path: root/gdb/valops.c

/* Perform non-arithmetic operations on values, for GDB.
   Copyright 1986, 1987, 1989, 1991, 1992 Free Software Foundation, Inc.

This file is part of GDB.

This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.  */

#include "defs.h"
#include "symtab.h"
#include "gdbtypes.h"
#include "value.h"
#include "frame.h"
#include "inferior.h"
#include "gdbcore.h"
#include "target.h"

#include <errno.h>

/* Local functions.  */

static CORE_ADDR
find_function_addr PARAMS ((value, struct type **));

static CORE_ADDR
value_push PARAMS ((CORE_ADDR, value));

static CORE_ADDR
value_arg_push PARAMS ((CORE_ADDR, value));

static value
search_struct_field PARAMS ((char *, value, int, struct type *, int));

static value
search_struct_method PARAMS ((char *, value, value *, int, int *,
			      struct type *));

static int
check_field_in PARAMS ((struct type *, const char *));


/* Cast value ARG2 to type TYPE and return as a value.
   More general than a C cast: accepts any two types of the same length,
   and if ARG2 is an lvalue it can be cast into anything at all.  */
/* In C++, casts may change pointer representations.  */

value
value_cast (type, arg2)
     struct type *type;
     register value arg2;
{
  register enum type_code code1;
  register enum type_code code2;
  register int scalar;

  /* Coerce arrays but not enums.  Enums will work as-is
     and coercing them would cause an infinite recursion.  */
  if (TYPE_CODE (VALUE_TYPE (arg2)) != TYPE_CODE_ENUM)
    COERCE_ARRAY (arg2);

  code1 = TYPE_CODE (type);
  code2 = TYPE_CODE (VALUE_TYPE (arg2));
  scalar = (code2 == TYPE_CODE_INT || code2 == TYPE_CODE_FLT
	    || code2 == TYPE_CODE_ENUM);

  if (code1 == TYPE_CODE_FLT && scalar)
    return value_from_double (type, value_as_double (arg2));
  else if ((code1 == TYPE_CODE_INT || code1 == TYPE_CODE_ENUM)
	   && (scalar || code2 == TYPE_CODE_PTR))
    return value_from_longest (type, value_as_long (arg2));
  else if (TYPE_LENGTH (type) == TYPE_LENGTH (VALUE_TYPE (arg2)))
    {
      if (code1 == TYPE_CODE_PTR && code2 == TYPE_CODE_PTR)
	{
	  /* Look in the type of the source to see if it contains the
	     type of the target as a superclass.  If so, we'll need to
	     offset the pointer rather than just change its type.  */
	  struct type *t1 = TYPE_TARGET_TYPE (type);
	  struct type *t2 = TYPE_TARGET_TYPE (VALUE_TYPE (arg2));
	  if (   TYPE_CODE (t1) == TYPE_CODE_STRUCT
	      && TYPE_CODE (t2) == TYPE_CODE_STRUCT
	      && TYPE_NAME (t1) != 0) /* if name unknown, can't have supercl */
	    {
	      value v = search_struct_field (type_name_no_tag (t1),
					     value_ind (arg2), 0, t2, 1);
	      if (v)
		{
		  v = value_addr (v);
		  VALUE_TYPE (v) = type;
		  return v;
		}
	    }
	  /* No superclass found, just fall through to change ptr type.  */
	}
      VALUE_TYPE (arg2) = type;
      return arg2;
    }
  else if (VALUE_LVAL (arg2) == lval_memory)
    {
      return value_at_lazy (type, VALUE_ADDRESS (arg2) + VALUE_OFFSET (arg2));
    }
  else if (code1 == TYPE_CODE_VOID)
    {
      return value_zero (builtin_type_void, not_lval);
    }
  else
    {
      error ("Invalid cast.");
      return 0;
    }
}

/* Create a value of type TYPE that is zero, and return it.  */

value
value_zero (type, lv)
     struct type *type;
     enum lval_type lv;
{
  register value val = allocate_value (type);

  memset (VALUE_CONTENTS (val), 0, TYPE_LENGTH (type));
  VALUE_LVAL (val) = lv;

  return val;
}

/* Return a value with type TYPE located at ADDR.  

   Call value_at only if the data needs to be fetched immediately;
   if we can be 'lazy' and defer the fetch, perhaps indefinately, call
   value_at_lazy instead.  value_at_lazy simply records the address of
   the data and sets the lazy-evaluation-required flag.  The lazy flag 
   is tested in the VALUE_CONTENTS macro, which is used if and when 
   the contents are actually required.  */

value
value_at (type, addr)
     struct type *type;
     CORE_ADDR addr;
{
  register value val = allocate_value (type);

  read_memory (addr, VALUE_CONTENTS_RAW (val), TYPE_LENGTH (type));

  VALUE_LVAL (val) = lval_memory;
  VALUE_ADDRESS (val) = addr;

  return val;
}

/* Return a lazy value with type TYPE located at ADDR (cf. value_at).  */

value
value_at_lazy (type, addr)
     struct type *type;
     CORE_ADDR addr;
{
  register value val = allocate_value (type);

  VALUE_LVAL (val) = lval_memory;
  VALUE_ADDRESS (val) = addr;
  VALUE_LAZY (val) = 1;

  return val;
}

/* Called only from the VALUE_CONTENTS macro, if the current data for
   a variable needs to be loaded into VALUE_CONTENTS(VAL).  Fetches the
   data from the user's process, and clears the lazy flag to indicate
   that the data in the buffer is valid.

   If the value is zero-length, we avoid calling read_memory, which would
   abort.  We mark the value as fetched anyway -- all 0 bytes of it.

   This function returns a value because it is used in the VALUE_CONTENTS
   macro as part of an expression, where a void would not work.  The
   value is ignored.  */

int
value_fetch_lazy (val)
     register value val;
{
  CORE_ADDR addr = VALUE_ADDRESS (val) + VALUE_OFFSET (val);

  if (TYPE_LENGTH (VALUE_TYPE (val)))
    read_memory (addr, VALUE_CONTENTS_RAW (val), 
	         TYPE_LENGTH (VALUE_TYPE (val)));
  VALUE_LAZY (val) = 0;
  return 0;
}


/* Store the contents of FROMVAL into the location of TOVAL.
   Return a new value with the location of TOVAL and contents of FROMVAL.  */

value
value_assign (toval, fromval)
     register value toval, fromval;
{
  register struct type *type = VALUE_TYPE (toval);
  register value val;
  char raw_buffer[MAX_REGISTER_RAW_SIZE];
  char virtual_buffer[MAX_REGISTER_VIRTUAL_SIZE];
  int use_buffer = 0;

  COERCE_ARRAY (fromval);
  COERCE_REF (toval);

  if (VALUE_LVAL (toval) != lval_internalvar)
    fromval = value_cast (type, fromval);

  /* If TOVAL is a special machine register requiring conversion
     of program values to a special raw format,
     convert FROMVAL's contents now, with result in `raw_buffer',
     and set USE_BUFFER to the number of bytes to write.  */

  if (VALUE_REGNO (toval) >= 0
      && REGISTER_CONVERTIBLE (VALUE_REGNO (toval)))
    {
      int regno = VALUE_REGNO (toval);
      if (VALUE_TYPE (fromval) != REGISTER_VIRTUAL_TYPE (regno))
	fromval = value_cast (REGISTER_VIRTUAL_TYPE (regno), fromval);
      memcpy (virtual_buffer, VALUE_CONTENTS (fromval),
	     REGISTER_VIRTUAL_SIZE (regno));
      target_convert_from_virtual (regno, virtual_buffer, raw_buffer);
      use_buffer = REGISTER_RAW_SIZE (regno);
    }

  switch (VALUE_LVAL (toval))
    {
    case lval_internalvar:
      set_internalvar (VALUE_INTERNALVAR (toval), fromval);
      break;

    case lval_internalvar_component:
      set_internalvar_component (VALUE_INTERNALVAR (toval),
				 VALUE_OFFSET (toval),
				 VALUE_BITPOS (toval),
				 VALUE_BITSIZE (toval),
				 fromval);
      break;

    case lval_memory:
      if (VALUE_BITSIZE (toval))
	{
	  int v;		/* FIXME, this won't work for large bitfields */
	  read_memory (VALUE_ADDRESS (toval) + VALUE_OFFSET (toval),
		       (char *) &v, sizeof v);
	  modify_field ((char *) &v, (int) value_as_long (fromval),
			VALUE_BITPOS (toval), VALUE_BITSIZE (toval));
	  write_memory (VALUE_ADDRESS (toval) + VALUE_OFFSET (toval),
			(char *)&v, sizeof v);
	}
      else if (use_buffer)
	write_memory (VALUE_ADDRESS (toval) + VALUE_OFFSET (toval),
		      raw_buffer, use_buffer);
      else
	write_memory (VALUE_ADDRESS (toval) + VALUE_OFFSET (toval),
		      VALUE_CONTENTS (fromval), TYPE_LENGTH (type));
      break;

    case lval_register:
      if (VALUE_BITSIZE (toval))
	{
	  int v;

	  read_register_bytes (VALUE_ADDRESS (toval) + VALUE_OFFSET (toval),
			       (char *) &v, sizeof v);
	  modify_field ((char *) &v, (int) value_as_long (fromval),
			VALUE_BITPOS (toval), VALUE_BITSIZE (toval));
	  write_register_bytes (VALUE_ADDRESS (toval) + VALUE_OFFSET (toval),
				(char *) &v, sizeof v);
	}
      else if (use_buffer)
	write_register_bytes (VALUE_ADDRESS (toval) + VALUE_OFFSET (toval),
			      raw_buffer, use_buffer);
      else
	write_register_bytes (VALUE_ADDRESS (toval) + VALUE_OFFSET (toval),
			      VALUE_CONTENTS (fromval), TYPE_LENGTH (type));
      break;

    case lval_reg_frame_relative:
      {
	/* value is stored in a series of registers in the frame
	   specified by the structure.  Copy that value out, modify
	   it, and copy it back in.  */
	int amount_to_copy = (VALUE_BITSIZE (toval) ? 1 : TYPE_LENGTH (type));
	int reg_size = REGISTER_RAW_SIZE (VALUE_FRAME_REGNUM (toval));
	int byte_offset = VALUE_OFFSET (toval) % reg_size;
	int reg_offset = VALUE_OFFSET (toval) / reg_size;
	int amount_copied;
	char *buffer = (char *) alloca (amount_to_copy);
	int regno;
	FRAME frame;

	/* Figure out which frame this is in currently.  */
	for (frame = get_current_frame ();
	     frame && FRAME_FP (frame) != VALUE_FRAME (toval);
	     frame = get_prev_frame (frame))
	  ;

	if (!frame)
	  error ("Value being assigned to is no longer active.");

	amount_to_copy += (reg_size - amount_to_copy % reg_size);

	/* Copy it out.  */
	for ((regno = VALUE_FRAME_REGNUM (toval) + reg_offset,
	      amount_copied = 0);
	     amount_copied < amount_to_copy;
	     amount_copied += reg_size, regno++)
	  {
	    get_saved_register (buffer + amount_copied,
				(int *)NULL, (CORE_ADDR)NULL,
				frame, regno, (enum lval_type *)NULL);
	  }

	/* Modify what needs to be modified.  */
	if (VALUE_BITSIZE (toval))
	  modify_field (buffer + byte_offset,
			(int) value_as_long (fromval),
			VALUE_BITPOS (toval), VALUE_BITSIZE (toval));
	else if (use_buffer)
	  bcopy (raw_buffer, buffer + byte_offset, use_buffer);
	else
	  bcopy (VALUE_CONTENTS (fromval), buffer + byte_offset,
		 TYPE_LENGTH (type));

	/* Copy it back.  */
	for ((regno = VALUE_FRAME_REGNUM (toval) + reg_offset,
	      amount_copied = 0);
	     amount_copied < amount_to_copy;
	     amount_copied += reg_size, regno++)
	  {
	    enum lval_type lval;
	    CORE_ADDR addr;
	    int optim;

	    /* Just find out where to put it.  */
	    get_saved_register ((char *)NULL,
			        &optim, &addr, frame, regno, &lval);
	    
	    if (optim)
	      error ("Attempt to assign to a value that was optimized out.");
	    if (lval == lval_memory)
	      write_memory (addr, buffer + amount_copied, reg_size);
	    else if (lval == lval_register)
	      write_register_bytes (addr, buffer + amount_copied, reg_size);
	    else
	      error ("Attempt to assign to an unmodifiable value.");
	  }
      }
      break;
	

    default:
      error ("Left side of = operation is not an lvalue.");
    }

  /* Return a value just like TOVAL except with the contents of FROMVAL
     (except in the case of the type if TOVAL is an internalvar).  */

  if (VALUE_LVAL (toval) == lval_internalvar
      || VALUE_LVAL (toval) == lval_internalvar_component)
    {
      type = VALUE_TYPE (fromval);
    }

  val = allocate_value (type);
  bcopy (toval, val, VALUE_CONTENTS_RAW (val) - (char *) val);
  bcopy (VALUE_CONTENTS (fromval), VALUE_CONTENTS_RAW (val), TYPE_LENGTH (type));
  VALUE_TYPE (val) = type;
  
  return val;
}

/* Extend a value VAL to COUNT repetitions of its type.  */

value
value_repeat (arg1, count)
     value arg1;
     int count;
{
  register value val;

  if (VALUE_LVAL (arg1) != lval_memory)
    error ("Only values in memory can be extended with '@'.");
  if (count < 1)
    error ("Invalid number %d of repetitions.", count);

  val = allocate_repeat_value (VALUE_TYPE (arg1), count);

  read_memory (VALUE_ADDRESS (arg1) + VALUE_OFFSET (arg1),
	       VALUE_CONTENTS_RAW (val),
	       TYPE_LENGTH (VALUE_TYPE (val)) * count);
  VALUE_LVAL (val) = lval_memory;
  VALUE_ADDRESS (val) = VALUE_ADDRESS (arg1) + VALUE_OFFSET (arg1);

  return val;
}

value
value_of_variable (var)
     struct symbol *var;
{
  value val;

  val = read_var_value (var, (FRAME) 0);
  if (val == 0)
    error ("Address of symbol \"%s\" is unknown.", SYMBOL_NAME (var));
  return val;
}

/* Given a value which is an array, return a value which is
   a pointer to its first (actually, zeroth) element. 
   FIXME, this should be subtracting the array's lower bound. */

value
value_coerce_array (arg1)
     value arg1;
{
  register struct type *type;

  if (VALUE_LVAL (arg1) != lval_memory)
    error ("Attempt to take address of value not located in memory.");

  /* Get type of elements.  */
  if (TYPE_CODE (VALUE_TYPE (arg1)) == TYPE_CODE_ARRAY)
    type = TYPE_TARGET_TYPE (VALUE_TYPE (arg1));
  else
    /* A phony array made by value_repeat.
       Its type is the type of the elements, not an array type.  */
    type = VALUE_TYPE (arg1);

  return value_from_longest (lookup_pointer_type (type),
		       (LONGEST) (VALUE_ADDRESS (arg1) + VALUE_OFFSET (arg1)));
}

/* Given a value which is a function, return a value which is a pointer
   to it.  */

value
value_coerce_function (arg1)
     value arg1;
{

  if (VALUE_LVAL (arg1) != lval_memory)
    error ("Attempt to take address of value not located in memory.");

  return value_from_longest (lookup_pointer_type (VALUE_TYPE (arg1)),
		(LONGEST) (VALUE_ADDRESS (arg1) + VALUE_OFFSET (arg1)));
}  

/* Return a pointer value for the object for which ARG1 is the contents.  */

value
value_addr (arg1)
     value arg1;
{
  struct type *type = VALUE_TYPE (arg1);
  if (TYPE_CODE (type) == TYPE_CODE_REF)
    {
      /* Copy the value, but change the type from (T&) to (T*).
	 We keep the same location information, which is efficient,
	 and allows &(&X) to get the location containing the reference. */
      value arg2 = value_copy (arg1);
      VALUE_TYPE (arg2) = lookup_pointer_type (TYPE_TARGET_TYPE (type));
      return arg2;
    }
  if (VALUE_REPEATED (arg1)
      || TYPE_CODE (type) == TYPE_CODE_ARRAY)
    return value_coerce_array (arg1);
  if (TYPE_CODE (type) == TYPE_CODE_FUNC)
    return value_coerce_function (arg1);

  if (VALUE_LVAL (arg1) != lval_memory)
    error ("Attempt to take address of value not located in memory.");

  return value_from_longest (lookup_pointer_type (type),
		(LONGEST) (VALUE_ADDRESS (arg1) + VALUE_OFFSET (arg1)));
}

/* Given a value of a pointer type, apply the C unary * operator to it.  */

value
value_ind (arg1)
     value arg1;
{
  COERCE_ARRAY (arg1);

  if (TYPE_CODE (VALUE_TYPE (arg1)) == TYPE_CODE_MEMBER)
    error ("not implemented: member types in value_ind");

  /* Allow * on an integer so we can cast it to whatever we want.
     This returns an int, which seems like the most C-like thing
     to do.  "long long" variables are rare enough that
     BUILTIN_TYPE_LONGEST would seem to be a mistake.  */
  if (TYPE_CODE (VALUE_TYPE (arg1)) == TYPE_CODE_INT)
    return value_at (builtin_type_int,
		     (CORE_ADDR) value_as_long (arg1));
  else if (TYPE_CODE (VALUE_TYPE (arg1)) == TYPE_CODE_PTR)
    return value_at_lazy (TYPE_TARGET_TYPE (VALUE_TYPE (arg1)),
			  value_as_pointer (arg1));
  error ("Attempt to take contents of a non-pointer value.");
  return 0;  /* For lint -- never reached */
}

/* Pushing small parts of stack frames.  */

/* Push one word (the size of object that a register holds).  */

CORE_ADDR
push_word (sp, buffer)
     CORE_ADDR sp;
     REGISTER_TYPE buffer;
{
  register int len = sizeof (REGISTER_TYPE);

  SWAP_TARGET_AND_HOST (&buffer, len);
#if 1 INNER_THAN 2
  sp -= len;
  write_memory (sp, (char *)&buffer, len);
#else /* stack grows upward */
  write_memory (sp, (char *)&buffer, len);
  sp += len;
#endif /* stack grows upward */

  return sp;
}

/* Push LEN bytes with data at BUFFER.  */

CORE_ADDR
push_bytes (sp, buffer, len)
     CORE_ADDR sp;
     char *buffer;
     int len;
{
#if 1 INNER_THAN 2
  sp -= len;
  write_memory (sp, buffer, len);
#else /* stack grows upward */
  write_memory (sp, buffer, len);
  sp += len;
#endif /* stack grows upward */

  return sp;
}

/* Push onto the stack the specified value VALUE.  */

static CORE_ADDR
value_push (sp, arg)
     register CORE_ADDR sp;
     value arg;
{
  register int len = TYPE_LENGTH (VALUE_TYPE (arg));

#if 1 INNER_THAN 2
  sp -= len;
  write_memory (sp, VALUE_CONTENTS (arg), len);
#else /* stack grows upward */
  write_memory (sp, VALUE_CONTENTS (arg), len);
  sp += len;
#endif /* stack grows upward */

  return sp;
}

/* Perform the standard coercions that are specified
   for arguments to be passed to C functions.  */

value
value_arg_coerce (arg)
     value arg;
{
  register struct type *type;

  COERCE_ENUM (arg);

  type = VALUE_TYPE (arg);

  if (TYPE_CODE (type) == TYPE_CODE_INT
      && TYPE_LENGTH (type) < TYPE_LENGTH (builtin_type_int))
    return value_cast (builtin_type_int, arg);

  if (TYPE_CODE (type) == TYPE_CODE_FLT
      && TYPE_LENGTH (type) < TYPE_LENGTH (builtin_type_double))
    return value_cast (builtin_type_double, arg);

  return arg;
}

/* Push the value ARG, first coercing it as an argument
   to a C function.  */

static CORE_ADDR
value_arg_push (sp, arg)
     register CORE_ADDR sp;
     value arg;
{
  return value_push (sp, value_arg_coerce (arg));
}

/* Determine a function's address and its return type from its value. 
   Calls error() if the function is not valid for calling.  */

static CORE_ADDR
find_function_addr (function, retval_type)
     value function;
     struct type **retval_type;
{
  register struct type *ftype = VALUE_TYPE (function);
  register enum type_code code = TYPE_CODE (ftype);
  struct type *value_type;
  CORE_ADDR funaddr;

  /* If it's a member function, just look at the function
     part of it.  */

  /* Determine address to call.  */
  if (code == TYPE_CODE_FUNC || code == TYPE_CODE_METHOD)
    {
      funaddr = VALUE_ADDRESS (function);
      value_type = TYPE_TARGET_TYPE (ftype);
    }
  else if (code == TYPE_CODE_PTR)
    {
      funaddr = value_as_pointer (function);
      if (TYPE_CODE (TYPE_TARGET_TYPE (ftype)) == TYPE_CODE_FUNC
	  || TYPE_CODE (TYPE_TARGET_TYPE (ftype)) == TYPE_CODE_METHOD)
	value_type = TYPE_TARGET_TYPE (TYPE_TARGET_TYPE (ftype));
      else
	value_type = builtin_type_int;
    }
  else if (code == TYPE_CODE_INT)
    {
      /* Handle the case of functions lacking debugging info.
	 Their values are characters since their addresses are char */
      if (TYPE_LENGTH (ftype) == 1)
	funaddr = value_as_pointer (value_addr (function));
      else
	/* Handle integer used as address of a function.  */
	funaddr = (CORE_ADDR) value_as_long (function);

      value_type = builtin_type_int;
    }
  else
    error ("Invalid data type for function to be called.");

  *retval_type = value_type;
  return funaddr;
}

#if defined (CALL_DUMMY)
/* All this stuff with a dummy frame may seem unnecessarily complicated
   (why not just save registers in GDB?).  The purpose of pushing a dummy
   frame which looks just like a real frame is so that if you call a
   function and then hit a breakpoint (get a signal, etc), "backtrace"
   will look right.  Whether the backtrace needs to actually show the
   stack at the time the inferior function was called is debatable, but
   it certainly needs to not display garbage.  So if you are contemplating
   making dummy frames be different from normal frames, consider that.  */

/* Perform a function call in the inferior.
   ARGS is a vector of values of arguments (NARGS of them).
   FUNCTION is a value, the function to be called.
   Returns a value representing what the function returned.
   May fail to return, if a breakpoint or signal is hit
   during the execution of the function.  */

value
call_function_by_hand (function, nargs, args)
     value function;
     int nargs;
     value *args;
{
  register CORE_ADDR sp;
  register int i;
  CORE_ADDR start_sp;
  /* CALL_DUMMY is an array of words (REGISTER_TYPE), but each word
     is in host byte order.  It is switched to target byte order before calling
     FIX_CALL_DUMMY.  */
  static REGISTER_TYPE dummy[] = CALL_DUMMY;
  REGISTER_TYPE dummy1[sizeof dummy / sizeof (REGISTER_TYPE)];
  CORE_ADDR old_sp;
  struct type *value_type;
  unsigned char struct_return;
  CORE_ADDR struct_addr;
  struct inferior_status inf_status;
  struct cleanup *old_chain;
  CORE_ADDR funaddr;
  int using_gcc;

  if (!target_has_execution)
    noprocess();

  save_inferior_status (&inf_status, 1);
  old_chain = make_cleanup (restore_inferior_status, &inf_status);

  /* PUSH_DUMMY_FRAME is responsible for saving the inferior registers
     (and POP_FRAME for restoring them).  (At least on most machines)
     they are saved on the stack in the inferior.  */
  PUSH_DUMMY_FRAME;

  old_sp = sp = read_register (SP_REGNUM);

#if 1 INNER_THAN 2		/* Stack grows down */
  sp -= sizeof dummy;
  start_sp = sp;
#else				/* Stack grows up */
  start_sp = sp;
  sp += sizeof dummy;
#endif

  funaddr = find_function_addr (function, &value_type);

  {
    struct block *b = block_for_pc (funaddr);
    /* If compiled without -g, assume GCC.  */
    using_gcc = b == NULL || BLOCK_GCC_COMPILED (b);
  }

  /* Are we returning a value using a structure return or a normal
     value return? */

  struct_return = using_struct_return (function, funaddr, value_type,
				       using_gcc);

  /* Create a call sequence customized for this function
     and the number of arguments for it.  */
  bcopy (dummy, dummy1, sizeof dummy);
  for (i = 0; i < sizeof dummy / sizeof (REGISTER_TYPE); i++)
    SWAP_TARGET_AND_HOST (&dummy1[i], sizeof (REGISTER_TYPE));
  FIX_CALL_DUMMY (dummy1, start_sp, funaddr, nargs, args,
		  value_type, using_gcc);

#if CALL_DUMMY_LOCATION == ON_STACK
  write_memory (start_sp, (char *)dummy1, sizeof dummy);

#else /* Not on stack.  */
#if CALL_DUMMY_LOCATION == BEFORE_TEXT_END
  /* Convex Unix prohibits executing in the stack segment. */
  /* Hope there is empty room at the top of the text segment. */
  {
    extern CORE_ADDR text_end;
    static checked = 0;
    if (!checked)
      for (start_sp = text_end - sizeof dummy; start_sp < text_end; ++start_sp)
	if (read_memory_integer (start_sp, 1) != 0)
	  error ("text segment full -- no place to put call");
    checked = 1;
    sp = old_sp;
    start_sp = text_end - sizeof dummy;
    write_memory (start_sp, (char *)dummy1, sizeof dummy);
  }
#else /* After text_end.  */
  {
    extern CORE_ADDR text_end;
    int errcode;
    sp = old_sp;
    start_sp = text_end;
    errcode = target_write_memory (start_sp, (char *)dummy1, sizeof dummy);
    if (errcode != 0)
      error ("Cannot write text segment -- call_function failed");
  }
#endif /* After text_end.  */
#endif /* Not on stack.  */

#ifdef lint
  sp = old_sp;		/* It really is used, for some ifdef's... */
#endif

#ifdef STACK_ALIGN
  /* If stack grows down, we must leave a hole at the top. */
  {
    int len = 0;

    /* Reserve space for the return structure to be written on the
       stack, if necessary */

    if (struct_return)
      len += TYPE_LENGTH (value_type);
    
    for (i = nargs - 1; i >= 0; i--)
      len += TYPE_LENGTH (VALUE_TYPE (value_arg_coerce (args[i])));
#ifdef CALL_DUMMY_STACK_ADJUST
    len += CALL_DUMMY_STACK_ADJUST;
#endif
#if 1 INNER_THAN 2
    sp -= STACK_ALIGN (len) - len;
#else
    sp += STACK_ALIGN (len) - len;
#endif
  }
#endif /* STACK_ALIGN */

    /* Reserve space for the return structure to be written on the
       stack, if necessary */

    if (struct_return)
      {
#if 1 INNER_THAN 2
	sp -= TYPE_LENGTH (value_type);
	struct_addr = sp;
#else
	struct_addr = sp;
	sp += TYPE_LENGTH (value_type);
#endif
      }

#if defined (REG_STRUCT_HAS_ADDR)
  {
    /* This is a machine like the sparc, where we need to pass a pointer
       to the structure, not the structure itself.  */
    if (REG_STRUCT_HAS_ADDR (using_gcc))
      for (i = nargs - 1; i >= 0; i--)
	if (TYPE_CODE (VALUE_TYPE (args[i])) == TYPE_CODE_STRUCT)
	  {
	    CORE_ADDR addr;
#if !(1 INNER_THAN 2)
	    /* The stack grows up, so the address of the thing we push
	       is the stack pointer before we push it.  */
	    addr = sp;
#endif
	    /* Push the structure.  */
	    sp = value_push (sp, args[i]);
#if 1 INNER_THAN 2
	    /* The stack grows down, so the address of the thing we push
	       is the stack pointer after we push it.  */
	    addr = sp;
#endif
	    /* The value we're going to pass is the address of the thing
	       we just pushed.  */
	    args[i] = value_from_longest (lookup_pointer_type (value_type),
				       (LONGEST) addr);
	  }
  }
#endif /* REG_STRUCT_HAS_ADDR.  */

#ifdef PUSH_ARGUMENTS
  PUSH_ARGUMENTS(nargs, args, sp, struct_return, struct_addr);
#else /* !PUSH_ARGUMENTS */
  for (i = nargs - 1; i >= 0; i--)
    sp = value_arg_push (sp, args[i]);
#endif /* !PUSH_ARGUMENTS */

#ifdef CALL_DUMMY_STACK_ADJUST
#if 1 INNER_THAN 2
  sp -= CALL_DUMMY_STACK_ADJUST;
#else
  sp += CALL_DUMMY_STACK_ADJUST;
#endif
#endif /* CALL_DUMMY_STACK_ADJUST */

  /* Store the address at which the structure is supposed to be
     written.  Note that this (and the code which reserved the space
     above) assumes that gcc was used to compile this function.  Since
     it doesn't cost us anything but space and if the function is pcc
     it will ignore this value, we will make that assumption.

     Also note that on some machines (like the sparc) pcc uses a 
     convention like gcc's.  */

  if (struct_return)
    STORE_STRUCT_RETURN (struct_addr, sp);

  /* Write the stack pointer.  This is here because the statements above
     might fool with it.  On SPARC, this write also stores the register
     window into the right place in the new stack frame, which otherwise
     wouldn't happen.  (See write_inferior_registers in sparc-xdep.c.)  */
  write_register (SP_REGNUM, sp);

  /* Figure out the value returned by the function.  */
  {
    char retbuf[REGISTER_BYTES];

    /* Execute the stack dummy routine, calling FUNCTION.
       When it is done, discard the empty frame
       after storing the contents of all regs into retbuf.  */
    run_stack_dummy (start_sp + CALL_DUMMY_START_OFFSET, retbuf);

    do_cleanups (old_chain);

    return value_being_returned (value_type, retbuf, struct_return);
  }
}
#else /* no CALL_DUMMY.  */
value
call_function_by_hand (function, nargs, args)
     value function;
     int nargs;
     value *args;
{
  error ("Cannot invoke functions on this machine.");
}
#endif /* no CALL_DUMMY.  */

/* Create a value for a string constant:
   Call the function malloc in the inferior to get space for it,
   then copy the data into that space
   and then return the address with type char *.
   PTR points to the string constant data; LEN is number of characters.  */

value
value_string (ptr, len)
     char *ptr;
     int len;
{
  register value val;
  register struct symbol *sym;
  value blocklen;
  register char *copy = (char *) alloca (len + 1);
  char *i = ptr;
  register char *o = copy, *ibeg = ptr;
  register int c;

  /* Copy the string into COPY, processing escapes.
     We could not conveniently process them in the parser
     because the string there wants to be a substring of the input.  */

  while (i - ibeg < len)
    {
      c = *i++;
      if (c == '\\')
	{
	  c = parse_escape (&i);
	  if (c == -1)
	    continue;
	}
      *o++ = c;
    }
  *o = 0;

  /* Get the length of the string after escapes are processed.  */

  len = o - copy;

  /* Find the address of malloc in the inferior.  */

  sym = lookup_symbol ("malloc", 0, VAR_NAMESPACE, 0, NULL);
  if (sym != 0)
    {
      if (SYMBOL_CLASS (sym) != LOC_BLOCK)
	error ("\"malloc\" exists in this program but is not a function.");
      val = value_of_variable (sym);
    }
  else
    {
      struct minimal_symbol *msymbol;
      msymbol = lookup_minimal_symbol ("malloc", (struct objfile *) NULL);
      if (msymbol != NULL)
	val =
	  value_from_longest (lookup_pointer_type (lookup_function_type (
				lookup_pointer_type (builtin_type_char))),
			      (LONGEST) msymbol -> address);
      else
	error ("String constants require the program to have a function \"malloc\".");
    }

  blocklen = value_from_longest (builtin_type_int, (LONGEST) (len + 1));
  val = call_function_by_hand (val, 1, &blocklen);
  if (value_zerop (val))
    error ("No memory available for string constant.");
  write_memory (value_as_pointer (val), copy, len + 1);
  VALUE_TYPE (val) = lookup_pointer_type (builtin_type_char);
  return val;
}

/* Helper function used by value_struct_elt to recurse through baseclasses.
   Look for a field NAME in ARG1. Adjust the address of ARG1 by OFFSET bytes,
   and search in it assuming it has (class) type TYPE.
   If found, return value, else return NULL.

   If LOOKING_FOR_BASECLASS, then instead of looking for struct fields,
   look for a baseclass named NAME.  */

static value
search_struct_field (name, arg1, offset, type, looking_for_baseclass)
     char *name;
     register value arg1;
     int offset;
     register struct type *type;
     int looking_for_baseclass;
{
  int i;

  check_stub_type (type);

  if (! looking_for_baseclass)
    for (i = TYPE_NFIELDS (type) - 1; i >= TYPE_N_BASECLASSES (type); i--)
      {
	char *t_field_name = TYPE_FIELD_NAME (type, i);

	if (t_field_name && !strcmp (t_field_name, name))
	  {
	    value v;
	    if (TYPE_FIELD_STATIC (type, i))
	      {
		char *phys_name = TYPE_FIELD_STATIC_PHYSNAME (type, i);
		struct symbol *sym =
		  lookup_symbol (phys_name, 0, VAR_NAMESPACE, 0, NULL);
		if (! sym) error (
	  "Internal error: could not find physical static variable named %s",
				  phys_name);
		v = value_at (TYPE_FIELD_TYPE (type, i),
			      (CORE_ADDR)SYMBOL_BLOCK_VALUE (sym));
	      }
	    else
	      v = value_primitive_field (arg1, offset, i, type);
	    if (v == 0)
	      error("there is no field named %s", name);
	    return v;
	  }
      }

  for (i = TYPE_N_BASECLASSES (type) - 1; i >= 0; i--)
    {
      value v;
      /* If we are looking for baseclasses, this is what we get when we
	 hit them.  */
      int found_baseclass = (looking_for_baseclass
			     && !strcmp (name, TYPE_BASECLASS_NAME (type, i)));

      if (BASETYPE_VIA_VIRTUAL (type, i))
	{
	  value v2;
	  baseclass_addr (type, i, VALUE_CONTENTS (arg1) + offset,
			  &v2, (int *)NULL);
	  if (v2 == 0)
	    error ("virtual baseclass botch");
	  if (found_baseclass)
	    return v2;
	  v = search_struct_field (name, v2, 0, TYPE_BASECLASS (type, i),
				   looking_for_baseclass);
	}
      else if (found_baseclass)
	v = value_primitive_field (arg1, offset, i, type);
      else
	v = search_struct_field (name, arg1,
				 offset + TYPE_BASECLASS_BITPOS (type, i) / 8,
				 TYPE_BASECLASS (type, i),
				 looking_for_baseclass);
      if (v) return v;
    }
  return NULL;
}

/* Helper function used by value_struct_elt to recurse through baseclasses.
   Look for a field NAME in ARG1. Adjust the address of ARG1 by OFFSET bytes,
   and search in it assuming it has (class) type TYPE.
   If found, return value, else return NULL. */

static value
search_struct_method (name, arg1, args, offset, static_memfuncp, type)
     char *name;
     register value arg1, *args;
     int offset, *static_memfuncp;
     register struct type *type;
{
  int i;

  check_stub_type (type);
  for (i = TYPE_NFN_FIELDS (type) - 1; i >= 0; i--)
    {
      char *t_field_name = TYPE_FN_FIELDLIST_NAME (type, i);
      if (t_field_name && !strcmp (t_field_name, name))
	{
	  int j = TYPE_FN_FIELDLIST_LENGTH (type, i) - 1;
	  struct fn_field *f = TYPE_FN_FIELDLIST1 (type, i);

	  if (j > 0 && args == 0)
	    error ("cannot resolve overloaded method `%s'", name);
	  while (j >= 0)
	    {
	      if (TYPE_FN_FIELD_STUB (f, j))
		check_stub_method (type, i, j);
	      if (!typecmp (TYPE_FN_FIELD_STATIC_P (f, j),
			    TYPE_FN_FIELD_ARGS (f, j), args))
		{
		  if (TYPE_FN_FIELD_VIRTUAL_P (f, j))
		    return (value)value_virtual_fn_field (arg1, f, j, type);
		  if (TYPE_FN_FIELD_STATIC_P (f, j) && static_memfuncp)
		    *static_memfuncp = 1;
		  return (value)value_fn_field (f, j);
		}
	      j--;
	    }
	}
    }

  for (i = TYPE_N_BASECLASSES (type) - 1; i >= 0; i--)
    {
      value v, v2;
      int base_offset;

      if (BASETYPE_VIA_VIRTUAL (type, i))
	{
	  baseclass_addr (type, i, VALUE_CONTENTS (arg1) + offset,
			  &v2, (int *)NULL);
	  if (v2 == 0)
	    error ("virtual baseclass botch");
	  base_offset = 0;
	}
      else
	{
	  v2 = arg1;
	  base_offset = TYPE_BASECLASS_BITPOS (type, i) / 8;
        }
      v = search_struct_method (name, v2, args, base_offset,
				static_memfuncp, TYPE_BASECLASS (type, i));
      if (v) return v;
    }
  return NULL;
}

/* Given *ARGP, a value of type (pointer to a)* structure/union,
   extract the component named NAME from the ultimate target structure/union
   and return it as a value with its appropriate type.
   ERR is used in the error message if *ARGP's type is wrong.

   C++: ARGS is a list of argument types to aid in the selection of
   an appropriate method. Also, handle derived types.

   STATIC_MEMFUNCP, if non-NULL, points to a caller-supplied location
   where the truthvalue of whether the function that was resolved was
   a static member function or not is stored.

   ERR is an error message to be printed in case the field is not found.  */

value
value_struct_elt (argp, args, name, static_memfuncp, err)
     register value *argp, *args;
     char *name;
     int *static_memfuncp;
     char *err;
{
  register struct type *t;
  value v;

  COERCE_ARRAY (*argp);

  t = VALUE_TYPE (*argp);

  /* Follow pointers until we get to a non-pointer.  */

  while (TYPE_CODE (t) == TYPE_CODE_PTR || TYPE_CODE (t) == TYPE_CODE_REF)
    {
      *argp = value_ind (*argp);
      /* Don't coerce fn pointer to fn and then back again!  */
      if (TYPE_CODE (VALUE_TYPE (*argp)) != TYPE_CODE_FUNC)
	COERCE_ARRAY (*argp);
      t = VALUE_TYPE (*argp);
    }

  if (TYPE_CODE (t) == TYPE_CODE_MEMBER)
    error ("not implemented: member type in value_struct_elt");

  if (   TYPE_CODE (t) != TYPE_CODE_STRUCT
      && TYPE_CODE (t) != TYPE_CODE_UNION)
    error ("Attempt to extract a component of a value that is not a %s.", err);

  /* Assume it's not, unless we see that it is.  */
  if (static_memfuncp)
    *static_memfuncp =0;

  if (!args)
    {
      /* if there are no arguments ...do this...  */

      /* Try as a field first, because if we succeed, there
	 is less work to be done.  */
      v = search_struct_field (name, *argp, 0, t, 0);
      if (v)
	return v;

      /* C++: If it was not found as a data field, then try to
         return it as a pointer to a method.  */

      if (destructor_name_p (name, t))
	error ("Cannot get value of destructor");

      v = search_struct_method (name, *argp, args, 0, static_memfuncp, t);

      if (v == 0)
	{
	  if (TYPE_NFN_FIELDS (t))
	    error ("There is no member or method named %s.", name);
	  else
	    error ("There is no member named %s.", name);
	}
      return v;
    }

  if (destructor_name_p (name, t))
    {
      if (!args[1])
	{
	  /* destructors are a special case.  */
	  return (value)value_fn_field (TYPE_FN_FIELDLIST1 (t, 0),
					TYPE_FN_FIELDLIST_LENGTH (t, 0));
	}
      else
	{
	  error ("destructor should not have any argument");
	}
    }
  else
    v = search_struct_method (name, *argp, args, 0, static_memfuncp, t);

  if (v == 0)
    {
      /* See if user tried to invoke data as function.  If so,
	 hand it back.  If it's not callable (i.e., a pointer to function),
	 gdb should give an error.  */
      v = search_struct_field (name, *argp, 0, t, 0);
    }

  if (!v)
    error ("Structure has no component named %s.", name);
  return v;
}

/* C++: return 1 is NAME is a legitimate name for the destructor
   of type TYPE.  If TYPE does not have a destructor, or
   if NAME is inappropriate for TYPE, an error is signaled.  */
int
destructor_name_p (name, type)
     const char *name;
     const struct type *type;
{
  /* destructors are a special case.  */

  if (name[0] == '~')
    {
      char *dname = type_name_no_tag (type);
      if (strcmp (dname, name+1))
	error ("name of destructor must equal name of class");
      else
	return 1;
    }
  return 0;
}

/* Helper function for check_field: Given TYPE, a structure/union,
   return 1 if the component named NAME from the ultimate
   target structure/union is defined, otherwise, return 0. */

static int
check_field_in (type, name)
     register struct type *type;
     const char *name;
{
  register int i;

  for (i = TYPE_NFIELDS (type) - 1; i >= TYPE_N_BASECLASSES (type); i--)
    {
      char *t_field_name = TYPE_FIELD_NAME (type, i);
      if (t_field_name && !strcmp (t_field_name, name))
	return 1;
    }

  /* C++: If it was not found as a data field, then try to
     return it as a pointer to a method.  */

  /* Destructors are a special case.  */
  if (destructor_name_p (name, type))
    return 1;

  for (i = TYPE_NFN_FIELDS (type) - 1; i >= 0; --i)
    {
      if (!strcmp (TYPE_FN_FIELDLIST_NAME (type, i), name))
	return 1;
    }

  for (i = TYPE_N_BASECLASSES (type) - 1; i >= 0; i--)
    if (check_field_in (TYPE_BASECLASS (type, i), name))
      return 1;
      
  return 0;
}


/* C++: Given ARG1, a value of type (pointer to a)* structure/union,
   return 1 if the component named NAME from the ultimate
   target structure/union is defined, otherwise, return 0.  */

int
check_field (arg1, name)
     register value arg1;
     const char *name;
{
  register struct type *t;

  COERCE_ARRAY (arg1);

  t = VALUE_TYPE (arg1);

  /* Follow pointers until we get to a non-pointer.  */

  while (TYPE_CODE (t) == TYPE_CODE_PTR || TYPE_CODE (t) == TYPE_CODE_REF)
    t = TYPE_TARGET_TYPE (t);

  if (TYPE_CODE (t) == TYPE_CODE_MEMBER)
    error ("not implemented: member type in check_field");

  if (   TYPE_CODE (t) != TYPE_CODE_STRUCT
      && TYPE_CODE (t) != TYPE_CODE_UNION)
    error ("Internal error: `this' is not an aggregate");

  return check_field_in (t, name);
}

/* C++: Given an aggregate type CURTYPE, and a member name NAME,
   return the address of this member as a "pointer to member"
   type.  If INTYPE is non-null, then it will be the type
   of the member we are looking for.  This will help us resolve
   "pointers to member functions".  This function is used
   to resolve user expressions of the form "DOMAIN::NAME".  */

value
value_struct_elt_for_reference (domain, curtype, name, intype)
     struct type *domain, *curtype, *intype;
     char *name;
{
  register struct type *t = curtype;
  register int i;
  value v;

  if (   TYPE_CODE (t) != TYPE_CODE_STRUCT
      && TYPE_CODE (t) != TYPE_CODE_UNION)
    error ("Internal error: non-aggregate type to value_struct_elt_for_reference");

  for (i = TYPE_NFIELDS (t) - 1; i >= TYPE_N_BASECLASSES (t); i--)
    {
      char *t_field_name = TYPE_FIELD_NAME (t, i);
      
      if (t_field_name && !strcmp (t_field_name, name))
	{
	  if (TYPE_FIELD_STATIC (t, i))
	    {
	      char *phys_name = TYPE_FIELD_STATIC_PHYSNAME (t, i);
	      struct symbol *sym =
		lookup_symbol (phys_name, 0, VAR_NAMESPACE, 0, NULL);
	      if (! sym)
		error (
	    "Internal error: could not find physical static variable named %s",
		       phys_name);
	      return value_at (SYMBOL_TYPE (sym),
			       (CORE_ADDR)SYMBOL_BLOCK_VALUE (sym));
	    }
	  if (TYPE_FIELD_PACKED (t, i))
	    error ("pointers to bitfield members not allowed");
	  
	  return value_from_longest
	    (lookup_reference_type (lookup_member_type (TYPE_FIELD_TYPE (t, i),
							domain)),
	     (LONGEST) (TYPE_FIELD_BITPOS (t, i) >> 3));
	}
    }

  /* C++: If it was not found as a data field, then try to
     return it as a pointer to a method.  */

  /* Destructors are a special case.  */
  if (destructor_name_p (name, t))
    {
      error ("member pointers to destructors not implemented yet");
    }

  /* Perform all necessary dereferencing.  */
  while (intype && TYPE_CODE (intype) == TYPE_CODE_PTR)
    intype = TYPE_TARGET_TYPE (intype);

  for (i = TYPE_NFN_FIELDS (t) - 1; i >= 0; --i)
    {
      if (!strcmp (TYPE_FN_FIELDLIST_NAME (t, i), name))
	{
	  int j = TYPE_FN_FIELDLIST_LENGTH (t, i);
	  struct fn_field *f = TYPE_FN_FIELDLIST1 (t, i);
	  
	  if (intype == 0 && j > 1)
	    error ("non-unique member `%s' requires type instantiation", name);
	  if (intype)
	    {
	      while (j--)
		if (TYPE_FN_FIELD_TYPE (f, j) == intype)
		  break;
	      if (j < 0)
		error ("no member function matches that type instantiation");
	    }
	  else
	    j = 0;
	  
	  if (TYPE_FN_FIELD_STUB (f, j))
	    check_stub_method (t, i, j);
	  if (TYPE_FN_FIELD_VIRTUAL_P (f, j))
	    {
	      return value_from_longest
		(lookup_reference_type
		 (lookup_member_type (TYPE_FN_FIELD_TYPE (f, j),
				      domain)),
		 (LONGEST) TYPE_FN_FIELD_VOFFSET (f, j));
	    }
	  else
	    {
	      struct symbol *s = lookup_symbol (TYPE_FN_FIELD_PHYSNAME (f, j),
						0, VAR_NAMESPACE, 0, NULL);
	      v = read_var_value (s, 0);
#if 0
	      VALUE_TYPE (v) = lookup_reference_type
		(lookup_member_type (TYPE_FN_FIELD_TYPE (f, j),
				     domain));
#endif
	      return v;
		}
	    }
	}

  for (i = TYPE_N_BASECLASSES (t) - 1; i >= 0; i--)
    {
      v = value_struct_elt_for_reference (domain,
					  TYPE_BASECLASS (t, i),
					  name,
					  intype);
      if (v)
	return v;
    }
  return 0;
}

/* Compare two argument lists and return the position in which they differ,
   or zero if equal.

   STATICP is nonzero if the T1 argument list came from a
   static member function.

   For non-static member functions, we ignore the first argument,
   which is the type of the instance variable.  This is because we want
   to handle calls with objects from derived classes.  This is not
   entirely correct: we should actually check to make sure that a
   requested operation is type secure, shouldn't we?  FIXME.  */

int
typecmp (staticp, t1, t2)
     int staticp;
     struct type *t1[];
     value t2[];
{
  int i;

  if (t2 == 0)
    return 1;
  if (staticp && t1 == 0)
    return t2[1] != 0;
  if (t1 == 0)
    return 1;
  if (t1[0]->code == TYPE_CODE_VOID) return 0;
  if (t1[!staticp] == 0) return 0;
  for (i = !staticp; t1[i] && t1[i]->code != TYPE_CODE_VOID; i++)
    {
      if (! t2[i]
	  || t1[i]->code != t2[i]->type->code
/* Too pessimistic:  || t1[i]->target_type != t2[i]->type->target_type */
 )
	return i+1;
    }
  if (!t1[i]) return 0;
  return t2[i] ? i+1 : 0;
}

/* C++: return the value of the class instance variable, if one exists.
   Flag COMPLAIN signals an error if the request is made in an
   inappropriate context.  */
value
value_of_this (complain)
     int complain;
{
  extern FRAME selected_frame;
  struct symbol *func, *sym;
  struct block *b;
  int i;
  static const char funny_this[] = "this";
  value this;

  if (selected_frame == 0)
    if (complain)
      error ("no frame selected");
    else return 0;

  func = get_frame_function (selected_frame);
  if (!func)
    {
      if (complain)
	error ("no `this' in nameless context");
      else return 0;
    }

  b = SYMBOL_BLOCK_VALUE (func);
  i = BLOCK_NSYMS (b);
  if (i <= 0)
    if (complain)
      error ("no args, no `this'");
    else return 0;

  /* Calling lookup_block_symbol is necessary to get the LOC_REGISTER
     symbol instead of the LOC_ARG one (if both exist).  */
  sym = lookup_block_symbol (b, funny_this, VAR_NAMESPACE);
  if (sym == NULL)
    {
      if (complain)
	error ("current stack frame not in method");
      else
	return NULL;
    }

  this = read_var_value (sym, selected_frame);
  if (this == 0 && complain)
    error ("`this' argument at unknown address");
  return this;
}