JGT)
+#define BPF_JMP_JGE	(BPF_JMP | BPF_JGE)
+#define BPF_JMP_JSET	(BPF_JMP | BPF_JSET)
+#define BPF_ALU_ADD	(BPF_ALU | BPF_ADD)
+#define BPF_ALU_SUB	(BPF_ALU | BPF_SUB)
+#define BPF_ALU_MUL	(BPF_ALU | BPF_MUL)
+#define BPF_ALU_DIV	(BPF_ALU | BPF_DIV)
+#define BPF_ALU_MOD	(BPF_ALU | BPF_MOD)
+#define BPF_ALU_NEG	(BPF_ALU | BPF_NEG)
+#define BPF_ALU_AND	(BPF_ALU | BPF_AND)
+#define BPF_ALU_OR	(BPF_ALU | BPF_OR)
+#define BPF_ALU_XOR	(BPF_ALU | BPF_XOR)
+#define BPF_ALU_LSH	(BPF_ALU | BPF_LSH)
+#define BPF_ALU_RSH	(BPF_ALU | BPF_RSH)
+#define BPF_MISC_TAX	(BPF_MISC | BPF_TAX)
+#define BPF_MISC_TXA	(BPF_MISC | BPF_TXA)
+#define BPF_LD_B	(BPF_LD | BPF_B)
+#define BPF_LD_H	(BPF_LD | BPF_H)
+#define BPF_LD_W	(BPF_LD | BPF_W)
+
+#ifndef array_size
+# define array_size(x)	(sizeof(x) / sizeof((x)[0]))
+#endif
+
+#ifndef __check_format_printf
+# define __check_format_printf(pos_fmtstr, pos_fmtargs) \
+	__attribute__ ((format (printf, (pos_fmtstr), (pos_fmtargs))))
+#endif
+
+#define CMD(_name, _func) { .name = _name, .func = _func, }
+#define OP(_op, _name)      [_op] = _name
+
+enum {
+	CMD_OK,
+	CMD_ERR,
+	CMD_EX,
+};
+
+struct shell_cmd {
+	const char *name;
+	int (*func)(char *args);
+};
+
+struct pcap_filehdr {
+	uint32_t magic;
+	uint16_t version_major;
+	uint16_t version_minor;
+	int32_t  thiszone;
+	uint32_t sigfigs;
+	uint32_t snaplen;
+	uint32_t linktype;
+};
+
+struct pcap_timeval {
+	int32_t tv_sec;
+	int32_t tv_usec;
+};
+
+struct pcap_pkthdr {
+	struct pcap_timeval ts;
+	uint32_t caplen;
+	uint32_t len;
+};
+
+struct bpf_regs {
+	uint32_t A;
+	uint32_t X;
+	uint32_t M[BPF_MEMWORDS];
+	uint32_t R;
+	bool     Rs;
+	uint16_t Pc;
+};
+
+static struct sock_filter bpf_image[BPF_MAXINSNS + 1];
+static unsigned int bpf_prog_len = 0;
+
+static int bpf_breakpoints[64];
+static struct bpf_regs bpf_regs[BPF_MAXINSNS + 1];
+static struct bpf_regs bpf_curr;
+static unsigned int bpf_regs_len = 0;
+
+static int pcap_fd = -1;
+static unsigned int pcap_packet = 0;
+static size_t pcap_map_size = 0;
+static char *pcap_ptr_va_start, *pcap_ptr_va_curr;
+
+static const char * const op_table[] = {
+	OP(BPF_ST, "st"),
+	OP(BPF_STX, "stx"),
+	OP(BPF_LD_B, "ldb"),
+	OP(BPF_LD_H, "ldh"),
+	OP(BPF_LD_W, "ld"),
+	OP(BPF_LDX, "ldx"),
+	OP(BPF_LDX_B, "ldxb"),
+	OP(BPF_JMP_JA, "ja"),
+	OP(BPF_JMP_JEQ, "jeq"),
+	OP(BPF_JMP_JGT, "jgt"),
+	OP(BPF_JMP_JGE, "jge"),
+	OP(BPF_JMP_JSET, "jset"),
+	OP(BPF_ALU_ADD, "add"),
+	OP(BPF_ALU_SUB, "sub"),
+	OP(BPF_ALU_MUL, "mul"),
+	OP(BPF_ALU_DIV, "div"),
+	OP(BPF_ALU_MOD, "mod"),
+	OP(BPF_ALU_NEG, "neg"),
+	OP(BPF_ALU_AND, "and"),
+	OP(BPF_ALU_OR, "or"),
+	OP(BPF_ALU_XOR, "xor"),
+	OP(BPF_ALU_LSH, "lsh"),
+	OP(BPF_ALU_RSH, "rsh"),
+	OP(BPF_MISC_TAX, "tax"),
+	OP(BPF_MISC_TXA, "txa"),
+	OP(BPF_RET, "ret"),
+};
+
+static __check_format_printf(1, 2) int rl_printf(const char *fmt, ...)
+{
+	int ret;
+	va_list vl;
+
+	va_start(vl, fmt);
+	ret = vfprintf(rl_outstream, fmt, vl);
+	va_end(vl);
+
+	return ret;
+}
+
+static int matches(const char *cmd, const char *pattern)
+{
+	int len = strlen(cmd);
+
+	if (len > strlen(pattern))
+		return -1;
+
+	return memcmp(pattern, cmd, len);
+}
+
+static void hex_dump(const uint8_t *buf, size_t len)
+{
+	int i;
+
+	rl_printf("%3u: ", 0);
+	for (i = 0; i < len; i++) {
+		if (i && !(i % 16))
+			rl_printf("\n%3u: ", i);
+		rl_printf("%02x ", buf[i]);
+	}
+	rl_printf("\n");
+}
+
+static bool bpf_prog_loaded(void)
+{
+	if (bpf_prog_len == 0)
+		rl_printf("no bpf program loaded!\n");
+
+	return bpf_prog_len > 0;
+}
+
+static void bpf_disasm(const struct sock_filter f, unsigned int i)
+{
+	const char *op, *fmt;
+	int val = f.k;
+	char buf[256];
+
+	switch (f.code) {
+	case BPF_RET | BPF_K:
+		op = op_table[BPF_RET];
+		fmt = "#%#x";
+		break;
+	case BPF_RET | BPF_A:
+		op = op_table[BPF_RET];
+		fmt = "a";
+		break;
+	case BPF_RET | BPF_X:
+		op = op_table[BPF_RET];
+		fmt = "x";
+		break;
+	case BPF_MISC_TAX:
+		op = op_table[BPF_MISC_TAX];
+		fmt = "";
+		break;
+	case BPF_MISC_TXA:
+		op = op_table[BPF_MISC_TXA];
+		fmt = "";
+		break;
+	case BPF_ST:
+		op = op_table[BPF_ST];
+		fmt = "M[%d]";
+		break;
+	case BPF_STX:
+		op = op_table[BPF_STX];
+		fmt = "M[%d]";
+		break;
+	case BPF_LD_W | BPF_ABS:
+		op = op_table[BPF_LD_W];
+		fmt = "[%d]";
+		break;
+	case BPF_LD_H | BPF_ABS:
+		op = op_table[BPF_LD_H];
+		fmt = "[%d]";
+		break;
+	case BPF_LD_B | BPF_ABS:
+		op = op_table[BPF_LD_B];
+		fmt = "[%d]";
+		break;
+	case BPF_LD_W | BPF_LEN:
+		op = op_table[BPF_LD_W];
+		fmt = "#len";
+		break;
+	case BPF_LD_W | BPF_IND:
+		op = op_table[BPF_LD_W];
+		fmt = "[x+%d]";
+		break;
+	case BPF_LD_H | BPF_IND:
+		op = op_table[BPF_LD_H];
+		fmt = "[x+%d]";
+		break;
+	case BPF_LD_B | BPF_IND:
+		op = op_table[BPF_LD_B];
+		fmt = "[x+%d]";
+		break;
+	case BPF_LD | BPF_IMM:
+		op = op_table[BPF_LD_W];
+		fmt = "#%#x";
+		break;
+	case BPF_LDX | BPF_IMM:
+		op = op_table[BPF_LDX];
+		fmt = "#%#x";
+		break;
+	case BPF_LDX_B | BPF_MSH:
+		op = op_table[BPF_LDX_B];
+		fmt = "4*([%d]&0xf)";
+		break;
+	case BPF_LD | BPF_MEM:
+		op = op_table[BPF_LD_W];
+		fmt = "M[%d]";
+		break;
+	case BPF_LDX | BPF_MEM:
+		op = op_table[BPF_LDX];
+		fmt = "M[%d]";
+		break;
+	case BPF_JMP_JA:
+		op = op_table[BPF_JMP_JA];
+		fmt = "%d";
+		val = i + 1 + f.k;
+		break;
+	case BPF_JMP_JGT | BPF_X:
+		op = op_table[BPF_JMP_JGT];
+		fmt = "x";
+		break;
+	case BPF_JMP_JGT | BPF_K:
+		op = op_table[BPF_JMP_JGT];
+		fmt = "#%#x";
+		break;
+	case BPF_JMP_JGE | BPF_X:
+		op = op_table[BPF_JMP_JGE];
+		fmt = "x";
+		break;
+	case BPF_JMP_JGE | BPF_K:
+		op = op_table[BPF_JMP_JGE];
+		fmt = "#%#x";
+		break;
+	case BPF_JMP_JEQ | BPF_X:
+		op = op_table[BPF_JMP_JEQ];
+		fmt = "x";
+		break;
+	case BPF_JMP_JEQ | BPF_K:
+		op = op_table[BPF_JMP_JEQ];
+		fmt = "#%#x";
+		break;
+	case BPF_JMP_JSET | BPF_X:
+		op = op_table[BPF_JMP_JSET];
+		fmt = "x";
+		break;
+	case BPF_JMP_JSET | BPF_K:
+		op = op_table[BPF_JMP_JSET];
+		fmt = "#%#x";
+		break;
+	case BPF_ALU_NEG:
+		op = op_table[BPF_ALU_NEG];
+		fmt = "";
+		break;
+	case BPF_ALU_LSH | BPF_X:
+		op = op_table[BPF_ALU_LSH];
+		fmt = "x";
+		break;
+	case BPF_ALU_LSH | BPF_K:
+		op = op_table[BPF_ALU_LSH];
+		fmt = "#%d";
+		break;
+	case BPF_ALU_RSH | BPF_X:
+		op = op_table[BPF_ALU_RSH];
+		fmt = "x";
+		break;
+	case BPF_ALU_RSH | BPF_K:
+		op = op_table[BPF_ALU_RSH];
+		fmt = "#%d";
+		break;
+	case BPF_ALU_ADD | BPF_X:
+		op = op_table[BPF_ALU_ADD];
+		fmt = "x";
+		break;
+	case BPF_ALU_ADD | BPF_K:
+		op = op_table[BPF_ALU_ADD];
+		fmt = "#%d";
+		break;
+	case BPF_ALU_SUB | BPF_X:
+		op = op_table[BPF_ALU_SUB];
+		fmt = "x";
+		break;
+	case BPF_ALU_SUB | BPF_K:
+		op = op_table[BPF_ALU_SUB];
+		fmt = "#%d";
+		break;
+	case BPF_ALU_MUL | BPF_X:
+		op = op_table[BPF_ALU_MUL];
+		fmt = "x";
+		break;
+	case BPF_ALU_MUL | BPF_K:
+		op = op_table[BPF_ALU_MUL];
+		fmt = "#%d";
+		break;
+	case BPF_ALU_DIV | BPF_X:
+		op = op_table[BPF_ALU_DIV];
+		fmt = "x";
+		break;
+	case BPF_ALU_DIV | BPF_K:
+		op = op_table[BPF_ALU_DIV];
+		fmt = "#%d";
+		break;
+	case BPF_ALU_MOD | BPF_X:
+		op = op_table[BPF_ALU_MOD];
+		fmt = "x";
+		break;
+	case BPF_ALU_MOD | BPF_K:
+		op = op_table[BPF_ALU_MOD];
+		fmt = "#%d";
+		break;
+	case BPF_ALU_AND | BPF_X:
+		op = op_table[BPF_ALU_AND];
+		fmt = "x";
+		break;
+	case BPF_ALU_AND | BPF_K:
+		op = op_table[BPF_ALU_AND];
+		fmt = "#%#x";
+		break;
+	case BPF_ALU_OR | BPF_X:
+		op = op_table[BPF_ALU_OR];
+		fmt = "x";
+		break;
+	case BPF_ALU_OR | BPF_K:
+		op = op_table[BPF_ALU_OR];
+		fmt = "#%#x";
+		break;
+	case BPF_ALU_XOR | BPF_X:
+		op = op_table[BPF_ALU_XOR];
+		fmt = "x";
+		break;
+	case BPF_ALU_XOR | BPF_K:
+		op = op_table[BPF_ALU_XOR];
+		fmt = "#%#x";
+		break;
+	default:
+		op = "nosup";
+		fmt = "%#x";
+		val = f.code;
+		break;
+	}
+
+	memset(buf, 0, sizeof(buf));
+	snprintf(buf, sizeof(buf), fmt, val);
+	buf[sizeof(buf) - 1] = 0;
+
+	if ((BPF_CLASS(f.code) == BPF_JMP && BPF_OP(f.code) != BPF_JA))
+		rl_printf("l%d:\t%s %s, l%d, l%d\n", i, op, buf,
+			  i + 1 + f.jt, i + 1 + f.jf);
+	else
+		rl_printf("l%d:\t%s %s\n", i, op, buf);
+}
+
+static void bpf_dump_curr(struct bpf_regs *r, struct sock_filter *f)
+{
+	int i, m = 0;
+
+	rl_printf("pc:       [%u]\n", r->Pc);
+	rl_printf("code:     [%u] jt[%u] jf[%u] k[%u]\n",
+		  f->code, f->jt, f->jf, f->k);
+	rl_printf("curr:     ");
+	bpf_disasm(*f, r->Pc);
+
+	if (f->jt || f->jf) {
+		rl_printf("jt:       ");
+		bpf_disasm(*(f + f->jt + 1), r->Pc + f->jt + 1);
+		rl_printf("jf:       ");
+		bpf_disasm(*(f + f->jf + 1), r->Pc + f->jf + 1);
+	}
+
+	rl_printf("A:        [%#08x][%u]\n", r->A, r->A);
+	rl_printf("X:        [%#08x][%u]\n", r->X, r->X);
+	if (r->Rs)
+		rl_printf("ret:      [%#08x][%u]!\n", r->R, r->R);
+
+	for (i = 0; i < BPF_MEMWORDS; i++) {
+		if (r->M[i]) {
+			m++;
+			rl_printf("M[%d]: [%#08x][%u]\n", i, r->M[i], r->M[i]);
+		}
+	}
+	if (m == 0)
+		rl_printf("M[0,%d]:  [%#08x][%u]\n", BPF_MEMWORDS - 1, 0, 0);
+}
+
+static void bpf_dump_pkt(uint8_t *pkt, uint32_t pkt_caplen, uint32_t pkt_len)
+{
+	if (pkt_caplen != pkt_len)
+		rl_printf("cap: %u, len: %u\n", pkt_caplen, pkt_len);
+	else
+		rl_printf("len: %u\n", pkt_len);
+
+	hex_dump(pkt, pkt_caplen);
+}
+
+static void bpf_disasm_all(const struct sock_filter *f, unsigned int len)
+{
+	unsigned int i;
+
+	for (i = 0; i < len; i++)
+		bpf_disasm(f[i], i);
+}
+
+static void bpf_dump_all(const struct sock_filter *f, unsigned int len)
+{
+	unsigned int i;
+
+	rl_printf("/* { op, jt, jf, k }, */\n");
+	for (i = 0; i < len; i++)
+		rl_printf("{ %#04x, %2u, %2u, %#010x },\n",
+			  f[i].code, f[i].jt, f[i].jf, f[i].k);
+}
+
+static bool bpf_runnable(struct sock_filter *f, unsigned int len)
+{
+	int sock, ret, i;
+	struct sock_fprog bpf = {
+		.filter = f,
+		.len = len,
+	};
+
+	sock = socket(AF_INET, SOCK_DGRAM, 0);
+	if (sock < 0) {
+		rl_printf("cannot open socket!\n");
+		return false;
+	}
+	ret = setsockopt(sock, SOL_SOCKET, SO_ATTACH_FILTER, &bpf, sizeof(bpf));
+	if (ret < 0) {
+		rl_printf("program not allowed to run by kernel!\n");
+		return false;
+	}
+	close(sock);
+	for (i = 0; i < len; i++) {
+		if (BPF_CLASS(f[i].code) == BPF_LD &&
+		    f[i].k > SKF_AD_OFF) {
+			rl_printf("extensions currently not supported!\n");
+			return false;
+		}
+	}
+
+	return true;
+}
+
+static void bpf_reset_breakpoints(void)
+{
+	int i;
+
+	for (i = 0; i < array_size(bpf_breakpoints); i++)
+		bpf_breakpoints[i] = -1;
+}
+
+static void bpf_set_breakpoints(unsigned int where)
+{
+	int i;
+	bool set = false;
+
+	for (i = 0; i < array_size(bpf_breakpoints); i++) {
+		if (bpf_breakpoints[i] == (int) where) {
+			rl_printf("breakpoint already set!\n");
+			set = true;
+			break;
+		}
+
+		if (bpf_breakpoints[i] == -1 && set == false) {
+			bpf_breakpoints[i] = where;
+			set = true;
+		}
+	}
+
+	if (!set)
+		rl_printf("too many breakpoints set, reset first!\n");
+}
+
+static void bpf_dump_breakpoints(void)
+{
+	int i;
+
+	rl_printf("breakpoints: ");
+
+	for (i = 0; i < array_size(bpf_breakpoints); i++) {
+		if (bpf_breakpoints[i] < 0)
+			continue;
+		rl_printf("%d ", bpf_breakpoints[i]);
+	}
+
+	rl_printf("\n");
+}
+
+static void bpf_reset(void)
+{
+	bpf_regs_len = 0;
+
+	memset(bpf_regs, 0, sizeof(bpf_regs));
+	memset(&bpf_curr, 0, sizeof(bpf_curr));
+}
+
+static void bpf_safe_regs(void)
+{
+	memcpy(&bpf_regs[bpf_regs_len++], &bpf_curr, sizeof(bpf_curr));
+}
+
+static bool bpf_restore_regs(int off)
+{
+	unsigned int index = bpf_regs_len - 1 + off;
+
+	if (index == 0) {
+		bpf_reset();
+		return true;
+	} else if (index < bpf_regs_len) {
+		memcpy(&bpf_curr, &bpf_regs[index], sizeof(bpf_curr));
+		bpf_regs_len = index;
+		return true;
+	} else {
+		rl_printf("reached bottom of register history stack!\n");
+		return false;
+	}
+}
+
+static uint32_t extract_u32(uint8_t *pkt, uint32_t off)
+{
+	uint32_t r;
+
+	memcpy(&r, &pkt[off], sizeof(r));
+
+	return ntohl(r);
+}
+
+static uint16_t extract_u16(uint8_t *pkt, uint32_t off)
+{
+	uint16_t r;
+
+	memcpy(&r, &pkt[off], sizeof(r));
+
+	return ntohs(r);
+}
+
+static uint8_t extract_u8(uint8_t *pkt, uint32_t off)
+{
+	return pkt[off];
+}
+
+static void set_return(struct bpf_regs *r)
+{
+	r->R = 0;
+	r->Rs = true;
+}
+
+static void bpf_single_step(struct bpf_regs *r, struct sock_filter *f,
+			    uint8_t *pkt, uint32_t pkt_caplen,
+			    uint32_t pkt_len)
+{
+	uint32_t K = f->k;
+	int d;
+
+	switch (f->code) {
+	case BPF_RET | BPF_K:
+		r->R = K;
+		r->Rs = true;
+		break;
+	case BPF_RET | BPF_A:
+		r->R = r->A;
+		r->Rs = true;
+		break;
+	case BPF_RET | BPF_X:
+		r->R = r->X;
+		r->Rs = true;
+		break;
+	case BPF_MISC_TAX:
+		r->X = r->A;
+		break;
+	case BPF_MISC_TXA:
+		r->A = r->X;
+		break;
+	case BPF_ST:
+		r->M[K] = r->A;
+		break;
+	case BPF_STX:
+		r->M[K] = r->X;
+		break;
+	case BPF_LD_W | BPF_ABS:
+		d = pkt_caplen - K;
+		if (d >= sizeof(uint32_t))
+			r->A = extract_u32(pkt, K);
+		else
+			set_return(r);
+		break;
+	case BPF_LD_H | BPF_ABS:
+		d = pkt_caplen - K;
+		if (d >= sizeof(uint16_t))
+			r->A = extract_u16(pkt, K);
+		else
+			set_return(r);
+		break;
+	case BPF_LD_B | BPF_ABS:
+		d = pkt_caplen - K;
+		if (d >= sizeof(uint8_t))
+			r->A = extract_u8(pkt, K);
+		else
+			set_return(r);
+		break;
+	case BPF_LD_W | BPF_IND:
+		d = pkt_caplen - (r->X + K);
+		if (d >= sizeof(uint32_t))
+			r->A = extract_u32(pkt, r->X + K);
+		break;
+	case BPF_LD_H | BPF_IND:
+		d = pkt_caplen - (r->X + K);
+		if (d >= sizeof(uint16_t))
+			r->A = extract_u16(pkt, r->X + K);
+		else
+			set_return(r);
+		break;
+	case BPF_LD_B | BPF_IND:
+		d = pkt_caplen - (r->X + K);
+		if (d >= sizeof(uint8_t))
+			r->A = extract_u8(pkt, r->X + K);
+		else
+			set_return(r);
+		break;
+	case BPF_LDX_B | BPF_MSH:
+		d = pkt_caplen - K;
+		if (d >= sizeof(uint8_t)) {
+			r->X = extract_u8(pkt, K);
+			r->X = (r->X & 0xf) << 2;
+		} else
+			set_return(r);
+		break;
+	case BPF_LD_W | BPF_LEN:
+		r->A = pkt_len;
+		break;
+	case BPF_LDX_W | BPF_LEN:
+		r->A = pkt_len;
+		break;
+	case BPF_LD | BPF_IMM:
+		r->A = K;
+		break;
+	case BPF_LDX | BPF_IMM:
+		r->X = K;
+		break;
+	case BPF_LD | BPF_MEM:
+		r->A = r->M[K];
+		break;
+	case BPF_LDX | BPF_MEM:
+		r->X = r->M[K];
+		break;
+	case BPF_JMP_JA:
+		r->Pc += K;
+		break;
+	case BPF_JMP_JGT | BPF_X:
+		r->Pc += r->A > r->X ? f->jt : f->jf;
+		break;
+	case BPF_JMP_JGT | BPF_K:
+		r->Pc += r->A > K ? f->jt : f->jf;
+		break;
+	case BPF_JMP_JGE | BPF_X:
+		r->Pc += r->A >= r->X ? f->jt : f->jf;
+		break;
+	case BPF_JMP_JGE | BPF_K:
+		r->Pc += r->A >= K ? f->jt : f->jf;
+		break;
+	case BPF_JMP_JEQ | BPF_X:
+		r->Pc += r->A == r->X ? f->jt : f->jf;
+		break;
+	case BPF_JMP_JEQ | BPF_K:
+		r->Pc += r->A == K ? f->jt : f->jf;
+		break;
+	case BPF_JMP_JSET | BPF_X:
+		r->Pc += r->A & r->X ? f->jt : f->jf;
+		break;
+	case BPF_JMP_JSET | BPF_K:
+		r->Pc += r->A & K ? f->jt : f->jf;
+		break;
+	case BPF_ALU_NEG:
+		r->A = -r->A;
+		break;
+	case BPF_ALU_LSH | BPF_X:
+		r->A <<= r->X;
+		break;
+	case BPF_ALU_LSH | BPF_K:
+		r->A <<= K;
+		break;
+	case BPF_ALU_RSH | BPF_X:
+		r->A >>= r->X;
+		break;
+	case BPF_ALU_RSH | BPF_K:
+		r->A >>= K;
+		break;
+	case BPF_ALU_ADD | BPF_X:
+		r->A += r->X;
+		break;
+	case BPF_ALU_ADD | BPF_K:
+		r->A += K;
+		break;
+	case BPF_ALU_SUB | BPF_X:
+		r->A -= r->X;
+		break;
+	case BPF_ALU_SUB | BPF_K:
+		r->A -= K;
+		break;
+	case BPF_ALU_MUL | BPF_X:
+		r->A *= r->X;
+		break;
+	case BPF_ALU_MUL | BPF_K:
+		r->A *= K;
+		break;
+	case BPF_ALU_DIV | BPF_X:
+	case BPF_ALU_MOD | BPF_X:
+		if (r->X == 0) {
+			set_return(r);
+			break;
+		}
+		goto do_div;
+	case BPF_ALU_DIV | BPF_K:
+	case BPF_ALU_MOD | BPF_K:
+		if (K == 0) {
+			set_return(r);
+			break;
+		}
+do_div:
+		switch (f->code) {
+		case BPF_ALU_DIV | BPF_X:
+			r->A /= r->X;
+			break;
+		case BPF_ALU_DIV | BPF_K:
+			r->A /= K;
+			break;
+		case BPF_ALU_MOD | BPF_X:
+			r->A %= r->X;
+			break;
+		case BPF_ALU_MOD | BPF_K:
+			r->A %= K;
+			break;
+		}
+		break;
+	case BPF_ALU_AND | BPF_X:
+		r->A &= r->X;
+		break;
+	case BPF_ALU_AND | BPF_K:
+		r->A &= r->X;
+		break;
+	case BPF_ALU_OR | BPF_X:
+		r->A |= r->X;
+		break;
+	case BPF_ALU_OR | BPF_K:
+		r->A |= K;
+		break;
+	case BPF_ALU_XOR | BPF_X:
+		r->A ^= r->X;
+		break;
+	case BPF_ALU_XOR | BPF_K:
+		r->A ^= K;
+		break;
+	}
+}
+
+static bool bpf_pc_has_breakpoint(uint16_t pc)
+{
+	int i;
+
+	for (i = 0; i < array_size(bpf_breakpoints); i++) {
+		if (bpf_breakpoints[i] < 0)
+			continue;
+		if (bpf_breakpoints[i] == pc)
+			return true;
+	}
+
+	return false;
+}
+
+static bool bpf_handle_breakpoint(struct bpf_regs *r, struct sock_filter *f,
+				  uint8_t *pkt, uint32_t pkt_caplen,
+				  uint32_t pkt_len)
+{
+	rl_printf("-- register dump --\n");
+	bpf_dump_curr(r, &f[r->Pc]);
+	rl_printf("-- packet dump --\n");
+	bpf_dump_pkt(pkt, pkt_caplen, pkt_len);
+	rl_printf("(breakpoint)\n");
+	return true;
+}
+
+static int bpf_run_all(struct sock_filter *f, uint16_t bpf_len, uint8_t *pkt,
+		       uint32_t pkt_caplen, uint32_t pkt_len)
+{
+	bool stop = false;
+
+	while (bpf_curr.Rs == false && stop == false) {
+		bpf_safe_regs();
+
+		if (bpf_pc_has_breakpoint(bpf_curr.Pc))
+			stop = bpf_handle_breakpoint(&bpf_curr, f, pkt,
+						     pkt_caplen, pkt_len);
+
+		bpf_single_step(&bpf_curr, &f[bpf_curr.Pc], pkt, pkt_caplen,
+				pkt_len);
+		bpf_curr.Pc++;
+	}
+
+	return stop ? -1 : bpf_curr.R;
+}
+
+static int bpf_run_stepping(struct sock_filter *f, uint16_t bpf_len,
+			    uint8_t *pkt, uint32_t pkt_caplen,
+			    uint32_t pkt_len, int next)
+{
+	bool stop = false;
+	int i = 1;
+
+	while (bpf_curr.Rs == false && stop == false) {
+		bpf_safe_regs();
+
+		if (i++ == next)
+			stop = bpf_handle_breakpoint(&bpf_curr, f, pkt,
+						     pkt_caplen, pkt_len);
+
+		bpf_single_step(&bpf_curr, &f[bpf_curr.Pc], pkt, pkt_caplen,
+				pkt_len);
+		bpf_curr.Pc++;
+	}
+
+	return stop ? -1 : bpf_curr.R;
+}
+
+static bool pcap_loaded(void)
+{
+	if (pcap_fd < 0)
+		rl_printf("no pcap file loaded!\n");
+
+	return pcap_fd >= 0;
+}
+
+static struct pcap_pkthdr *pcap_curr_pkt(void)
+{
+	return (void *) pcap_ptr_va_curr;
+}
+
+static bool pcap_next_pkt(void)
+{
+	struct pcap_pkthdr *hdr = pcap_curr_pkt();
+
+	if (pcap_ptr_va_curr + sizeof(*hdr) -
+	    pcap_ptr_va_start >= pcap_map_size)
+		return false;
+	if (hdr->caplen == 0 || hdr->len == 0 || hdr->caplen > hdr->len)
+		return false;
+	if (pcap_ptr_va_curr + sizeof(*hdr) + hdr->caplen -
+	    pcap_ptr_va_start >= pcap_map_size)
+		return false;
+
+	pcap_ptr_va_curr += (sizeof(*hdr) + hdr->caplen);
+	return true;
+}
+
+static void pcap_reset_pkt(void)
+{
+	pcap_ptr_va_curr = pcap_ptr_va_start + sizeof(struct pcap_filehdr);
+}
+
+static int try_load_pcap(const char *file)
+{
+	struct pcap_filehdr *hdr;
+	struct stat sb;
+	int ret;
+
+	pcap_fd = open(file, O_RDONLY);
+	if (pcap_fd < 0) {
+		rl_printf("cannot open pcap [%s]!\n", strerror(errno));
+		return CMD_ERR;
+	}
+
+	ret = fstat(pcap_fd, &sb);
+	if (ret < 0) {
+		rl_printf("cannot fstat pcap file!\n");
+		return CMD_ERR;
+	}
+
+	if (!S_ISREG(sb.st_mode)) {
+		rl_printf("not a regular pcap file, duh!\n");
+		return CMD_ERR;
+	}
+
+	pcap_map_size = sb.st_size;
+	if (pcap_map_size <= sizeof(struct pcap_filehdr)) {
+		rl_printf("pcap file too small!\n");
+		return CMD_ERR;
+	}
+
+	pcap_ptr_va_start = mmap(NULL, pcap_map_size, PROT_READ,
+				 MAP_SHARED | MAP_LOCKED, pcap_fd, 0);
+	if (pcap_ptr_va_start == MAP_FAILED) {
+		rl_printf("mmap of file failed!");
+		return CMD_ERR;
+	}
+
+	hdr = (void *) pcap_ptr_va_start;
+	if (hdr->magic != TCPDUMP_MAGIC) {
+		rl_printf("wrong pcap magic!\n");
+		return CMD_ERR;
+	}
+
+	pcap_reset_pkt();
+
+	return CMD_OK;
+
+}
+
+static void try_close_pcap(void)
+{
+	if (pcap_fd >= 0) {
+		munmap(pcap_ptr_va_start, pcap_map_size);
+		close(pcap_fd);
+
+		pcap_ptr_va_start = pcap_ptr_va_curr = NULL;
+		pcap_map_size = 0;
+		pcap_packet = 0;
+		pcap_fd = -1;
+	}
+}
+
+static int cmd_load_bpf(char *bpf_string)
+{
+	char sp, *token, separator = ',';
+	unsigned short bpf_len, i = 0;
+	struct sock_filter tmp;
+
+	bpf_prog_len = 0;
+	memset(bpf_image, 0, sizeof(bpf_image));
+
+	if (sscanf(bpf_string, "%hu%c", &bpf_len, &sp) != 2 ||
+	    sp != separator || bpf_len > BPF_MAXINSNS || bpf_len == 0) {
+		rl_printf("syntax error in head length encoding!\n");
+		return CMD_ERR;
+	}
+
+	token = bpf_string;
+	while ((token = strchr(token, separator)) && (++token)[0]) {
+		if (i >= bpf_len) {
+			rl_printf("program exceeds encoded length!\n");
+			return CMD_ERR;
+		}
+
+		if (sscanf(token, "%hu %hhu %hhu %u,",
+			   &tmp.code, &tmp.jt, &tmp.jf, &tmp.k) != 4) {
+			rl_printf("syntax error at instruction %d!\n", i);
+			return CMD_ERR;
+		}
+
+		bpf_image[i].code = tmp.code;
+		bpf_image[i].jt = tmp.jt;
+		bpf_image[i].jf = tmp.jf;
+		bpf_image[i].k = tmp.k;
+
+		i++;
+	}
+
+	if (i != bpf_len) {
+		rl_printf("syntax error exceeding encoded length!\n");
+		return CMD_ERR;
+	} else
+		bpf_prog_len = bpf_len;
+	if (!bpf_runnable(bpf_image, bpf_prog_len))
+		bpf_prog_len = 0;
+
+	return CMD_OK;
+}
+
+static int cmd_load_pcap(char *file)
+{
+	char *file_trim, *tmp;
+
+	file_trim = strtok_r(file, " ", &tmp);
+	if (file_trim == NULL)
+		return CMD_ERR;
+
+	try_close_pcap();
+
+	return try_load_pcap(file_trim);
+}
+
+static int cmd_load(char *arg)
+{
+	char *subcmd, *cont, *tmp = strdup(arg);
+	int ret = CMD_OK;
+
+	subcmd = strtok_r(tmp, " ", &cont);
+	if (subcmd == NULL)
+		goto out;
+	if (matches(subcmd, "bpf") == 0) {
+		bpf_reset();
+		bpf_reset_breakpoints();
+
+		ret = cmd_load_bpf(cont);
+	} else if (matches(subcmd, "pcap") == 0) {
+		ret = cmd_load_pcap(cont);
+	} else {
+out:
+		rl_printf("bpf <code>:  load bpf code\n");
+		rl_printf("pcap <file>: load pcap file\n");
+		ret = CMD_ERR;
+	}
+
+	free(tmp);
+	return ret;
+}
+
+static int cmd_step(char *num)
+{
+	struct pcap_pkthdr *hdr;
+	int steps, ret;
+
+	if (!bpf_prog_loaded() || !pcap_loaded())
+		return CMD_ERR;
+
+	steps = strtol(num, NULL, 10);
+	if (steps == 0 || strlen(num) == 0)
+		steps = 1;
+	if (steps < 0) {
+		if (!bpf_restore_regs(steps))
+			return CMD_ERR;
+		steps = 1;
+	}
+
+	hdr = pcap_curr_pkt();
+	ret = bpf_run_stepping(bpf_image, bpf_prog_len,
+			       (uint8_t *) hdr + sizeof(*hdr),
+			       hdr->caplen, hdr->len, steps);
+	if (ret >= 0 || bpf_curr.Rs) {
+		bpf_reset();
+		if (!pcap_next_pkt()) {
+			rl_printf("(going back to first packet)\n");
+			pcap_reset_pkt();
+		} else {
+			rl_printf("(next packet)\n");
+		}
+	}
+
+	return CMD_OK;
+}
+
+static int cmd_select(char *num)
+{
+	unsigned int which, i;
+	struct pcap_pkthdr *hdr;
+	bool have_next = true;
+
+	if (!pcap_loaded() || strlen(num) == 0)
+		return CMD_ERR;
+
+	which = strtoul(num, NULL, 10);
+	if (which == 0) {
+		rl_printf("packet count starts with 1, clamping!\n");
+		which = 1;
+	}
+
+	pcap_reset_pkt();
+	bpf_reset();
+
+	for (i = 0; i < which && (have_next = pcap_next_pkt()); i++)
+		/* noop */;
+	if (!have_next || (hdr = pcap_curr_pkt()) == NULL) {
+		rl_printf("no packet #%u available!\n", which);
+		pcap_reset_pkt();
+		return CMD_ERR;
+	}
+
+	return CMD_OK;
+}
+
+static int cmd_breakpoint(char *subcmd)
+{
+	if (!bpf_prog_loaded())
+		return CMD_ERR;
+	if (strlen(subcmd) == 0)
+		bpf_dump_breakpoints();
+	else if (matches(subcmd, "reset") == 0)
+		bpf_reset_breakpoints();
+	else {
+		unsigned int where = strtoul(subcmd, NULL, 10);
+
+		if (where < bpf_prog_len) {
+			bpf_set_breakpoints(where);
+			rl_printf("breakpoint at: ");
+			bpf_disasm(bpf_image[where], where);
+		}
+	}
+
+	return CMD_OK;
+}
+
+static int cmd_run(char *num)
+{
+	static uint32_t pass = 0, fail = 0;
+	struct pcap_pkthdr *hdr;
+	bool has_limit = true;
+	int ret, pkts = 0, i = 0;
+
+	if (!bpf_prog_loaded() || !pcap_loaded())
+		return CMD_ERR;
+
+	pkts = strtol(num, NULL, 10);
+	if (pkts == 0 || strlen(num) == 0)
+		has_limit = false;
+
+	do {
+		hdr = pcap_curr_pkt();
+		ret = bpf_run_all(bpf_image, bpf_prog_len,
+				  (uint8_t *) hdr + sizeof(*hdr),
+				  hdr->caplen, hdr->len);
+		if (ret > 0)
+			pass++;
+		else if (ret == 0)
+			fail++;
+		else
+			return CMD_OK;
+		bpf_reset();
+	} while (pcap_next_pkt() && (!has_limit || (has_limit && ++i < pkts)));
+
+	rl_printf("bpf passes:%u fails:%u\n", pass, fail);
+
+	pcap_reset_pkt();
+	bpf_reset();
+
+	pass = fail = 0;
+	return CMD_OK;
+}
+
+static int cmd_disassemble(char *line_string)
+{
+	bool single_line = false;
+	unsigned long line;
+
+	if (!bpf_prog_loaded())
+		return CMD_ERR;
+	if (strlen(line_string) > 0 &&
+	    (line = strtoul(line_string, NULL, 10)) < bpf_prog_len)
+		single_line = true;
+	if (single_line)
+		bpf_disasm(bpf_image[line], line);
+	else
+		bpf_disasm_all(bpf_image, bpf_prog_len);
+
+	return CMD_OK;
+}
+
+static int cmd_dump(char *dontcare)
+{
+	if (!bpf_prog_loaded())
+		return CMD_ERR;
+
+	bpf_dump_all(bpf_image, bpf_prog_len);
+
+	return CMD_OK;
+}
+
+static int cmd_quit(char *dontcare)
+{
+	return CMD_EX;
+}
+
+static const struct shell_cmd cmds[] = {
+	CMD("load",		cmd_load),
+	CMD("select",		cmd_select),
+	CMD("step",		cmd_step),
+	CMD("run",		cmd_run),
+	CMD("breakpoint",	cmd_breakpoint),
+	CMD("disassemble",	cmd_disassemble),
+	CMD("dump",		cmd_dump),
+	CMD("quit",		cmd_quit),
+};
+
+static int execf(char *arg)
+{
+	char *cmd, *cont, *tmp = strdup(arg);
+	int i, ret = 0, len;
+
+	cmd = strtok_r(tmp, " ", &cont);
+	if (cmd == NULL)
+		goto out;
+	len = strlen(cmd);
+	for (i = 0; i < array_size(cmds); i++) {
+		if (len != strlen(cmds[i].name))
+			continue;
+		if (strncmp(cmds[i].name, cmd, len) == 0) {
+			ret = cmds[i].func(cont);
+			break;
+		}
+	}
+out:
+	free(tmp);
+	return ret;
+}
+
+static char *shell_comp_gen(const char *buf, int state)
+{
+	static int list_index, len;
+	const char *name;
+
+	if (!state) {
+		list_index = 0;
+		len = strlen(buf);
+	}
+
+	for (; list_index < array_size(cmds); ) {
+		name = cmds[list_index].name;
+		list_index++;
+
+		if (strncmp(name, buf, len) == 0)
+			return strdup(name);
+	}
+
+	return NULL;
+}
+
+static char **shell_completion(const char *buf, int start, int end)
+{
+	char **matches = NULL;
+
+	if (start == 0)
+		matches = rl_completion_matches(buf, shell_comp_gen);
+
+	return matches;
+}
+
+static void intr_shell(int sig)
+{
+	if (rl_end)
+		rl_kill_line(-1, 0);
+
+	rl_crlf();
+	rl_refresh_line(0, 0);
+	rl_free_line_state();
+}
+
+static void init_shell(FILE *fin, FILE *fout)
+{
+	char file[128];
+
+	memset(file, 0, sizeof(file));
+	snprintf(file, sizeof(file) - 1,
+		 "%s/.bpf_dbg_history", getenv("HOME"));
+
+	read_history(file);
+
+	memset(file, 0, sizeof(file));
+	snprintf(file, sizeof(file) - 1,
+		 "%s/.bpf_dbg_init", getenv("HOME"));
+
+	rl_instream = fin;
+	rl_outstream = fout;
+
+	rl_readline_name = "bpf_dbg";
+	rl_terminal_name = getenv("TERM");
+
+	rl_catch_signals = 0;
+	rl_catch_sigwinch = 1;
+
+	rl_attempted_completion_function = shell_completion;
+
+	rl_bind_key('\t', rl_complete);
+
+	rl_bind_key_in_map('\t', rl_complete, emacs_meta_keymap);
+	rl_bind_key_in_map('\033', rl_complete, emacs_meta_keymap);
+
+	rl_read_init_file(file);
+	rl_prep_terminal(0);
+	rl_set_signals();
+
+	signal(SIGINT, intr_shell);
+}
+
+static void exit_shell(void)
+{
+	char file[128];
+
+	memset(file, 0, sizeof(file));
+	snprintf(file, sizeof(file) - 1,
+		 "%s/.bpf_dbg_history", getenv("HOME"));
+
+	write_history(file);
+	clear_history();
+	rl_deprep_terminal();
+
+	try_close_pcap();
+}
+
+static int run_shell_loop(FILE *fin, FILE *fout)
+{
+	char *buf;
+	int ret;
+
+	init_shell(fin, fout);
+
+	while ((buf = readline("> ")) != NULL) {
+		ret = execf(buf);
+		if (ret == CMD_EX)
+			break;
+		if (ret == CMD_OK && strlen(buf) > 0)
+			add_history(buf);
+
+		free(buf);
+	}
+
+	exit_shell();
+	return 0;
+}
+
+int main(int argc, char **argv)
+{
+	FILE *fin = NULL, *fout = NULL;
+
+	if (argc >= 2)
+		fin = fopen(argv[1], "r");
+	if (argc >= 3)
+		fout = fopen(argv[2], "w");
+
+	return run_shell_loop(fin ? : stdin, fout ? : stdout);
+}