/*
 * Minimal BPF JIT image disassembler
 *
 * Disassembles BPF JIT compiler emitted opcodes back to asm insn's for
 * debugging or verification purposes.
 *
 * To get the disassembly of the JIT code, do the following:
 *
 *  1) `echo 2 > /proc/sys/net/core/bpf_jit_enable`
 *  2) Load a BPF filter (e.g. `tcpdump -p -n -s 0 -i eth1 host 192.168.20.0/24`)
 *  3) Run e.g. `bpf_jit_disasm -o` to read out the last JIT code
 *
 * Copyright 2013 Daniel Borkmann <borkmann@redhat.com>
 * Licensed under the GNU General Public License, version 2.0 (GPLv2)
 */

#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
#include <unistd.h>
#include <string.h>
#include <bfd.h>
#include <dis-asm.h>
#include <sys/klog.h>
#include <sys/types.h>
#include <regex.h>

static void get_exec_path(char *tpath, size_t size)
{
        char *path;
        ssize_t len;

        snprintf(tpath, size, "/proc/%d/exe", (int) getpid());
        tpath[size - 1] = 0;

        path = strdup(tpath);
        assert(path);

        len = readlink(path, tpath, size);
        tpath[len] = 0;

        free(path);
}

static void get_asm_insns(uint8_t *image, size_t len, unsigned long base,
                          int opcodes)
{
        int count, i, pc = 0;
        char tpath[256];
        struct disassemble_info info;
        disassembler_ftype disassemble;
        bfd *bfdf;

        memset(tpath, 0, sizeof(tpath));
        get_exec_path(tpath, sizeof(tpath));

        bfdf = bfd_openr(tpath, NULL);
        assert(bfdf);
        assert(bfd_check_format(bfdf, bfd_object));

        init_disassemble_info(&info, stdout, (fprintf_ftype) fprintf);
        info.arch = bfd_get_arch(bfdf);
        info.mach = bfd_get_mach(bfdf);
        info.buffer = image;
        info.buffer_length = len;

        disassemble_init_for_target(&info);

        disassemble = disassembler(bfdf);
        assert(disassemble);

        do {
                printf("%4x:\t", pc);

                count = disassemble(pc, &info);

                if (opcodes) {
                        printf("\n\t");
                        for (i = 0; i < count; ++i)
                                printf("%02x ", (uint8_t) image[pc + i]);
                }
                printf("\n");

                pc += count;
        } while(count > 0 && pc < len);

        bfd_close(bfdf);
}

static char *get_klog_buff(int *klen)
{
        int ret, len = klogctl(10, NULL, 0);
        char *buff = malloc(len);

        assert(buff && klen);
        ret = klogctl(3, buff, len);
        assert(ret >= 0);
        *klen = ret;

        return buff;
}

static void put_klog_buff(char *buff)
{
        free(buff);
}

static int get_last_jit_image(char *haystack, size_t hlen,
                              uint8_t *image, size_t ilen,
                              unsigned long *base)
{
        char *ptr, *pptr, *tmp;
        off_t off = 0;
        int ret, flen, proglen, pass, ulen = 0;
        regmatch_t pmatch[1];
        regex_t regex;

        if (hlen == 0)
                return 0;

        ret = regcomp(&regex, "flen=[[:alnum:]]+ proglen=[[:digit:]]+ "
                      "pass=[[:digit:]]+ image=[[:xdigit:]]+", REG_EXTENDED);
        assert(ret == 0);

        ptr = haystack;
        while (1) {
                ret = regexec(&regex, ptr, 1, pmatch, 0);
                if (ret == 0) {
                        ptr += pmatch[0].rm_eo;
                        off += pmatch[0].rm_eo;
                        assert(off < hlen);
                } else
                        break;
        }

        ptr = haystack + off - (pmatch[0].rm_eo - pmatch[0].rm_so);
        ret = sscanf(ptr, "flen=%d proglen=%d pass=%d image=%lx",
                     &flen, &proglen, &pass, base);
        if (ret != 4)
                return 0;

        tmp = ptr = haystack + off;
        while ((ptr = strtok(tmp, "\n")) != NULL && ulen < ilen) {
                tmp = NULL;
                if (!strstr(ptr, "JIT code"))
                        continue;
                pptr = ptr;
                while ((ptr = strstr(pptr, ":")))
                        pptr = ptr + 1;
                ptr = pptr;
                do {
                        image[ulen++] = (uint8_t) strtoul(pptr, &pptr, 16);
                        if (ptr == pptr || ulen >= ilen) {
                                ulen--;
                                break;
                        }
                        ptr = pptr;
                } while (1);
        }

        assert(ulen == proglen);
        printf("%d bytes emitted from JIT compiler (pass:%d, flen:%d)\n",
               proglen, pass, flen);
        printf("%lx + <x>:\n", *base);

        regfree(&regex);
        return ulen;
}

int main(int argc, char **argv)
{
        int len, klen, opcodes = 0;
        char *kbuff;
        unsigned long base;
        uint8_t image[4096];

        if (argc > 1) {
                if (!strncmp("-o", argv[argc - 1], 2)) {
                        opcodes = 1;
                } else {
                        printf("usage: bpf_jit_disasm [-o: show opcodes]\n");
                        exit(0);
                }
        }

        bfd_init();
        memset(image, 0, sizeof(image));

        kbuff = get_klog_buff(&klen);

        len = get_last_jit_image(kbuff, klen, image, sizeof(image), &base);
        if (len > 0 && base > 0)
                get_asm_insns(image, len, base, opcodes);

        put_klog_buff(kbuff);

        return 0;
}