1 /* Low level packing and unpacking of values for GDB, the GNU Debugger.
3 Copyright (C) 1986, 1987, 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995,
4 1996, 1997, 1998, 1999, 2000, 2002, 2003, 2004, 2005, 2006, 2007, 2008
5 Free Software Foundation, Inc.
7 This file is part of GDB.
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.
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.
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/>. */
23 #include "gdb_string.h"
34 #include "gdb_assert.h"
40 #include "python/python.h"
42 /* Prototypes for exported functions. */
44 void _initialize_values (void);
48 /* Type of value; either not an lval, or one of the various
49 different possible kinds of lval. */
52 /* Is it modifiable? Only relevant if lval != not_lval. */
55 /* Location of value (if lval). */
58 /* If lval == lval_memory, this is the address in the inferior.
59 If lval == lval_register, this is the byte offset into the
60 registers structure. */
63 /* Pointer to internal variable. */
64 struct internalvar
*internalvar
;
67 /* Describes offset of a value within lval of a structure in bytes.
68 If lval == lval_memory, this is an offset to the address. If
69 lval == lval_register, this is a further offset from
70 location.address within the registers structure. Note also the
71 member embedded_offset below. */
74 /* Only used for bitfields; number of bits contained in them. */
77 /* Only used for bitfields; position of start of field. For
78 gdbarch_bits_big_endian=0 targets, it is the position of the LSB. For
79 gdbarch_bits_big_endian=1 targets, it is the position of the MSB. */
82 /* Frame register value is relative to. This will be described in
83 the lval enum above as "lval_register". */
84 struct frame_id frame_id
;
86 /* Type of the value. */
89 /* If a value represents a C++ object, then the `type' field gives
90 the object's compile-time type. If the object actually belongs
91 to some class derived from `type', perhaps with other base
92 classes and additional members, then `type' is just a subobject
93 of the real thing, and the full object is probably larger than
96 If `type' is a dynamic class (i.e. one with a vtable), then GDB
97 can actually determine the object's run-time type by looking at
98 the run-time type information in the vtable. When this
99 information is available, we may elect to read in the entire
100 object, for several reasons:
102 - When printing the value, the user would probably rather see the
103 full object, not just the limited portion apparent from the
106 - If `type' has virtual base classes, then even printing `type'
107 alone may require reaching outside the `type' portion of the
108 object to wherever the virtual base class has been stored.
110 When we store the entire object, `enclosing_type' is the run-time
111 type -- the complete object -- and `embedded_offset' is the
112 offset of `type' within that larger type, in bytes. The
113 value_contents() macro takes `embedded_offset' into account, so
114 most GDB code continues to see the `type' portion of the value,
115 just as the inferior would.
117 If `type' is a pointer to an object, then `enclosing_type' is a
118 pointer to the object's run-time type, and `pointed_to_offset' is
119 the offset in bytes from the full object to the pointed-to object
120 -- that is, the value `embedded_offset' would have if we followed
121 the pointer and fetched the complete object. (I don't really see
122 the point. Why not just determine the run-time type when you
123 indirect, and avoid the special case? The contents don't matter
124 until you indirect anyway.)
126 If we're not doing anything fancy, `enclosing_type' is equal to
127 `type', and `embedded_offset' is zero, so everything works
129 struct type
*enclosing_type
;
131 int pointed_to_offset
;
133 /* Values are stored in a chain, so that they can be deleted easily
134 over calls to the inferior. Values assigned to internal
135 variables, put into the value history or exposed to Python are
136 taken off this list. */
139 /* Register number if the value is from a register. */
142 /* If zero, contents of this value are in the contents field. If
143 nonzero, contents are in inferior. If the lval field is lval_memory,
144 the contents are in inferior memory at location.address plus offset.
145 The lval field may also be lval_register.
147 WARNING: This field is used by the code which handles watchpoints
148 (see breakpoint.c) to decide whether a particular value can be
149 watched by hardware watchpoints. If the lazy flag is set for
150 some member of a value chain, it is assumed that this member of
151 the chain doesn't need to be watched as part of watching the
152 value itself. This is how GDB avoids watching the entire struct
153 or array when the user wants to watch a single struct member or
154 array element. If you ever change the way lazy flag is set and
155 reset, be sure to consider this use as well! */
158 /* If nonzero, this is the value of a variable which does not
159 actually exist in the program. */
162 /* If value is a variable, is it initialized or not. */
165 /* Actual contents of the value. For use of this value; setting it
166 uses the stuff above. Not valid if lazy is nonzero. Target
167 byte-order. We force it to be aligned properly for any possible
168 value. Note that a value therefore extends beyond what is
172 gdb_byte contents
[1];
173 DOUBLEST force_doublest_align
;
174 LONGEST force_longest_align
;
175 CORE_ADDR force_core_addr_align
;
176 void *force_pointer_align
;
178 /* Do not add any new members here -- contents above will trash
182 /* Prototypes for local functions. */
184 static void show_values (char *, int);
186 static void show_convenience (char *, int);
189 /* The value-history records all the values printed
190 by print commands during this session. Each chunk
191 records 60 consecutive values. The first chunk on
192 the chain records the most recent values.
193 The total number of values is in value_history_count. */
195 #define VALUE_HISTORY_CHUNK 60
197 struct value_history_chunk
199 struct value_history_chunk
*next
;
200 struct value
*values
[VALUE_HISTORY_CHUNK
];
203 /* Chain of chunks now in use. */
205 static struct value_history_chunk
*value_history_chain
;
207 static int value_history_count
; /* Abs number of last entry stored */
209 /* List of all value objects currently allocated
210 (except for those released by calls to release_value)
211 This is so they can be freed after each command. */
213 static struct value
*all_values
;
215 /* Allocate a value that has the correct length for type TYPE. */
218 allocate_value (struct type
*type
)
221 struct type
*atype
= check_typedef (type
);
223 val
= (struct value
*) xzalloc (sizeof (struct value
) + TYPE_LENGTH (atype
));
224 val
->next
= all_values
;
227 val
->enclosing_type
= type
;
228 VALUE_LVAL (val
) = not_lval
;
229 VALUE_ADDRESS (val
) = 0;
230 VALUE_FRAME_ID (val
) = null_frame_id
;
234 VALUE_REGNUM (val
) = -1;
236 val
->optimized_out
= 0;
237 val
->embedded_offset
= 0;
238 val
->pointed_to_offset
= 0;
240 val
->initialized
= 1; /* Default to initialized. */
244 /* Allocate a value that has the correct length
245 for COUNT repetitions of type TYPE. */
248 allocate_repeat_value (struct type
*type
, int count
)
250 int low_bound
= current_language
->string_lower_bound
; /* ??? */
251 /* FIXME-type-allocation: need a way to free this type when we are
253 struct type
*range_type
254 = create_range_type ((struct type
*) NULL
, builtin_type_int32
,
255 low_bound
, count
+ low_bound
- 1);
256 /* FIXME-type-allocation: need a way to free this type when we are
258 return allocate_value (create_array_type ((struct type
*) NULL
,
262 /* Needed if another module needs to maintain its on list of values. */
264 value_prepend_to_list (struct value
**head
, struct value
*val
)
270 /* Needed if another module needs to maintain its on list of values. */
272 value_remove_from_list (struct value
**head
, struct value
*val
)
277 *head
= (*head
)->next
;
279 for (prev
= *head
; prev
->next
; prev
= prev
->next
)
280 if (prev
->next
== val
)
282 prev
->next
= val
->next
;
287 /* Accessor methods. */
290 value_next (struct value
*value
)
296 value_type (struct value
*value
)
301 deprecated_set_value_type (struct value
*value
, struct type
*type
)
307 value_offset (struct value
*value
)
309 return value
->offset
;
312 set_value_offset (struct value
*value
, int offset
)
314 value
->offset
= offset
;
318 value_bitpos (struct value
*value
)
320 return value
->bitpos
;
323 set_value_bitpos (struct value
*value
, int bit
)
329 value_bitsize (struct value
*value
)
331 return value
->bitsize
;
334 set_value_bitsize (struct value
*value
, int bit
)
336 value
->bitsize
= bit
;
340 value_contents_raw (struct value
*value
)
342 return value
->aligner
.contents
+ value
->embedded_offset
;
346 value_contents_all_raw (struct value
*value
)
348 return value
->aligner
.contents
;
352 value_enclosing_type (struct value
*value
)
354 return value
->enclosing_type
;
358 value_contents_all (struct value
*value
)
361 value_fetch_lazy (value
);
362 return value
->aligner
.contents
;
366 value_lazy (struct value
*value
)
372 set_value_lazy (struct value
*value
, int val
)
378 value_contents (struct value
*value
)
380 return value_contents_writeable (value
);
384 value_contents_writeable (struct value
*value
)
387 value_fetch_lazy (value
);
388 return value_contents_raw (value
);
391 /* Return non-zero if VAL1 and VAL2 have the same contents. Note that
392 this function is different from value_equal; in C the operator ==
393 can return 0 even if the two values being compared are equal. */
396 value_contents_equal (struct value
*val1
, struct value
*val2
)
402 type1
= check_typedef (value_type (val1
));
403 type2
= check_typedef (value_type (val2
));
404 len
= TYPE_LENGTH (type1
);
405 if (len
!= TYPE_LENGTH (type2
))
408 return (memcmp (value_contents (val1
), value_contents (val2
), len
) == 0);
412 value_optimized_out (struct value
*value
)
414 return value
->optimized_out
;
418 set_value_optimized_out (struct value
*value
, int val
)
420 value
->optimized_out
= val
;
424 value_embedded_offset (struct value
*value
)
426 return value
->embedded_offset
;
430 set_value_embedded_offset (struct value
*value
, int val
)
432 value
->embedded_offset
= val
;
436 value_pointed_to_offset (struct value
*value
)
438 return value
->pointed_to_offset
;
442 set_value_pointed_to_offset (struct value
*value
, int val
)
444 value
->pointed_to_offset
= val
;
448 deprecated_value_lval_hack (struct value
*value
)
454 deprecated_value_address_hack (struct value
*value
)
456 return &value
->location
.address
;
459 struct internalvar
**
460 deprecated_value_internalvar_hack (struct value
*value
)
462 return &value
->location
.internalvar
;
466 deprecated_value_frame_id_hack (struct value
*value
)
468 return &value
->frame_id
;
472 deprecated_value_regnum_hack (struct value
*value
)
474 return &value
->regnum
;
478 deprecated_value_modifiable (struct value
*value
)
480 return value
->modifiable
;
483 deprecated_set_value_modifiable (struct value
*value
, int modifiable
)
485 value
->modifiable
= modifiable
;
488 /* Return a mark in the value chain. All values allocated after the
489 mark is obtained (except for those released) are subject to being freed
490 if a subsequent value_free_to_mark is passed the mark. */
497 /* Free all values allocated since MARK was obtained by value_mark
498 (except for those released). */
500 value_free_to_mark (struct value
*mark
)
505 for (val
= all_values
; val
&& val
!= mark
; val
= next
)
513 /* Free all the values that have been allocated (except for those released).
514 Called after each command, successful or not. */
517 free_all_values (void)
522 for (val
= all_values
; val
; val
= next
)
531 /* Remove VAL from the chain all_values
532 so it will not be freed automatically. */
535 release_value (struct value
*val
)
539 if (all_values
== val
)
541 all_values
= val
->next
;
545 for (v
= all_values
; v
; v
= v
->next
)
555 /* Release all values up to mark */
557 value_release_to_mark (struct value
*mark
)
562 for (val
= next
= all_values
; next
; next
= next
->next
)
563 if (next
->next
== mark
)
565 all_values
= next
->next
;
573 /* Return a copy of the value ARG.
574 It contains the same contents, for same memory address,
575 but it's a different block of storage. */
578 value_copy (struct value
*arg
)
580 struct type
*encl_type
= value_enclosing_type (arg
);
581 struct value
*val
= allocate_value (encl_type
);
582 val
->type
= arg
->type
;
583 VALUE_LVAL (val
) = VALUE_LVAL (arg
);
584 val
->location
= arg
->location
;
585 val
->offset
= arg
->offset
;
586 val
->bitpos
= arg
->bitpos
;
587 val
->bitsize
= arg
->bitsize
;
588 VALUE_FRAME_ID (val
) = VALUE_FRAME_ID (arg
);
589 VALUE_REGNUM (val
) = VALUE_REGNUM (arg
);
590 val
->lazy
= arg
->lazy
;
591 val
->optimized_out
= arg
->optimized_out
;
592 val
->embedded_offset
= value_embedded_offset (arg
);
593 val
->pointed_to_offset
= arg
->pointed_to_offset
;
594 val
->modifiable
= arg
->modifiable
;
595 if (!value_lazy (val
))
597 memcpy (value_contents_all_raw (val
), value_contents_all_raw (arg
),
598 TYPE_LENGTH (value_enclosing_type (arg
)));
604 /* Access to the value history. */
606 /* Record a new value in the value history.
607 Returns the absolute history index of the entry.
608 Result of -1 indicates the value was not saved; otherwise it is the
609 value history index of this new item. */
612 record_latest_value (struct value
*val
)
616 /* We don't want this value to have anything to do with the inferior anymore.
617 In particular, "set $1 = 50" should not affect the variable from which
618 the value was taken, and fast watchpoints should be able to assume that
619 a value on the value history never changes. */
620 if (value_lazy (val
))
621 value_fetch_lazy (val
);
622 /* We preserve VALUE_LVAL so that the user can find out where it was fetched
623 from. This is a bit dubious, because then *&$1 does not just return $1
624 but the current contents of that location. c'est la vie... */
628 /* Here we treat value_history_count as origin-zero
629 and applying to the value being stored now. */
631 i
= value_history_count
% VALUE_HISTORY_CHUNK
;
634 struct value_history_chunk
*new
635 = (struct value_history_chunk
*)
636 xmalloc (sizeof (struct value_history_chunk
));
637 memset (new->values
, 0, sizeof new->values
);
638 new->next
= value_history_chain
;
639 value_history_chain
= new;
642 value_history_chain
->values
[i
] = val
;
644 /* Now we regard value_history_count as origin-one
645 and applying to the value just stored. */
647 return ++value_history_count
;
650 /* Return a copy of the value in the history with sequence number NUM. */
653 access_value_history (int num
)
655 struct value_history_chunk
*chunk
;
660 absnum
+= value_history_count
;
665 error (_("The history is empty."));
667 error (_("There is only one value in the history."));
669 error (_("History does not go back to $$%d."), -num
);
671 if (absnum
> value_history_count
)
672 error (_("History has not yet reached $%d."), absnum
);
676 /* Now absnum is always absolute and origin zero. */
678 chunk
= value_history_chain
;
679 for (i
= (value_history_count
- 1) / VALUE_HISTORY_CHUNK
- absnum
/ VALUE_HISTORY_CHUNK
;
683 return value_copy (chunk
->values
[absnum
% VALUE_HISTORY_CHUNK
]);
687 show_values (char *num_exp
, int from_tty
)
695 /* "show values +" should print from the stored position.
696 "show values <exp>" should print around value number <exp>. */
697 if (num_exp
[0] != '+' || num_exp
[1] != '\0')
698 num
= parse_and_eval_long (num_exp
) - 5;
702 /* "show values" means print the last 10 values. */
703 num
= value_history_count
- 9;
709 for (i
= num
; i
< num
+ 10 && i
<= value_history_count
; i
++)
711 val
= access_value_history (i
);
712 printf_filtered (("$%d = "), i
);
713 value_print (val
, gdb_stdout
, 0, Val_pretty_default
);
714 printf_filtered (("\n"));
717 /* The next "show values +" should start after what we just printed. */
720 /* Hitting just return after this command should do the same thing as
721 "show values +". If num_exp is null, this is unnecessary, since
722 "show values +" is not useful after "show values". */
723 if (from_tty
&& num_exp
)
730 /* Internal variables. These are variables within the debugger
731 that hold values assigned by debugger commands.
732 The user refers to them with a '$' prefix
733 that does not appear in the variable names stored internally. */
735 static struct internalvar
*internalvars
;
737 /* If the variable does not already exist create it and give it the value given.
738 If no value is given then the default is zero. */
740 init_if_undefined_command (char* args
, int from_tty
)
742 struct internalvar
* intvar
;
744 /* Parse the expression - this is taken from set_command(). */
745 struct expression
*expr
= parse_expression (args
);
746 register struct cleanup
*old_chain
=
747 make_cleanup (free_current_contents
, &expr
);
749 /* Validate the expression.
750 Was the expression an assignment?
751 Or even an expression at all? */
752 if (expr
->nelts
== 0 || expr
->elts
[0].opcode
!= BINOP_ASSIGN
)
753 error (_("Init-if-undefined requires an assignment expression."));
755 /* Extract the variable from the parsed expression.
756 In the case of an assign the lvalue will be in elts[1] and elts[2]. */
757 if (expr
->elts
[1].opcode
!= OP_INTERNALVAR
)
758 error (_("The first parameter to init-if-undefined should be a GDB variable."));
759 intvar
= expr
->elts
[2].internalvar
;
761 /* Only evaluate the expression if the lvalue is void.
762 This may still fail if the expresssion is invalid. */
763 if (TYPE_CODE (value_type (intvar
->value
)) == TYPE_CODE_VOID
)
764 evaluate_expression (expr
);
766 do_cleanups (old_chain
);
770 /* Look up an internal variable with name NAME. NAME should not
771 normally include a dollar sign.
773 If the specified internal variable does not exist,
774 the return value is NULL. */
777 lookup_only_internalvar (char *name
)
779 struct internalvar
*var
;
781 for (var
= internalvars
; var
; var
= var
->next
)
782 if (strcmp (var
->name
, name
) == 0)
789 /* Create an internal variable with name NAME and with a void value.
790 NAME should not normally include a dollar sign. */
793 create_internalvar (char *name
)
795 struct internalvar
*var
;
796 var
= (struct internalvar
*) xmalloc (sizeof (struct internalvar
));
797 var
->name
= concat (name
, (char *)NULL
);
798 var
->value
= allocate_value (builtin_type_void
);
799 var
->endian
= gdbarch_byte_order (current_gdbarch
);
800 release_value (var
->value
);
801 var
->next
= internalvars
;
807 /* Look up an internal variable with name NAME. NAME should not
808 normally include a dollar sign.
810 If the specified internal variable does not exist,
811 one is created, with a void value. */
814 lookup_internalvar (char *name
)
816 struct internalvar
*var
;
818 var
= lookup_only_internalvar (name
);
822 return create_internalvar (name
);
826 value_of_internalvar (struct internalvar
*var
)
832 val
= value_copy (var
->value
);
833 if (value_lazy (val
))
834 value_fetch_lazy (val
);
835 VALUE_LVAL (val
) = lval_internalvar
;
836 VALUE_INTERNALVAR (val
) = var
;
838 /* Values are always stored in the target's byte order. When connected to a
839 target this will most likely always be correct, so there's normally no
840 need to worry about it.
842 However, internal variables can be set up before the target endian is
843 known and so may become out of date. Fix it up before anybody sees.
845 Internal variables usually hold simple scalar values, and we can
846 correct those. More complex values (e.g. structures and floating
847 point types) are left alone, because they would be too complicated
850 if (var
->endian
!= gdbarch_byte_order (current_gdbarch
))
852 gdb_byte
*array
= value_contents_raw (val
);
853 struct type
*type
= check_typedef (value_enclosing_type (val
));
854 switch (TYPE_CODE (type
))
858 /* Reverse the bytes. */
859 for (i
= 0, j
= TYPE_LENGTH (type
) - 1; i
< j
; i
++, j
--)
873 set_internalvar_component (struct internalvar
*var
, int offset
, int bitpos
,
874 int bitsize
, struct value
*newval
)
876 gdb_byte
*addr
= value_contents_writeable (var
->value
) + offset
;
879 modify_field (addr
, value_as_long (newval
),
882 memcpy (addr
, value_contents (newval
), TYPE_LENGTH (value_type (newval
)));
886 set_internalvar (struct internalvar
*var
, struct value
*val
)
888 struct value
*newval
;
890 newval
= value_copy (val
);
891 newval
->modifiable
= 1;
893 /* Force the value to be fetched from the target now, to avoid problems
894 later when this internalvar is referenced and the target is gone or
896 if (value_lazy (newval
))
897 value_fetch_lazy (newval
);
899 /* Begin code which must not call error(). If var->value points to
900 something free'd, an error() obviously leaves a dangling pointer.
901 But we also get a danling pointer if var->value points to
902 something in the value chain (i.e., before release_value is
903 called), because after the error free_all_values will get called before
907 var
->endian
= gdbarch_byte_order (current_gdbarch
);
908 release_value (newval
);
909 /* End code which must not call error(). */
913 internalvar_name (struct internalvar
*var
)
918 /* Update VALUE before discarding OBJFILE. COPIED_TYPES is used to
919 prevent cycles / duplicates. */
922 preserve_one_value (struct value
*value
, struct objfile
*objfile
,
925 if (TYPE_OBJFILE (value
->type
) == objfile
)
926 value
->type
= copy_type_recursive (objfile
, value
->type
, copied_types
);
928 if (TYPE_OBJFILE (value
->enclosing_type
) == objfile
)
929 value
->enclosing_type
= copy_type_recursive (objfile
,
930 value
->enclosing_type
,
934 /* Update the internal variables and value history when OBJFILE is
935 discarded; we must copy the types out of the objfile. New global types
936 will be created for every convenience variable which currently points to
937 this objfile's types, and the convenience variables will be adjusted to
938 use the new global types. */
941 preserve_values (struct objfile
*objfile
)
944 struct value_history_chunk
*cur
;
945 struct internalvar
*var
;
949 /* Create the hash table. We allocate on the objfile's obstack, since
950 it is soon to be deleted. */
951 copied_types
= create_copied_types_hash (objfile
);
953 for (cur
= value_history_chain
; cur
; cur
= cur
->next
)
954 for (i
= 0; i
< VALUE_HISTORY_CHUNK
; i
++)
956 preserve_one_value (cur
->values
[i
], objfile
, copied_types
);
958 for (var
= internalvars
; var
; var
= var
->next
)
959 preserve_one_value (var
->value
, objfile
, copied_types
);
961 for (val
= values_in_python
; val
; val
= val
->next
)
962 preserve_one_value (val
, objfile
, copied_types
);
964 htab_delete (copied_types
);
968 show_convenience (char *ignore
, int from_tty
)
970 struct internalvar
*var
;
973 for (var
= internalvars
; var
; var
= var
->next
)
979 printf_filtered (("$%s = "), var
->name
);
980 value_print (value_of_internalvar (var
), gdb_stdout
,
981 0, Val_pretty_default
);
982 printf_filtered (("\n"));
985 printf_unfiltered (_("\
986 No debugger convenience variables now defined.\n\
987 Convenience variables have names starting with \"$\";\n\
988 use \"set\" as in \"set $foo = 5\" to define them.\n"));
991 /* Extract a value as a C number (either long or double).
992 Knows how to convert fixed values to double, or
993 floating values to long.
994 Does not deallocate the value. */
997 value_as_long (struct value
*val
)
999 /* This coerces arrays and functions, which is necessary (e.g.
1000 in disassemble_command). It also dereferences references, which
1001 I suspect is the most logical thing to do. */
1002 val
= coerce_array (val
);
1003 return unpack_long (value_type (val
), value_contents (val
));
1007 value_as_double (struct value
*val
)
1012 foo
= unpack_double (value_type (val
), value_contents (val
), &inv
);
1014 error (_("Invalid floating value found in program."));
1018 /* Extract a value as a C pointer. Does not deallocate the value.
1019 Note that val's type may not actually be a pointer; value_as_long
1020 handles all the cases. */
1022 value_as_address (struct value
*val
)
1024 /* Assume a CORE_ADDR can fit in a LONGEST (for now). Not sure
1025 whether we want this to be true eventually. */
1027 /* gdbarch_addr_bits_remove is wrong if we are being called for a
1028 non-address (e.g. argument to "signal", "info break", etc.), or
1029 for pointers to char, in which the low bits *are* significant. */
1030 return gdbarch_addr_bits_remove (current_gdbarch
, value_as_long (val
));
1033 /* There are several targets (IA-64, PowerPC, and others) which
1034 don't represent pointers to functions as simply the address of
1035 the function's entry point. For example, on the IA-64, a
1036 function pointer points to a two-word descriptor, generated by
1037 the linker, which contains the function's entry point, and the
1038 value the IA-64 "global pointer" register should have --- to
1039 support position-independent code. The linker generates
1040 descriptors only for those functions whose addresses are taken.
1042 On such targets, it's difficult for GDB to convert an arbitrary
1043 function address into a function pointer; it has to either find
1044 an existing descriptor for that function, or call malloc and
1045 build its own. On some targets, it is impossible for GDB to
1046 build a descriptor at all: the descriptor must contain a jump
1047 instruction; data memory cannot be executed; and code memory
1050 Upon entry to this function, if VAL is a value of type `function'
1051 (that is, TYPE_CODE (VALUE_TYPE (val)) == TYPE_CODE_FUNC), then
1052 VALUE_ADDRESS (val) is the address of the function. This is what
1053 you'll get if you evaluate an expression like `main'. The call
1054 to COERCE_ARRAY below actually does all the usual unary
1055 conversions, which includes converting values of type `function'
1056 to `pointer to function'. This is the challenging conversion
1057 discussed above. Then, `unpack_long' will convert that pointer
1058 back into an address.
1060 So, suppose the user types `disassemble foo' on an architecture
1061 with a strange function pointer representation, on which GDB
1062 cannot build its own descriptors, and suppose further that `foo'
1063 has no linker-built descriptor. The address->pointer conversion
1064 will signal an error and prevent the command from running, even
1065 though the next step would have been to convert the pointer
1066 directly back into the same address.
1068 The following shortcut avoids this whole mess. If VAL is a
1069 function, just return its address directly. */
1070 if (TYPE_CODE (value_type (val
)) == TYPE_CODE_FUNC
1071 || TYPE_CODE (value_type (val
)) == TYPE_CODE_METHOD
)
1072 return VALUE_ADDRESS (val
);
1074 val
= coerce_array (val
);
1076 /* Some architectures (e.g. Harvard), map instruction and data
1077 addresses onto a single large unified address space. For
1078 instance: An architecture may consider a large integer in the
1079 range 0x10000000 .. 0x1000ffff to already represent a data
1080 addresses (hence not need a pointer to address conversion) while
1081 a small integer would still need to be converted integer to
1082 pointer to address. Just assume such architectures handle all
1083 integer conversions in a single function. */
1087 I think INTEGER_TO_ADDRESS is a good idea as proposed --- but we
1088 must admonish GDB hackers to make sure its behavior matches the
1089 compiler's, whenever possible.
1091 In general, I think GDB should evaluate expressions the same way
1092 the compiler does. When the user copies an expression out of
1093 their source code and hands it to a `print' command, they should
1094 get the same value the compiler would have computed. Any
1095 deviation from this rule can cause major confusion and annoyance,
1096 and needs to be justified carefully. In other words, GDB doesn't
1097 really have the freedom to do these conversions in clever and
1100 AndrewC pointed out that users aren't complaining about how GDB
1101 casts integers to pointers; they are complaining that they can't
1102 take an address from a disassembly listing and give it to `x/i'.
1103 This is certainly important.
1105 Adding an architecture method like integer_to_address() certainly
1106 makes it possible for GDB to "get it right" in all circumstances
1107 --- the target has complete control over how things get done, so
1108 people can Do The Right Thing for their target without breaking
1109 anyone else. The standard doesn't specify how integers get
1110 converted to pointers; usually, the ABI doesn't either, but
1111 ABI-specific code is a more reasonable place to handle it. */
1113 if (TYPE_CODE (value_type (val
)) != TYPE_CODE_PTR
1114 && TYPE_CODE (value_type (val
)) != TYPE_CODE_REF
1115 && gdbarch_integer_to_address_p (current_gdbarch
))
1116 return gdbarch_integer_to_address (current_gdbarch
, value_type (val
),
1117 value_contents (val
));
1119 return unpack_long (value_type (val
), value_contents (val
));
1123 /* Unpack raw data (copied from debugee, target byte order) at VALADDR
1124 as a long, or as a double, assuming the raw data is described
1125 by type TYPE. Knows how to convert different sizes of values
1126 and can convert between fixed and floating point. We don't assume
1127 any alignment for the raw data. Return value is in host byte order.
1129 If you want functions and arrays to be coerced to pointers, and
1130 references to be dereferenced, call value_as_long() instead.
1132 C++: It is assumed that the front-end has taken care of
1133 all matters concerning pointers to members. A pointer
1134 to member which reaches here is considered to be equivalent
1135 to an INT (or some size). After all, it is only an offset. */
1138 unpack_long (struct type
*type
, const gdb_byte
*valaddr
)
1140 enum type_code code
= TYPE_CODE (type
);
1141 int len
= TYPE_LENGTH (type
);
1142 int nosign
= TYPE_UNSIGNED (type
);
1146 case TYPE_CODE_TYPEDEF
:
1147 return unpack_long (check_typedef (type
), valaddr
);
1148 case TYPE_CODE_ENUM
:
1149 case TYPE_CODE_FLAGS
:
1150 case TYPE_CODE_BOOL
:
1152 case TYPE_CODE_CHAR
:
1153 case TYPE_CODE_RANGE
:
1154 case TYPE_CODE_MEMBERPTR
:
1156 return extract_unsigned_integer (valaddr
, len
);
1158 return extract_signed_integer (valaddr
, len
);
1161 return extract_typed_floating (valaddr
, type
);
1163 case TYPE_CODE_DECFLOAT
:
1164 /* libdecnumber has a function to convert from decimal to integer, but
1165 it doesn't work when the decimal number has a fractional part. */
1166 return decimal_to_doublest (valaddr
, len
);
1170 /* Assume a CORE_ADDR can fit in a LONGEST (for now). Not sure
1171 whether we want this to be true eventually. */
1172 return extract_typed_address (valaddr
, type
);
1175 error (_("Value can't be converted to integer."));
1177 return 0; /* Placate lint. */
1180 /* Return a double value from the specified type and address.
1181 INVP points to an int which is set to 0 for valid value,
1182 1 for invalid value (bad float format). In either case,
1183 the returned double is OK to use. Argument is in target
1184 format, result is in host format. */
1187 unpack_double (struct type
*type
, const gdb_byte
*valaddr
, int *invp
)
1189 enum type_code code
;
1193 *invp
= 0; /* Assume valid. */
1194 CHECK_TYPEDEF (type
);
1195 code
= TYPE_CODE (type
);
1196 len
= TYPE_LENGTH (type
);
1197 nosign
= TYPE_UNSIGNED (type
);
1198 if (code
== TYPE_CODE_FLT
)
1200 /* NOTE: cagney/2002-02-19: There was a test here to see if the
1201 floating-point value was valid (using the macro
1202 INVALID_FLOAT). That test/macro have been removed.
1204 It turns out that only the VAX defined this macro and then
1205 only in a non-portable way. Fixing the portability problem
1206 wouldn't help since the VAX floating-point code is also badly
1207 bit-rotten. The target needs to add definitions for the
1208 methods gdbarch_float_format and gdbarch_double_format - these
1209 exactly describe the target floating-point format. The
1210 problem here is that the corresponding floatformat_vax_f and
1211 floatformat_vax_d values these methods should be set to are
1212 also not defined either. Oops!
1214 Hopefully someone will add both the missing floatformat
1215 definitions and the new cases for floatformat_is_valid (). */
1217 if (!floatformat_is_valid (floatformat_from_type (type
), valaddr
))
1223 return extract_typed_floating (valaddr
, type
);
1225 else if (code
== TYPE_CODE_DECFLOAT
)
1226 return decimal_to_doublest (valaddr
, len
);
1229 /* Unsigned -- be sure we compensate for signed LONGEST. */
1230 return (ULONGEST
) unpack_long (type
, valaddr
);
1234 /* Signed -- we are OK with unpack_long. */
1235 return unpack_long (type
, valaddr
);
1239 /* Unpack raw data (copied from debugee, target byte order) at VALADDR
1240 as a CORE_ADDR, assuming the raw data is described by type TYPE.
1241 We don't assume any alignment for the raw data. Return value is in
1244 If you want functions and arrays to be coerced to pointers, and
1245 references to be dereferenced, call value_as_address() instead.
1247 C++: It is assumed that the front-end has taken care of
1248 all matters concerning pointers to members. A pointer
1249 to member which reaches here is considered to be equivalent
1250 to an INT (or some size). After all, it is only an offset. */
1253 unpack_pointer (struct type
*type
, const gdb_byte
*valaddr
)
1255 /* Assume a CORE_ADDR can fit in a LONGEST (for now). Not sure
1256 whether we want this to be true eventually. */
1257 return unpack_long (type
, valaddr
);
1261 /* Get the value of the FIELDN'th field (which must be static) of
1262 TYPE. Return NULL if the field doesn't exist or has been
1266 value_static_field (struct type
*type
, int fieldno
)
1268 struct value
*retval
;
1270 if (TYPE_FIELD_LOC_KIND (type
, fieldno
) == FIELD_LOC_KIND_PHYSADDR
)
1272 retval
= value_at (TYPE_FIELD_TYPE (type
, fieldno
),
1273 TYPE_FIELD_STATIC_PHYSADDR (type
, fieldno
));
1277 char *phys_name
= TYPE_FIELD_STATIC_PHYSNAME (type
, fieldno
);
1278 struct symbol
*sym
= lookup_symbol (phys_name
, 0, VAR_DOMAIN
, 0);
1281 /* With some compilers, e.g. HP aCC, static data members are reported
1282 as non-debuggable symbols */
1283 struct minimal_symbol
*msym
= lookup_minimal_symbol (phys_name
, NULL
, NULL
);
1288 retval
= value_at (TYPE_FIELD_TYPE (type
, fieldno
),
1289 SYMBOL_VALUE_ADDRESS (msym
));
1294 /* SYM should never have a SYMBOL_CLASS which will require
1295 read_var_value to use the FRAME parameter. */
1296 if (symbol_read_needs_frame (sym
))
1297 warning (_("static field's value depends on the current "
1298 "frame - bad debug info?"));
1299 retval
= read_var_value (sym
, NULL
);
1301 if (retval
&& VALUE_LVAL (retval
) == lval_memory
)
1302 SET_FIELD_PHYSADDR (TYPE_FIELD (type
, fieldno
),
1303 VALUE_ADDRESS (retval
));
1308 /* Change the enclosing type of a value object VAL to NEW_ENCL_TYPE.
1309 You have to be careful here, since the size of the data area for the value
1310 is set by the length of the enclosing type. So if NEW_ENCL_TYPE is bigger
1311 than the old enclosing type, you have to allocate more space for the data.
1312 The return value is a pointer to the new version of this value structure. */
1315 value_change_enclosing_type (struct value
*val
, struct type
*new_encl_type
)
1317 if (TYPE_LENGTH (new_encl_type
) <= TYPE_LENGTH (value_enclosing_type (val
)))
1319 val
->enclosing_type
= new_encl_type
;
1324 struct value
*new_val
;
1327 new_val
= (struct value
*) xrealloc (val
, sizeof (struct value
) + TYPE_LENGTH (new_encl_type
));
1329 new_val
->enclosing_type
= new_encl_type
;
1331 /* We have to make sure this ends up in the same place in the value
1332 chain as the original copy, so it's clean-up behavior is the same.
1333 If the value has been released, this is a waste of time, but there
1334 is no way to tell that in advance, so... */
1336 if (val
!= all_values
)
1338 for (prev
= all_values
; prev
!= NULL
; prev
= prev
->next
)
1340 if (prev
->next
== val
)
1342 prev
->next
= new_val
;
1352 /* Given a value ARG1 (offset by OFFSET bytes)
1353 of a struct or union type ARG_TYPE,
1354 extract and return the value of one of its (non-static) fields.
1355 FIELDNO says which field. */
1358 value_primitive_field (struct value
*arg1
, int offset
,
1359 int fieldno
, struct type
*arg_type
)
1364 CHECK_TYPEDEF (arg_type
);
1365 type
= TYPE_FIELD_TYPE (arg_type
, fieldno
);
1367 /* Handle packed fields */
1369 if (TYPE_FIELD_BITSIZE (arg_type
, fieldno
))
1371 v
= value_from_longest (type
,
1372 unpack_field_as_long (arg_type
,
1373 value_contents (arg1
)
1376 v
->bitpos
= TYPE_FIELD_BITPOS (arg_type
, fieldno
) % 8;
1377 v
->bitsize
= TYPE_FIELD_BITSIZE (arg_type
, fieldno
);
1378 v
->offset
= value_offset (arg1
) + offset
1379 + TYPE_FIELD_BITPOS (arg_type
, fieldno
) / 8;
1381 else if (fieldno
< TYPE_N_BASECLASSES (arg_type
))
1383 /* This field is actually a base subobject, so preserve the
1384 entire object's contents for later references to virtual
1386 v
= allocate_value (value_enclosing_type (arg1
));
1389 /* Lazy register values with offsets are not supported. */
1390 if (VALUE_LVAL (arg1
) == lval_register
&& value_lazy (arg1
))
1391 value_fetch_lazy (arg1
);
1393 if (value_lazy (arg1
))
1394 set_value_lazy (v
, 1);
1396 memcpy (value_contents_all_raw (v
), value_contents_all_raw (arg1
),
1397 TYPE_LENGTH (value_enclosing_type (arg1
)));
1398 v
->offset
= value_offset (arg1
);
1399 v
->embedded_offset
= (offset
+ value_embedded_offset (arg1
)
1400 + TYPE_FIELD_BITPOS (arg_type
, fieldno
) / 8);
1404 /* Plain old data member */
1405 offset
+= TYPE_FIELD_BITPOS (arg_type
, fieldno
) / 8;
1406 v
= allocate_value (type
);
1408 /* Lazy register values with offsets are not supported. */
1409 if (VALUE_LVAL (arg1
) == lval_register
&& value_lazy (arg1
))
1410 value_fetch_lazy (arg1
);
1412 if (value_lazy (arg1
))
1413 set_value_lazy (v
, 1);
1415 memcpy (value_contents_raw (v
),
1416 value_contents_raw (arg1
) + offset
,
1417 TYPE_LENGTH (type
));
1418 v
->offset
= (value_offset (arg1
) + offset
1419 + value_embedded_offset (arg1
));
1421 VALUE_LVAL (v
) = VALUE_LVAL (arg1
);
1422 if (VALUE_LVAL (arg1
) == lval_internalvar
)
1423 VALUE_LVAL (v
) = lval_internalvar_component
;
1424 v
->location
= arg1
->location
;
1425 VALUE_REGNUM (v
) = VALUE_REGNUM (arg1
);
1426 VALUE_FRAME_ID (v
) = VALUE_FRAME_ID (arg1
);
1430 /* Given a value ARG1 of a struct or union type,
1431 extract and return the value of one of its (non-static) fields.
1432 FIELDNO says which field. */
1435 value_field (struct value
*arg1
, int fieldno
)
1437 return value_primitive_field (arg1
, 0, fieldno
, value_type (arg1
));
1440 /* Return a non-virtual function as a value.
1441 F is the list of member functions which contains the desired method.
1442 J is an index into F which provides the desired method.
1444 We only use the symbol for its address, so be happy with either a
1445 full symbol or a minimal symbol.
1449 value_fn_field (struct value
**arg1p
, struct fn_field
*f
, int j
, struct type
*type
,
1453 struct type
*ftype
= TYPE_FN_FIELD_TYPE (f
, j
);
1454 char *physname
= TYPE_FN_FIELD_PHYSNAME (f
, j
);
1456 struct minimal_symbol
*msym
;
1458 sym
= lookup_symbol (physname
, 0, VAR_DOMAIN
, 0);
1465 gdb_assert (sym
== NULL
);
1466 msym
= lookup_minimal_symbol (physname
, NULL
, NULL
);
1471 v
= allocate_value (ftype
);
1474 VALUE_ADDRESS (v
) = BLOCK_START (SYMBOL_BLOCK_VALUE (sym
));
1478 /* The minimal symbol might point to a function descriptor;
1479 resolve it to the actual code address instead. */
1480 struct objfile
*objfile
= msymbol_objfile (msym
);
1481 struct gdbarch
*gdbarch
= get_objfile_arch (objfile
);
1484 = gdbarch_convert_from_func_ptr_addr
1485 (gdbarch
, SYMBOL_VALUE_ADDRESS (msym
), ¤t_target
);
1490 if (type
!= value_type (*arg1p
))
1491 *arg1p
= value_ind (value_cast (lookup_pointer_type (type
),
1492 value_addr (*arg1p
)));
1494 /* Move the `this' pointer according to the offset.
1495 VALUE_OFFSET (*arg1p) += offset;
1503 /* Unpack a field FIELDNO of the specified TYPE, from the anonymous object at
1506 Extracting bits depends on endianness of the machine. Compute the
1507 number of least significant bits to discard. For big endian machines,
1508 we compute the total number of bits in the anonymous object, subtract
1509 off the bit count from the MSB of the object to the MSB of the
1510 bitfield, then the size of the bitfield, which leaves the LSB discard
1511 count. For little endian machines, the discard count is simply the
1512 number of bits from the LSB of the anonymous object to the LSB of the
1515 If the field is signed, we also do sign extension. */
1518 unpack_field_as_long (struct type
*type
, const gdb_byte
*valaddr
, int fieldno
)
1522 int bitpos
= TYPE_FIELD_BITPOS (type
, fieldno
);
1523 int bitsize
= TYPE_FIELD_BITSIZE (type
, fieldno
);
1525 struct type
*field_type
;
1527 val
= extract_unsigned_integer (valaddr
+ bitpos
/ 8, sizeof (val
));
1528 field_type
= TYPE_FIELD_TYPE (type
, fieldno
);
1529 CHECK_TYPEDEF (field_type
);
1531 /* Extract bits. See comment above. */
1533 if (gdbarch_bits_big_endian (current_gdbarch
))
1534 lsbcount
= (sizeof val
* 8 - bitpos
% 8 - bitsize
);
1536 lsbcount
= (bitpos
% 8);
1539 /* If the field does not entirely fill a LONGEST, then zero the sign bits.
1540 If the field is signed, and is negative, then sign extend. */
1542 if ((bitsize
> 0) && (bitsize
< 8 * (int) sizeof (val
)))
1544 valmask
= (((ULONGEST
) 1) << bitsize
) - 1;
1546 if (!TYPE_UNSIGNED (field_type
))
1548 if (val
& (valmask
^ (valmask
>> 1)))
1557 /* Modify the value of a bitfield. ADDR points to a block of memory in
1558 target byte order; the bitfield starts in the byte pointed to. FIELDVAL
1559 is the desired value of the field, in host byte order. BITPOS and BITSIZE
1560 indicate which bits (in target bit order) comprise the bitfield.
1561 Requires 0 < BITSIZE <= lbits, 0 <= BITPOS+BITSIZE <= lbits, and
1562 0 <= BITPOS, where lbits is the size of a LONGEST in bits. */
1565 modify_field (gdb_byte
*addr
, LONGEST fieldval
, int bitpos
, int bitsize
)
1568 ULONGEST mask
= (ULONGEST
) -1 >> (8 * sizeof (ULONGEST
) - bitsize
);
1570 /* If a negative fieldval fits in the field in question, chop
1571 off the sign extension bits. */
1572 if ((~fieldval
& ~(mask
>> 1)) == 0)
1575 /* Warn if value is too big to fit in the field in question. */
1576 if (0 != (fieldval
& ~mask
))
1578 /* FIXME: would like to include fieldval in the message, but
1579 we don't have a sprintf_longest. */
1580 warning (_("Value does not fit in %d bits."), bitsize
);
1582 /* Truncate it, otherwise adjoining fields may be corrupted. */
1586 oword
= extract_unsigned_integer (addr
, sizeof oword
);
1588 /* Shifting for bit field depends on endianness of the target machine. */
1589 if (gdbarch_bits_big_endian (current_gdbarch
))
1590 bitpos
= sizeof (oword
) * 8 - bitpos
- bitsize
;
1592 oword
&= ~(mask
<< bitpos
);
1593 oword
|= fieldval
<< bitpos
;
1595 store_unsigned_integer (addr
, sizeof oword
, oword
);
1598 /* Pack NUM into BUF using a target format of TYPE. */
1601 pack_long (gdb_byte
*buf
, struct type
*type
, LONGEST num
)
1605 type
= check_typedef (type
);
1606 len
= TYPE_LENGTH (type
);
1608 switch (TYPE_CODE (type
))
1611 case TYPE_CODE_CHAR
:
1612 case TYPE_CODE_ENUM
:
1613 case TYPE_CODE_FLAGS
:
1614 case TYPE_CODE_BOOL
:
1615 case TYPE_CODE_RANGE
:
1616 case TYPE_CODE_MEMBERPTR
:
1617 store_signed_integer (buf
, len
, num
);
1622 store_typed_address (buf
, type
, (CORE_ADDR
) num
);
1626 error (_("Unexpected type (%d) encountered for integer constant."),
1632 /* Convert C numbers into newly allocated values. */
1635 value_from_longest (struct type
*type
, LONGEST num
)
1637 struct value
*val
= allocate_value (type
);
1639 pack_long (value_contents_raw (val
), type
, num
);
1645 /* Create a value representing a pointer of type TYPE to the address
1648 value_from_pointer (struct type
*type
, CORE_ADDR addr
)
1650 struct value
*val
= allocate_value (type
);
1651 store_typed_address (value_contents_raw (val
), type
, addr
);
1656 /* Create a value for a string constant to be stored locally
1657 (not in the inferior's memory space, but in GDB memory).
1658 This is analogous to value_from_longest, which also does not
1659 use inferior memory. String shall NOT contain embedded nulls. */
1662 value_from_string (char *ptr
)
1665 int len
= strlen (ptr
);
1666 int lowbound
= current_language
->string_lower_bound
;
1667 struct type
*string_char_type
;
1668 struct type
*rangetype
;
1669 struct type
*stringtype
;
1671 rangetype
= create_range_type ((struct type
*) NULL
,
1673 lowbound
, len
+ lowbound
- 1);
1674 string_char_type
= language_string_char_type (current_language
,
1676 stringtype
= create_array_type ((struct type
*) NULL
,
1679 val
= allocate_value (stringtype
);
1680 memcpy (value_contents_raw (val
), ptr
, len
);
1685 value_from_double (struct type
*type
, DOUBLEST num
)
1687 struct value
*val
= allocate_value (type
);
1688 struct type
*base_type
= check_typedef (type
);
1689 enum type_code code
= TYPE_CODE (base_type
);
1690 int len
= TYPE_LENGTH (base_type
);
1692 if (code
== TYPE_CODE_FLT
)
1694 store_typed_floating (value_contents_raw (val
), base_type
, num
);
1697 error (_("Unexpected type encountered for floating constant."));
1703 value_from_decfloat (struct type
*type
, const gdb_byte
*dec
)
1705 struct value
*val
= allocate_value (type
);
1707 memcpy (value_contents_raw (val
), dec
, TYPE_LENGTH (type
));
1713 coerce_ref (struct value
*arg
)
1715 struct type
*value_type_arg_tmp
= check_typedef (value_type (arg
));
1716 if (TYPE_CODE (value_type_arg_tmp
) == TYPE_CODE_REF
)
1717 arg
= value_at_lazy (TYPE_TARGET_TYPE (value_type_arg_tmp
),
1718 unpack_pointer (value_type (arg
),
1719 value_contents (arg
)));
1724 coerce_array (struct value
*arg
)
1726 arg
= coerce_ref (arg
);
1727 if (current_language
->c_style_arrays
1728 && TYPE_CODE (value_type (arg
)) == TYPE_CODE_ARRAY
)
1729 arg
= value_coerce_array (arg
);
1730 if (TYPE_CODE (value_type (arg
)) == TYPE_CODE_FUNC
)
1731 arg
= value_coerce_function (arg
);
1736 /* Return true if the function returning the specified type is using
1737 the convention of returning structures in memory (passing in the
1738 address as a hidden first parameter). */
1741 using_struct_return (struct type
*func_type
, struct type
*value_type
)
1743 enum type_code code
= TYPE_CODE (value_type
);
1745 if (code
== TYPE_CODE_ERROR
)
1746 error (_("Function return type unknown."));
1748 if (code
== TYPE_CODE_VOID
)
1749 /* A void return value is never in memory. See also corresponding
1750 code in "print_return_value". */
1753 /* Probe the architecture for the return-value convention. */
1754 return (gdbarch_return_value (current_gdbarch
, func_type
, value_type
,
1756 != RETURN_VALUE_REGISTER_CONVENTION
);
1759 /* Set the initialized field in a value struct. */
1762 set_value_initialized (struct value
*val
, int status
)
1764 val
->initialized
= status
;
1767 /* Return the initialized field in a value struct. */
1770 value_initialized (struct value
*val
)
1772 return val
->initialized
;
1776 _initialize_values (void)
1778 add_cmd ("convenience", no_class
, show_convenience
, _("\
1779 Debugger convenience (\"$foo\") variables.\n\
1780 These variables are created when you assign them values;\n\
1781 thus, \"print $foo=1\" gives \"$foo\" the value 1. Values may be any type.\n\
1783 A few convenience variables are given values automatically:\n\
1784 \"$_\"holds the last address examined with \"x\" or \"info lines\",\n\
1785 \"$__\" holds the contents of the last address examined with \"x\"."),
1788 add_cmd ("values", no_class
, show_values
,
1789 _("Elements of value history around item number IDX (or last ten)."),
1792 add_com ("init-if-undefined", class_vars
, init_if_undefined_command
, _("\
1793 Initialize a convenience variable if necessary.\n\
1794 init-if-undefined VARIABLE = EXPRESSION\n\
1795 Set an internal VARIABLE to the result of the EXPRESSION if it does not\n\
1796 exist or does not contain a value. The EXPRESSION is not evaluated if the\n\
1797 VARIABLE is already initialized."));