blob: cfe0cdcda3de990793b70d128e2267f53baac5ba [file] [log] [blame]
Daniel Borkmanne306e2c2013-03-20 12:11:47 +00001/*
2 * Minimal BPF JIT image disassembler
3 *
4 * Disassembles BPF JIT compiler emitted opcodes back to asm insn's for
5 * debugging or verification purposes.
6 *
7 * To get the disassembly of the JIT code, do the following:
8 *
9 * 1) `echo 2 > /proc/sys/net/core/bpf_jit_enable`
10 * 2) Load a BPF filter (e.g. `tcpdump -p -n -s 0 -i eth1 host 192.168.20.0/24`)
11 * 3) Run e.g. `bpf_jit_disasm -o` to read out the last JIT code
12 *
13 * Copyright 2013 Daniel Borkmann <borkmann@redhat.com>
14 * Licensed under the GNU General Public License, version 2.0 (GPLv2)
15 */
16
17#include <stdint.h>
18#include <stdio.h>
19#include <stdlib.h>
20#include <assert.h>
21#include <unistd.h>
22#include <string.h>
23#include <bfd.h>
24#include <dis-asm.h>
25#include <sys/klog.h>
26#include <sys/types.h>
27#include <regex.h>
28
29static void get_exec_path(char *tpath, size_t size)
30{
31 char *path;
32 ssize_t len;
33
34 snprintf(tpath, size, "/proc/%d/exe", (int) getpid());
35 tpath[size - 1] = 0;
36
37 path = strdup(tpath);
38 assert(path);
39
40 len = readlink(path, tpath, size);
41 tpath[len] = 0;
42
43 free(path);
44}
45
46static void get_asm_insns(uint8_t *image, size_t len, unsigned long base,
47 int opcodes)
48{
49 int count, i, pc = 0;
50 char tpath[256];
51 struct disassemble_info info;
52 disassembler_ftype disassemble;
53 bfd *bfdf;
54
55 memset(tpath, 0, sizeof(tpath));
56 get_exec_path(tpath, sizeof(tpath));
57
58 bfdf = bfd_openr(tpath, NULL);
59 assert(bfdf);
60 assert(bfd_check_format(bfdf, bfd_object));
61
62 init_disassemble_info(&info, stdout, (fprintf_ftype) fprintf);
63 info.arch = bfd_get_arch(bfdf);
64 info.mach = bfd_get_mach(bfdf);
65 info.buffer = image;
66 info.buffer_length = len;
67
68 disassemble_init_for_target(&info);
69
70 disassemble = disassembler(bfdf);
71 assert(disassemble);
72
73 do {
74 printf("%4x:\t", pc);
75
76 count = disassemble(pc, &info);
77
78 if (opcodes) {
79 printf("\n\t");
80 for (i = 0; i < count; ++i)
81 printf("%02x ", (uint8_t) image[pc + i]);
82 }
83 printf("\n");
84
85 pc += count;
86 } while(count > 0 && pc < len);
87
88 bfd_close(bfdf);
89}
90
91static char *get_klog_buff(int *klen)
92{
93 int ret, len = klogctl(10, NULL, 0);
94 char *buff = malloc(len);
95
96 assert(buff && klen);
97 ret = klogctl(3, buff, len);
98 assert(ret >= 0);
99 *klen = ret;
100
101 return buff;
102}
103
104static void put_klog_buff(char *buff)
105{
106 free(buff);
107}
108
109static int get_last_jit_image(char *haystack, size_t hlen,
110 uint8_t *image, size_t ilen,
111 unsigned long *base)
112{
113 char *ptr, *pptr, *tmp;
114 off_t off = 0;
115 int ret, flen, proglen, pass, ulen = 0;
116 regmatch_t pmatch[1];
117 regex_t regex;
118
119 if (hlen == 0)
120 return 0;
121
122 ret = regcomp(&regex, "flen=[[:alnum:]]+ proglen=[[:digit:]]+ "
123 "pass=[[:digit:]]+ image=[[:xdigit:]]+", REG_EXTENDED);
124 assert(ret == 0);
125
126 ptr = haystack;
127 while (1) {
128 ret = regexec(&regex, ptr, 1, pmatch, 0);
129 if (ret == 0) {
130 ptr += pmatch[0].rm_eo;
131 off += pmatch[0].rm_eo;
132 assert(off < hlen);
133 } else
134 break;
135 }
136
137 ptr = haystack + off - (pmatch[0].rm_eo - pmatch[0].rm_so);
138 ret = sscanf(ptr, "flen=%d proglen=%d pass=%d image=%lx",
139 &flen, &proglen, &pass, base);
140 if (ret != 4)
141 return 0;
142
143 tmp = ptr = haystack + off;
144 while ((ptr = strtok(tmp, "\n")) != NULL && ulen < ilen) {
145 tmp = NULL;
146 if (!strstr(ptr, "JIT code"))
147 continue;
148 pptr = ptr;
149 while ((ptr = strstr(pptr, ":")))
150 pptr = ptr + 1;
151 ptr = pptr;
152 do {
153 image[ulen++] = (uint8_t) strtoul(pptr, &pptr, 16);
154 if (ptr == pptr || ulen >= ilen) {
155 ulen--;
156 break;
157 }
158 ptr = pptr;
159 } while (1);
160 }
161
162 assert(ulen == proglen);
163 printf("%d bytes emitted from JIT compiler (pass:%d, flen:%d)\n",
164 proglen, pass, flen);
165 printf("%lx + <x>:\n", *base);
166
167 regfree(&regex);
168 return ulen;
169}
170
171int main(int argc, char **argv)
172{
173 int len, klen, opcodes = 0;
174 char *kbuff;
175 unsigned long base;
176 uint8_t image[4096];
177
178 if (argc > 1) {
179 if (!strncmp("-o", argv[argc - 1], 2)) {
180 opcodes = 1;
181 } else {
182 printf("usage: bpf_jit_disasm [-o: show opcodes]\n");
183 exit(0);
184 }
185 }
186
187 bfd_init();
188 memset(image, 0, sizeof(image));
189
190 kbuff = get_klog_buff(&klen);
191
192 len = get_last_jit_image(kbuff, klen, image, sizeof(image), &base);
193 if (len > 0 && base > 0)
194 get_asm_insns(image, len, base, opcodes);
195
196 put_klog_buff(kbuff);
197
198 return 0;
199}