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 #include <stdarg.h>
  14 #include <stdint.h>
  15 #include <stdio.h>
  16 #include <stdlib.h>
  17 #include <assert.h>
  18 #include <unistd.h>
  19 #include <string.h>
  20 #include <bfd.h>
  21 #include <dis-asm.h>
  22 #include <sys/types.h>
  23 #include <sys/stat.h>
  24 #include <limits.h>
  25
  26 #include "json_writer.h"
  27 #include "main.h"
  28
  29 static void get_exec_path(char *tpath, size_t size)
  30 {
  31         ssize_t len;
  32         char *path;
  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 - 1);
  41         assert(len > 0);
  42         tpath[len] = 0;
  43
  44         free(path);
  45 }
  46
  47 static int oper_count;
  48 static int fprintf_json(void *out, const char *fmt, ...)
  49 {
  50         va_list ap;
  51         char *s;
  52
  53         va_start(ap, fmt);
  54         if (!oper_count) {
  55                 int i;
  56
  57                 s = va_arg(ap, char *);
  58
  59                 /* Strip trailing spaces */
  60                 i = strlen(s) - 1;
  61                 while (s[i] == ' ')
  62                         s[i--] = '\0';
  63
  64                 jsonw_string_field(json_wtr, "operation", s);
  65                 jsonw_name(json_wtr, "operands");
  66                 jsonw_start_array(json_wtr);
  67                 oper_count++;
  68         } else if (!strcmp(fmt, ",")) {
  69                    /* Skip */
  70         } else {
  71                 s = va_arg(ap, char *);
  72                 jsonw_string(json_wtr, s);
  73                 oper_count++;
  74         }
  75         va_end(ap);
  76         return 0;
  77 }
  78
  79 void disasm_print_insn(unsigned char *image, ssize_t len, int opcodes)
  80 {
  81         disassembler_ftype disassemble;
  82         struct disassemble_info info;
  83         int count, i, pc = 0;
  84         char tpath[PATH_MAX];
  85         bfd *bfdf;
  86
  87         if (!len)
  88                 return;
  89
  90         memset(tpath, 0, sizeof(tpath));
  91         get_exec_path(tpath, sizeof(tpath));
  92
  93         bfdf = bfd_openr(tpath, NULL);
  94         assert(bfdf);
  95         assert(bfd_check_format(bfdf, bfd_object));
  96
  97         if (json_output)
  98                 init_disassemble_info(&info, stdout,
  99                                       (fprintf_ftype) fprintf_json);
 100         else
 101                 init_disassemble_info(&info, stdout,
 102                                       (fprintf_ftype) fprintf);
 103         info.arch = bfd_get_arch(bfdf);
 104         info.mach = bfd_get_mach(bfdf);
 105         info.buffer = image;
 106         info.buffer_length = len;
 107
 108         disassemble_init_for_target(&info);
 109
 110         disassemble = disassembler(bfdf);
 111         assert(disassemble);
 112
 113         if (json_output)
 114                 jsonw_start_array(json_wtr);
 115         do {
 116                 if (json_output) {
 117                         jsonw_start_object(json_wtr);
 118                         oper_count = 0;
 119                         jsonw_name(json_wtr, "pc");
 120                         jsonw_printf(json_wtr, "\"0x%x\"", pc);
 121                 } else {
 122                         printf("%4x:\t", pc);
 123                 }
 124
 125                 count = disassemble(pc, &info);
 126                 if (json_output) {
 127                         /* Operand array, was started in fprintf_json. Before
 128                          * that, make sure we have a _null_ value if no operand
 129                          * other than operation code was present.
 130                          */
 131                         if (oper_count == 1)
 132                                 jsonw_null(json_wtr);
 133                         jsonw_end_array(json_wtr);
 134                 }
 135
 136                 if (opcodes) {
 137                         if (json_output) {
 138                                 jsonw_name(json_wtr, "opcodes");
 139                                 jsonw_start_array(json_wtr);
 140                                 for (i = 0; i < count; ++i)
 141                                         jsonw_printf(json_wtr, "\"0x%02hhx\"",
 142                                                      (uint8_t)image[pc + i]);
 143                                 jsonw_end_array(json_wtr);
 144                         } else {
 145                                 printf("\n\t");
 146                                 for (i = 0; i < count; ++i)
 147                                         printf("%02x ",
 148                                                (uint8_t)image[pc + i]);
 149                         }
 150                 }
 151                 if (json_output)
 152                         jsonw_end_object(json_wtr);
 153                 else
 154                         printf("\n");
 155
 156                 pc += count;
 157         } while (count > 0 && pc < len);
 158         if (json_output)
 159                 jsonw_end_array(json_wtr);
 160
 161         bfd_close(bfdf);
 162 }