gdb/findvar.c

   1 /* Find a variable's value in memory, for GDB, the GNU debugger.
   2
   3    Copyright (C) 1986, 1987, 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995,
   4    1996, 1997, 1998, 1999, 2000, 2001, 2003, 2004, 2005, 2007, 2008
   5    Free Software Foundation, Inc.
   6
   7    This file is part of GDB.
   8
   9    This program is free software; you can redistribute it and/or modify
  10    it under the terms of the GNU General Public License as published by
  11    the Free Software Foundation; either version 3 of the License, or
  12    (at your option) any later version.
  13
  14    This program is distributed in the hope that it will be useful,
  15    but WITHOUT ANY WARRANTY; without even the implied warranty of
  16    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  17    GNU General Public License for more details.
  18
  19    You should have received a copy of the GNU General Public License
  20    along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
  21
  22 #include "defs.h"
  23 #include "symtab.h"
  24 #include "gdbtypes.h"
  25 #include "frame.h"
  26 #include "value.h"
  27 #include "gdbcore.h"
  28 #include "inferior.h"
  29 #include "target.h"
  30 #include "gdb_string.h"
  31 #include "gdb_assert.h"
  32 #include "floatformat.h"
  33 #include "symfile.h"            /* for overlay functions */
  34 #include "regcache.h"
  35 #include "user-regs.h"
  36 #include "block.h"
  37
  38 /* Basic byte-swapping routines.  GDB has needed these for a long time...
  39    All extract a target-format integer at ADDR which is LEN bytes long.  */
  40
  41 #if TARGET_CHAR_BIT != 8 || HOST_CHAR_BIT != 8
  42   /* 8 bit characters are a pretty safe assumption these days, so we
  43      assume it throughout all these swapping routines.  If we had to deal with
  44      9 bit characters, we would need to make len be in bits and would have
  45      to re-write these routines...  */
  46 you lose
  47 #endif
  48
  49 LONGEST
  50 extract_signed_integer (const gdb_byte *addr, int len)
  51 {
  52   LONGEST retval;
  53   const unsigned char *p;
  54   const unsigned char *startaddr = addr;
  55   const unsigned char *endaddr = startaddr + len;
  56
  57   if (len > (int) sizeof (LONGEST))
  58     error (_("\
  59 That operation is not available on integers of more than %d bytes."),
  60            (int) sizeof (LONGEST));
  61
  62   /* Start at the most significant end of the integer, and work towards
  63      the least significant.  */
  64   if (gdbarch_byte_order (current_gdbarch) == BFD_ENDIAN_BIG)
  65     {
  66       p = startaddr;
  67       /* Do the sign extension once at the start.  */
  68       retval = ((LONGEST) * p ^ 0x80) - 0x80;
  69       for (++p; p < endaddr; ++p)
  70         retval = (retval << 8) | *p;
  71     }
  72   else
  73     {
  74       p = endaddr - 1;
  75       /* Do the sign extension once at the start.  */
  76       retval = ((LONGEST) * p ^ 0x80) - 0x80;
  77       for (--p; p >= startaddr; --p)
  78         retval = (retval << 8) | *p;
  79     }
  80   return retval;
  81 }
  82
  83 ULONGEST
  84 extract_unsigned_integer (const gdb_byte *addr, int len)
  85 {
  86   ULONGEST retval;
  87   const unsigned char *p;
  88   const unsigned char *startaddr = addr;
  89   const unsigned char *endaddr = startaddr + len;
  90
  91   if (len > (int) sizeof (ULONGEST))
  92     error (_("\
  93 That operation is not available on integers of more than %d bytes."),
  94            (int) sizeof (ULONGEST));
  95
  96   /* Start at the most significant end of the integer, and work towards
  97      the least significant.  */
  98   retval = 0;
  99   if (gdbarch_byte_order (current_gdbarch) == BFD_ENDIAN_BIG)
 100     {
 101       for (p = startaddr; p < endaddr; ++p)
 102         retval = (retval << 8) | *p;
 103     }
 104   else
 105     {
 106       for (p = endaddr - 1; p >= startaddr; --p)
 107         retval = (retval << 8) | *p;
 108     }
 109   return retval;
 110 }
 111
 112 /* Sometimes a long long unsigned integer can be extracted as a
 113    LONGEST value.  This is done so that we can print these values
 114    better.  If this integer can be converted to a LONGEST, this
 115    function returns 1 and sets *PVAL.  Otherwise it returns 0.  */
 116
 117 int
 118 extract_long_unsigned_integer (const gdb_byte *addr, int orig_len,
 119                                LONGEST *pval)
 120 {
 121   const gdb_byte *p;
 122   const gdb_byte *first_addr;
 123   int len;
 124
 125   len = orig_len;
 126   if (gdbarch_byte_order (current_gdbarch) == BFD_ENDIAN_BIG)
 127     {
 128       for (p = addr;
 129            len > (int) sizeof (LONGEST) && p < addr + orig_len;
 130            p++)
 131         {
 132           if (*p == 0)
 133             len--;
 134           else
 135             break;
 136         }
 137       first_addr = p;
 138     }
 139   else
 140     {
 141       first_addr = addr;
 142       for (p = addr + orig_len - 1;
 143            len > (int) sizeof (LONGEST) && p >= addr;
 144            p--)
 145         {
 146           if (*p == 0)
 147             len--;
 148           else
 149             break;
 150         }
 151     }
 152
 153   if (len <= (int) sizeof (LONGEST))
 154     {
 155       *pval = (LONGEST) extract_unsigned_integer (first_addr,
 156                                                   sizeof (LONGEST));
 157       return 1;
 158     }
 159
 160   return 0;
 161 }
 162
 163
 164 /* Treat the bytes at BUF as a pointer of type TYPE, and return the
 165    address it represents.  */
 166 CORE_ADDR
 167 extract_typed_address (const gdb_byte *buf, struct type *type)
 168 {
 169   if (TYPE_CODE (type) != TYPE_CODE_PTR
 170       && TYPE_CODE (type) != TYPE_CODE_REF)
 171     internal_error (__FILE__, __LINE__,
 172                     _("extract_typed_address: "
 173                     "type is not a pointer or reference"));
 174
 175   return gdbarch_pointer_to_address (current_gdbarch, type, buf);
 176 }
 177
 178
 179 void
 180 store_signed_integer (gdb_byte *addr, int len, LONGEST val)
 181 {
 182   gdb_byte *p;
 183   gdb_byte *startaddr = addr;
 184   gdb_byte *endaddr = startaddr + len;
 185
 186   /* Start at the least significant end of the integer, and work towards
 187      the most significant.  */
 188   if (gdbarch_byte_order (current_gdbarch) == BFD_ENDIAN_BIG)
 189     {
 190       for (p = endaddr - 1; p >= startaddr; --p)
 191         {
 192           *p = val & 0xff;
 193           val >>= 8;
 194         }
 195     }
 196   else
 197     {
 198       for (p = startaddr; p < endaddr; ++p)
 199         {
 200           *p = val & 0xff;
 201           val >>= 8;
 202         }
 203     }
 204 }
 205
 206 void
 207 store_unsigned_integer (gdb_byte *addr, int len, ULONGEST val)
 208 {
 209   unsigned char *p;
 210   unsigned char *startaddr = (unsigned char *) addr;
 211   unsigned char *endaddr = startaddr + len;
 212
 213   /* Start at the least significant end of the integer, and work towards
 214      the most significant.  */
 215   if (gdbarch_byte_order (current_gdbarch) == BFD_ENDIAN_BIG)
 216     {
 217       for (p = endaddr - 1; p >= startaddr; --p)
 218         {
 219           *p = val & 0xff;
 220           val >>= 8;
 221         }
 222     }
 223   else
 224     {
 225       for (p = startaddr; p < endaddr; ++p)
 226         {
 227           *p = val & 0xff;
 228           val >>= 8;
 229         }
 230     }
 231 }
 232
 233 /* Store the address ADDR as a pointer of type TYPE at BUF, in target
 234    form.  */
 235 void
 236 store_typed_address (gdb_byte *buf, struct type *type, CORE_ADDR addr)
 237 {
 238   if (TYPE_CODE (type) != TYPE_CODE_PTR
 239       && TYPE_CODE (type) != TYPE_CODE_REF)
 240     internal_error (__FILE__, __LINE__,
 241                     _("store_typed_address: "
 242                     "type is not a pointer or reference"));
 243
 244   gdbarch_address_to_pointer (current_gdbarch, type, buf, addr);
 245 }
 246
 247
 248
 249 /* Return a `value' with the contents of (virtual or cooked) register
 250    REGNUM as found in the specified FRAME.  The register's type is
 251    determined by register_type().  */
 252
 253 struct value *
 254 value_of_register (int regnum, struct frame_info *frame)
 255 {
 256   struct gdbarch *gdbarch = get_frame_arch (frame);
 257   CORE_ADDR addr;
 258   int optim;
 259   struct value *reg_val;
 260   int realnum;
 261   gdb_byte raw_buffer[MAX_REGISTER_SIZE];
 262   enum lval_type lval;
 263
 264   /* User registers lie completely outside of the range of normal
 265      registers.  Catch them early so that the target never sees them.  */
 266   if (regnum >= gdbarch_num_regs (gdbarch)
 267                 + gdbarch_num_pseudo_regs (gdbarch))
 268     return value_of_user_reg (regnum, frame);
 269
 270   frame_register (frame, regnum, &optim, &lval, &addr, &realnum, raw_buffer);
 271
 272   reg_val = allocate_value (register_type (gdbarch, regnum));
 273
 274   memcpy (value_contents_raw (reg_val), raw_buffer,
 275           register_size (gdbarch, regnum));
 276   VALUE_LVAL (reg_val) = lval;
 277   VALUE_ADDRESS (reg_val) = addr;
 278   VALUE_REGNUM (reg_val) = regnum;
 279   set_value_optimized_out (reg_val, optim);
 280   VALUE_FRAME_ID (reg_val) = get_frame_id (frame);
 281   return reg_val;
 282 }
 283
 284 /* Return a `value' with the contents of (virtual or cooked) register
 285    REGNUM as found in the specified FRAME.  The register's type is
 286    determined by register_type().  The value is not fetched.  */
 287
 288 struct value *
 289 value_of_register_lazy (struct frame_info *frame, int regnum)
 290 {
 291   struct gdbarch *gdbarch = get_frame_arch (frame);
 292   struct value *reg_val;
 293
 294   gdb_assert (regnum < (gdbarch_num_regs (gdbarch)
 295                         + gdbarch_num_pseudo_regs (gdbarch)));
 296
 297   /* We should have a valid (i.e. non-sentinel) frame.  */
 298   gdb_assert (frame_id_p (get_frame_id (frame)));
 299
 300   reg_val = allocate_value (register_type (gdbarch, regnum));
 301   VALUE_LVAL (reg_val) = lval_register;
 302   VALUE_REGNUM (reg_val) = regnum;
 303   VALUE_FRAME_ID (reg_val) = get_frame_id (frame);
 304   set_value_lazy (reg_val, 1);
 305   return reg_val;
 306 }
 307
 308 /* Given a pointer of type TYPE in target form in BUF, return the
 309    address it represents.  */
 310 CORE_ADDR
 311 unsigned_pointer_to_address (struct type *type, const gdb_byte *buf)
 312 {
 313   return extract_unsigned_integer (buf, TYPE_LENGTH (type));
 314 }
 315
 316 CORE_ADDR
 317 signed_pointer_to_address (struct type *type, const gdb_byte *buf)
 318 {
 319   return extract_signed_integer (buf, TYPE_LENGTH (type));
 320 }
 321
 322 /* Given an address, store it as a pointer of type TYPE in target
 323    format in BUF.  */
 324 void
 325 unsigned_address_to_pointer (struct type *type, gdb_byte *buf,
 326                              CORE_ADDR addr)
 327 {
 328   store_unsigned_integer (buf, TYPE_LENGTH (type), addr);
 329 }
 330
 331 void
 332 address_to_signed_pointer (struct type *type, gdb_byte *buf, CORE_ADDR addr)
 333 {
 334   store_signed_integer (buf, TYPE_LENGTH (type), addr);
 335 }
 336 \f
 337 /* Will calling read_var_value or locate_var_value on SYM end
 338    up caring what frame it is being evaluated relative to?  SYM must
 339    be non-NULL.  */
 340 int
 341 symbol_read_needs_frame (struct symbol *sym)
 342 {
 343   switch (SYMBOL_CLASS (sym))
 344     {
 345       /* All cases listed explicitly so that gcc -Wall will detect it if
 346          we failed to consider one.  */
 347     case LOC_COMPUTED:
 348     case LOC_COMPUTED_ARG:
 349       /* FIXME: cagney/2004-01-26: It should be possible to
 350          unconditionally call the SYMBOL_OPS method when available.
 351          Unfortunately DWARF 2 stores the frame-base (instead of the
 352          function) location in a function's symbol.  Oops!  For the
 353          moment enable this when/where applicable.  */
 354       return SYMBOL_OPS (sym)->read_needs_frame (sym);
 355
 356     case LOC_REGISTER:
 357     case LOC_ARG:
 358     case LOC_REF_ARG:
 359     case LOC_REGPARM:
 360     case LOC_REGPARM_ADDR:
 361     case LOC_LOCAL:
 362     case LOC_BASEREG:
 363     case LOC_BASEREG_ARG:
 364       return 1;
 365
 366     case LOC_UNDEF:
 367     case LOC_CONST:
 368     case LOC_STATIC:
 369     case LOC_TYPEDEF:
 370
 371     case LOC_LABEL:
 372       /* Getting the address of a label can be done independently of the block,
 373          even if some *uses* of that address wouldn't work so well without
 374          the right frame.  */
 375
 376     case LOC_BLOCK:
 377     case LOC_CONST_BYTES:
 378     case LOC_UNRESOLVED:
 379     case LOC_OPTIMIZED_OUT:
 380       return 0;
 381     }
 382   return 1;
 383 }
 384
 385 /* Given a struct symbol for a variable,
 386    and a stack frame id, read the value of the variable
 387    and return a (pointer to a) struct value containing the value.
 388    If the variable cannot be found, return a zero pointer.
 389    If FRAME is NULL, use the selected frame.  */
 390
 391 struct value *
 392 read_var_value (struct symbol *var, struct frame_info *frame)
 393 {
 394   struct value *v;
 395   struct type *type = SYMBOL_TYPE (var);
 396   CORE_ADDR addr;
 397   int len;
 398
 399   if (SYMBOL_CLASS (var) == LOC_COMPUTED
 400       || SYMBOL_CLASS (var) == LOC_COMPUTED_ARG
 401       || SYMBOL_CLASS (var) == LOC_REGISTER
 402       || SYMBOL_CLASS (var) == LOC_REGPARM)
 403     /* These cases do not use V.  */
 404     v = NULL;
 405   else
 406     {
 407       v = allocate_value (type);
 408       VALUE_LVAL (v) = lval_memory;     /* The most likely possibility.  */
 409     }
 410
 411   len = TYPE_LENGTH (type);
 412
 413   /* FIXME drow/2003-09-06: this call to the selected frame should be
 414      pushed upwards to the callers.  */
 415   if (frame == NULL)
 416     frame = deprecated_safe_get_selected_frame ();
 417
 418   switch (SYMBOL_CLASS (var))
 419     {
 420     case LOC_CONST:
 421       /* Put the constant back in target format.  */
 422       store_signed_integer (value_contents_raw (v), len,
 423                             (LONGEST) SYMBOL_VALUE (var));
 424       VALUE_LVAL (v) = not_lval;
 425       return v;
 426
 427     case LOC_LABEL:
 428       /* Put the constant back in target format.  */
 429       if (overlay_debugging)
 430         {
 431           CORE_ADDR addr
 432             = symbol_overlayed_address (SYMBOL_VALUE_ADDRESS (var),
 433                                         SYMBOL_BFD_SECTION (var));
 434           store_typed_address (value_contents_raw (v), type, addr);
 435         }
 436       else
 437         store_typed_address (value_contents_raw (v), type,
 438                               SYMBOL_VALUE_ADDRESS (var));
 439       VALUE_LVAL (v) = not_lval;
 440       return v;
 441
 442     case LOC_CONST_BYTES:
 443       {
 444         memcpy (value_contents_raw (v), SYMBOL_VALUE_BYTES (var), len);
 445         VALUE_LVAL (v) = not_lval;
 446         return v;
 447       }
 448
 449     case LOC_STATIC:
 450       if (overlay_debugging)
 451         addr = symbol_overlayed_address (SYMBOL_VALUE_ADDRESS (var),
 452                                          SYMBOL_BFD_SECTION (var));
 453       else
 454         addr = SYMBOL_VALUE_ADDRESS (var);
 455       break;
 456
 457     case LOC_ARG:
 458       if (frame == NULL)
 459         return 0;
 460       addr = get_frame_args_address (frame);
 461       if (!addr)
 462         return 0;
 463       addr += SYMBOL_VALUE (var);
 464       break;
 465
 466     case LOC_REF_ARG:
 467       {
 468         struct value *ref;
 469         CORE_ADDR argref;
 470         if (frame == NULL)
 471           return 0;
 472         argref = get_frame_args_address (frame);
 473         if (!argref)
 474           return 0;
 475         argref += SYMBOL_VALUE (var);
 476         ref = value_at (lookup_pointer_type (type), argref);
 477         addr = value_as_address (ref);
 478         break;
 479       }
 480
 481     case LOC_LOCAL:
 482       if (frame == NULL)
 483         return 0;
 484       addr = get_frame_locals_address (frame);
 485       addr += SYMBOL_VALUE (var);
 486       break;
 487
 488     case LOC_BASEREG:
 489     case LOC_BASEREG_ARG:
 490       {
 491         struct value *regval;
 492
 493         regval = value_from_register (lookup_pointer_type (type),
 494                                       SYMBOL_BASEREG (var), frame);
 495         if (regval == NULL)
 496           error (_("Value of base register not available."));
 497         addr = value_as_address (regval);
 498         addr += SYMBOL_VALUE (var);
 499         break;
 500       }
 501
 502     case LOC_TYPEDEF:
 503       error (_("Cannot look up value of a typedef"));
 504       break;
 505
 506     case LOC_BLOCK:
 507       if (overlay_debugging)
 508         VALUE_ADDRESS (v) = symbol_overlayed_address
 509           (BLOCK_START (SYMBOL_BLOCK_VALUE (var)), SYMBOL_BFD_SECTION (var));
 510       else
 511         VALUE_ADDRESS (v) = BLOCK_START (SYMBOL_BLOCK_VALUE (var));
 512       return v;
 513
 514     case LOC_REGISTER:
 515     case LOC_REGPARM:
 516     case LOC_REGPARM_ADDR:
 517       {
 518         struct block *b;
 519         int regno = SYMBOL_VALUE (var);
 520         struct value *regval;
 521
 522         if (frame == NULL)
 523           return 0;
 524         b = get_frame_block (frame, 0);
 525
 526         if (SYMBOL_CLASS (var) == LOC_REGPARM_ADDR)
 527           {
 528             regval = value_from_register (lookup_pointer_type (type),
 529                                           regno,
 530                                           frame);
 531
 532             if (regval == NULL)
 533               error (_("Value of register variable not available."));
 534
 535             addr = value_as_address (regval);
 536             VALUE_LVAL (v) = lval_memory;
 537           }
 538         else
 539           {
 540             regval = value_from_register (type, regno, frame);
 541
 542             if (regval == NULL)
 543               error (_("Value of register variable not available."));
 544             return regval;
 545           }
 546       }
 547       break;
 548
 549     case LOC_COMPUTED:
 550     case LOC_COMPUTED_ARG:
 551       /* FIXME: cagney/2004-01-26: It should be possible to
 552          unconditionally call the SYMBOL_OPS method when available.
 553          Unfortunately DWARF 2 stores the frame-base (instead of the
 554          function) location in a function's symbol.  Oops!  For the
 555          moment enable this when/where applicable.  */
 556       if (frame == 0 && SYMBOL_OPS (var)->read_needs_frame (var))
 557         return 0;
 558       return SYMBOL_OPS (var)->read_variable (var, frame);
 559
 560     case LOC_UNRESOLVED:
 561       {
 562         struct minimal_symbol *msym;
 563
 564         msym = lookup_minimal_symbol (DEPRECATED_SYMBOL_NAME (var), NULL, NULL);
 565         if (msym == NULL)
 566           return 0;
 567         if (overlay_debugging)
 568           addr = symbol_overlayed_address (SYMBOL_VALUE_ADDRESS (msym),
 569                                            SYMBOL_BFD_SECTION (msym));
 570         else
 571           addr = SYMBOL_VALUE_ADDRESS (msym);
 572       }
 573       break;
 574
 575     case LOC_OPTIMIZED_OUT:
 576       VALUE_LVAL (v) = not_lval;
 577       set_value_optimized_out (v, 1);
 578       return v;
 579
 580     default:
 581       error (_("Cannot look up value of a botched symbol."));
 582       break;
 583     }
 584
 585   VALUE_ADDRESS (v) = addr;
 586   set_value_lazy (v, 1);
 587   return v;
 588 }
 589
 590 /* Install default attributes for register values.  */
 591
 592 struct value *
 593 default_value_from_register (struct type *type, int regnum,
 594                              struct frame_info *frame)
 595 {
 596   struct gdbarch *gdbarch = get_frame_arch (frame);
 597   int len = TYPE_LENGTH (type);
 598   struct value *value = allocate_value (type);
 599
 600   VALUE_LVAL (value) = lval_register;
 601   VALUE_FRAME_ID (value) = get_frame_id (frame);
 602   VALUE_REGNUM (value) = regnum;
 603
 604   /* Any structure stored in more than one register will always be
 605      an integral number of registers.  Otherwise, you need to do
 606      some fiddling with the last register copied here for little
 607      endian machines.  */
 608   if (gdbarch_byte_order (gdbarch) == BFD_ENDIAN_BIG
 609       && len < register_size (gdbarch, regnum))
 610     /* Big-endian, and we want less than full size.  */
 611     set_value_offset (value, register_size (gdbarch, regnum) - len);
 612   else
 613     set_value_offset (value, 0);
 614
 615   return value;
 616 }
 617
 618 /* Return a value of type TYPE, stored in register REGNUM, in frame FRAME.  */
 619
 620 struct value *
 621 value_from_register (struct type *type, int regnum, struct frame_info *frame)
 622 {
 623   struct gdbarch *gdbarch = get_frame_arch (frame);
 624   struct type *type1 = check_typedef (type);
 625   struct value *v;
 626
 627   if (gdbarch_convert_register_p (gdbarch, regnum, type1))
 628     {
 629       /* The ISA/ABI need to something weird when obtaining the
 630          specified value from this register.  It might need to
 631          re-order non-adjacent, starting with REGNUM (see MIPS and
 632          i386).  It might need to convert the [float] register into
 633          the corresponding [integer] type (see Alpha).  The assumption
 634          is that gdbarch_register_to_value populates the entire value
 635          including the location.  */
 636       v = allocate_value (type);
 637       VALUE_LVAL (v) = lval_register;
 638       VALUE_FRAME_ID (v) = get_frame_id (frame);
 639       VALUE_REGNUM (v) = regnum;
 640       gdbarch_register_to_value (gdbarch,
 641                                  frame, regnum, type1, value_contents_raw (v));
 642     }
 643   else
 644     {
 645       int len = TYPE_LENGTH (type);
 646
 647       /* Construct the value.  */
 648       v = gdbarch_value_from_register (gdbarch, type, regnum, frame);
 649
 650       /* Get the data.  */
 651       if (!get_frame_register_bytes (frame, regnum, value_offset (v), len,
 652                                      value_contents_raw (v)))
 653         set_value_optimized_out (v, 1);
 654     }
 655   return v;
 656 }
 657
 658 /* Return contents of register REGNUM in frame FRAME as address,
 659    interpreted as value of type TYPE.   Will abort if register
 660    value is not available.  */
 661
 662 CORE_ADDR
 663 address_from_register (struct type *type, int regnum, struct frame_info *frame)
 664 {
 665   struct value *value;
 666   CORE_ADDR result;
 667
 668   value = value_from_register (type, regnum, frame);
 669   gdb_assert (value);
 670
 671   result = value_as_address (value);
 672   release_value (value);
 673   value_free (value);
 674
 675   return result;
 676 }
 677
 678 \f
 679 /* Given a struct symbol for a variable or function,
 680    and a stack frame id,
 681    return a (pointer to a) struct value containing the properly typed
 682    address.  */
 683
 684 struct value *
 685 locate_var_value (struct symbol *var, struct frame_info *frame)
 686 {
 687   struct gdbarch *gdbarch = get_frame_arch (frame);
 688   CORE_ADDR addr = 0;
 689   struct type *type = SYMBOL_TYPE (var);
 690   struct value *lazy_value;
 691
 692   /* Evaluate it first; if the result is a memory address, we're fine.
 693      Lazy evaluation pays off here. */
 694
 695   lazy_value = read_var_value (var, frame);
 696   if (lazy_value == 0)
 697     error (_("Address of \"%s\" is unknown."), SYMBOL_PRINT_NAME (var));
 698
 699   if ((VALUE_LVAL (lazy_value) == lval_memory && value_lazy (lazy_value))
 700       || TYPE_CODE (type) == TYPE_CODE_FUNC)
 701     {
 702       struct value *val;
 703
 704       addr = VALUE_ADDRESS (lazy_value);
 705       val = value_from_pointer (lookup_pointer_type (type), addr);
 706       return val;
 707     }
 708
 709   /* Not a memory address; check what the problem was.  */
 710   switch (VALUE_LVAL (lazy_value))
 711     {
 712     case lval_register:
 713       gdb_assert (gdbarch_register_name
 714                    (gdbarch, VALUE_REGNUM (lazy_value)) != NULL
 715                   && *gdbarch_register_name
 716                     (gdbarch, VALUE_REGNUM (lazy_value)) != '\0');
 717       error (_("Address requested for identifier "
 718                "\"%s\" which is in register $%s"),
 719             SYMBOL_PRINT_NAME (var),
 720             gdbarch_register_name (gdbarch, VALUE_REGNUM (lazy_value)));
 721       break;
 722
 723     default:
 724       error (_("Can't take address of \"%s\" which isn't an lvalue."),
 725              SYMBOL_PRINT_NAME (var));
 726       break;
 727     }
 728   return 0;                     /* For lint -- never reached */
 729 }