opcodes/z80-dis.c

   1 /* Print Z80 and R800 instructions
   2    Copyright 2005 Free Software Foundation, Inc.
   3    Contributed by Arnold Metselaar <arnold_m@operamail.com>
   4
   5    This file is free software; you can redistribute it and/or modify
   6    it under the terms of the GNU General Public License as published by
   7    the Free Software Foundation; either version 2 of the License, or
   8    (at your option) any later version.
   9
  10    This program is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13    GNU General Public License for more details.
  14
  15    You should have received a copy of the GNU General Public License
  16    along with this program; if not, write to the Free Software
  17    Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston,
  18    MA 02110-1301, USA.  */
  19
  20 #include "sysdep.h"
  21 #include "dis-asm.h"
  22 #include <stdio.h>
  23
  24 struct buffer
  25 {
  26   bfd_vma base;
  27   int n_fetch;
  28   int n_used;
  29   signed char data[4];
  30 } ;
  31
  32 typedef int (*func)(struct buffer *, disassemble_info *, char *);
  33
  34 struct tab_elt
  35 {
  36   unsigned char val;
  37   unsigned char mask;
  38   func          fp;
  39   char *        text;
  40 } ;
  41
  42 #define TXTSIZ 24
  43 /* Names of 16-bit registers.  */
  44 static char * rr_str[] = { "bc", "de", "hl", "sp" };
  45 /* Names of 8-bit registers.  */
  46 static char * r_str[]  = { "b", "c", "d", "e", "h", "l", "(hl)", "a" };
  47 /* Texts for condition codes.  */
  48 static char * cc_str[] = { "nz", "z", "nc", "c", "po", "pe", "p", "m" };
  49 /* Instruction names for 8-bit arithmetic, operand "a" is often implicit */
  50 static char * arit_str[] =
  51 {
  52   "add a,", "adc a,", "sub ", "sbc a,", "and ", "xor ", "or ", "cp "
  53 } ;
  54 \f
  55 static int
  56 fetch_data (struct buffer *buf, disassemble_info * info, int n)
  57 {
  58   int r;
  59
  60   if (buf->n_fetch + n > 4)
  61     abort ();
  62
  63   r = info->read_memory_func (buf->base + buf->n_fetch,
  64                               (unsigned char*) buf->data + buf->n_fetch,
  65                               n, info);
  66   if (r == 0)
  67     buf->n_fetch += n;
  68   return !r;
  69 }
  70
  71 static int
  72 prt (struct buffer *buf, disassemble_info * info, char *txt)
  73 {
  74   info->fprintf_func (info->stream, "%s", txt);
  75   buf->n_used = buf->n_fetch;
  76   return 1;
  77 }
  78
  79 static int
  80 prt_e (struct buffer *buf, disassemble_info * info, char *txt)
  81 {
  82   char e;
  83   int target_addr;
  84
  85   if (fetch_data (buf, info, 1))
  86     {
  87       e = buf->data[1];
  88       target_addr = (buf->base + 2 + e) & 0xffff;
  89       buf->n_used = buf->n_fetch;
  90       info->fprintf_func (info->stream, "%s0x%04x", txt, target_addr);
  91     }
  92   else
  93     buf->n_used = -1;
  94
  95   return buf->n_used;
  96 }
  97
  98 static int
  99 jr_cc (struct buffer *buf, disassemble_info * info, char *txt)
 100 {
 101   char mytxt[TXTSIZ];
 102
 103   snprintf (mytxt, TXTSIZ, txt, cc_str[(buf->data[0] >> 3) & 3]);
 104   return prt_e (buf, info, mytxt);
 105 }
 106
 107 static int
 108 prt_nn (struct buffer *buf, disassemble_info * info, char *txt)
 109 {
 110   int nn;
 111   unsigned char *p;
 112
 113   p = (unsigned char*) buf->data + buf->n_fetch;
 114   if (fetch_data (buf, info, 2))
 115     {
 116       nn = p[0] + (p[1] << 8);
 117       info->fprintf_func (info->stream, txt, nn);
 118       buf->n_used = buf->n_fetch;
 119     }
 120   else
 121     buf->n_used = -1;
 122   return buf->n_used;
 123 }
 124
 125 static int
 126 prt_rr_nn (struct buffer *buf, disassemble_info * info, char *txt)
 127 {
 128   char mytxt[TXTSIZ];
 129
 130   snprintf (mytxt, TXTSIZ, txt, rr_str[(buf->data[0] >> 4) & 3]);
 131   return prt_nn (buf, info, mytxt);
 132 }
 133
 134 static int
 135 prt_rr (struct buffer *buf, disassemble_info * info, char *txt)
 136 {
 137   info->fprintf_func (info->stream, "%s%s", txt,
 138                       rr_str[(buf->data[buf->n_fetch - 1] >> 4) & 3]);
 139   buf->n_used = buf->n_fetch;
 140   return buf->n_used;
 141 }
 142
 143 static int
 144 prt_n (struct buffer *buf, disassemble_info * info, char *txt)
 145 {
 146   int n;
 147   unsigned char *p;
 148
 149   p = (unsigned char*) buf->data + buf->n_fetch;
 150
 151   if (fetch_data (buf, info, 1))
 152     {
 153       n = p[0];
 154       info->fprintf_func (info->stream, txt, n);
 155       buf->n_used = buf->n_fetch;
 156     }
 157   else
 158     buf->n_used = -1;
 159
 160   return buf->n_used;
 161 }
 162
 163 static int
 164 ld_r_n (struct buffer *buf, disassemble_info * info, char *txt)
 165 {
 166   char mytxt[TXTSIZ];
 167
 168   snprintf (mytxt, TXTSIZ, txt, r_str[(buf->data[0] >> 3) & 7]);
 169   return prt_n (buf, info, mytxt);
 170 }
 171
 172 static int
 173 prt_r (struct buffer *buf, disassemble_info * info, char *txt)
 174 {
 175   info->fprintf_func (info->stream, txt,
 176                       r_str[(buf->data[buf->n_fetch - 1] >> 3) & 7]);
 177   buf->n_used = buf->n_fetch;
 178   return buf->n_used;
 179 }
 180
 181 static int
 182 ld_r_r (struct buffer *buf, disassemble_info * info, char *txt)
 183 {
 184   info->fprintf_func (info->stream, txt,
 185                       r_str[(buf->data[buf->n_fetch - 1] >> 3) & 7],
 186                       r_str[buf->data[buf->n_fetch - 1] & 7]);
 187   buf->n_used = buf->n_fetch;
 188   return buf->n_used;
 189 }
 190
 191 static int
 192 arit_r (struct buffer *buf, disassemble_info * info, char *txt)
 193 {
 194   info->fprintf_func (info->stream, txt,
 195                       arit_str[(buf->data[buf->n_fetch - 1] >> 3) & 7],
 196                       r_str[buf->data[buf->n_fetch - 1] & 7]);
 197   buf->n_used = buf->n_fetch;
 198   return buf->n_used;
 199 }
 200
 201 static int
 202 prt_cc (struct buffer *buf, disassemble_info * info, char *txt)
 203 {
 204   info->fprintf_func (info->stream, "%s%s", txt,
 205                       cc_str[(buf->data[0] >> 3) & 7]);
 206   buf->n_used = buf->n_fetch;
 207   return buf->n_used;
 208 }
 209
 210 static int
 211 pop_rr (struct buffer *buf, disassemble_info * info, char *txt)
 212 {
 213   static char *rr_stack[] = { "bc","de","hl","af"};
 214
 215   info->fprintf_func (info->stream, "%s %s", txt,
 216                       rr_stack[(buf->data[0] >> 4) & 3]);
 217   buf->n_used = buf->n_fetch;
 218   return buf->n_used;
 219 }
 220
 221
 222 static int
 223 jp_cc_nn (struct buffer *buf, disassemble_info * info, char *txt)
 224 {
 225   char mytxt[TXTSIZ];
 226
 227   snprintf (mytxt,TXTSIZ,
 228             "%s%s,0x%%04x", txt, cc_str[(buf->data[0] >> 3) & 7]);
 229   return prt_nn (buf, info, mytxt);
 230 }
 231
 232 static int
 233 arit_n (struct buffer *buf, disassemble_info * info, char *txt)
 234 {
 235   char mytxt[TXTSIZ];
 236
 237   snprintf (mytxt,TXTSIZ, txt, arit_str[(buf->data[0] >> 3) & 7]);
 238   return prt_n (buf, info, mytxt);
 239 }
 240
 241 static int
 242 rst (struct buffer *buf, disassemble_info * info, char *txt)
 243 {
 244   info->fprintf_func (info->stream, txt, buf->data[0] & 0x38);
 245   buf->n_used = buf->n_fetch;
 246   return buf->n_used;
 247 }
 248
 249 \f
 250 static int
 251 cis (struct buffer *buf, disassemble_info * info, char *txt ATTRIBUTE_UNUSED)
 252 {
 253   static char * opar[] = { "ld", "cp", "in", "out" };
 254   char * op;
 255   char c;
 256
 257   c = buf->data[1];
 258   op = ((0x13 & c) == 0x13) ? "ot" : (opar[c & 3]);
 259   info->fprintf_func (info->stream,
 260                       "%s%c%s", op,
 261                       (c & 0x08) ? 'd' : 'i',
 262                       (c & 0x10) ? "r" : "");
 263   buf->n_used = 2;
 264   return buf->n_used;
 265 }
 266
 267 static int
 268 dump (struct buffer *buf, disassemble_info * info, char *txt)
 269 {
 270   int i;
 271
 272   info->fprintf_func (info->stream, "defb ");
 273   for (i = 0; txt[i]; ++i)
 274     info->fprintf_func (info->stream, i ? ", 0x%02x" : "0x%02x",
 275                         (unsigned char) buf->data[i]);
 276   buf->n_used = i;
 277   return buf->n_used;
 278 }
 279 \f
 280 /* Table to disassemble machine codes with prefix 0xED.  */
 281 struct tab_elt opc_ed[] =
 282 {
 283   { 0x70, 0xFF, prt, "in f,(c)" },
 284   { 0x70, 0xFF, dump, "xx" },
 285   { 0x40, 0xC7, prt_r, "in %s,(c)" },
 286   { 0x71, 0xFF, prt, "out (c),0" },
 287   { 0x70, 0xFF, dump, "xx" },
 288   { 0x41, 0xC7, prt_r, "out (c),%s" },
 289   { 0x42, 0xCF, prt_rr, "sbc hl," },
 290   { 0x43, 0xCF, prt_rr_nn, "ld (0x%%04x),%s" },
 291   { 0x44, 0xFF, prt, "neg" },
 292   { 0x45, 0xFF, prt, "retn" },
 293   { 0x46, 0xFF, prt, "im 0" },
 294   { 0x47, 0xFF, prt, "ld i,a" },
 295   { 0x4A, 0xCF, prt_rr, "adc hl," },
 296   { 0x4B, 0xCF, prt_rr_nn, "ld %s,(0x%%04x)" },
 297   { 0x4D, 0xFF, prt, "reti" },
 298   { 0x56, 0xFF, prt, "im 1" },
 299   { 0x57, 0xFF, prt, "ld a,i" },
 300   { 0x5E, 0xFF, prt, "im 2" },
 301   { 0x67, 0xFF, prt, "rrd" },
 302   { 0x6F, 0xFF, prt, "rld" },
 303   { 0xA0, 0xE4, cis, "" },
 304   { 0xC3, 0xFF, prt, "muluw hl,bc" },
 305   { 0xC5, 0xE7, prt_r, "mulub a,%s" },
 306   { 0xF3, 0xFF, prt, "muluw hl,sp" },
 307   { 0x00, 0x00, dump, "xx" }
 308 };
 309
 310 static int
 311 pref_ed (struct buffer * buf, disassemble_info * info,
 312          char* txt ATTRIBUTE_UNUSED)
 313 {
 314   struct tab_elt *p;
 315
 316   if (fetch_data(buf, info, 1))
 317     {
 318       for (p = opc_ed; p->val != (buf->data[1] & p->mask); ++p)
 319         ;
 320       p->fp (buf, info, p->text);
 321     }
 322   else
 323     buf->n_used = -1;
 324
 325   return buf->n_used;
 326 }
 327 \f
 328 /* Instruction names for the instructions addressing single bits.  */
 329 static char *cb1_str[] = { "", "bit", "res", "set"};
 330 /* Instruction names for shifts and rotates.  */
 331 static char *cb2_str[] =
 332 {
 333   "rlc", "rrc", "rl", "rr", "sla", "sra", "sli", "srl"
 334 };
 335
 336 static int
 337 pref_cb (struct buffer * buf, disassemble_info * info,
 338          char* txt ATTRIBUTE_UNUSED)
 339 {
 340   if (fetch_data (buf, info, 1))
 341     {
 342       buf->n_used = 2;
 343       if ((buf->data[1] & 0xc0) == 0)
 344         info->fprintf_func (info->stream, "%s %s",
 345                             cb2_str[(buf->data[1] >> 3) & 7],
 346                             r_str[buf->data[1] & 7]);
 347       else
 348         info->fprintf_func (info->stream, "%s %d,%s",
 349                             cb1_str[(buf->data[1] >> 6) & 3],
 350                             (buf->data[1] >> 3) & 7,
 351                             r_str[buf->data[1] & 7]);
 352     }
 353   else
 354     buf->n_used = -1;
 355
 356   return buf->n_used;
 357 }
 358 \f
 359 static int
 360 addvv (struct buffer * buf, disassemble_info * info, char* txt)
 361 {
 362   info->fprintf_func (info->stream, "add %s,%s", txt, txt);
 363
 364   return buf->n_used = buf->n_fetch;
 365 }
 366
 367 static int
 368 ld_v_v (struct buffer * buf, disassemble_info * info, char* txt)
 369 {
 370   char mytxt[TXTSIZ];
 371
 372   snprintf (mytxt, TXTSIZ, "ld %s%%s,%s%%s", txt, txt);
 373   return ld_r_r (buf, info, mytxt);
 374 }
 375
 376 static int
 377 prt_d (struct buffer *buf, disassemble_info * info, char *txt)
 378 {
 379   int d;
 380   signed char *p;
 381
 382   p = buf->data + buf->n_fetch;
 383
 384   if (fetch_data (buf, info, 1))
 385     {
 386       d = p[0];
 387       info->fprintf_func (info->stream, txt, d);
 388       buf->n_used = buf->n_fetch;
 389     }
 390   else
 391     buf->n_used = -1;
 392
 393   return buf->n_used;
 394 }
 395
 396 static int
 397 prt_d_n (struct buffer *buf, disassemble_info * info, char *txt)
 398 {
 399   char mytxt[TXTSIZ];
 400   int d;
 401   signed char *p;
 402
 403   p = buf->data + buf->n_fetch;
 404
 405   if (fetch_data (buf, info, 1))
 406     {
 407       d = p[0];
 408       snprintf (mytxt, TXTSIZ, txt, d);
 409       return prt_n (buf, info, mytxt);
 410     }
 411   else
 412     buf->n_used = -1;
 413
 414   return buf->n_used;
 415 }
 416
 417 static int
 418 arit_d (struct buffer *buf, disassemble_info * info, char *txt)
 419 {
 420   char mytxt[TXTSIZ];
 421   signed char c;
 422
 423   c = buf->data[buf->n_fetch - 1];
 424   snprintf (mytxt, TXTSIZ, txt, arit_str[(c >> 3) & 7]);
 425   return prt_d (buf, info, mytxt);
 426 }
 427
 428 static int
 429 ld_r_d (struct buffer *buf, disassemble_info * info, char *txt)
 430 {
 431   char mytxt[TXTSIZ];
 432   signed char c;
 433
 434   c = buf->data[buf->n_fetch - 1];
 435   snprintf (mytxt, TXTSIZ, txt, r_str[(c >> 3) & 7]);
 436   return prt_d (buf, info, mytxt);
 437 }
 438
 439 static int
 440 ld_d_r(struct buffer *buf, disassemble_info * info, char *txt)
 441 {
 442   char mytxt[TXTSIZ];
 443   signed char c;
 444
 445   c = buf->data[buf->n_fetch - 1];
 446   snprintf (mytxt, TXTSIZ, txt, r_str[c & 7]);
 447   return prt_d (buf, info, mytxt);
 448 }
 449
 450 static int
 451 pref_xd_cb (struct buffer * buf, disassemble_info * info, char* txt)
 452 {
 453   if (fetch_data (buf, info, 2))
 454     {
 455       int d;
 456       char arg[TXTSIZ];
 457       signed char *p;
 458
 459       buf->n_used = 4;
 460       p = buf->data;
 461       d = p[2];
 462
 463       if (((p[3] & 0xC0) == 0x40) || ((p[3] & 7) == 0x06))
 464         snprintf (arg, TXTSIZ, "(%s%+d)", txt, d);
 465       else
 466         snprintf (arg, TXTSIZ, "(%s%+d),%s", txt, d, r_str[p[3] & 7]);
 467
 468       if ((p[3] & 0xc0) == 0)
 469         info->fprintf_func (info->stream, "%s %s",
 470                             cb2_str[(buf->data[3] >> 3) & 7],
 471                             arg);
 472       else
 473         info->fprintf_func (info->stream, "%s %d,%s",
 474                             cb1_str[(buf->data[3] >> 6) & 3],
 475                             (buf->data[3] >> 3) & 7,
 476                             arg);
 477     }
 478   else
 479     buf->n_used = -1;
 480
 481   return buf->n_used;
 482 }
 483 \f
 484 /* Table to disassemble machine codes with prefix 0xDD or 0xFD.  */
 485 static struct tab_elt opc_ind[] =
 486 {
 487   { 0x24, 0xF7, prt_r, "inc %s%%s" },
 488   { 0x25, 0xF7, prt_r, "dec %s%%s" },
 489   { 0x26, 0xF7, ld_r_n, "ld %s%%s,0x%%%%02x" },
 490   { 0x21, 0xFF, prt_nn, "ld %s,0x%%04x" },
 491   { 0x22, 0xFF, prt_nn, "ld (0x%%04x),%s" },
 492   { 0x2A, 0xFF, prt_nn, "ld %s,(0x%%04x)" },
 493   { 0x23, 0xFF, prt, "inc %s" },
 494   { 0x2B, 0xFF, prt, "dec %s" },
 495   { 0x29, 0xFF, addvv, "%s" },
 496   { 0x09, 0xCF, prt_rr, "add %s," },
 497   { 0x34, 0xFF, prt_d, "inc (%s%%+d)" },
 498   { 0x35, 0xFF, prt_d, "dec (%s%%+d)" },
 499   { 0x36, 0xFF, prt_d_n, "ld (%s%%+d),0x%%%%02x" },
 500
 501   { 0x76, 0xFF, dump, "h" },
 502   { 0x46, 0xC7, ld_r_d, "ld %%s,(%s%%%%+d)" },
 503   { 0x70, 0xF8, ld_d_r, "ld (%s%%%%+d),%%s" },
 504   { 0x64, 0xF6, ld_v_v, "%s" },
 505   { 0x60, 0xF0, ld_r_r, "ld %s%%s,%%s" },
 506   { 0x44, 0xC6, ld_r_r, "ld %%s,%s%%s" },
 507
 508   { 0x86, 0xC7, arit_d, "%%s(%s%%%%+d)" },
 509   { 0x84, 0xC6, arit_r, "%%s%s%%s" },
 510
 511   { 0xE1, 0xFF, prt, "pop %s" },
 512   { 0xE5, 0xFF, prt, "push %s" },
 513   { 0xCB, 0xFF, pref_xd_cb, "%s" },
 514   { 0xE3, 0xFF, prt, "ex (sp),%s" },
 515   { 0xE9, 0xFF, prt, "jp (%s)" },
 516   { 0xF9, 0xFF, prt, "ld sp,%s" },
 517   { 0x00, 0x00, dump, "?" },
 518 } ;
 519
 520 static int
 521 pref_ind (struct buffer * buf, disassemble_info * info, char* txt)
 522 {
 523   if (fetch_data (buf, info, 1))
 524     {
 525       char mytxt[TXTSIZ];
 526       struct tab_elt *p;
 527
 528       for (p = opc_ind; p->val != (buf->data[1] & p->mask); ++p)
 529         ;
 530       snprintf (mytxt, TXTSIZ, p->text, txt);
 531       p->fp (buf, info, mytxt);
 532     }
 533   else
 534     buf->n_used = -1;
 535
 536   return buf->n_used;
 537 }
 538
 539 /* Table to disassemble machine codes without prefix.  */
 540 static struct tab_elt opc_main[] =
 541 {
 542   { 0x00, 0xFF, prt, "nop" },
 543   { 0x01, 0xCF, prt_rr_nn, "ld %s,0x%%04x" },
 544   { 0x02, 0xFF, prt, "ld (bc),a" },
 545   { 0x03, 0xCF, prt_rr, "inc " },
 546   { 0x04, 0xC7, prt_r, "inc %s" },
 547   { 0x05, 0xC7, prt_r, "dec %s" },
 548   { 0x06, 0xC7, ld_r_n, "ld %s,0x%%02x" },
 549   { 0x07, 0xFF, prt, "rlca" },
 550   { 0x08, 0xFF, prt, "ex af,af'" },
 551   { 0x09, 0xCF, prt_rr, "add hl," },
 552   { 0x0A, 0xFF, prt, "ld a,(bc)" },
 553   { 0x0B, 0xCF, prt_rr, "dec " },
 554   { 0x0F, 0xFF, prt, "rrca" },
 555   { 0x10, 0xFF, prt_e, "djnz " },
 556   { 0x12, 0xFF, prt, "ld (de),a" },
 557   { 0x17, 0xFF, prt, "rla" },
 558   { 0x18, 0xFF, prt_e, "jr "},
 559   { 0x1A, 0xFF, prt, "ld a,(de)" },
 560   { 0x1F, 0xFF, prt, "rra" },
 561   { 0x20, 0xE7, jr_cc, "jr %s,"},
 562   { 0x22, 0xFF, prt_nn, "ld (0x%04x),hl" },
 563   { 0x27, 0xFF, prt, "daa"},
 564   { 0x2A, 0xFF, prt_nn, "ld hl,(0x%04x)" },
 565   { 0x2F, 0xFF, prt, "cpl" },
 566   { 0x32, 0xFF, prt_nn, "ld (0x%04x),a" },
 567   { 0x37, 0xFF, prt, "scf" },
 568   { 0x3A, 0xFF, prt_nn, "ld a,(0x%04x)" },
 569   { 0x3F, 0xFF, prt, "ccf" },
 570
 571   { 0x76, 0xFF, prt, "halt" },
 572   { 0x40, 0xC0, ld_r_r, "ld %s,%s"},
 573
 574   { 0x80, 0xC0, arit_r, "%s%s" },
 575
 576   { 0xC0, 0xC7, prt_cc, "ret " },
 577   { 0xC1, 0xCF, pop_rr, "pop" },
 578   { 0xC2, 0xC7, jp_cc_nn, "jp " },
 579   { 0xC3, 0xFF, prt_nn, "jp 0x%04x" },
 580   { 0xC4, 0xC7, jp_cc_nn, "call " },
 581   { 0xC5, 0xCF, pop_rr, "push" },
 582   { 0xC6, 0xC7, arit_n, "%s0x%%02x" },
 583   { 0xC7, 0xC7, rst, "rst 0x%02x" },
 584   { 0xC9, 0xFF, prt, "ret" },
 585   { 0xCB, 0xFF, pref_cb, "" },
 586   { 0xCD, 0xFF, prt_nn, "call 0x%04x" },
 587   { 0xD3, 0xFF, prt_n, "out (0x%02x),a" },
 588   { 0xD9, 0xFF, prt, "exx" },
 589   { 0xDB, 0xFF, prt_n, "in a,(0x%02x)" },
 590   { 0xDD, 0xFF, pref_ind, "ix" },
 591   { 0xE3, 0xFF, prt, "ex (sp),hl" },
 592   { 0xE9, 0xFF, prt, "jp (hl)" },
 593   { 0xEB, 0xFF, prt, "ex de,hl" },
 594   { 0xED, 0xFF, pref_ed, ""},
 595   { 0xF3, 0xFF, prt, "di" },
 596   { 0xF9, 0xFF, prt, "ld sp,hl" },
 597   { 0xFB, 0xFF, prt, "ei" },
 598   { 0xFD, 0xFF, pref_ind, "iy" },
 599   { 0x00, 0x00, prt, "????" },
 600 } ;
 601
 602 int
 603 print_insn_z80 (bfd_vma addr, disassemble_info * info)
 604 {
 605   struct buffer buf;
 606   struct tab_elt *p;
 607
 608   buf.base = addr;
 609   buf.n_fetch = 0;
 610   buf.n_used = 0;
 611
 612   if (! fetch_data (& buf, info, 1))
 613     return -1;
 614
 615   for (p = opc_main; p->val != (buf.data[0] & p->mask); ++p)
 616     ;
 617   p->fp (& buf, info, p->text);
 618
 619   return buf.n_used;
 620 }