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 /* Given a pointer of type TYPE in target form in BUF, return the
 285    address it represents.  */
 286 CORE_ADDR
 287 unsigned_pointer_to_address (struct type *type, const gdb_byte *buf)
 288 {
 289   return extract_unsigned_integer (buf, TYPE_LENGTH (type));
 290 }
 291
 292 CORE_ADDR
 293 signed_pointer_to_address (struct type *type, const gdb_byte *buf)
 294 {
 295   return extract_signed_integer (buf, TYPE_LENGTH (type));
 296 }
 297
 298 /* Given an address, store it as a pointer of type TYPE in target
 299    format in BUF.  */
 300 void
 301 unsigned_address_to_pointer (struct type *type, gdb_byte *buf,
 302                              CORE_ADDR addr)
 303 {
 304   store_unsigned_integer (buf, TYPE_LENGTH (type), addr);
 305 }
 306
 307 void
 308 address_to_signed_pointer (struct type *type, gdb_byte *buf, CORE_ADDR addr)
 309 {
 310   store_signed_integer (buf, TYPE_LENGTH (type), addr);
 311 }
 312 \f
 313 /* Will calling read_var_value or locate_var_value on SYM end
 314    up caring what frame it is being evaluated relative to?  SYM must
 315    be non-NULL.  */
 316 int
 317 symbol_read_needs_frame (struct symbol *sym)
 318 {
 319   switch (SYMBOL_CLASS (sym))
 320     {
 321       /* All cases listed explicitly so that gcc -Wall will detect it if
 322          we failed to consider one.  */
 323     case LOC_COMPUTED:
 324     case LOC_COMPUTED_ARG:
 325       /* FIXME: cagney/2004-01-26: It should be possible to
 326          unconditionally call the SYMBOL_OPS method when available.
 327          Unfortunately DWARF 2 stores the frame-base (instead of the
 328          function) location in a function's symbol.  Oops!  For the
 329          moment enable this when/where applicable.  */
 330       return SYMBOL_OPS (sym)->read_needs_frame (sym);
 331
 332     case LOC_REGISTER:
 333     case LOC_ARG:
 334     case LOC_REF_ARG:
 335     case LOC_REGPARM:
 336     case LOC_REGPARM_ADDR:
 337     case LOC_LOCAL:
 338     case LOC_LOCAL_ARG:
 339     case LOC_BASEREG:
 340     case LOC_BASEREG_ARG:
 341     case LOC_HP_THREAD_LOCAL_STATIC:
 342       return 1;
 343
 344     case LOC_UNDEF:
 345     case LOC_CONST:
 346     case LOC_STATIC:
 347     case LOC_INDIRECT:
 348     case LOC_TYPEDEF:
 349
 350     case LOC_LABEL:
 351       /* Getting the address of a label can be done independently of the block,
 352          even if some *uses* of that address wouldn't work so well without
 353          the right frame.  */
 354
 355     case LOC_BLOCK:
 356     case LOC_CONST_BYTES:
 357     case LOC_UNRESOLVED:
 358     case LOC_OPTIMIZED_OUT:
 359       return 0;
 360     }
 361   return 1;
 362 }
 363
 364 /* Given a struct symbol for a variable,
 365    and a stack frame id, read the value of the variable
 366    and return a (pointer to a) struct value containing the value.
 367    If the variable cannot be found, return a zero pointer.
 368    If FRAME is NULL, use the selected frame.  */
 369
 370 struct value *
 371 read_var_value (struct symbol *var, struct frame_info *frame)
 372 {
 373   struct value *v;
 374   struct type *type = SYMBOL_TYPE (var);
 375   CORE_ADDR addr;
 376   int len;
 377
 378   if (SYMBOL_CLASS (var) == LOC_COMPUTED
 379       || SYMBOL_CLASS (var) == LOC_COMPUTED_ARG
 380       || SYMBOL_CLASS (var) == LOC_REGISTER
 381       || SYMBOL_CLASS (var) == LOC_REGPARM)
 382     /* These cases do not use V.  */
 383     v = NULL;
 384   else
 385     {
 386       v = allocate_value (type);
 387       VALUE_LVAL (v) = lval_memory;     /* The most likely possibility.  */
 388     }
 389
 390   len = TYPE_LENGTH (type);
 391
 392   /* FIXME drow/2003-09-06: this call to the selected frame should be
 393      pushed upwards to the callers.  */
 394   if (frame == NULL)
 395     frame = deprecated_safe_get_selected_frame ();
 396
 397   switch (SYMBOL_CLASS (var))
 398     {
 399     case LOC_CONST:
 400       /* Put the constant back in target format.  */
 401       store_signed_integer (value_contents_raw (v), len,
 402                             (LONGEST) SYMBOL_VALUE (var));
 403       VALUE_LVAL (v) = not_lval;
 404       return v;
 405
 406     case LOC_LABEL:
 407       /* Put the constant back in target format.  */
 408       if (overlay_debugging)
 409         {
 410           CORE_ADDR addr
 411             = symbol_overlayed_address (SYMBOL_VALUE_ADDRESS (var),
 412                                         SYMBOL_BFD_SECTION (var));
 413           store_typed_address (value_contents_raw (v), type, addr);
 414         }
 415       else
 416         store_typed_address (value_contents_raw (v), type,
 417                               SYMBOL_VALUE_ADDRESS (var));
 418       VALUE_LVAL (v) = not_lval;
 419       return v;
 420
 421     case LOC_CONST_BYTES:
 422       {
 423         memcpy (value_contents_raw (v), SYMBOL_VALUE_BYTES (var), len);
 424         VALUE_LVAL (v) = not_lval;
 425         return v;
 426       }
 427
 428     case LOC_STATIC:
 429       if (overlay_debugging)
 430         addr = symbol_overlayed_address (SYMBOL_VALUE_ADDRESS (var),
 431                                          SYMBOL_BFD_SECTION (var));
 432       else
 433         addr = SYMBOL_VALUE_ADDRESS (var);
 434       break;
 435
 436     case LOC_INDIRECT:
 437       {
 438         /* The import slot does not have a real address in it from the
 439            dynamic loader (dld.sl on HP-UX), if the target hasn't
 440            begun execution yet, so check for that. */
 441         CORE_ADDR locaddr;
 442         struct value *loc;
 443         if (!target_has_execution)
 444           error (_("\
 445 Attempt to access variable defined in different shared object or load module when\n\
 446 addresses have not been bound by the dynamic loader. Try again when executable is running."));
 447
 448         locaddr = SYMBOL_VALUE_ADDRESS (var);
 449         loc = value_at (lookup_pointer_type (type), locaddr);
 450         addr = value_as_address (loc);
 451         break;
 452       }
 453
 454     case LOC_ARG:
 455       if (frame == NULL)
 456         return 0;
 457       addr = get_frame_args_address (frame);
 458       if (!addr)
 459         return 0;
 460       addr += SYMBOL_VALUE (var);
 461       break;
 462
 463     case LOC_REF_ARG:
 464       {
 465         struct value *ref;
 466         CORE_ADDR argref;
 467         if (frame == NULL)
 468           return 0;
 469         argref = get_frame_args_address (frame);
 470         if (!argref)
 471           return 0;
 472         argref += SYMBOL_VALUE (var);
 473         ref = value_at (lookup_pointer_type (type), argref);
 474         addr = value_as_address (ref);
 475         break;
 476       }
 477
 478     case LOC_LOCAL:
 479     case LOC_LOCAL_ARG:
 480       if (frame == NULL)
 481         return 0;
 482       addr = get_frame_locals_address (frame);
 483       addr += SYMBOL_VALUE (var);
 484       break;
 485
 486     case LOC_BASEREG:
 487     case LOC_BASEREG_ARG:
 488     case LOC_HP_THREAD_LOCAL_STATIC:
 489       {
 490         struct value *regval;
 491
 492         regval = value_from_register (lookup_pointer_type (type),
 493                                       SYMBOL_BASEREG (var), frame);
 494         if (regval == NULL)
 495           error (_("Value of base register not available."));
 496         addr = value_as_address (regval);
 497         addr += SYMBOL_VALUE (var);
 498         break;
 499       }
 500
 501     case LOC_TYPEDEF:
 502       error (_("Cannot look up value of a typedef"));
 503       break;
 504
 505     case LOC_BLOCK:
 506       if (overlay_debugging)
 507         VALUE_ADDRESS (v) = symbol_overlayed_address
 508           (BLOCK_START (SYMBOL_BLOCK_VALUE (var)), SYMBOL_BFD_SECTION (var));
 509       else
 510         VALUE_ADDRESS (v) = BLOCK_START (SYMBOL_BLOCK_VALUE (var));
 511       return v;
 512
 513     case LOC_REGISTER:
 514     case LOC_REGPARM:
 515     case LOC_REGPARM_ADDR:
 516       {
 517         struct block *b;
 518         int regno = SYMBOL_VALUE (var);
 519         struct value *regval;
 520
 521         if (frame == NULL)
 522           return 0;
 523         b = get_frame_block (frame, 0);
 524
 525         if (SYMBOL_CLASS (var) == LOC_REGPARM_ADDR)
 526           {
 527             regval = value_from_register (lookup_pointer_type (type),
 528                                           regno,
 529                                           frame);
 530
 531             if (regval == NULL)
 532               error (_("Value of register variable not available."));
 533
 534             addr = value_as_address (regval);
 535             VALUE_LVAL (v) = lval_memory;
 536           }
 537         else
 538           {
 539             regval = value_from_register (type, regno, frame);
 540
 541             if (regval == NULL)
 542               error (_("Value of register variable not available."));
 543             return regval;
 544           }
 545       }
 546       break;
 547
 548     case LOC_COMPUTED:
 549     case LOC_COMPUTED_ARG:
 550       /* FIXME: cagney/2004-01-26: It should be possible to
 551          unconditionally call the SYMBOL_OPS method when available.
 552          Unfortunately DWARF 2 stores the frame-base (instead of the
 553          function) location in a function's symbol.  Oops!  For the
 554          moment enable this when/where applicable.  */
 555       if (frame == 0 && SYMBOL_OPS (var)->read_needs_frame (var))
 556         return 0;
 557       return SYMBOL_OPS (var)->read_variable (var, frame);
 558
 559     case LOC_UNRESOLVED:
 560       {
 561         struct minimal_symbol *msym;
 562
 563         msym = lookup_minimal_symbol (DEPRECATED_SYMBOL_NAME (var), NULL, NULL);
 564         if (msym == NULL)
 565           return 0;
 566         if (overlay_debugging)
 567           addr = symbol_overlayed_address (SYMBOL_VALUE_ADDRESS (msym),
 568                                            SYMBOL_BFD_SECTION (msym));
 569         else
 570           addr = SYMBOL_VALUE_ADDRESS (msym);
 571       }
 572       break;
 573
 574     case LOC_OPTIMIZED_OUT:
 575       VALUE_LVAL (v) = not_lval;
 576       set_value_optimized_out (v, 1);
 577       return v;
 578
 579     default:
 580       error (_("Cannot look up value of a botched symbol."));
 581       break;
 582     }
 583
 584   VALUE_ADDRESS (v) = addr;
 585   set_value_lazy (v, 1);
 586   return v;
 587 }
 588
 589 /* Install default attributes for register values.  */
 590
 591 struct value *
 592 default_value_from_register (struct type *type, int regnum,
 593                              struct frame_info *frame)
 594 {
 595   struct gdbarch *gdbarch = get_frame_arch (frame);
 596   int len = TYPE_LENGTH (type);
 597   struct value *value = allocate_value (type);
 598
 599   VALUE_LVAL (value) = lval_register;
 600   VALUE_FRAME_ID (value) = get_frame_id (frame);
 601   VALUE_REGNUM (value) = regnum;
 602
 603   /* Any structure stored in more than one register will always be
 604      an integral number of registers.  Otherwise, you need to do
 605      some fiddling with the last register copied here for little
 606      endian machines.  */
 607   if (gdbarch_byte_order (gdbarch) == BFD_ENDIAN_BIG
 608       && len < register_size (gdbarch, regnum))
 609     /* Big-endian, and we want less than full size.  */
 610     set_value_offset (value, register_size (gdbarch, regnum) - len);
 611   else
 612     set_value_offset (value, 0);
 613
 614   return value;
 615 }
 616
 617 /* Return a value of type TYPE, stored in register REGNUM, in frame FRAME.  */
 618
 619 struct value *
 620 value_from_register (struct type *type, int regnum, struct frame_info *frame)
 621 {
 622   struct gdbarch *gdbarch = get_frame_arch (frame);
 623   struct type *type1 = check_typedef (type);
 624   struct value *v;
 625
 626   if (gdbarch_convert_register_p (gdbarch, regnum, type1))
 627     {
 628       /* The ISA/ABI need to something weird when obtaining the
 629          specified value from this register.  It might need to
 630          re-order non-adjacent, starting with REGNUM (see MIPS and
 631          i386).  It might need to convert the [float] register into
 632          the corresponding [integer] type (see Alpha).  The assumption
 633          is that gdbarch_register_to_value populates the entire value
 634          including the location.  */
 635       v = allocate_value (type);
 636       VALUE_LVAL (v) = lval_register;
 637       VALUE_FRAME_ID (v) = get_frame_id (frame);
 638       VALUE_REGNUM (v) = regnum;
 639       gdbarch_register_to_value (gdbarch,
 640                                  frame, regnum, type1, value_contents_raw (v));
 641     }
 642   else
 643     {
 644       int len = TYPE_LENGTH (type);
 645
 646       /* Construct the value.  */
 647       v = gdbarch_value_from_register (gdbarch, type, regnum, frame);
 648
 649       /* Get the data.  */
 650       if (!get_frame_register_bytes (frame, regnum, value_offset (v), len,
 651                                      value_contents_raw (v)))
 652         set_value_optimized_out (v, 1);
 653     }
 654   return v;
 655 }
 656
 657 /* Return contents of register REGNUM in frame FRAME as address,
 658    interpreted as value of type TYPE.   Will abort if register
 659    value is not available.  */
 660
 661 CORE_ADDR
 662 address_from_register (struct type *type, int regnum, struct frame_info *frame)
 663 {
 664   struct value *value;
 665   CORE_ADDR result;
 666
 667   value = value_from_register (type, regnum, frame);
 668   gdb_assert (value);
 669
 670   result = value_as_address (value);
 671   release_value (value);
 672   value_free (value);
 673
 674   return result;
 675 }
 676
 677 \f
 678 /* Given a struct symbol for a variable or function,
 679    and a stack frame id,
 680    return a (pointer to a) struct value containing the properly typed
 681    address.  */
 682
 683 struct value *
 684 locate_var_value (struct symbol *var, struct frame_info *frame)
 685 {
 686   struct gdbarch *gdbarch = get_frame_arch (frame);
 687   CORE_ADDR addr = 0;
 688   struct type *type = SYMBOL_TYPE (var);
 689   struct value *lazy_value;
 690
 691   /* Evaluate it first; if the result is a memory address, we're fine.
 692      Lazy evaluation pays off here. */
 693
 694   lazy_value = read_var_value (var, frame);
 695   if (lazy_value == 0)
 696     error (_("Address of \"%s\" is unknown."), SYMBOL_PRINT_NAME (var));
 697
 698   if (value_lazy (lazy_value)
 699       || TYPE_CODE (type) == TYPE_CODE_FUNC)
 700     {
 701       struct value *val;
 702
 703       addr = VALUE_ADDRESS (lazy_value);
 704       val = value_from_pointer (lookup_pointer_type (type), addr);
 705       return val;
 706     }
 707
 708   /* Not a memory address; check what the problem was.  */
 709   switch (VALUE_LVAL (lazy_value))
 710     {
 711     case lval_register:
 712       gdb_assert (gdbarch_register_name
 713                    (gdbarch, VALUE_REGNUM (lazy_value)) != NULL
 714                   && *gdbarch_register_name
 715                     (gdbarch, VALUE_REGNUM (lazy_value)) != '\0');
 716       error (_("Address requested for identifier "
 717                "\"%s\" which is in register $%s"),
 718             SYMBOL_PRINT_NAME (var),
 719             gdbarch_register_name (gdbarch, VALUE_REGNUM (lazy_value)));
 720       break;
 721
 722     default:
 723       error (_("Can't take address of \"%s\" which isn't an lvalue."),
 724              SYMBOL_PRINT_NAME (var));
 725       break;
 726     }
 727   return 0;                     /* For lint -- never reached */
 728 }