binutils-gdb/gdb/stack.c

/* Print and select stack frames for GDB, the GNU debugger.
   Copyright (C) 1986, 1987, 1989 Free Software Foundation, Inc.

This file is part of GDB.

GDB 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 1, or (at your option)
any later version.

GDB 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 GDB; see the file COPYING.  If not, write to
the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.  */

#include <stdio.h>

#include "defs.h"
#include "param.h"
#include "symtab.h"
#include "frame.h"
#include "gdbcmd.h"
#include "value.h"
#include "gdbcore.h"
#include "target.h"
#include "breakpoint.h"

extern int addressprint;	/* Print addresses, or stay symbolic only? */
extern int info_verbose;	/* Verbosity of symbol reading msgs */
extern char *reg_names[];	/* Names of registers */

/* Thie "selected" stack frame is used by default for local and arg access.
   May be zero, for no selected frame.  */

FRAME selected_frame;

/* Level of the selected frame:
   0 for innermost, 1 for its caller, ...
   or -1 for frame specified by address with no defined level.  */

int selected_frame_level;

/* Nonzero means print the full filename and linenumber
   when a frame is printed, and do so in a format programs can parse.  */

int frame_file_full_name = 0;

void print_frame_info ();

/* Print a stack frame briefly.  FRAME should be the frame id
   and LEVEL should be its level in the stack (or -1 for level not defined).
   This prints the level, the function executing, the arguments,
   and the file name and line number.
   If the pc is not at the beginning of the source line,
   the actual pc is printed at the beginning.

   If SOURCE is 1, print the source line as well.
   If SOURCE is -1, print ONLY the source line.  */

static void
print_stack_frame (frame, level, source)
     FRAME frame;
     int level;
     int source;
{
  struct frame_info *fi;

  fi = get_frame_info (frame);

  print_frame_info (fi, level, source, 1);
}

void
print_frame_info (fi, level, source, args)
     struct frame_info *fi;
     register int level;
     int source;
     int args;
{
  struct symtab_and_line sal;
  struct symbol *func;
  register char *funname = 0;
  int numargs;

#if 0	/* Symbol reading is fast enough now */
  struct partial_symtab *pst;

  /* Don't give very much information if we haven't readin the
     symbol table yet.  */
  pst = find_pc_psymtab (fi->pc);
  if (pst && !pst->readin)
    {
      /* Abbreviated information.  */
      char *fname;

      if (!find_pc_partial_function (fi->pc, &fname, 0))
	fname = "??";
	
      printf_filtered ("#%-2d ", level);
      if (addressprint)
        printf_filtered ("0x%x in ", fi->pc);

      fputs_demangled (fname, stdout, -1);
      fputs_filtered (" (...)\n", stdout);
      
      return;
    }
#endif

  sal = find_pc_line (fi->pc, fi->next_frame);
  func = find_pc_function (fi->pc);
  if (func)
    {
      /* In certain pathological cases, the symtabs give the wrong
	 function (when we are in the first function in a file which
	 is compiled without debugging symbols, the previous function
	 is compiled with debugging symbols, and the "foo.o" symbol
	 that is supposed to tell us where the file with debugging symbols
	 ends has been truncated by ar because it is longer than 15
	 characters).

	 So look in the misc_function_vector as well, and if it comes
	 up with a larger address for the function use that instead.
	 I don't think this can ever cause any problems;
	 there shouldn't be any
	 misc_function_vector symbols in the middle of a function.  */
      int misc_index = find_pc_misc_function (fi->pc);
      if (misc_index >= 0
	  && (misc_function_vector[misc_index].address
	      > BLOCK_START (SYMBOL_BLOCK_VALUE (func))))
	{
	  /* In this case we have no way of knowing the source file
	     and line number, so don't print them.  */
	  sal.symtab = 0;
	  /* We also don't know anything about the function besides
	     its address and name.  */
	  func = 0;
	  funname = misc_function_vector[misc_index].name;
	}
      else
	funname = SYMBOL_NAME (func);
    }
  else
    {
      register int misc_index = find_pc_misc_function (fi->pc);
      if (misc_index >= 0)
	funname = misc_function_vector[misc_index].name;
    }

  if (source >= 0 || !sal.symtab)
    {
      if (level >= 0)
	printf_filtered ("#%-2d ", level);
      if (addressprint)
	if (fi->pc != sal.pc || !sal.symtab)
	  printf_filtered ("0x%x in ", fi->pc);
      fputs_demangled (funname ? funname : "??", stdout, -1);
      wrap_here ("   ");
      fputs_filtered (" (", stdout);
      if (args)
	{
	  FRAME_NUM_ARGS (numargs, fi);
	  print_frame_args (func, fi, numargs, stdout);
	}
      printf_filtered (")");
      if (sal.symtab && sal.symtab->filename)
	{
          wrap_here ("   ");
	  printf_filtered (" at %s:%d", sal.symtab->filename, sal.line);
	}
      printf_filtered ("\n");
    }

  if ((source != 0) && sal.symtab)
    {
      int done = 0;
      int mid_statement = source < 0 && fi->pc != sal.pc;
      if (frame_file_full_name)
	done = identify_source_line (sal.symtab, sal.line, mid_statement);
      if (!done)
	{
	  if (addressprint && mid_statement)
	    printf_filtered ("0x%x\t", fi->pc);
	  print_source_lines (sal.symtab, sal.line, sal.line + 1, 0);
	}
      current_source_line = max (sal.line - lines_to_list () / 2, 1);
    }
  if (source != 0)
    set_default_breakpoint (1, fi->pc, sal.symtab, sal.line);

  fflush (stdout);
}

/* Call here to print info on selected frame, after a trap.  */

void
print_sel_frame (just_source)
     int just_source;
{
  print_stack_frame (selected_frame, -1, just_source ? -1 : 1);
}

/* Print info on the selected frame, including level number
   but not source.  */

void
print_selected_frame ()
{
  print_stack_frame (selected_frame, selected_frame_level, 0);
}

void flush_cached_frames ();

#ifdef FRAME_SPECIFICATION_DYADIC
extern FRAME setup_arbitrary_frame ();
#endif

/*
 * Read a frame specification in whatever the appropriate format is.
 * Call error() if the specification is in any way invalid (i.e.
 * this function never returns NULL).
 */
static FRAME
parse_frame_specification (frame_exp)
     char *frame_exp;
{
  int numargs = 0;
  int arg1, arg2;
  
  if (frame_exp)
    {
      char *addr_string, *p;
      struct cleanup *tmp_cleanup;

      while (*frame_exp == ' ') frame_exp++;
      for (p = frame_exp; *p && *p != ' '; p++)
	;

      if (*frame_exp)
	{
	  numargs = 1;
	  addr_string = savestring(frame_exp, p - frame_exp);

	  {
	    tmp_cleanup = make_cleanup (free, addr_string);
	    arg1 = parse_and_eval_address (addr_string);
	    do_cleanups (tmp_cleanup);
	  }

	  while (*p == ' ') p++;
	  
	  if (*p)
	    {
	      numargs = 2;
	      arg2 = parse_and_eval_address (p);
	    }
	}
    }

  switch (numargs)
    {
    case 0:
      if (selected_frame == NULL)
	error ("No selected frame.");
      return selected_frame;
      /* NOTREACHED */
    case 1:
      {
	int level = arg1;
	FRAME fid = find_relative_frame (get_current_frame (), &level);
	FRAME tfid;

	if (level == 0)
	  /* find_relative_frame was successful */
	  return fid;

	/* If (s)he specifies the frame with an address, he deserves what
	   (s)he gets.  Still, give the highest one that matches.  */

	for (fid = get_current_frame ();
	     fid && FRAME_FP (fid) != arg1;
	     fid = get_prev_frame (fid))
	  ;

	if (fid)
	  while ((tfid = get_prev_frame (fid)) &&
		 (FRAME_FP (tfid) == arg1))
	    fid = tfid;
	  
#ifdef FRAME_SPECIFICATION_DYADIC
	if (!fid)
	  error ("Incorrect number of args in frame specification");

	return fid;
#else
	return create_new_frame (arg1, 0);
#endif
      }
      /* NOTREACHED */
    case 2:
      /* Must be addresses */
#ifndef FRAME_SPECIFICATION_DYADIC
      error ("Incorrect number of args in frame specification");
#else
      return setup_arbitrary_frame (arg1, arg2);
#endif
      /* NOTREACHED */
    }
  fatal ("Internal: Error in parsing in parse_frame_specification");
  /* NOTREACHED */
}

/* FRAME_ARGS_ADDRESS_CORRECT is just like FRAME_ARGS_ADDRESS except
   that if it is unsure about the answer, it returns 0
   instead of guessing (this happens on the VAX and i960, for example).

   On most machines, we never have to guess about the args address,
   so FRAME_ARGS_ADDRESS{,_CORRECT} are the same.  */
#if !defined (FRAME_ARGS_ADDRESS_CORRECT)
#define FRAME_ARGS_ADDRESS_CORRECT FRAME_ARGS_ADDRESS
#endif

/* Print verbosely the selected frame or the frame at address ADDR.
   This means absolutely all information in the frame is printed.  */

static void
frame_info (addr_exp)
     char *addr_exp;
{
  FRAME frame;
  struct frame_info *fi;
  struct frame_saved_regs fsr;
  struct symtab_and_line sal;
  struct symbol *func;
  FRAME calling_frame;
  int i, count;
  char *funname = 0;

  if (!target_has_stack)
    error ("No inferior or core file.");

  frame = parse_frame_specification (addr_exp);
  if (!frame)
    error ("Invalid frame specified.");

  fi = get_frame_info (frame);
  sal = find_pc_line (fi->pc, fi->next_frame);
  func = get_frame_function (frame);
  if (func)
    funname = SYMBOL_NAME (func);
  else
    {
      register int misc_index = find_pc_misc_function (fi->pc);
      if (misc_index >= 0)
	funname = misc_function_vector[misc_index].name;
    }
  calling_frame = get_prev_frame (frame);

  if (!addr_exp && selected_frame_level >= 0)
    printf_filtered ("Stack level %d, frame at 0x%x:\n %s = 0x%x",
	    selected_frame_level, FRAME_FP(frame),
	    reg_names[PC_REGNUM], fi->pc);
  else
    printf_filtered ("Stack frame at 0x%x:\n %s = 0x%x",
	    FRAME_FP(frame), reg_names[PC_REGNUM], fi->pc);

  wrap_here ("   ");
  if (funname)
    printf_filtered (" in %s", funname);
  wrap_here ("   ");
  if (sal.symtab)
    printf_filtered (" (%s:%d)", sal.symtab->filename, sal.line);
  puts_filtered ("; ");
  wrap_here ("    ");
  printf_filtered ("saved %s 0x%x\n", reg_names[PC_REGNUM],
				      FRAME_SAVED_PC (frame));
  if (calling_frame)
    printf_filtered (" called by frame at 0x%x", FRAME_FP (calling_frame));
  if (fi->next_frame && calling_frame)
    puts_filtered (",");
  wrap_here ("   ");
  if (fi->next_frame)
    printf_filtered (" caller of frame at 0x%x", fi->next_frame);
  if (fi->next_frame || calling_frame)
    puts_filtered ("\n");

  {
    /* Address of the argument list for this frame, or 0.  */
    CORE_ADDR arg_list = FRAME_ARGS_ADDRESS_CORRECT (fi);
    /* Number of args for this frame, or -1 if unknown.  */
    int numargs;

    if (arg_list == 0)
	printf_filtered (" Arglist at unknown address.\n");
    else
      {
	printf_filtered (" Arglist at 0x%x,", arg_list);

	FRAME_NUM_ARGS (numargs, fi);
	if (numargs < 0)
	  puts_filtered (" args: ");
	else if (numargs == 0)
	  puts_filtered (" no args.");
	else if (numargs == 1)
	  puts_filtered (" 1 arg: ");
	else
	  printf_filtered (" %d args: ", numargs);
	print_frame_args (func, fi, numargs, stdout);
	puts_filtered ("\n");
      }
  }

#if defined (FRAME_FIND_SAVED_REGS)  
  get_frame_saved_regs (fi, &fsr);
  /* The sp is special; what's returned isn't the save address, but
     actually the value of the previous frame's sp.  */
  printf_filtered (" Previous frame's sp is 0x%x\n", fsr.regs[SP_REGNUM]);
  count = 0;
  for (i = 0; i < NUM_REGS; i++)
    if (fsr.regs[i] && i != SP_REGNUM)
      {
	if (count == 0)
	  puts_filtered (" Saved registers:\n ");
	else
	  puts_filtered (",");
	wrap_here (" ");
	printf_filtered (" %s at 0x%x", reg_names[i], fsr.regs[i]);
	count++;
      }
  if (count)
    puts_filtered ("\n");
#endif /* Have FRAME_FIND_SAVED_REGS.  */
}

#if 0
/* Set a limit on the number of frames printed by default in a
   backtrace.  */

static int backtrace_limit;

static void
set_backtrace_limit_command (count_exp, from_tty)
     char *count_exp;
     int from_tty;
{
  int count = parse_and_eval_address (count_exp);

  if (count < 0)
    error ("Negative argument not meaningful as backtrace limit.");

  backtrace_limit = count;
}

static void
backtrace_limit_info (arg, from_tty)
     char *arg;
     int from_tty;
{
  if (arg)
    error ("\"Info backtrace-limit\" takes no arguments.");

  printf ("Backtrace limit: %d.\n", backtrace_limit);
}
#endif

/* Print briefly all stack frames or just the innermost COUNT frames.  */

static void
backtrace_command (count_exp, from_tty)
     char *count_exp;
     int from_tty;
{
  struct frame_info *fi;
  register int count;
  register FRAME frame;
  register int i;
  register FRAME trailing;
  register int trailing_level;

  if (!target_has_stack)
    error ("No stack.");

  /* The following code must do two things.  First, it must
     set the variable TRAILING to the frame from which we should start
     printing.  Second, it must set the variable count to the number
     of frames which we should print, or -1 if all of them.  */
  trailing = get_current_frame ();
  trailing_level = 0;
  if (count_exp)
    {
      count = parse_and_eval_address (count_exp);
      if (count < 0)
	{
	  FRAME current;

	  count = -count;

	  current = trailing;
	  while (current && count--)
	    {
	      QUIT;
	      current = get_prev_frame (current);
	    }
	  
	  /* Will stop when CURRENT reaches the top of the stack.  TRAILING
	     will be COUNT below it.  */
	  while (current)
	    {
	      QUIT;
	      trailing = get_prev_frame (trailing);
	      current = get_prev_frame (current);
	      trailing_level++;
	    }
	  
	  count = -1;
	}
    }
  else
    count = -1;

  if (info_verbose)
    {
      struct partial_symtab *ps;
      
      /* Read in symbols for all of the frames.  Need to do this in
	 a separate pass so that "Reading in symbols for xxx" messages
	 don't screw up the appearance of the backtrace.  Also
	 if people have strong opinions against reading symbols for
	 backtrace this may have to be an option.  */
      i = count;
      for (frame = trailing;
	   frame != NULL && i--;
	   frame = get_prev_frame (frame))
	{
	  QUIT;
	  fi = get_frame_info (frame);
	  ps = find_pc_psymtab (fi->pc);
	  if (ps)
	    (void) PSYMTAB_TO_SYMTAB (ps);	/* Force syms to come in */
	}
    }

  for (i = 0, frame = trailing;
       frame && count--;
       i++, frame = get_prev_frame (frame))
    {
      QUIT;
      fi = get_frame_info (frame);
      print_frame_info (fi, trailing_level + i, 0, 1);
    }

  /* If we've stopped before the end, mention that.  */
  if (frame && from_tty)
    printf_filtered ("(More stack frames follow...)\n");
}

/* Print the local variables of a block B active in FRAME.
   Return 1 if any variables were printed; 0 otherwise.  */

static int
print_block_frame_locals (b, frame, stream)
     struct block *b;
     register FRAME frame;
     register FILE *stream;
{
  int nsyms;
  register int i;
  register struct symbol *sym;
  register int values_printed = 0;

  nsyms = BLOCK_NSYMS (b);

  for (i = 0; i < nsyms; i++)
    {
      sym = BLOCK_SYM (b, i);
      if (SYMBOL_CLASS (sym) == LOC_LOCAL
	  || SYMBOL_CLASS (sym) == LOC_REGISTER
	  || SYMBOL_CLASS (sym) == LOC_STATIC)
	{
	  values_printed = 1;
	  fprint_symbol (stream, SYMBOL_NAME (sym));
	  fputs_filtered (" = ", stream);
	  print_variable_value (sym, frame, stream);
	  fprintf_filtered (stream, "\n");
	  fflush (stream);
	}
    }
  return values_printed;
}

/* Same, but print labels.
   FIXME, this does not even reference FRAME... --gnu  */

static int
print_block_frame_labels (b, frame, have_default, stream)
     struct block *b;
     register FRAME frame;
     int *have_default;
     register FILE *stream;
{
  int nsyms;
  register int i;
  register struct symbol *sym;
  register int values_printed = 0;

  nsyms = BLOCK_NSYMS (b);

  for (i = 0; i < nsyms; i++)
    {
      sym = BLOCK_SYM (b, i);
      if (! strcmp (SYMBOL_NAME (sym), "default"))
	{
	  if (*have_default)
	    continue;
	  *have_default = 1;
	}
      if (SYMBOL_CLASS (sym) == LOC_LABEL)
	{
	  struct symtab_and_line sal;
	  sal = find_pc_line (SYMBOL_VALUE_ADDRESS (sym), 0);
	  values_printed = 1;
	  fputs_demangled (SYMBOL_NAME (sym), stream, 1);
	  if (addressprint)
	    fprintf_filtered (stream, " 0x%x", SYMBOL_VALUE_ADDRESS (sym));
	  fprintf_filtered (stream, " in file %s, line %d\n",
			    sal.symtab->filename, sal.line);
	  fflush (stream);
	}
    }
  return values_printed;
}

/* Print on STREAM all the local variables in frame FRAME,
   including all the blocks active in that frame
   at its current pc.

   Returns 1 if the job was done,
   or 0 if nothing was printed because we have no info
   on the function running in FRAME.  */

static int
print_frame_local_vars (frame, stream)
     register FRAME frame;
     register FILE *stream;
{
  register struct block *block = get_frame_block (frame);
  register int values_printed = 0;

  if (block == 0)
    {
      fprintf_filtered (stream, "No symbol table info available.\n");
      fflush (stream);
      return 0;
    }
  
  while (block != 0)
    {
      if (print_block_frame_locals (block, frame, stream))
	values_printed = 1;
      /* After handling the function's top-level block, stop.
	 Don't continue to its superblock, the block of
	 per-file symbols.  */
      if (BLOCK_FUNCTION (block))
	break;
      block = BLOCK_SUPERBLOCK (block);
    }

  if (!values_printed)
    {
      fprintf_filtered (stream, "No locals.\n");
      fflush (stream);
    }
  
  return 1;
}

/* Same, but print labels.  */

static int
print_frame_label_vars (frame, this_level_only, stream)
     register FRAME frame;
     int this_level_only;
     register FILE *stream;
{
  extern struct blockvector *blockvector_for_pc ();
  register struct blockvector *bl;
  register struct block *block = get_frame_block (frame);
  register int values_printed = 0;
  int index, have_default = 0;
  char *blocks_printed;
  struct frame_info *fi = get_frame_info (frame);
  CORE_ADDR pc = fi->pc;

  if (block == 0)
    {
      fprintf_filtered (stream, "No symbol table info available.\n");
      fflush (stream);
      return 0;
    }

  bl = blockvector_for_pc (BLOCK_END (block) - 4, &index);
  blocks_printed = (char *) alloca (BLOCKVECTOR_NBLOCKS (bl) * sizeof (char));
  bzero (blocks_printed, BLOCKVECTOR_NBLOCKS (bl) * sizeof (char));

  while (block != 0)
    {
      CORE_ADDR end = BLOCK_END (block) - 4;
      int last_index;

      if (bl != blockvector_for_pc (end, &index))
	error ("blockvector blotch");
      if (BLOCKVECTOR_BLOCK (bl, index) != block)
	error ("blockvector botch");
      last_index = BLOCKVECTOR_NBLOCKS (bl);
      index += 1;

      /* Don't print out blocks that have gone by.  */
      while (index < last_index
	     && BLOCK_END (BLOCKVECTOR_BLOCK (bl, index)) < pc)
	index++;

      while (index < last_index
	     && BLOCK_END (BLOCKVECTOR_BLOCK (bl, index)) < end)
	{
	  if (blocks_printed[index] == 0)
	    {
	      if (print_block_frame_labels (BLOCKVECTOR_BLOCK (bl, index), frame, &have_default, stream))
		values_printed = 1;
	      blocks_printed[index] = 1;
	    }
	  index++;
	}
      if (have_default)
	return 1;
      if (values_printed && this_level_only)
	return 1;

      /* After handling the function's top-level block, stop.
	 Don't continue to its superblock, the block of
	 per-file symbols.  */
      if (BLOCK_FUNCTION (block))
	break;
      block = BLOCK_SUPERBLOCK (block);
    }

  if (!values_printed && !this_level_only)
    {
      fprintf_filtered (stream, "No catches.\n");
      fflush (stream);
    }
  
  return values_printed;
}

static void
locals_info (args, from_tty)
     char *args;
     int from_tty;
{
  if (!target_has_stack)
    error ("No stack.");

  print_frame_local_vars (selected_frame, stdout);
}

static void
catch_info ()
{
  if (!target_has_stack)
    error ("No stack.");

  print_frame_label_vars (selected_frame, 0, stdout);
}

static int
print_frame_arg_vars (frame, stream)
     register FRAME frame;
     register FILE *stream;
{
  struct symbol *func = get_frame_function (frame);
  register struct block *b;
  int nsyms;
  register int i;
  register struct symbol *sym, *sym2;
  register int values_printed = 0;

  if (func == 0)
    {
      fprintf_filtered (stream, "No symbol table info available.\n");
      fflush (stream);
      return 0;
    }

  b = SYMBOL_BLOCK_VALUE (func);
  nsyms = BLOCK_NSYMS (b);

  for (i = 0; i < nsyms; i++)
    {
      sym = BLOCK_SYM (b, i);
      if (SYMBOL_CLASS (sym) == LOC_ARG
	  || SYMBOL_CLASS (sym) == LOC_LOCAL_ARG
	  || SYMBOL_CLASS (sym) == LOC_REF_ARG
	  || SYMBOL_CLASS (sym) == LOC_REGPARM)
	{
	  values_printed = 1;
	  fprint_symbol (stream, SYMBOL_NAME (sym));
	  fputs_filtered (" = ", stream);
	  /* We have to look up the symbol because arguments often have
	     two entries (one a parameter, one a register) and the one
	     we want is the register, which lookup_symbol will find for
	     us.  */
	  sym2 = lookup_symbol (SYMBOL_NAME (sym),
			b, VAR_NAMESPACE, (int *)NULL, (struct symtab **)NULL);
	  print_variable_value (sym2, frame, stream);
	  fprintf_filtered (stream, "\n");
	  fflush (stream);
	}
    }

  if (!values_printed)
    {
      fprintf_filtered (stream, "No arguments.\n");
      fflush (stream);
    }

  return 1;
}

static void
args_info ()
{
  if (!target_has_stack)
    error ("No stack.");
  print_frame_arg_vars (selected_frame, stdout);
}

/* Select frame FRAME, and note that its stack level is LEVEL.
   LEVEL may be -1 if an actual level number is not known.  */

void
select_frame (frame, level)
     FRAME frame;
     int level;
{
  selected_frame = frame;
  selected_frame_level = level;
  /* Ensure that symbols for this frame are readin.  */
  if (frame)
    find_pc_symtab (get_frame_info (frame)->pc);
}

/* Store the selected frame and its level into *FRAMEP and *LEVELP.
   If there is no selected frame, *FRAMEP is set to NULL.  */

void
record_selected_frame (frameaddrp, levelp)
     FRAME_ADDR *frameaddrp;
     int *levelp;
{
  *frameaddrp = selected_frame ? FRAME_FP (selected_frame) : NULL;
  *levelp = selected_frame_level;
}

/* Return the symbol-block in which the selected frame is executing.
   Can return zero under various legitimate circumstances.  */

struct block *
get_selected_block ()
{
  if (!target_has_stack)
    return 0;

  if (!selected_frame)
    return get_current_block ();
  return get_frame_block (selected_frame);
}

/* Find a frame a certain number of levels away from FRAME.
   LEVEL_OFFSET_PTR points to an int containing the number of levels.
   Positive means go to earlier frames (up); negative, the reverse.
   The int that contains the number of levels is counted toward
   zero as the frames for those levels are found.
   If the top or bottom frame is reached, that frame is returned,
   but the final value of *LEVEL_OFFSET_PTR is nonzero and indicates
   how much farther the original request asked to go.  */

FRAME
find_relative_frame (frame, level_offset_ptr)
     register FRAME frame;
     register int* level_offset_ptr;
{
  register FRAME prev;
  register FRAME frame1, frame2;

  /* Going up is simple: just do get_prev_frame enough times
     or until initial frame is reached.  */
  while (*level_offset_ptr > 0)
    {
      prev = get_prev_frame (frame);
      if (prev == 0)
	break;
      (*level_offset_ptr)--;
      frame = prev;
    }
  /* Going down could be done by iterating get_frame_info to
     find the next frame, but that would be quadratic
     since get_frame_info must scan all the way from the current frame.
     The following algorithm is linear.  */
  if (*level_offset_ptr < 0)
    {
      /* First put frame1 at innermost frame
	 and frame2 N levels up from there.  */
      frame1 = get_current_frame ();
      frame2 = frame1;
      while (*level_offset_ptr < 0 && frame2 != frame)
	{
	  frame2 = get_prev_frame (frame2);
	  (*level_offset_ptr) ++;
	}
      /* Then slide frame1 and frame2 up in synchrony
	 and when frame2 reaches our starting point
	 frame1 must be N levels down from there.  */
      while (frame2 != frame)
	{
	  frame1 = get_prev_frame (frame1);
	  frame2 = get_prev_frame (frame2);
	}
      return frame1;
    }
  return frame;
}

/* The "frame" command.  With no arg, print selected frame briefly.
   With arg LEVEL_EXP, select the frame at level LEVEL if it is a
   valid level.  Otherwise, treat level_exp as an address expression
   and print it.  See parse_frame_specification for more info on proper
   frame expressions. */

static void
frame_command (level_exp, from_tty)
     char *level_exp;
     int from_tty;
{
  register FRAME frame, frame1;
  unsigned int level = 0;

  if (!target_has_stack)
    error ("No stack.");

  frame = parse_frame_specification (level_exp);

  for (frame1 = get_prev_frame (0);
       frame1 && frame1 != frame;
       frame1 = get_prev_frame (frame1))
    level++;

  if (!frame1)
    level = 0;

  select_frame (frame, level);

  if (!from_tty)
    return;

  print_stack_frame (selected_frame, selected_frame_level, 1);
}

/* Select the frame up one or COUNT stack levels
   from the previously selected frame, and print it briefly.  */

static void
up_silently_command (count_exp, from_tty)
     char *count_exp;
     int from_tty;
{
  register FRAME frame;
  int count = 1, count1;
  if (count_exp)
    count = parse_and_eval_address (count_exp);
  count1 = count;
  
  if (!target_has_stack)
    error ("No stack.");

  frame = find_relative_frame (selected_frame, &count1);
  if (count1 != 0 && count_exp == 0)
    error ("Initial frame selected; you cannot go up.");
  select_frame (frame, selected_frame_level + count - count1);
}

static void
up_command (count_exp, from_tty)
     char *count_exp;
     int from_tty;
{
  up_silently_command (count_exp, from_tty);
  print_stack_frame (selected_frame, selected_frame_level, 1);
}

/* Select the frame down one or COUNT stack levels
   from the previously selected frame, and print it briefly.  */

static void
down_silently_command (count_exp, from_tty)
     char *count_exp;
     int from_tty;
{
  register FRAME frame;
  int count = -1, count1;
  if (count_exp)
    count = - parse_and_eval_address (count_exp);
  count1 = count;
  
  frame = find_relative_frame (selected_frame, &count1);
  if (count1 != 0 && count_exp == 0)
    error ("Bottom (i.e., innermost) frame selected; you cannot go down.");
  select_frame (frame, selected_frame_level + count - count1);
}


static void
down_command (count_exp, from_tty)
     char *count_exp;
     int from_tty;
{
  down_silently_command (count_exp, from_tty);
  print_stack_frame (selected_frame, selected_frame_level, 1);
}

static void
return_command (retval_exp, from_tty)
     char *retval_exp;
     int from_tty;
{
  struct symbol *thisfun;
  FRAME_ADDR selected_frame_addr;
  CORE_ADDR selected_frame_pc;
  FRAME frame;

  if (selected_frame == NULL)
    error ("No selected frame.");
  thisfun = get_frame_function (selected_frame);
  selected_frame_addr = FRAME_FP (selected_frame);
  selected_frame_pc = (get_frame_info (selected_frame))->pc;

  /* If interactive, require confirmation.  */

  if (from_tty)
    {
      if (thisfun != 0)
	{
	  if (!query ("Make %s return now? ", SYMBOL_NAME (thisfun)))
	    error ("Not confirmed.");
	}
      else
	if (!query ("Make selected stack frame return now? "))
	  error ("Not confirmed.");
    }

  /* Do the real work.  Pop until the specified frame is current.  We
     use this method because the selected_frame is not valid after
     a POP_FRAME.  The pc comparison makes this work even if the
     selected frame shares its fp with another frame.  */

  while ( selected_frame_addr != FRAME_FP (frame = get_current_frame())
       || selected_frame_pc   != (get_frame_info (frame))->pc  )
    POP_FRAME;

  /* Then pop that frame.  */

  POP_FRAME;

  /* Compute the return value (if any) and store in the place
     for return values.  */

  if (retval_exp)
    set_return_value (parse_and_eval (retval_exp));

  /* If interactive, print the frame that is now current.  */

  if (from_tty)
    frame_command ("0", 1);
}

void
_initialize_stack ()
{
#if 0  
  backtrace_limit = 30;
#endif

  add_com ("return", class_stack, return_command,
	   "Make selected stack frame return to its caller.\n\
Control remains in the debugger, but when you continue\n\
execution will resume in the frame above the one now selected.\n\
If an argument is given, it is an expression for the value to return.");

  add_com ("up", class_stack, up_command,
	   "Select and print stack frame that called this one.\n\
An argument says how many frames up to go.");
  add_com ("up-silently", class_support, up_silently_command,
	   "Same as the `up' command, but does not print anything.\n\
This is useful in command scripts.");

  add_com ("down", class_stack, down_command,
	   "Select and print stack frame called by this one.\n\
An argument says how many frames down to go.");
  add_com_alias ("do", "down", class_stack, 1);
  add_com ("down-silently", class_support, down_silently_command,
	   "Same as the `down' command, but does not print anything.\n\
This is useful in command scripts.");

  add_com ("frame", class_stack, frame_command,
	   "Select and print a stack frame.\n\
With no argument, print the selected stack frame.  (See also \"info frame\").\n\
An argument specifies the frame to select.\n\
It can be a stack frame number or the address of the frame.\n\
With argument, nothing is printed if input is coming from\n\
a command file or a user-defined command.");

  add_com_alias ("f", "frame", class_stack, 1);

  add_com ("backtrace", class_stack, backtrace_command,
	   "Print backtrace of all stack frames, or innermost COUNT frames.\n\
With a negative argument, print outermost -COUNT frames.");
  add_com_alias ("bt", "backtrace", class_stack, 0);
  add_com_alias ("where", "backtrace", class_alias, 0);
  add_info ("stack", backtrace_command,
	    "Backtrace of the stack, or innermost COUNT frames.");
  add_info_alias ("s", "stack", 1);
  add_info ("frame", frame_info,
	    "All about selected stack frame, or frame at ADDR.");
  add_info_alias ("f", "frame", 1);
  add_info ("locals", locals_info,
	    "Local variables of current stack frame.");
  add_info ("args", args_info,
	    "Argument variables of current stack frame.");
  add_info ("catch", catch_info,
	    "Exceptions that can be caught in the current stack frame.");

#if 0
  add_cmd ("backtrace-limit", class_stack, set_backtrace_limit_command, 
	   "Specify maximum number of frames for \"backtrace\" to print by default.",
	   &setlist);
  add_info ("backtrace-limit", backtrace_limit_info,
	    "The maximum number of frames for \"backtrace\" to print by default.");
#endif
}