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 * To get the disassembly of the JIT code, do the following:
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
13 * Copyright 2013 Daniel Borkmann <borkmann@redhat.com>
14 * Licensed under the GNU General Public License, version 2.0 (GPLv2)
28 #include <sys/types.h>
31 #define CMD_ACTION_SIZE_BUFFER 10
32 #define CMD_ACTION_READ_ALL 3
34 static void get_exec_path(char *tpath, size_t size)
39 snprintf(tpath, size, "/proc/%d/exe", (int) getpid());
45 len = readlink(path, tpath, size);
51 static void get_asm_insns(uint8_t *image, size_t len, int opcodes)
55 struct disassemble_info info;
56 disassembler_ftype disassemble;
59 memset(tpath, 0, sizeof(tpath));
60 get_exec_path(tpath, sizeof(tpath));
62 bfdf = bfd_openr(tpath, NULL);
64 assert(bfd_check_format(bfdf, bfd_object));
66 init_disassemble_info(&info, stdout, (fprintf_ftype) fprintf);
67 info.arch = bfd_get_arch(bfdf);
68 info.mach = bfd_get_mach(bfdf);
70 info.buffer_length = len;
72 disassemble_init_for_target(&info);
74 disassemble = disassembler(bfdf);
80 count = disassemble(pc, &info);
84 for (i = 0; i < count; ++i)
85 printf("%02x ", (uint8_t) image[pc + i]);
90 } while(count > 0 && pc < len);
95 static char *get_klog_buff(unsigned int *klen)
100 len = klogctl(CMD_ACTION_SIZE_BUFFER, NULL, 0);
108 ret = klogctl(CMD_ACTION_READ_ALL, buff, len);
118 static char *get_flog_buff(const char *file, unsigned int *klen)
124 fd = open(file, O_RDONLY);
128 ret = fstat(fd, &fi);
129 if (ret < 0 || !S_ISREG(fi.st_mode))
132 len = fi.st_size + 1;
137 memset(buff, 0, len);
138 ret = read(fd, buff, len - 1);
152 static char *get_log_buff(const char *file, unsigned int *klen)
154 return file ? get_flog_buff(file, klen) : get_klog_buff(klen);
157 static void put_log_buff(char *buff)
162 static uint8_t *get_last_jit_image(char *haystack, size_t hlen,
165 char *ptr, *pptr, *tmp;
167 int ret, flen, proglen, pass, ulen = 0;
168 regmatch_t pmatch[1];
176 ret = regcomp(®ex, "flen=[[:alnum:]]+ proglen=[[:digit:]]+ "
177 "pass=[[:digit:]]+ image=[[:xdigit:]]+", REG_EXTENDED);
181 memset(pmatch, 0, sizeof(pmatch));
184 ret = regexec(®ex, ptr, 1, pmatch, 0);
186 ptr += pmatch[0].rm_eo;
187 off += pmatch[0].rm_eo;
193 ptr = haystack + off - (pmatch[0].rm_eo - pmatch[0].rm_so);
194 ret = sscanf(ptr, "flen=%d proglen=%d pass=%d image=%lx",
195 &flen, &proglen, &pass, &base);
200 if (proglen > 1000000) {
201 printf("proglen of %d too big, stopping\n", proglen);
205 image = malloc(proglen);
207 printf("Out of memory\n");
210 memset(image, 0, proglen);
212 tmp = ptr = haystack + off;
213 while ((ptr = strtok(tmp, "\n")) != NULL && ulen < proglen) {
215 if (!strstr(ptr, "JIT code"))
218 while ((ptr = strstr(pptr, ":")))
222 image[ulen++] = (uint8_t) strtoul(pptr, &pptr, 16);
233 assert(ulen == proglen);
234 printf("%d bytes emitted from JIT compiler (pass:%d, flen:%d)\n",
235 proglen, pass, flen);
236 printf("%lx + <x>:\n", base);
243 static void usage(void)
245 printf("Usage: bpf_jit_disasm [...]\n");
246 printf(" -o Also display related opcodes (default: off).\n");
247 printf(" -O <file> Write binary image of code to file, don't disassemble to stdout.\n");
248 printf(" -f <file> Read last image dump from file or stdin (default: klog).\n");
249 printf(" -h Display this help.\n");
252 int main(int argc, char **argv)
254 unsigned int len, klen, opt, opcodes = 0;
255 char *kbuff, *file = NULL;
260 uint8_t *image = NULL;
262 while ((opt = getopt(argc, argv, "of:O:")) != -1) {
281 kbuff = get_log_buff(file, &klen);
283 fprintf(stderr, "Could not retrieve log buffer!\n");
287 image = get_last_jit_image(kbuff, klen, &len);
289 fprintf(stderr, "No JIT image found!\n");
293 get_asm_insns(image, len, opcodes);
297 ofd = open(ofile, O_WRONLY | O_CREAT | O_TRUNC, DEFFILEMODE);
299 fprintf(stderr, "Could not open file %s for writing: ", ofile);
305 nr = write(ofd, pos, len);
307 fprintf(stderr, "Could not write data to %s: ", ofile);