gdb/value.h

   1 /* Definitions for values of C expressions, for GDB.
   2
   3    Copyright (C) 1986-2020 Free Software Foundation, Inc.
   4
   5    This file is part of GDB.
   6
   7    This program is free software; you can redistribute it and/or modify
   8    it under the terms of the GNU General Public License as published by
   9    the Free Software Foundation; either version 3 of the License, or
  10    (at your option) any later version.
  11
  12    This program is distributed in the hope that it will be useful,
  13    but WITHOUT ANY WARRANTY; without even the implied warranty of
  14    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15    GNU General Public License for more details.
  16
  17    You should have received a copy of the GNU General Public License
  18    along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
  19
  20 #if !defined (VALUE_H)
  21 #define VALUE_H 1
  22
  23 #include "frame.h"              /* For struct frame_id.  */
  24 #include "extension.h"
  25 #include "gdbsupport/gdb_ref_ptr.h"
  26
  27 struct block;
  28 struct expression;
  29 struct regcache;
  30 struct symbol;
  31 struct type;
  32 struct ui_file;
  33 struct language_defn;
  34 struct value_print_options;
  35
  36 /* Values can be partially 'optimized out' and/or 'unavailable'.
  37    These are distinct states and have different string representations
  38    and related error strings.
  39
  40    'unavailable' has a specific meaning in this context.  It means the
  41    value exists in the program (at the machine level), but GDB has no
  42    means to get to it.  Such a value is normally printed as
  43    <unavailable>.  Examples of how to end up with an unavailable value
  44    would be:
  45
  46     - We're inspecting a traceframe, and the memory or registers the
  47       debug information says the value lives on haven't been collected.
  48
  49     - We're inspecting a core dump, the memory or registers the debug
  50       information says the value lives aren't present in the dump
  51       (that is, we have a partial/trimmed core dump, or we don't fully
  52       understand/handle the core dump's format).
  53
  54     - We're doing live debugging, but the debug API has no means to
  55       get at where the value lives in the machine, like e.g., ptrace
  56       not having access to some register or register set.
  57
  58     - Any other similar scenario.
  59
  60   OTOH, "optimized out" is about what the compiler decided to generate
  61   (or not generate).  A chunk of a value that was optimized out does
  62   not actually exist in the program.  There's no way to get at it
  63   short of compiling the program differently.
  64
  65   A register that has not been saved in a frame is likewise considered
  66   optimized out, except not-saved registers have a different string
  67   representation and related error strings.  E.g., we'll print them as
  68   <not-saved> instead of <optimized out>, as in:
  69
  70     (gdb) p/x $rax
  71     $1 = <not saved>
  72     (gdb) info registers rax
  73     rax            <not saved>
  74
  75   If the debug info describes a variable as being in such a register,
  76   we'll still print the variable as <optimized out>.  IOW, <not saved>
  77   is reserved for inspecting registers at the machine level.
  78
  79   When comparing value contents, optimized out chunks, unavailable
  80   chunks, and valid contents data are all considered different.  See
  81   value_contents_eq for more info.
  82 */
  83
  84 extern bool overload_resolution;
  85
  86 /* The structure which defines the type of a value.  It should never
  87    be possible for a program lval value to survive over a call to the
  88    inferior (i.e. to be put into the history list or an internal
  89    variable).  */
  90
  91 struct value;
  92
  93 /* Increase VAL's reference count.  */
  94
  95 extern void value_incref (struct value *val);
  96
  97 /* Decrease VAL's reference count.  When the reference count drops to
  98    0, VAL will be freed.  */
  99
 100 extern void value_decref (struct value *val);
 101
 102 /* A policy class to interface gdb::ref_ptr with struct value.  */
 103
 104 struct value_ref_policy
 105 {
 106   static void incref (struct value *ptr)
 107   {
 108     value_incref (ptr);
 109   }
 110
 111   static void decref (struct value *ptr)
 112   {
 113     value_decref (ptr);
 114   }
 115 };
 116
 117 /* A gdb:;ref_ptr pointer to a struct value.  */
 118
 119 typedef gdb::ref_ptr<struct value, value_ref_policy> value_ref_ptr;
 120
 121 /* Values are stored in a chain, so that they can be deleted easily
 122    over calls to the inferior.  Values assigned to internal variables,
 123    put into the value history or exposed to Python are taken off this
 124    list.  */
 125
 126 struct value *value_next (const struct value *);
 127
 128 /* Type of the value.  */
 129
 130 extern struct type *value_type (const struct value *);
 131
 132 /* Return the gdbarch associated with the value. */
 133
 134 extern struct gdbarch *get_value_arch (const struct value *value);
 135
 136 /* This is being used to change the type of an existing value, that
 137    code should instead be creating a new value with the changed type
 138    (but possibly shared content).  */
 139
 140 extern void deprecated_set_value_type (struct value *value,
 141                                        struct type *type);
 142
 143 /* Only used for bitfields; number of bits contained in them.  */
 144
 145 extern LONGEST value_bitsize (const struct value *);
 146 extern void set_value_bitsize (struct value *, LONGEST bit);
 147
 148 /* Only used for bitfields; position of start of field.  For
 149    little-endian targets, it is the position of the LSB.  For
 150    big-endian targets, it is the position of the MSB.  */
 151
 152 extern LONGEST value_bitpos (const struct value *);
 153 extern void set_value_bitpos (struct value *, LONGEST bit);
 154
 155 /* Only used for bitfields; the containing value.  This allows a
 156    single read from the target when displaying multiple
 157    bitfields.  */
 158
 159 struct value *value_parent (const struct value *);
 160 extern void set_value_parent (struct value *value, struct value *parent);
 161
 162 /* Describes offset of a value within lval of a structure in bytes.
 163    If lval == lval_memory, this is an offset to the address.  If lval
 164    == lval_register, this is a further offset from location.address
 165    within the registers structure.  Note also the member
 166    embedded_offset below.  */
 167
 168 extern LONGEST value_offset (const struct value *);
 169 extern void set_value_offset (struct value *, LONGEST offset);
 170
 171 /* The comment from "struct value" reads: ``Is it modifiable?  Only
 172    relevant if lval != not_lval.''.  Shouldn't the value instead be
 173    not_lval and be done with it?  */
 174
 175 extern int deprecated_value_modifiable (const struct value *value);
 176
 177 /* If a value represents a C++ object, then the `type' field gives the
 178    object's compile-time type.  If the object actually belongs to some
 179    class derived from `type', perhaps with other base classes and
 180    additional members, then `type' is just a subobject of the real
 181    thing, and the full object is probably larger than `type' would
 182    suggest.
 183
 184    If `type' is a dynamic class (i.e. one with a vtable), then GDB can
 185    actually determine the object's run-time type by looking at the
 186    run-time type information in the vtable.  When this information is
 187    available, we may elect to read in the entire object, for several
 188    reasons:
 189
 190    - When printing the value, the user would probably rather see the
 191      full object, not just the limited portion apparent from the
 192      compile-time type.
 193
 194    - If `type' has virtual base classes, then even printing `type'
 195      alone may require reaching outside the `type' portion of the
 196      object to wherever the virtual base class has been stored.
 197
 198    When we store the entire object, `enclosing_type' is the run-time
 199    type -- the complete object -- and `embedded_offset' is the offset
 200    of `type' within that larger type, in bytes.  The value_contents()
 201    macro takes `embedded_offset' into account, so most GDB code
 202    continues to see the `type' portion of the value, just as the
 203    inferior would.
 204
 205    If `type' is a pointer to an object, then `enclosing_type' is a
 206    pointer to the object's run-time type, and `pointed_to_offset' is
 207    the offset in bytes from the full object to the pointed-to object
 208    -- that is, the value `embedded_offset' would have if we followed
 209    the pointer and fetched the complete object.  (I don't really see
 210    the point.  Why not just determine the run-time type when you
 211    indirect, and avoid the special case?  The contents don't matter
 212    until you indirect anyway.)
 213
 214    If we're not doing anything fancy, `enclosing_type' is equal to
 215    `type', and `embedded_offset' is zero, so everything works
 216    normally.  */
 217
 218 extern struct type *value_enclosing_type (const struct value *);
 219 extern void set_value_enclosing_type (struct value *val,
 220                                       struct type *new_type);
 221
 222 /* Returns value_type or value_enclosing_type depending on
 223    value_print_options.objectprint.
 224
 225    If RESOLVE_SIMPLE_TYPES is 0 the enclosing type will be resolved
 226    only for pointers and references, else it will be returned
 227    for all the types (e.g. structures).  This option is useful
 228    to prevent retrieving enclosing type for the base classes fields.
 229
 230    REAL_TYPE_FOUND is used to inform whether the real type was found
 231    (or just static type was used).  The NULL may be passed if it is not
 232    necessary. */
 233
 234 extern struct type *value_actual_type (struct value *value,
 235                                        int resolve_simple_types,
 236                                        int *real_type_found);
 237
 238 extern LONGEST value_pointed_to_offset (const struct value *value);
 239 extern void set_value_pointed_to_offset (struct value *value, LONGEST val);
 240 extern LONGEST value_embedded_offset (const struct value *value);
 241 extern void set_value_embedded_offset (struct value *value, LONGEST val);
 242
 243 /* For lval_computed values, this structure holds functions used to
 244    retrieve and set the value (or portions of the value).
 245
 246    For each function, 'V' is the 'this' pointer: an lval_funcs
 247    function F may always assume that the V it receives is an
 248    lval_computed value, and has F in the appropriate slot of its
 249    lval_funcs structure.  */
 250
 251 struct lval_funcs
 252 {
 253   /* Fill in VALUE's contents.  This is used to "un-lazy" values.  If
 254      a problem arises in obtaining VALUE's bits, this function should
 255      call 'error'.  If it is NULL value_fetch_lazy on "un-lazy"
 256      non-optimized-out value is an internal error.  */
 257   void (*read) (struct value *v);
 258
 259   /* Handle an assignment TOVAL = FROMVAL by writing the value of
 260      FROMVAL to TOVAL's location.  The contents of TOVAL have not yet
 261      been updated.  If a problem arises in doing so, this function
 262      should call 'error'.  If it is NULL such TOVAL assignment is an error as
 263      TOVAL is not considered as an lvalue.  */
 264   void (*write) (struct value *toval, struct value *fromval);
 265
 266   /* If non-NULL, this is used to implement pointer indirection for
 267      this value.  This method may return NULL, in which case value_ind
 268      will fall back to ordinary indirection.  */
 269   struct value *(*indirect) (struct value *value);
 270
 271   /* If non-NULL, this is used to implement reference resolving for
 272      this value.  This method may return NULL, in which case coerce_ref
 273      will fall back to ordinary references resolving.  */
 274   struct value *(*coerce_ref) (const struct value *value);
 275
 276   /* If non-NULL, this is used to determine whether the indicated bits
 277      of VALUE are a synthetic pointer.  */
 278   int (*check_synthetic_pointer) (const struct value *value,
 279                                   LONGEST offset, int length);
 280
 281   /* Return a duplicate of VALUE's closure, for use in a new value.
 282      This may simply return the same closure, if VALUE's is
 283      reference-counted or statically allocated.
 284
 285      This may be NULL, in which case VALUE's closure is re-used in the
 286      new value.  */
 287   void *(*copy_closure) (const struct value *v);
 288
 289   /* Drop VALUE's reference to its closure.  Maybe this frees the
 290      closure; maybe this decrements a reference count; maybe the
 291      closure is statically allocated and this does nothing.
 292
 293      This may be NULL, in which case no action is taken to free
 294      VALUE's closure.  */
 295   void (*free_closure) (struct value *v);
 296 };
 297
 298 /* Create a computed lvalue, with type TYPE, function pointers FUNCS,
 299    and closure CLOSURE.  */
 300
 301 extern struct value *allocate_computed_value (struct type *type,
 302                                               const struct lval_funcs *funcs,
 303                                               void *closure);
 304
 305 /* Helper function to check the validity of some bits of a value.
 306
 307    If TYPE represents some aggregate type (e.g., a structure), return 1.
 308
 309    Otherwise, any of the bytes starting at OFFSET and extending for
 310    TYPE_LENGTH(TYPE) bytes are invalid, print a message to STREAM and
 311    return 0.  The checking is done using FUNCS.
 312
 313    Otherwise, return 1.  */
 314
 315 extern int valprint_check_validity (struct ui_file *stream, struct type *type,
 316                                     LONGEST embedded_offset,
 317                                     const struct value *val);
 318
 319 extern struct value *allocate_optimized_out_value (struct type *type);
 320
 321 /* If VALUE is lval_computed, return its lval_funcs structure.  */
 322
 323 extern const struct lval_funcs *value_computed_funcs (const struct value *);
 324
 325 /* If VALUE is lval_computed, return its closure.  The meaning of the
 326    returned value depends on the functions VALUE uses.  */
 327
 328 extern void *value_computed_closure (const struct value *value);
 329
 330 /* If zero, contents of this value are in the contents field.  If
 331    nonzero, contents are in inferior.  If the lval field is lval_memory,
 332    the contents are in inferior memory at location.address plus offset.
 333    The lval field may also be lval_register.
 334
 335    WARNING: This field is used by the code which handles watchpoints
 336    (see breakpoint.c) to decide whether a particular value can be
 337    watched by hardware watchpoints.  If the lazy flag is set for some
 338    member of a value chain, it is assumed that this member of the
 339    chain doesn't need to be watched as part of watching the value
 340    itself.  This is how GDB avoids watching the entire struct or array
 341    when the user wants to watch a single struct member or array
 342    element.  If you ever change the way lazy flag is set and reset, be
 343    sure to consider this use as well!  */
 344
 345 extern int value_lazy (const struct value *);
 346 extern void set_value_lazy (struct value *value, int val);
 347
 348 extern int value_stack (const struct value *);
 349 extern void set_value_stack (struct value *value, int val);
 350
 351 /* Throw an error complaining that the value has been optimized
 352    out.  */
 353
 354 extern void error_value_optimized_out (void);
 355
 356 /* value_contents() and value_contents_raw() both return the address
 357    of the gdb buffer used to hold a copy of the contents of the lval.
 358    value_contents() is used when the contents of the buffer are needed
 359    -- it uses value_fetch_lazy() to load the buffer from the process
 360    being debugged if it hasn't already been loaded
 361    (value_contents_writeable() is used when a writeable but fetched
 362    buffer is required)..  value_contents_raw() is used when data is
 363    being stored into the buffer, or when it is certain that the
 364    contents of the buffer are valid.
 365
 366    Note: The contents pointer is adjusted by the offset required to
 367    get to the real subobject, if the value happens to represent
 368    something embedded in a larger run-time object.  */
 369
 370 extern gdb_byte *value_contents_raw (struct value *);
 371
 372 /* Actual contents of the value.  For use of this value; setting it
 373    uses the stuff above.  Not valid if lazy is nonzero.  Target
 374    byte-order.  We force it to be aligned properly for any possible
 375    value.  Note that a value therefore extends beyond what is
 376    declared here.  */
 377
 378 extern const gdb_byte *value_contents (struct value *);
 379 extern gdb_byte *value_contents_writeable (struct value *);
 380
 381 /* The ALL variants of the above two macros do not adjust the returned
 382    pointer by the embedded_offset value.  */
 383
 384 extern gdb_byte *value_contents_all_raw (struct value *);
 385 extern const gdb_byte *value_contents_all (struct value *);
 386
 387 /* Like value_contents_all, but does not require that the returned
 388    bits be valid.  This should only be used in situations where you
 389    plan to check the validity manually.  */
 390 extern const gdb_byte *value_contents_for_printing (struct value *value);
 391
 392 /* Like value_contents_for_printing, but accepts a constant value
 393    pointer.  Unlike value_contents_for_printing however, the pointed
 394    value must _not_ be lazy.  */
 395 extern const gdb_byte *
 396   value_contents_for_printing_const (const struct value *value);
 397
 398 extern void value_fetch_lazy (struct value *val);
 399
 400 /* If nonzero, this is the value of a variable which does not actually
 401    exist in the program, at least partially.  If the value is lazy,
 402    this may fetch it now.  */
 403 extern int value_optimized_out (struct value *value);
 404
 405 /* Given a value, return true if any of the contents bits starting at
 406    OFFSET and extending for LENGTH bits is optimized out, false
 407    otherwise.  */
 408
 409 extern int value_bits_any_optimized_out (const struct value *value,
 410                                          int bit_offset, int bit_length);
 411
 412 /* Like value_optimized_out, but return true iff the whole value is
 413    optimized out.  */
 414 extern int value_entirely_optimized_out (struct value *value);
 415
 416 /* Mark VALUE's content bytes starting at OFFSET and extending for
 417    LENGTH bytes as optimized out.  */
 418
 419 extern void mark_value_bytes_optimized_out (struct value *value,
 420                                             int offset, int length);
 421
 422 /* Mark VALUE's content bits starting at OFFSET and extending for
 423    LENGTH bits as optimized out.  */
 424
 425 extern void mark_value_bits_optimized_out (struct value *value,
 426                                            LONGEST offset, LONGEST length);
 427
 428 /* Set or return field indicating whether a variable is initialized or
 429    not, based on debugging information supplied by the compiler.
 430    1 = initialized; 0 = uninitialized.  */
 431 extern int value_initialized (const struct value *);
 432 extern void set_value_initialized (struct value *, int);
 433
 434 /* Set COMPONENT's location as appropriate for a component of WHOLE
 435    --- regardless of what kind of lvalue WHOLE is.  */
 436 extern void set_value_component_location (struct value *component,
 437                                           const struct value *whole);
 438
 439 /* While the following fields are per- VALUE .CONTENT .PIECE (i.e., a
 440    single value might have multiple LVALs), this hacked interface is
 441    limited to just the first PIECE.  Expect further change.  */
 442 /* Type of value; either not an lval, or one of the various different
 443    possible kinds of lval.  */
 444 extern enum lval_type *deprecated_value_lval_hack (struct value *);
 445 #define VALUE_LVAL(val) (*deprecated_value_lval_hack (val))
 446
 447 /* Like VALUE_LVAL, except the parameter can be const.  */
 448 extern enum lval_type value_lval_const (const struct value *value);
 449
 450 /* If lval == lval_memory, return the address in the inferior.  If
 451    lval == lval_register, return the byte offset into the registers
 452    structure.  Otherwise, return 0.  The returned address
 453    includes the offset, if any.  */
 454 extern CORE_ADDR value_address (const struct value *);
 455
 456 /* Like value_address, except the result does not include value's
 457    offset.  */
 458 extern CORE_ADDR value_raw_address (const struct value *);
 459
 460 /* Set the address of a value.  */
 461 extern void set_value_address (struct value *, CORE_ADDR);
 462
 463 /* Pointer to internal variable.  */
 464 extern struct internalvar **deprecated_value_internalvar_hack (struct value *);
 465 #define VALUE_INTERNALVAR(val) (*deprecated_value_internalvar_hack (val))
 466
 467 /* Frame ID of "next" frame to which a register value is relative.  A
 468    register value is indicated by VALUE_LVAL being set to lval_register.
 469    So, if the register value is found relative to frame F, then the
 470    frame id of F->next will be stored in VALUE_NEXT_FRAME_ID.  */
 471 extern struct frame_id *deprecated_value_next_frame_id_hack (struct value *);
 472 #define VALUE_NEXT_FRAME_ID(val) (*deprecated_value_next_frame_id_hack (val))
 473
 474 /* Frame ID of frame to which a register value is relative.  This is
 475    similar to VALUE_NEXT_FRAME_ID, above, but may not be assigned to.
 476    Note that VALUE_FRAME_ID effectively undoes the "next" operation
 477    that was performed during the assignment to VALUE_NEXT_FRAME_ID.  */
 478 #define VALUE_FRAME_ID(val) (get_prev_frame_id_by_id (VALUE_NEXT_FRAME_ID (val)))
 479
 480 /* Register number if the value is from a register.  */
 481 extern int *deprecated_value_regnum_hack (struct value *);
 482 #define VALUE_REGNUM(val) (*deprecated_value_regnum_hack (val))
 483
 484 /* Return value after lval_funcs->coerce_ref (after check_typedef).  Return
 485    NULL if lval_funcs->coerce_ref is not applicable for whatever reason.  */
 486
 487 extern struct value *coerce_ref_if_computed (const struct value *arg);
 488
 489 /* Setup a new value type and enclosing value type for dereferenced value VALUE.
 490    ENC_TYPE is the new enclosing type that should be set.  ORIGINAL_TYPE and
 491    ORIGINAL_VAL are the type and value of the original reference or
 492    pointer.  ORIGINAL_VALUE_ADDRESS is the address within VALUE, that is
 493    the address that was dereferenced.
 494
 495    Note, that VALUE is modified by this function.
 496
 497    It is a common implementation for coerce_ref and value_ind.  */
 498
 499 extern struct value * readjust_indirect_value_type (struct value *value,
 500                                                     struct type *enc_type,
 501                                                     const struct type *original_type,
 502                                                     struct value *original_val,
 503                                                     CORE_ADDR original_value_address);
 504
 505 /* Convert a REF to the object referenced.  */
 506
 507 extern struct value *coerce_ref (struct value *value);
 508
 509 /* If ARG is an array, convert it to a pointer.
 510    If ARG is a function, convert it to a function pointer.
 511
 512    References are dereferenced.  */
 513
 514 extern struct value *coerce_array (struct value *value);
 515
 516 /* Given a value, determine whether the bits starting at OFFSET and
 517    extending for LENGTH bits are a synthetic pointer.  */
 518
 519 extern int value_bits_synthetic_pointer (const struct value *value,
 520                                          LONGEST offset, LONGEST length);
 521
 522 /* Given a value, determine whether the contents bytes starting at
 523    OFFSET and extending for LENGTH bytes are available.  This returns
 524    nonzero if all bytes in the given range are available, zero if any
 525    byte is unavailable.  */
 526
 527 extern int value_bytes_available (const struct value *value,
 528                                   LONGEST offset, LONGEST length);
 529
 530 /* Given a value, determine whether the contents bits starting at
 531    OFFSET and extending for LENGTH bits are available.  This returns
 532    nonzero if all bits in the given range are available, zero if any
 533    bit is unavailable.  */
 534
 535 extern int value_bits_available (const struct value *value,
 536                                  LONGEST offset, LONGEST length);
 537
 538 /* Like value_bytes_available, but return false if any byte in the
 539    whole object is unavailable.  */
 540 extern int value_entirely_available (struct value *value);
 541
 542 /* Like value_entirely_available, but return false if any byte in the
 543    whole object is available.  */
 544 extern int value_entirely_unavailable (struct value *value);
 545
 546 /* Mark VALUE's content bytes starting at OFFSET and extending for
 547    LENGTH bytes as unavailable.  */
 548
 549 extern void mark_value_bytes_unavailable (struct value *value,
 550                                           LONGEST offset, LONGEST length);
 551
 552 /* Mark VALUE's content bits starting at OFFSET and extending for
 553    LENGTH bits as unavailable.  */
 554
 555 extern void mark_value_bits_unavailable (struct value *value,
 556                                          LONGEST offset, LONGEST length);
 557
 558 /* Compare LENGTH bytes of VAL1's contents starting at OFFSET1 with
 559    LENGTH bytes of VAL2's contents starting at OFFSET2.
 560
 561    Note that "contents" refers to the whole value's contents
 562    (value_contents_all), without any embedded offset adjustment.  For
 563    example, to compare a complete object value with itself, including
 564    its enclosing type chunk, you'd do:
 565
 566      int len = TYPE_LENGTH (check_typedef (value_enclosing_type (val)));
 567      value_contents_eq (val, 0, val, 0, len);
 568
 569    Returns true iff the set of available/valid contents match.
 570
 571    Optimized-out contents are equal to optimized-out contents, and are
 572    not equal to non-optimized-out contents.
 573
 574    Unavailable contents are equal to unavailable contents, and are not
 575    equal to non-unavailable contents.
 576
 577    For example, if 'x's represent an unavailable byte, and 'V' and 'Z'
 578    represent different available/valid bytes, in a value with length
 579    16:
 580
 581      offset:   0   4   8   12  16
 582      contents: xxxxVVVVxxxxVVZZ
 583
 584    then:
 585
 586      value_contents_eq(val, 0, val, 8, 6) => true
 587      value_contents_eq(val, 0, val, 4, 4) => false
 588      value_contents_eq(val, 0, val, 8, 8) => false
 589      value_contents_eq(val, 4, val, 12, 2) => true
 590      value_contents_eq(val, 4, val, 12, 4) => true
 591      value_contents_eq(val, 3, val, 4, 4) => true
 592
 593    If 'x's represent an unavailable byte, 'o' represents an optimized
 594    out byte, in a value with length 8:
 595
 596      offset:   0   4   8
 597      contents: xxxxoooo
 598
 599    then:
 600
 601      value_contents_eq(val, 0, val, 2, 2) => true
 602      value_contents_eq(val, 4, val, 6, 2) => true
 603      value_contents_eq(val, 0, val, 4, 4) => true
 604
 605    We only know whether a value chunk is unavailable or optimized out
 606    if we've tried to read it.  As this routine is used by printing
 607    routines, which may be printing values in the value history, long
 608    after the inferior is gone, it works with const values.  Therefore,
 609    this routine must not be called with lazy values.  */
 610
 611 extern bool value_contents_eq (const struct value *val1, LONGEST offset1,
 612                                const struct value *val2, LONGEST offset2,
 613                                LONGEST length);
 614
 615 /* Read LENGTH addressable memory units starting at MEMADDR into BUFFER,
 616    which is (or will be copied to) VAL's contents buffer offset by
 617    BIT_OFFSET bits.  Marks value contents ranges as unavailable if
 618    the corresponding memory is likewise unavailable.  STACK indicates
 619    whether the memory is known to be stack memory.  */
 620
 621 extern void read_value_memory (struct value *val, LONGEST bit_offset,
 622                                int stack, CORE_ADDR memaddr,
 623                                gdb_byte *buffer, size_t length);
 624
 625 /* Cast SCALAR_VALUE to the element type of VECTOR_TYPE, then replicate
 626    into each element of a new vector value with VECTOR_TYPE.  */
 627
 628 struct value *value_vector_widen (struct value *scalar_value,
 629                                   struct type *vector_type);
 630
 631 \f
 632
 633 #include "symtab.h"
 634 #include "gdbtypes.h"
 635 #include "expression.h"
 636
 637 struct frame_info;
 638 struct fn_field;
 639
 640 extern int print_address_demangle (const struct value_print_options *,
 641                                    struct gdbarch *, CORE_ADDR,
 642                                    struct ui_file *, int);
 643
 644 /* Returns true if VAL is of floating-point type.  In addition,
 645    throws an error if the value is an invalid floating-point value.  */
 646 extern bool is_floating_value (struct value *val);
 647
 648 extern LONGEST value_as_long (struct value *val);
 649 extern CORE_ADDR value_as_address (struct value *val);
 650
 651 extern LONGEST unpack_long (struct type *type, const gdb_byte *valaddr);
 652 extern CORE_ADDR unpack_pointer (struct type *type, const gdb_byte *valaddr);
 653
 654 extern LONGEST unpack_field_as_long (struct type *type,
 655                                      const gdb_byte *valaddr,
 656                                      int fieldno);
 657
 658 /* Unpack a bitfield of the specified FIELD_TYPE, from the object at
 659    VALADDR, and store the result in *RESULT.
 660    The bitfield starts at BITPOS bits and contains BITSIZE bits; if
 661    BITSIZE is zero, then the length is taken from FIELD_TYPE.
 662
 663    Extracting bits depends on endianness of the machine.  Compute the
 664    number of least significant bits to discard.  For big endian machines,
 665    we compute the total number of bits in the anonymous object, subtract
 666    off the bit count from the MSB of the object to the MSB of the
 667    bitfield, then the size of the bitfield, which leaves the LSB discard
 668    count.  For little endian machines, the discard count is simply the
 669    number of bits from the LSB of the anonymous object to the LSB of the
 670    bitfield.
 671
 672    If the field is signed, we also do sign extension.  */
 673
 674 extern LONGEST unpack_bits_as_long (struct type *field_type,
 675                                     const gdb_byte *valaddr,
 676                                     LONGEST bitpos, LONGEST bitsize);
 677
 678 extern int unpack_value_field_as_long (struct type *type, const gdb_byte *valaddr,
 679                                 LONGEST embedded_offset, int fieldno,
 680                                 const struct value *val, LONGEST *result);
 681
 682 extern void unpack_value_bitfield (struct value *dest_val,
 683                                    LONGEST bitpos, LONGEST bitsize,
 684                                    const gdb_byte *valaddr,
 685                                    LONGEST embedded_offset,
 686                                    const struct value *val);
 687
 688 extern struct value *value_field_bitfield (struct type *type, int fieldno,
 689                                            const gdb_byte *valaddr,
 690                                            LONGEST embedded_offset,
 691                                            const struct value *val);
 692
 693 extern void pack_long (gdb_byte *buf, struct type *type, LONGEST num);
 694
 695 extern struct value *value_from_longest (struct type *type, LONGEST num);
 696 extern struct value *value_from_ulongest (struct type *type, ULONGEST num);
 697 extern struct value *value_from_pointer (struct type *type, CORE_ADDR addr);
 698 extern struct value *value_from_host_double (struct type *type, double d);
 699 extern struct value *value_from_history_ref (const char *, const char **);
 700 extern struct value *value_from_component (struct value *, struct type *,
 701                                            LONGEST);
 702
 703 extern struct value *value_at (struct type *type, CORE_ADDR addr);
 704 extern struct value *value_at_lazy (struct type *type, CORE_ADDR addr);
 705
 706 extern struct value *value_from_contents_and_address_unresolved
 707      (struct type *, const gdb_byte *, CORE_ADDR);
 708 extern struct value *value_from_contents_and_address (struct type *,
 709                                                       const gdb_byte *,
 710                                                       CORE_ADDR);
 711 extern struct value *value_from_contents (struct type *, const gdb_byte *);
 712
 713 extern struct value *default_value_from_register (struct gdbarch *gdbarch,
 714                                                   struct type *type,
 715                                                   int regnum,
 716                                                   struct frame_id frame_id);
 717
 718 extern void read_frame_register_value (struct value *value,
 719                                        struct frame_info *frame);
 720
 721 extern struct value *value_from_register (struct type *type, int regnum,
 722                                           struct frame_info *frame);
 723
 724 extern CORE_ADDR address_from_register (int regnum,
 725                                         struct frame_info *frame);
 726
 727 extern struct value *value_of_variable (struct symbol *var,
 728                                         const struct block *b);
 729
 730 extern struct value *address_of_variable (struct symbol *var,
 731                                           const struct block *b);
 732
 733 extern struct value *value_of_register (int regnum, struct frame_info *frame);
 734
 735 struct value *value_of_register_lazy (struct frame_info *frame, int regnum);
 736
 737 /* Return the symbol's reading requirement.  */
 738
 739 extern enum symbol_needs_kind symbol_read_needs (struct symbol *);
 740
 741 /* Return true if the symbol needs a frame.  This is a wrapper for
 742    symbol_read_needs that simply checks for SYMBOL_NEEDS_FRAME.  */
 743
 744 extern int symbol_read_needs_frame (struct symbol *);
 745
 746 extern struct value *read_var_value (struct symbol *var,
 747                                      const struct block *var_block,
 748                                      struct frame_info *frame);
 749
 750 extern struct value *allocate_value (struct type *type);
 751 extern struct value *allocate_value_lazy (struct type *type);
 752 extern void value_contents_copy (struct value *dst, LONGEST dst_offset,
 753                                  struct value *src, LONGEST src_offset,
 754                                  LONGEST length);
 755 extern void value_contents_copy_raw (struct value *dst, LONGEST dst_offset,
 756                                      struct value *src, LONGEST src_offset,
 757                                      LONGEST length);
 758
 759 extern struct value *allocate_repeat_value (struct type *type, int count);
 760
 761 extern struct value *value_mark (void);
 762
 763 extern void value_free_to_mark (const struct value *mark);
 764
 765 /* A helper class that uses value_mark at construction time and calls
 766    value_free_to_mark in the destructor.  This is used to clear out
 767    temporary values created during the lifetime of this object.  */
 768 class scoped_value_mark
 769 {
 770  public:
 771
 772   scoped_value_mark ()
 773     : m_value (value_mark ())
 774   {
 775   }
 776
 777   ~scoped_value_mark ()
 778   {
 779     free_to_mark ();
 780   }
 781
 782   scoped_value_mark (scoped_value_mark &&other) = default;
 783
 784   DISABLE_COPY_AND_ASSIGN (scoped_value_mark);
 785
 786   /* Free the values currently on the value stack.  */
 787   void free_to_mark ()
 788   {
 789     if (m_value != NULL)
 790       {
 791         value_free_to_mark (m_value);
 792         m_value = NULL;
 793       }
 794   }
 795
 796  private:
 797
 798   const struct value *m_value;
 799 };
 800
 801 extern struct value *value_cstring (const char *ptr, ssize_t len,
 802                                     struct type *char_type);
 803 extern struct value *value_string (const char *ptr, ssize_t len,
 804                                    struct type *char_type);
 805
 806 extern struct value *value_array (int lowbound, int highbound,
 807                                   struct value **elemvec);
 808
 809 extern struct value *value_concat (struct value *arg1, struct value *arg2);
 810
 811 extern struct value *value_binop (struct value *arg1, struct value *arg2,
 812                                   enum exp_opcode op);
 813
 814 extern struct value *value_ptradd (struct value *arg1, LONGEST arg2);
 815
 816 extern LONGEST value_ptrdiff (struct value *arg1, struct value *arg2);
 817
 818 /* Return true if VAL does not live in target memory, but should in order
 819    to operate on it.  Otherwise return false.  */
 820
 821 extern bool value_must_coerce_to_target (struct value *arg1);
 822
 823 extern struct value *value_coerce_to_target (struct value *arg1);
 824
 825 extern struct value *value_coerce_array (struct value *arg1);
 826
 827 extern struct value *value_coerce_function (struct value *arg1);
 828
 829 extern struct value *value_ind (struct value *arg1);
 830
 831 extern struct value *value_addr (struct value *arg1);
 832
 833 extern struct value *value_ref (struct value *arg1, enum type_code refcode);
 834
 835 extern struct value *value_assign (struct value *toval,
 836                                    struct value *fromval);
 837
 838 extern struct value *value_pos (struct value *arg1);
 839
 840 extern struct value *value_neg (struct value *arg1);
 841
 842 extern struct value *value_complement (struct value *arg1);
 843
 844 extern struct value *value_struct_elt (struct value **argp,
 845                                        struct value **args,
 846                                        const char *name, int *static_memfuncp,
 847                                        const char *err);
 848
 849 extern struct value *value_struct_elt_bitpos (struct value **argp,
 850                                               int bitpos,
 851                                               struct type *field_type,
 852                                               const char *err);
 853
 854 extern struct value *value_aggregate_elt (struct type *curtype,
 855                                           const char *name,
 856                                           struct type *expect_type,
 857                                           int want_address,
 858                                           enum noside noside);
 859
 860 extern struct value *value_static_field (struct type *type, int fieldno);
 861
 862 enum oload_search_type { NON_METHOD, METHOD, BOTH };
 863
 864 extern int find_overload_match (gdb::array_view<value *> args,
 865                                 const char *name,
 866                                 enum oload_search_type method,
 867                                 struct value **objp, struct symbol *fsym,
 868                                 struct value **valp, struct symbol **symp,
 869                                 int *staticp, const int no_adl,
 870                                 enum noside noside);
 871
 872 extern struct value *value_field (struct value *arg1, int fieldno);
 873
 874 extern struct value *value_primitive_field (struct value *arg1, LONGEST offset,
 875                                             int fieldno,
 876                                             struct type *arg_type);
 877
 878
 879 extern struct type *value_rtti_indirect_type (struct value *, int *, LONGEST *,
 880                                               int *);
 881
 882 extern struct value *value_full_object (struct value *, struct type *, int,
 883                                         int, int);
 884
 885 extern struct value *value_cast_pointers (struct type *, struct value *, int);
 886
 887 extern struct value *value_cast (struct type *type, struct value *arg2);
 888
 889 extern struct value *value_reinterpret_cast (struct type *type,
 890                                              struct value *arg);
 891
 892 extern struct value *value_dynamic_cast (struct type *type, struct value *arg);
 893
 894 extern struct value *value_zero (struct type *type, enum lval_type lv);
 895
 896 extern struct value *value_one (struct type *type);
 897
 898 extern struct value *value_repeat (struct value *arg1, int count);
 899
 900 extern struct value *value_subscript (struct value *array, LONGEST index);
 901
 902 extern struct value *value_bitstring_subscript (struct type *type,
 903                                                 struct value *bitstring,
 904                                                 LONGEST index);
 905
 906 extern struct value *register_value_being_returned (struct type *valtype,
 907                                                     struct regcache *retbuf);
 908
 909 extern int value_in (struct value *element, struct value *set);
 910
 911 extern int value_bit_index (struct type *type, const gdb_byte *addr,
 912                             int index);
 913
 914 extern enum return_value_convention
 915 struct_return_convention (struct gdbarch *gdbarch, struct value *function,
 916                           struct type *value_type);
 917
 918 extern int using_struct_return (struct gdbarch *gdbarch,
 919                                 struct value *function,
 920                                 struct type *value_type);
 921
 922 extern struct value *evaluate_expression (struct expression *exp);
 923
 924 extern struct value *evaluate_type (struct expression *exp);
 925
 926 extern struct value *evaluate_subexp (struct type *expect_type,
 927                                       struct expression *exp,
 928                                       int *pos, enum noside noside);
 929
 930 extern struct value *evaluate_subexpression_type (struct expression *exp,
 931                                                   int subexp);
 932
 933 extern value *evaluate_var_value (enum noside noside, const block *blk,
 934                                   symbol *var);
 935
 936 extern value *evaluate_var_msym_value (enum noside noside,
 937                                        struct objfile *objfile,
 938                                        minimal_symbol *msymbol);
 939
 940 extern value *eval_skip_value (expression *exp);
 941
 942 extern void fetch_subexp_value (struct expression *exp, int *pc,
 943                                 struct value **valp, struct value **resultp,
 944                                 std::vector<value_ref_ptr> *val_chain,
 945                                 int preserve_errors);
 946
 947 extern const char *extract_field_op (struct expression *exp, int *subexp);
 948
 949 extern struct value *evaluate_subexp_with_coercion (struct expression *,
 950                                                     int *, enum noside);
 951
 952 extern struct value *parse_and_eval (const char *exp);
 953
 954 extern struct value *parse_to_comma_and_eval (const char **expp);
 955
 956 extern struct type *parse_and_eval_type (char *p, int length);
 957
 958 extern CORE_ADDR parse_and_eval_address (const char *exp);
 959
 960 extern LONGEST parse_and_eval_long (const char *exp);
 961
 962 extern void unop_promote (const struct language_defn *language,
 963                           struct gdbarch *gdbarch,
 964                           struct value **arg1);
 965
 966 extern void binop_promote (const struct language_defn *language,
 967                            struct gdbarch *gdbarch,
 968                            struct value **arg1, struct value **arg2);
 969
 970 extern struct value *access_value_history (int num);
 971
 972 extern struct value *value_of_internalvar (struct gdbarch *gdbarch,
 973                                            struct internalvar *var);
 974
 975 extern int get_internalvar_integer (struct internalvar *var, LONGEST *l);
 976
 977 extern void set_internalvar (struct internalvar *var, struct value *val);
 978
 979 extern void set_internalvar_integer (struct internalvar *var, LONGEST l);
 980
 981 extern void set_internalvar_string (struct internalvar *var,
 982                                     const char *string);
 983
 984 extern void clear_internalvar (struct internalvar *var);
 985
 986 extern void set_internalvar_component (struct internalvar *var,
 987                                        LONGEST offset,
 988                                        LONGEST bitpos, LONGEST bitsize,
 989                                        struct value *newvalue);
 990
 991 extern struct internalvar *lookup_only_internalvar (const char *name);
 992
 993 extern struct internalvar *create_internalvar (const char *name);
 994
 995 extern void complete_internalvar (completion_tracker &tracker,
 996                                   const char *name);
 997
 998 /* An internalvar can be dynamically computed by supplying a vector of
 999    function pointers to perform various operations.  */
1000
1001 struct internalvar_funcs
1002 {
1003   /* Compute the value of the variable.  The DATA argument passed to
1004      the function is the same argument that was passed to
1005      `create_internalvar_type_lazy'.  */
1006
1007   struct value *(*make_value) (struct gdbarch *arch,
1008                                struct internalvar *var,
1009                                void *data);
1010
1011   /* Update the agent expression EXPR with bytecode to compute the
1012      value.  VALUE is the agent value we are updating.  The DATA
1013      argument passed to this function is the same argument that was
1014      passed to `create_internalvar_type_lazy'.  If this pointer is
1015      NULL, then the internalvar cannot be compiled to an agent
1016      expression.  */
1017
1018   void (*compile_to_ax) (struct internalvar *var,
1019                          struct agent_expr *expr,
1020                          struct axs_value *value,
1021                          void *data);
1022
1023   /* If non-NULL, this is called to destroy DATA.  The DATA argument
1024      passed to this function is the same argument that was passed to
1025      `create_internalvar_type_lazy'.  */
1026
1027   void (*destroy) (void *data);
1028 };
1029
1030 extern struct internalvar *create_internalvar_type_lazy (const char *name,
1031                                 const struct internalvar_funcs *funcs,
1032                                 void *data);
1033
1034 /* Compile an internal variable to an agent expression.  VAR is the
1035    variable to compile; EXPR and VALUE are the agent expression we are
1036    updating.  This will return 0 if there is no known way to compile
1037    VAR, and 1 if VAR was successfully compiled.  It may also throw an
1038    exception on error.  */
1039
1040 extern int compile_internalvar_to_ax (struct internalvar *var,
1041                                       struct agent_expr *expr,
1042                                       struct axs_value *value);
1043
1044 extern struct internalvar *lookup_internalvar (const char *name);
1045
1046 extern int value_equal (struct value *arg1, struct value *arg2);
1047
1048 extern int value_equal_contents (struct value *arg1, struct value *arg2);
1049
1050 extern int value_less (struct value *arg1, struct value *arg2);
1051
1052 extern int value_logical_not (struct value *arg1);
1053
1054 /* C++ */
1055
1056 extern struct value *value_of_this (const struct language_defn *lang);
1057
1058 extern struct value *value_of_this_silent (const struct language_defn *lang);
1059
1060 extern struct value *value_x_binop (struct value *arg1, struct value *arg2,
1061                                     enum exp_opcode op,
1062                                     enum exp_opcode otherop,
1063                                     enum noside noside);
1064
1065 extern struct value *value_x_unop (struct value *arg1, enum exp_opcode op,
1066                                    enum noside noside);
1067
1068 extern struct value *value_fn_field (struct value **arg1p, struct fn_field *f,
1069                                      int j, struct type *type, LONGEST offset);
1070
1071 extern int binop_types_user_defined_p (enum exp_opcode op,
1072                                        struct type *type1,
1073                                        struct type *type2);
1074
1075 extern int binop_user_defined_p (enum exp_opcode op, struct value *arg1,
1076                                  struct value *arg2);
1077
1078 extern int unop_user_defined_p (enum exp_opcode op, struct value *arg1);
1079
1080 extern int destructor_name_p (const char *name, struct type *type);
1081
1082 extern value_ref_ptr release_value (struct value *val);
1083
1084 extern int record_latest_value (struct value *val);
1085
1086 extern void modify_field (struct type *type, gdb_byte *addr,
1087                           LONGEST fieldval, LONGEST bitpos, LONGEST bitsize);
1088
1089 extern void type_print (struct type *type, const char *varstring,
1090                         struct ui_file *stream, int show);
1091
1092 extern std::string type_to_string (struct type *type);
1093
1094 extern gdb_byte *baseclass_addr (struct type *type, int index,
1095                                  gdb_byte *valaddr,
1096                                  struct value **valuep, int *errp);
1097
1098 extern void print_longest (struct ui_file *stream, int format,
1099                            int use_local, LONGEST val);
1100
1101 extern void print_floating (const gdb_byte *valaddr, struct type *type,
1102                             struct ui_file *stream);
1103
1104 extern void value_print (struct value *val, struct ui_file *stream,
1105                          const struct value_print_options *options);
1106
1107 extern void value_print_array_elements (struct value *val,
1108                                         struct ui_file *stream, int format,
1109                                         enum val_prettyformat pretty);
1110
1111 /* Release values from the value chain and return them.  Values
1112    created after MARK are released.  If MARK is nullptr, or if MARK is
1113    not found on the value chain, then all values are released.  Values
1114    are returned in reverse order of creation; that is, newest
1115    first.  */
1116
1117 extern std::vector<value_ref_ptr> value_release_to_mark
1118     (const struct value *mark);
1119
1120 extern void common_val_print (struct value *val,
1121                               struct ui_file *stream, int recurse,
1122                               const struct value_print_options *options,
1123                               const struct language_defn *language);
1124
1125 extern int val_print_string (struct type *elttype, const char *encoding,
1126                              CORE_ADDR addr, int len,
1127                              struct ui_file *stream,
1128                              const struct value_print_options *options);
1129
1130 extern void print_variable_and_value (const char *name,
1131                                       struct symbol *var,
1132                                       struct frame_info *frame,
1133                                       struct ui_file *stream,
1134                                       int indent);
1135
1136 extern void typedef_print (struct type *type, struct symbol *news,
1137                            struct ui_file *stream);
1138
1139 extern char *internalvar_name (const struct internalvar *var);
1140
1141 extern void preserve_values (struct objfile *);
1142
1143 /* From values.c */
1144
1145 extern struct value *value_copy (struct value *);
1146
1147 extern struct value *value_non_lval (struct value *);
1148
1149 extern void value_force_lval (struct value *, CORE_ADDR);
1150
1151 extern struct value *make_cv_value (int, int, struct value *);
1152
1153 extern void preserve_one_value (struct value *, struct objfile *, htab_t);
1154
1155 /* From valops.c */
1156
1157 extern struct value *varying_to_slice (struct value *);
1158
1159 extern struct value *value_slice (struct value *, int, int);
1160
1161 /* Create a complex number.  The type is the complex type; the values
1162    are cast to the underlying scalar type before the complex number is
1163    created.  */
1164
1165 extern struct value *value_literal_complex (struct value *, struct value *,
1166                                             struct type *);
1167
1168 /* Return the real part of a complex value.  */
1169
1170 extern struct value *value_real_part (struct value *value);
1171
1172 /* Return the imaginary part of a complex value.  */
1173
1174 extern struct value *value_imaginary_part (struct value *value);
1175
1176 extern struct value *find_function_in_inferior (const char *,
1177                                                 struct objfile **);
1178
1179 extern struct value *value_allocate_space_in_inferior (int);
1180
1181 extern struct value *value_subscripted_rvalue (struct value *array,
1182                                                LONGEST index,
1183                                                LONGEST lowerbound);
1184
1185 /* User function handler.  */
1186
1187 typedef struct value *(*internal_function_fn) (struct gdbarch *gdbarch,
1188                                                const struct language_defn *language,
1189                                                void *cookie,
1190                                                int argc,
1191                                                struct value **argv);
1192
1193 /* Add a new internal function.  NAME is the name of the function; DOC
1194    is a documentation string describing the function.  HANDLER is
1195    called when the function is invoked.  COOKIE is an arbitrary
1196    pointer which is passed to HANDLER and is intended for "user
1197    data".  */
1198
1199 extern void add_internal_function (const char *name, const char *doc,
1200                                    internal_function_fn handler,
1201                                    void *cookie);
1202
1203 /* This overload takes an allocated documentation string.  */
1204
1205 extern void add_internal_function (gdb::unique_xmalloc_ptr<char> &&name,
1206                                    gdb::unique_xmalloc_ptr<char> &&doc,
1207                                    internal_function_fn handler,
1208                                    void *cookie);
1209
1210 struct value *call_internal_function (struct gdbarch *gdbarch,
1211                                       const struct language_defn *language,
1212                                       struct value *function,
1213                                       int argc, struct value **argv);
1214
1215 char *value_internal_function_name (struct value *);
1216
1217 /* Build a value wrapping and representing WORKER.  The value takes ownership
1218    of the xmethod_worker object.  */
1219
1220 extern struct value *value_from_xmethod (xmethod_worker_up &&worker);
1221
1222 extern struct type *result_type_of_xmethod (struct value *method,
1223                                             gdb::array_view<value *> argv);
1224
1225 extern struct value *call_xmethod (struct value *method,
1226                                    gdb::array_view<value *> argv);
1227
1228 /* Destroy the values currently allocated.  This is called when GDB is
1229    exiting (e.g., on quit_force).  */
1230 extern void finalize_values ();
1231
1232 #endif /* !defined (VALUE_H) */