eval.c

   1 /* eval.c    expression evaluator for the Netwide Assembler
   2  *
   3  * The Netwide Assembler is copyright (C) 1996 Simon Tatham and
   4  * Julian Hall. All rights reserved. The software is
   5  * redistributable under the licence given in the file "Licence"
   6  * distributed in the NASM archive.
   7  *
   8  * initial version 27/iii/95 by Simon Tatham
   9  */
  10
  11 #include <stdio.h>
  12 #include <stdlib.h>
  13 #include <stddef.h>
  14 #include <string.h>
  15 #include <ctype.h>
  16
  17 #include "nasm.h"
  18 #include "nasmlib.h"
  19 #include "eval.h"
  20 #include "labels.h"
  21
  22 #define TEMPEXPRS_DELTA 128
  23 #define TEMPEXPR_DELTA 8
  24
  25 static scanner scan;    /* Address of scanner routine */
  26 static efunc error;     /* Address of error reporting routine */
  27 static lfunc labelfunc; /* Address of label routine */
  28
  29 static struct ofmt *outfmt;  /* Structure of addresses of output routines */
  30
  31 static expr **tempexprs = NULL;
  32 static int    ntempexprs;
  33 static int    tempexprs_size = 0;
  34
  35 static expr  *tempexpr;
  36 static int   ntempexpr;
  37 static int   tempexpr_size;
  38
  39 static struct tokenval *tokval;   /* The current token */
  40 static int i;                     /* The t_type of tokval */
  41
  42 static void *scpriv;
  43 static loc_t *location;         /* Pointer to current line's segment,offset */
  44 static int *opflags;
  45
  46 static struct eval_hints *hint;
  47
  48 /*
  49  * Unimportant cleanup is done to avoid confusing people who are trying
  50  * to debug real memory leaks
  51  */
  52 void eval_cleanup(void)
  53 {
  54     while (ntempexprs)
  55         nasm_free (tempexprs[--ntempexprs]);
  56     nasm_free (tempexprs);
  57 }
  58
  59 /*
  60  * Construct a temporary expression.
  61  */
  62 static void begintemp(void)
  63 {
  64     tempexpr = NULL;
  65     tempexpr_size = ntempexpr = 0;
  66 }
  67
  68 static void addtotemp(long type, long value)
  69 {
  70     while (ntempexpr >= tempexpr_size) {
  71         tempexpr_size += TEMPEXPR_DELTA;
  72         tempexpr = nasm_realloc(tempexpr,
  73                                  tempexpr_size*sizeof(*tempexpr));
  74     }
  75     tempexpr[ntempexpr].type = type;
  76     tempexpr[ntempexpr++].value = value;
  77 }
  78
  79 static expr *finishtemp(void)
  80 {
  81     addtotemp (0L, 0L);                /* terminate */
  82     while (ntempexprs >= tempexprs_size) {
  83         tempexprs_size += TEMPEXPRS_DELTA;
  84         tempexprs = nasm_realloc(tempexprs,
  85                                  tempexprs_size*sizeof(*tempexprs));
  86     }
  87     return tempexprs[ntempexprs++] = tempexpr;
  88 }
  89
  90 /*
  91  * Add two vector datatypes. We have some bizarre behaviour on far-
  92  * absolute segment types: we preserve them during addition _only_
  93  * if one of the segments is a truly pure scalar.
  94  */
  95 static expr *add_vectors(expr *p, expr *q)
  96 {
  97     int preserve;
  98
  99     preserve = is_really_simple(p) || is_really_simple(q);
 100
 101     begintemp();
 102
 103     while (p->type && q->type &&
 104            p->type < EXPR_SEGBASE+SEG_ABS &&
 105            q->type < EXPR_SEGBASE+SEG_ABS)
 106     {
 107         int lasttype;
 108
 109         if (p->type > q->type) {
 110             addtotemp(q->type, q->value);
 111             lasttype = q++->type;
 112         } else if (p->type < q->type) {
 113             addtotemp(p->type, p->value);
 114             lasttype = p++->type;
 115         } else {                       /* *p and *q have same type */
 116             long sum = p->value + q->value;
 117             if (sum)
 118                 addtotemp(p->type, sum);
 119             lasttype = p->type;
 120             p++, q++;
 121         }
 122         if (lasttype == EXPR_UNKNOWN) {
 123             return finishtemp();
 124         }
 125     }
 126     while (p->type &&
 127            (preserve || p->type < EXPR_SEGBASE+SEG_ABS))
 128     {
 129         addtotemp(p->type, p->value);
 130         p++;
 131     }
 132     while (q->type &&
 133            (preserve || q->type < EXPR_SEGBASE+SEG_ABS))
 134     {
 135         addtotemp(q->type, q->value);
 136         q++;
 137     }
 138
 139     return finishtemp();
 140 }
 141
 142 /*
 143  * Multiply a vector by a scalar. Strip far-absolute segment part
 144  * if present.
 145  *
 146  * Explicit treatment of UNKNOWN is not required in this routine,
 147  * since it will silently do the Right Thing anyway.
 148  *
 149  * If `affect_hints' is set, we also change the hint type to
 150  * NOTBASE if a MAKEBASE hint points at a register being
 151  * multiplied. This allows [eax*1+ebx] to hint EBX rather than EAX
 152  * as the base register.
 153  */
 154 static expr *scalar_mult(expr *vect, long scalar, int affect_hints)
 155 {
 156     expr *p = vect;
 157
 158     while (p->type && p->type < EXPR_SEGBASE+SEG_ABS) {
 159         p->value = scalar * (p->value);
 160         if (hint && hint->type == EAH_MAKEBASE &&
 161             p->type == hint->base && affect_hints)
 162             hint->type = EAH_NOTBASE;
 163         p++;
 164     }
 165     p->type = 0;
 166
 167     return vect;
 168 }
 169
 170 static expr *scalarvect (long scalar)
 171 {
 172     begintemp();
 173     addtotemp(EXPR_SIMPLE, scalar);
 174     return finishtemp();
 175 }
 176
 177 static expr *unknown_expr (void)
 178 {
 179     begintemp();
 180     addtotemp(EXPR_UNKNOWN, 1L);
 181     return finishtemp();
 182 }
 183
 184 /*
 185  * The SEG operator: calculate the segment part of a relocatable
 186  * value. Return NULL, as usual, if an error occurs. Report the
 187  * error too.
 188  */
 189 static expr *segment_part (expr *e)
 190 {
 191     long seg;
 192
 193     if (is_unknown(e))
 194         return unknown_expr();
 195
 196     if (!is_reloc(e)) {
 197         error(ERR_NONFATAL, "cannot apply SEG to a non-relocatable value");
 198         return NULL;
 199     }
 200
 201     seg = reloc_seg(e);
 202     if (seg == NO_SEG) {
 203         error(ERR_NONFATAL, "cannot apply SEG to a non-relocatable value");
 204         return NULL;
 205     } else if (seg & SEG_ABS) {
 206         return scalarvect(seg & ~SEG_ABS);
 207     } else if (seg & 1) {
 208         error(ERR_NONFATAL, "SEG applied to something which"
 209               " is already a segment base");
 210         return NULL;
 211     }
 212     else {
 213         long base = outfmt->segbase(seg+1);
 214
 215         begintemp();
 216         addtotemp((base == NO_SEG ? EXPR_UNKNOWN : EXPR_SEGBASE+base), 1L);
 217         return finishtemp();
 218     }
 219 }
 220
 221 /*
 222  * Recursive-descent parser. Called with a single boolean operand,
 223  * which is TRUE if the evaluation is critical (i.e. unresolved
 224  * symbols are an error condition). Must update the global `i' to
 225  * reflect the token after the parsed string. May return NULL.
 226  *
 227  * evaluate() should report its own errors: on return it is assumed
 228  * that if NULL has been returned, the error has already been
 229  * reported.
 230  */
 231
 232 /*
 233  * Grammar parsed is:
 234  *
 235  * expr  : bexpr [ WRT expr6 ]
 236  * bexpr : rexp0 or expr0 depending on relative-mode setting
 237  * rexp0 : rexp1 [ {||} rexp1...]
 238  * rexp1 : rexp2 [ {^^} rexp2...]
 239  * rexp2 : rexp3 [ {&&} rexp3...]
 240  * rexp3 : expr0 [ {=,==,<>,!=,<,>,<=,>=} expr0 ]
 241  * expr0 : expr1 [ {|} expr1...]
 242  * expr1 : expr2 [ {^} expr2...]
 243  * expr2 : expr3 [ {&} expr3...]
 244  * expr3 : expr4 [ {<<,>>} expr4...]
 245  * expr4 : expr5 [ {+,-} expr5...]
 246  * expr5 : expr6 [ {*,/,%,//,%%} expr6...]
 247  * expr6 : { ~,+,-,SEG } expr6
 248  *       | (bexpr)
 249  *       | symbol
 250  *       | $
 251  *       | number
 252  */
 253
 254 static expr *rexp0(int), *rexp1(int), *rexp2(int), *rexp3(int);
 255
 256 static expr *expr0(int), *expr1(int), *expr2(int), *expr3(int);
 257 static expr *expr4(int), *expr5(int), *expr6(int);
 258
 259 static expr *(*bexpr)(int);
 260
 261 static expr *rexp0(int critical)
 262 {
 263     expr *e, *f;
 264
 265     e = rexp1(critical);
 266     if (!e)
 267         return NULL;
 268
 269     while (i == TOKEN_DBL_OR)
 270     {
 271         i = scan(scpriv, tokval);
 272         f = rexp1(critical);
 273         if (!f)
 274             return NULL;
 275         if (!(is_simple(e) || is_just_unknown(e)) ||
 276             !(is_simple(f) || is_just_unknown(f)))
 277         {
 278             error(ERR_NONFATAL, "`|' operator may only be applied to"
 279                   " scalar values");
 280         }
 281
 282         if (is_just_unknown(e) || is_just_unknown(f))
 283             e = unknown_expr();
 284         else
 285             e = scalarvect ((long) (reloc_value(e) || reloc_value(f)));
 286     }
 287     return e;
 288 }
 289
 290 static expr *rexp1(int critical)
 291 {
 292     expr *e, *f;
 293
 294     e = rexp2(critical);
 295     if (!e)
 296         return NULL;
 297
 298     while (i == TOKEN_DBL_XOR)
 299     {
 300         i = scan(scpriv, tokval);
 301         f = rexp2(critical);
 302         if (!f)
 303             return NULL;
 304         if (!(is_simple(e) || is_just_unknown(e)) ||
 305             !(is_simple(f) || is_just_unknown(f)))
 306         {
 307             error(ERR_NONFATAL, "`^' operator may only be applied to"
 308                   " scalar values");
 309         }
 310
 311         if (is_just_unknown(e) || is_just_unknown(f))
 312             e = unknown_expr();
 313         else
 314             e = scalarvect ((long) (!reloc_value(e) ^ !reloc_value(f)));
 315     }
 316     return e;
 317 }
 318
 319 static expr *rexp2(int critical)
 320 {
 321     expr *e, *f;
 322
 323     e = rexp3(critical);
 324     if (!e)
 325         return NULL;
 326     while (i == TOKEN_DBL_AND)
 327     {
 328         i = scan(scpriv, tokval);
 329         f = rexp3(critical);
 330         if (!f)
 331             return NULL;
 332         if (!(is_simple(e) || is_just_unknown(e)) ||
 333             !(is_simple(f) || is_just_unknown(f)))
 334         {
 335             error(ERR_NONFATAL, "`&' operator may only be applied to"
 336                   " scalar values");
 337         }
 338         if (is_just_unknown(e) || is_just_unknown(f))
 339             e = unknown_expr();
 340         else
 341             e = scalarvect ((long) (reloc_value(e) && reloc_value(f)));
 342     }
 343     return e;
 344 }
 345
 346 static expr *rexp3(int critical)
 347 {
 348     expr *e, *f;
 349     long v;
 350
 351     e = expr0(critical);
 352     if (!e)
 353         return NULL;
 354
 355     while (i == TOKEN_EQ || i == TOKEN_LT || i == TOKEN_GT ||
 356            i == TOKEN_NE || i == TOKEN_LE || i == TOKEN_GE)
 357     {
 358         int j = i;
 359         i = scan(scpriv, tokval);
 360         f = expr0(critical);
 361         if (!f)
 362             return NULL;
 363
 364         e = add_vectors (e, scalar_mult(f, -1L, FALSE));
 365
 366         switch (j)
 367         {
 368           case TOKEN_EQ: case TOKEN_NE:
 369             if (is_unknown(e))
 370                 v = -1;                /* means unknown */
 371             else if (!is_really_simple(e) || reloc_value(e) != 0)
 372                 v = (j == TOKEN_NE);   /* unequal, so return TRUE if NE */
 373             else
 374                 v = (j == TOKEN_EQ);   /* equal, so return TRUE if EQ */
 375             break;
 376           default:
 377             if (is_unknown(e))
 378                 v = -1;                /* means unknown */
 379             else if (!is_really_simple(e)) {
 380                 error(ERR_NONFATAL, "`%s': operands differ by a non-scalar",
 381                       (j == TOKEN_LE ? "<=" : j == TOKEN_LT ? "<" :
 382                        j == TOKEN_GE ? ">=" : ">"));
 383                 v = 0;                 /* must set it to _something_ */
 384             } else {
 385                 int vv = reloc_value(e);
 386                 if (vv == 0)
 387                     v = (j == TOKEN_LE || j == TOKEN_GE);
 388                 else if (vv > 0)
 389                     v = (j == TOKEN_GE || j == TOKEN_GT);
 390                 else /* vv < 0 */
 391                     v = (j == TOKEN_LE || j == TOKEN_LT);
 392             }
 393             break;
 394         }
 395
 396         if (v == -1)
 397             e = unknown_expr();
 398         else
 399             e = scalarvect(v);
 400     }
 401     return e;
 402 }
 403
 404 static expr *expr0(int critical)
 405 {
 406     expr *e, *f;
 407
 408     e = expr1(critical);
 409     if (!e)
 410         return NULL;
 411
 412     while (i == '|')
 413     {
 414         i = scan(scpriv, tokval);
 415         f = expr1(critical);
 416         if (!f)
 417             return NULL;
 418         if (!(is_simple(e) || is_just_unknown(e)) ||
 419             !(is_simple(f) || is_just_unknown(f)))
 420         {
 421             error(ERR_NONFATAL, "`|' operator may only be applied to"
 422                   " scalar values");
 423         }
 424         if (is_just_unknown(e) || is_just_unknown(f))
 425             e = unknown_expr();
 426         else
 427             e = scalarvect (reloc_value(e) | reloc_value(f));
 428     }
 429     return e;
 430 }
 431
 432 static expr *expr1(int critical)
 433 {
 434     expr *e, *f;
 435
 436     e = expr2(critical);
 437     if (!e)
 438         return NULL;
 439
 440     while (i == '^') {
 441         i = scan(scpriv, tokval);
 442         f = expr2(critical);
 443         if (!f)
 444             return NULL;
 445         if (!(is_simple(e) || is_just_unknown(e)) ||
 446             !(is_simple(f) || is_just_unknown(f)))
 447         {
 448             error(ERR_NONFATAL, "`^' operator may only be applied to"
 449                   " scalar values");
 450         }
 451         if (is_just_unknown(e) || is_just_unknown(f))
 452             e = unknown_expr();
 453         else
 454             e = scalarvect (reloc_value(e) ^ reloc_value(f));
 455     }
 456     return e;
 457 }
 458
 459 static expr *expr2(int critical)
 460 {
 461     expr *e, *f;
 462
 463     e = expr3(critical);
 464     if (!e)
 465         return NULL;
 466
 467     while (i == '&') {
 468         i = scan(scpriv, tokval);
 469         f = expr3(critical);
 470         if (!f)
 471             return NULL;
 472         if (!(is_simple(e) || is_just_unknown(e)) ||
 473             !(is_simple(f) || is_just_unknown(f)))
 474         {
 475             error(ERR_NONFATAL, "`&' operator may only be applied to"
 476                   " scalar values");
 477         }
 478         if (is_just_unknown(e) || is_just_unknown(f))
 479             e = unknown_expr();
 480         else
 481             e = scalarvect (reloc_value(e) & reloc_value(f));
 482     }
 483     return e;
 484 }
 485
 486 static expr *expr3(int critical)
 487 {
 488     expr *e, *f;
 489
 490     e = expr4(critical);
 491     if (!e)
 492         return NULL;
 493
 494     while (i == TOKEN_SHL || i == TOKEN_SHR)
 495     {
 496         int j = i;
 497         i = scan(scpriv, tokval);
 498         f = expr4(critical);
 499         if (!f)
 500             return NULL;
 501         if (!(is_simple(e) || is_just_unknown(e)) ||
 502             !(is_simple(f) || is_just_unknown(f)))
 503         {
 504             error(ERR_NONFATAL, "shift operator may only be applied to"
 505                   " scalar values");
 506         } else if (is_just_unknown(e) || is_just_unknown(f)) {
 507             e = unknown_expr();
 508         } else switch (j) {
 509           case TOKEN_SHL:
 510             e = scalarvect (reloc_value(e) << reloc_value(f));
 511             break;
 512           case TOKEN_SHR:
 513             e = scalarvect (((unsigned long)reloc_value(e)) >>
 514                             reloc_value(f));
 515             break;
 516         }
 517     }
 518     return e;
 519 }
 520
 521 static expr *expr4(int critical)
 522 {
 523     expr *e, *f;
 524
 525     e = expr5(critical);
 526     if (!e)
 527         return NULL;
 528     while (i == '+' || i == '-')
 529     {
 530         int j = i;
 531         i = scan(scpriv, tokval);
 532         f = expr5(critical);
 533         if (!f)
 534             return NULL;
 535         switch (j) {
 536           case '+':
 537             e = add_vectors (e, f);
 538             break;
 539           case '-':
 540             e = add_vectors (e, scalar_mult(f, -1L, FALSE));
 541             break;
 542         }
 543     }
 544     return e;
 545 }
 546
 547 static expr *expr5(int critical)
 548 {
 549     expr *e, *f;
 550
 551     e = expr6(critical);
 552     if (!e)
 553         return NULL;
 554     while (i == '*' || i == '/' || i == '%' ||
 555            i == TOKEN_SDIV || i == TOKEN_SMOD)
 556     {
 557         int j = i;
 558         i = scan(scpriv, tokval);
 559         f = expr6(critical);
 560         if (!f)
 561             return NULL;
 562         if (j != '*' && (!(is_simple(e) || is_just_unknown(e)) ||
 563                          !(is_simple(f) || is_just_unknown(f))))
 564         {
 565             error(ERR_NONFATAL, "division operator may only be applied to"
 566                   " scalar values");
 567             return NULL;
 568         }
 569         if (j != '*' && !is_unknown(f) && reloc_value(f) == 0) {
 570             error(ERR_NONFATAL, "division by zero");
 571             return NULL;
 572         }
 573         switch (j) {
 574           case '*':
 575             if (is_simple(e))
 576                 e = scalar_mult (f, reloc_value(e), TRUE);
 577             else if (is_simple(f))
 578                 e = scalar_mult (e, reloc_value(f), TRUE);
 579             else if (is_just_unknown(e) && is_just_unknown(f))
 580                 e = unknown_expr();
 581             else {
 582                 error(ERR_NONFATAL, "unable to multiply two "
 583                       "non-scalar objects");
 584                 return NULL;
 585             }
 586             break;
 587           case '/':
 588             if (is_just_unknown(e) || is_just_unknown(f))
 589                 e = unknown_expr();
 590             else
 591                 e = scalarvect (((unsigned long)reloc_value(e)) /
 592                                 ((unsigned long)reloc_value(f)));
 593             break;
 594           case '%':
 595             if (is_just_unknown(e) || is_just_unknown(f))
 596                 e = unknown_expr();
 597             else
 598                 e = scalarvect (((unsigned long)reloc_value(e)) %
 599                                 ((unsigned long)reloc_value(f)));
 600             break;
 601           case TOKEN_SDIV:
 602             if (is_just_unknown(e) || is_just_unknown(f))
 603                 e = unknown_expr();
 604             else
 605                 e = scalarvect (((signed long)reloc_value(e)) /
 606                                 ((signed long)reloc_value(f)));
 607             break;
 608           case TOKEN_SMOD:
 609             if (is_just_unknown(e) || is_just_unknown(f))
 610                 e = unknown_expr();
 611             else
 612                 e = scalarvect (((signed long)reloc_value(e)) %
 613                                 ((signed long)reloc_value(f)));
 614             break;
 615         }
 616     }
 617     return e;
 618 }
 619
 620 static expr *expr6(int critical)
 621 {
 622     long type;
 623     expr *e;
 624     long label_seg, label_ofs;
 625
 626     if (i == '-') {
 627         i = scan(scpriv, tokval);
 628         e = expr6(critical);
 629         if (!e)
 630             return NULL;
 631         return scalar_mult (e, -1L, FALSE);
 632     } else if (i == '+') {
 633         i = scan(scpriv, tokval);
 634         return expr6(critical);
 635     } else if (i == '~') {
 636         i = scan(scpriv, tokval);
 637         e = expr6(critical);
 638         if (!e)
 639             return NULL;
 640         if (is_just_unknown(e))
 641             return unknown_expr();
 642         else if (!is_simple(e)) {
 643             error(ERR_NONFATAL, "`~' operator may only be applied to"
 644                   " scalar values");
 645             return NULL;
 646         }
 647         return scalarvect(~reloc_value(e));
 648     } else if (i == TOKEN_SEG) {
 649         i = scan(scpriv, tokval);
 650         e = expr6(critical);
 651         if (!e)
 652             return NULL;
 653         e = segment_part(e);
 654         if (is_unknown(e) && critical) {
 655             error(ERR_NONFATAL, "unable to determine segment base");
 656             return NULL;
 657         }
 658         return e;
 659     } else if (i == '(') {
 660         i = scan(scpriv, tokval);
 661         e = bexpr(critical);
 662         if (!e)
 663             return NULL;
 664         if (i != ')') {
 665             error(ERR_NONFATAL, "expecting `)'");
 666             return NULL;
 667         }
 668         i = scan(scpriv, tokval);
 669         return e;
 670     }
 671     else if (i == TOKEN_NUM || i == TOKEN_REG || i == TOKEN_ID ||
 672              i == TOKEN_HERE || i == TOKEN_BASE)
 673     {
 674         begintemp();
 675         switch (i) {
 676           case TOKEN_NUM:
 677             addtotemp(EXPR_SIMPLE, tokval->t_integer);
 678             break;
 679           case TOKEN_REG:
 680             addtotemp(tokval->t_integer, 1L);
 681             if (hint && hint->type == EAH_NOHINT)
 682                 hint->base = tokval->t_integer, hint->type = EAH_MAKEBASE;
 683             break;
 684           case TOKEN_ID:
 685           case TOKEN_HERE:
 686           case TOKEN_BASE:
 687             /*
 688              * If !location->known, this indicates that no
 689              * symbol, Here or Base references are valid because we
 690              * are in preprocess-only mode.
 691              */
 692             if (!location->known) {
 693                 error(ERR_NONFATAL,
 694                       "%s not supported in preprocess-only mode",
 695                       (i == TOKEN_ID ? "symbol references" :
 696                        i == TOKEN_HERE ? "`$'" : "`$$'"));
 697                 addtotemp(EXPR_UNKNOWN, 1L);
 698                 break;
 699             }
 700
 701             /*
 702              * Since the whole line is parsed before the label it
 703              * defines is given to the label manager, we have
 704              * problems with lines such as
 705              *
 706              *   end: TIMES 512-(end-start) DB 0
 707              *
 708              * where `end' is not known on pass one, despite not
 709              * really being a forward reference, and due to
 710              * criticality it is _needed_. Hence we check our label
 711              * against the currently defined one, and do our own
 712              * resolution of it if we have to.
 713              */
 714             type = EXPR_SIMPLE;        /* might get overridden by UNKNOWN */
 715             if (i == TOKEN_BASE) {
 716                 label_seg = location->segment;
 717                 label_ofs = 0;
 718             } else if (i == TOKEN_HERE) {
 719                 label_seg = location->segment;
 720                 label_ofs = location->offset;
 721             } else if (!labelfunc(tokval->t_charptr,&label_seg,&label_ofs)) {
 722                 if (critical == 2) {
 723                     error (ERR_NONFATAL, "symbol `%s' undefined",
 724                            tokval->t_charptr);
 725                     return NULL;
 726                 } else if (critical == 1) {
 727                     error (ERR_NONFATAL, "symbol `%s' not defined before use",
 728                            tokval->t_charptr);
 729                     return NULL;
 730                 } else {
 731                     if (opflags)
 732                         *opflags |= 1;
 733                     type = EXPR_UNKNOWN;
 734                     label_seg = NO_SEG;
 735                     label_ofs = 1;
 736                 }
 737             }
 738             addtotemp(type, label_ofs);
 739             if (label_seg!=NO_SEG) {
 740                 addtotemp(EXPR_SEGBASE + label_seg, 1L);
 741                 if (opflags && is_extern (tokval->t_charptr))
 742                     *opflags |= OPFLAG_EXTERN;
 743             }
 744             break;
 745         }
 746         i = scan(scpriv, tokval);
 747         return finishtemp();
 748     } else {
 749         error(ERR_NONFATAL, "expression syntax error");
 750         return NULL;
 751     }
 752 }
 753
 754 void eval_global_info (struct ofmt *output, lfunc lookup_label, loc_t *locp)
 755 {
 756     outfmt = output;
 757     labelfunc = lookup_label;
 758     location = locp;
 759 }
 760
 761 expr *evaluate (scanner sc, void *scprivate, struct tokenval *tv,
 762                 int *fwref, int critical, efunc report_error,
 763                 struct eval_hints *hints)
 764 {
 765     expr *e;
 766     expr *f = NULL;
 767
 768     hint = hints;
 769     if (hint)
 770         hint->type = EAH_NOHINT;
 771
 772     if (critical & 0x10) {
 773         critical &= ~0x10;
 774         bexpr = rexp0;
 775     } else
 776         bexpr = expr0;
 777
 778     scan = sc;
 779     scpriv = scprivate;
 780     tokval = tv;
 781     error = report_error;
 782     opflags = fwref;
 783
 784     if (tokval->t_type == TOKEN_INVALID)
 785         i = scan(scpriv, tokval);
 786     else
 787         i = tokval->t_type;
 788
 789     while (ntempexprs)                 /* initialise temporary storage */
 790         nasm_free (tempexprs[--ntempexprs]);
 791
 792     e = bexpr (critical);
 793     if (!e)
 794         return NULL;
 795
 796     if (i == TOKEN_WRT) {
 797         i = scan(scpriv, tokval);      /* eat the WRT */
 798         f = expr6 (critical);
 799         if (!f)
 800             return NULL;
 801     }
 802     e = scalar_mult (e, 1L, FALSE);    /* strip far-absolute segment part */
 803     if (f) {
 804         expr *g;
 805         if (is_just_unknown(f))
 806             g = unknown_expr();
 807         else {
 808             long value;
 809             begintemp();
 810             if (!is_reloc(f)) {
 811                 error(ERR_NONFATAL, "invalid right-hand operand to WRT");
 812                 return NULL;
 813             }
 814             value = reloc_seg(f);
 815             if (value == NO_SEG)
 816                 value = reloc_value(f) | SEG_ABS;
 817             else if (!(value & SEG_ABS) && !(value % 2) && critical)
 818             {
 819                 error(ERR_NONFATAL, "invalid right-hand operand to WRT");
 820                 return NULL;
 821             }
 822             addtotemp(EXPR_WRT, value);
 823             g = finishtemp();
 824         }
 825         e = add_vectors (e, g);
 826     }
 827     return e;
 828 }