netsniff-ng: Add cooked cmdline option.
[netsniff-ng.git] / bpf_jit_disasm.c
blob6d1df6e0aa8074baf31786f7f4fefe719a57cd46
1 /*
2 * Minimal BPF JIT image disassembler
4 * Disassembles BPF JIT compiler emitted opcodes back to asm insn's for
5 * debugging or verification purposes.
7 * There is no Makefile. Compile with
9 * `gcc -Wall -O2 bpf_jit_disasm.c -o bpf_jit_disasm -lopcodes -lbfd -ldl`
11 * or similar.
13 * To get the disassembly of the JIT code, do the following:
15 * 1) `echo 2 > /proc/sys/net/core/bpf_jit_enable`
16 * 2) Load a BPF filter (e.g. `tcpdump -p -n -s 0 -i eth1 host 192.168.20.0/24`)
17 * 3) Run e.g. `bpf_jit_disasm -o` to read out the last JIT code
19 * Copyright 2013 Daniel Borkmann <borkmann@redhat.com>
20 * Licensed under the GNU General Public License, version 2.0 (GPLv2)
22 * Note: this is part of the Linux kernel and can be found under tools/net/.
25 #include <stdint.h>
26 #include <stdio.h>
27 #include <stdlib.h>
28 #include <assert.h>
29 #include <unistd.h>
30 #include <string.h>
31 #include <bfd.h>
32 #include <dis-asm.h>
33 #include <sys/klog.h>
34 #include <sys/types.h>
35 #include <regex.h>
37 static void get_exec_path(char *tpath, size_t size)
39 char *path;
40 ssize_t len;
42 snprintf(tpath, size, "/proc/%d/exe", (int) getpid());
43 tpath[size - 1] = 0;
45 path = strdup(tpath);
46 assert(path);
48 len = readlink(path, tpath, size);
49 tpath[len] = 0;
51 free(path);
54 static void get_asm_insns(uint8_t *image, size_t len, unsigned long base,
55 int opcodes)
57 int count, i, pc = 0;
58 char tpath[256];
59 struct disassemble_info info;
60 disassembler_ftype disassemble;
61 bfd *bfdf;
63 memset(tpath, 0, sizeof(tpath));
64 get_exec_path(tpath, sizeof(tpath));
66 bfdf = bfd_openr(tpath, NULL);
67 assert(bfdf);
68 assert(bfd_check_format(bfdf, bfd_object));
70 init_disassemble_info(&info, stdout, (fprintf_ftype) fprintf);
71 info.arch = bfd_get_arch(bfdf);
72 info.mach = bfd_get_mach(bfdf);
73 info.buffer = image;
74 info.buffer_length = len;
76 disassemble_init_for_target(&info);
78 disassemble = disassembler(bfdf);
79 assert(disassemble);
81 do {
82 printf("%4x:\t", pc);
84 count = disassemble(pc, &info);
86 if (opcodes) {
87 printf("\n\t");
88 for (i = 0; i < count; ++i)
89 printf("%02x ", (uint8_t) image[pc + i]);
91 printf("\n");
93 pc += count;
94 } while(count > 0 && pc < len);
96 bfd_close(bfdf);
99 static char *get_klog_buff(int *klen)
101 int ret, len = klogctl(10, NULL, 0);
102 char *buff = malloc(len);
104 assert(buff && klen);
105 ret = klogctl(3, buff, len);
106 assert(ret >= 0);
107 *klen = ret;
109 return buff;
112 static void put_klog_buff(char *buff)
114 free(buff);
117 static int get_last_jit_image(char *haystack, size_t hlen,
118 uint8_t *image, size_t ilen,
119 unsigned long *base)
121 char *ptr, *pptr, *tmp;
122 off_t off = 0;
123 int ret, flen, proglen, pass, ulen = 0;
124 regmatch_t pmatch[1];
125 regex_t regex;
127 if (hlen == 0)
128 return 0;
130 ret = regcomp(&regex, "flen=[[:alnum:]]+ proglen=[[:digit:]]+ "
131 "pass=[[:digit:]]+ image=[[:xdigit:]]+", REG_EXTENDED);
132 assert(ret == 0);
134 ptr = haystack;
135 while (1) {
136 ret = regexec(&regex, ptr, 1, pmatch, 0);
137 if (ret == 0) {
138 ptr += pmatch[0].rm_eo;
139 off += pmatch[0].rm_eo;
140 assert(off < hlen);
141 } else
142 break;
145 ptr = haystack + off - (pmatch[0].rm_eo - pmatch[0].rm_so);
146 ret = sscanf(ptr, "flen=%d proglen=%d pass=%d image=%lx",
147 &flen, &proglen, &pass, base);
148 if (ret != 4)
149 return 0;
151 tmp = ptr = haystack + off;
152 while ((ptr = strtok(tmp, "\n")) != NULL && ulen < ilen) {
153 tmp = NULL;
154 if (!strstr(ptr, "JIT code"))
155 continue;
156 pptr = ptr;
157 while ((ptr = strstr(pptr, ":")))
158 pptr = ptr + 1;
159 ptr = pptr;
160 do {
161 image[ulen++] = (uint8_t) strtoul(pptr, &pptr, 16);
162 if (ptr == pptr || ulen >= ilen) {
163 ulen--;
164 break;
166 ptr = pptr;
167 } while (1);
170 assert(ulen == proglen);
171 printf("%d bytes emitted from JIT compiler (pass:%d, flen:%d)\n",
172 proglen, pass, flen);
173 printf("%lx + <x>:\n", *base);
175 regfree(&regex);
176 return ulen;
179 int main(int argc, char **argv)
181 int len, klen, opcodes = 0;
182 char *kbuff;
183 unsigned long base;
184 uint8_t image[4096];
186 if (argc > 1) {
187 if (!strncmp("-o", argv[argc - 1], 2)) {
188 opcodes = 1;
189 } else {
190 printf("usage: bpf_jit_disasm [-o: show opcodes]\n");
191 exit(0);
195 bfd_init();
196 memset(image, 0, sizeof(image));
198 kbuff = get_klog_buff(&klen);
200 len = get_last_jit_image(kbuff, klen, image, sizeof(image), &base);
201 if (len > 0 && base > 0)
202 get_asm_insns(image, len, base, opcodes);
204 put_klog_buff(kbuff);
206 return 0;