tools/bpf/bpftool/jit_disasm.c

   1 /*
   2  * Based on:
   3  *
   4  * Minimal BPF JIT image disassembler
   5  *
   6  * Disassembles BPF JIT compiler emitted opcodes back to asm insn's for
   7  * debugging or verification purposes.
   8  *
   9  * Copyright 2013 Daniel Borkmann <daniel@iogearbox.net>
  10  * Licensed under the GNU General Public License, version 2.0 (GPLv2)
  11  */
  12
  13 #define _GNU_SOURCE
  14 #include <stdio.h>
  15 #include <stdarg.h>
  16 #include <stdint.h>
  17 #include <stdio.h>
  18 #include <stdlib.h>
  19 #include <assert.h>
  20 #include <unistd.h>
  21 #include <string.h>
  22 #include <bfd.h>
  23 #include <dis-asm.h>
  24 #include <sys/types.h>
  25 #include <sys/stat.h>
  26 #include <limits.h>
  27
  28 #include "json_writer.h"
  29 #include "main.h"
  30
  31 static void get_exec_path(char *tpath, size_t size)
  32 {
  33         ssize_t len;
  34         char *path;
  35
  36         snprintf(tpath, size, "/proc/%d/exe", (int) getpid());
  37         tpath[size - 1] = 0;
  38
  39         path = strdup(tpath);
  40         assert(path);
  41
  42         len = readlink(path, tpath, size - 1);
  43         assert(len > 0);
  44         tpath[len] = 0;
  45
  46         free(path);
  47 }
  48
  49 static int oper_count;
  50 static int fprintf_json(void *out, const char *fmt, ...)
  51 {
  52         va_list ap;
  53         char *s;
  54
  55         va_start(ap, fmt);
  56         if (vasprintf(&s, fmt, ap) < 0)
  57                 return -1;
  58         va_end(ap);
  59
  60         if (!oper_count) {
  61                 int i;
  62
  63                 /* Strip trailing spaces */
  64                 i = strlen(s) - 1;
  65                 while (s[i] == ' ')
  66                         s[i--] = '\0';
  67
  68                 jsonw_string_field(json_wtr, "operation", s);
  69                 jsonw_name(json_wtr, "operands");
  70                 jsonw_start_array(json_wtr);
  71                 oper_count++;
  72         } else if (!strcmp(fmt, ",")) {
  73                    /* Skip */
  74         } else {
  75                 jsonw_string(json_wtr, s);
  76                 oper_count++;
  77         }
  78         free(s);
  79         return 0;
  80 }
  81
  82 void disasm_print_insn(unsigned char *image, ssize_t len, int opcodes)
  83 {
  84         disassembler_ftype disassemble;
  85         struct disassemble_info info;
  86         int count, i, pc = 0;
  87         char tpath[PATH_MAX];
  88         bfd *bfdf;
  89
  90         if (!len)
  91                 return;
  92
  93         memset(tpath, 0, sizeof(tpath));
  94         get_exec_path(tpath, sizeof(tpath));
  95
  96         bfdf = bfd_openr(tpath, NULL);
  97         assert(bfdf);
  98         assert(bfd_check_format(bfdf, bfd_object));
  99
 100         if (json_output)
 101                 init_disassemble_info(&info, stdout,
 102                                       (fprintf_ftype) fprintf_json);
 103         else
 104                 init_disassemble_info(&info, stdout,
 105                                       (fprintf_ftype) fprintf);
 106         info.arch = bfd_get_arch(bfdf);
 107         info.mach = bfd_get_mach(bfdf);
 108         info.buffer = image;
 109         info.buffer_length = len;
 110
 111         disassemble_init_for_target(&info);
 112
 113 #ifdef DISASM_FOUR_ARGS_SIGNATURE
 114         disassemble = disassembler(info.arch,
 115                                    bfd_big_endian(bfdf),
 116                                    info.mach,
 117                                    bfdf);
 118 #else
 119         disassemble = disassembler(bfdf);
 120 #endif
 121         assert(disassemble);
 122
 123         if (json_output)
 124                 jsonw_start_array(json_wtr);
 125         do {
 126                 if (json_output) {
 127                         jsonw_start_object(json_wtr);
 128                         oper_count = 0;
 129                         jsonw_name(json_wtr, "pc");
 130                         jsonw_printf(json_wtr, "\"0x%x\"", pc);
 131                 } else {
 132                         printf("%4x:\t", pc);
 133                 }
 134
 135                 count = disassemble(pc, &info);
 136                 if (json_output) {
 137                         /* Operand array, was started in fprintf_json. Before
 138                          * that, make sure we have a _null_ value if no operand
 139                          * other than operation code was present.
 140                          */
 141                         if (oper_count == 1)
 142                                 jsonw_null(json_wtr);
 143                         jsonw_end_array(json_wtr);
 144                 }
 145
 146                 if (opcodes) {
 147                         if (json_output) {
 148                                 jsonw_name(json_wtr, "opcodes");
 149                                 jsonw_start_array(json_wtr);
 150                                 for (i = 0; i < count; ++i)
 151                                         jsonw_printf(json_wtr, "\"0x%02hhx\"",
 152                                                      (uint8_t)image[pc + i]);
 153                                 jsonw_end_array(json_wtr);
 154                         } else {
 155                                 printf("\n\t");
 156                                 for (i = 0; i < count; ++i)
 157                                         printf("%02x ",
 158                                                (uint8_t)image[pc + i]);
 159                         }
 160                 }
 161                 if (json_output)
 162                         jsonw_end_object(json_wtr);
 163                 else
 164                         printf("\n");
 165
 166                 pc += count;
 167         } while (count > 0 && pc < len);
 168         if (json_output)
 169                 jsonw_end_array(json_wtr);
 170
 171         bfd_close(bfdf);
 172 }