formatting cleanups

[deliverable/binutils-gdb.git] / gdb / mips-tdep.c

/* Target-dependent code for the MIPS architecture, for GDB, the GNU Debugger.
   Copyright 1988, 1989, 1990, 1991, 1992, 1993 Free Software Foundation, Inc.
   Contributed by Alessandro Forin(af@cs.cmu.edu) at CMU
   and by Per Bothner(bothner@cs.wisc.edu) at U.Wisconsin.

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 "frame.h"
#include "inferior.h"
#include "symtab.h"
#include "value.h"
#include "gdbcmd.h"
#include "language.h"
#include "gdbcore.h"
#include "symfile.h"
#include "objfiles.h"

#include "opcode/mips.h"

#define VM_MIN_ADDRESS (unsigned)0x400000
\f
static int mips_in_lenient_prologue PARAMS ((CORE_ADDR, CORE_ADDR));

/* Some MIPS boards don't support floating point, so we permit the
   user to turn it off.  */
int mips_fpu = 1;

/* Heuristic_proc_start may hunt through the text section for a long
   time across a 2400 baud serial line.  Allows the user to limit this
   search.  */
static unsigned int heuristic_fence_post = 0;

#define PROC_LOW_ADDR(proc) ((proc)->pdr.adr) /* least address */
#define PROC_HIGH_ADDR(proc) ((proc)->pdr.iline) /* upper address bound */
#define PROC_FRAME_OFFSET(proc) ((proc)->pdr.frameoffset)
#define PROC_FRAME_REG(proc) ((proc)->pdr.framereg)
#define PROC_REG_MASK(proc) ((proc)->pdr.regmask)
#define PROC_FREG_MASK(proc) ((proc)->pdr.fregmask)
#define PROC_REG_OFFSET(proc) ((proc)->pdr.regoffset)
#define PROC_FREG_OFFSET(proc) ((proc)->pdr.fregoffset)
#define PROC_PC_REG(proc) ((proc)->pdr.pcreg)
#define PROC_SYMBOL(proc) (*(struct symbol**)&(proc)->pdr.isym)
#define _PROC_MAGIC_ 0x0F0F0F0F
#define PROC_DESC_IS_DUMMY(proc) ((proc)->pdr.isym == _PROC_MAGIC_)
#define SET_PROC_DESC_IS_DUMMY(proc) ((proc)->pdr.isym = _PROC_MAGIC_)

struct linked_proc_info
{
  struct mips_extra_func_info info;
  struct linked_proc_info *next;
} *linked_proc_desc_table = NULL;

\f
#define READ_FRAME_REG(fi, regno) read_next_frame_reg((fi)->next, regno)

static int
read_next_frame_reg(fi, regno)
     FRAME fi;
     int regno;
{
  /* If it is the frame for sigtramp we have a complete sigcontext
     immediately below the frame and we get the saved registers from there.
     If the stack layout for sigtramp changes we might have to change these
     constants and the companion fixup_sigtramp in mipsread.c  */
#ifndef SIGFRAME_BASE
#define SIGFRAME_BASE           0x12c   /* sizeof(sigcontext) */
#define SIGFRAME_PC_OFF         (-SIGFRAME_BASE + 2 * 4)
#define SIGFRAME_REGSAVE_OFF    (-SIGFRAME_BASE + 3 * 4)
#endif
  for (; fi; fi = fi->next)
      if (in_sigtramp(fi->pc, 0)) {
          int offset;
          if (regno == PC_REGNUM) offset = SIGFRAME_PC_OFF;
          else if (regno < 32) offset = SIGFRAME_REGSAVE_OFF + regno * 4;
          else return 0;
          return read_memory_integer(fi->frame + offset, 4);
      }
      else if (regno == SP_REGNUM) return fi->frame;
      else if (fi->saved_regs->regs[regno])
        return read_memory_integer(fi->saved_regs->regs[regno], 4);
  return read_register(regno);
}

int
mips_frame_saved_pc(frame)
     FRAME frame;
{
  mips_extra_func_info_t proc_desc = frame->proc_desc;
  int pcreg = proc_desc ? PROC_PC_REG(proc_desc) : RA_REGNUM;

  if (proc_desc && PROC_DESC_IS_DUMMY(proc_desc))
      return read_memory_integer(frame->frame - 4, 4);

  return read_next_frame_reg(frame, pcreg);
}

static struct mips_extra_func_info temp_proc_desc;
static struct frame_saved_regs temp_saved_regs;

/* This fencepost looks highly suspicious to me.  Removing it also
   seems suspicious as it could affect remote debugging across serial
   lines.  */

static CORE_ADDR
heuristic_proc_start(pc)
    CORE_ADDR pc;
{
    CORE_ADDR start_pc = pc;
    CORE_ADDR fence = start_pc - heuristic_fence_post;

    if (start_pc == 0)  return 0;

    if (heuristic_fence_post == UINT_MAX
        || fence < VM_MIN_ADDRESS)
      fence = VM_MIN_ADDRESS;

    /* search back for previous return */
    for (start_pc -= 4; ; start_pc -= 4)
        if (start_pc < fence)
          {
            /* It's not clear to me why we reach this point when
               stop_soon_quietly, but with this test, at least we
               don't print out warnings for every child forked (eg, on
               decstation).  22apr93 rich@cygnus.com.  */
            if (!stop_soon_quietly)
              {
                static int blurb_printed = 0;

                if (fence == VM_MIN_ADDRESS)
                  warning("Hit beginning of text section without finding");
                else
                  warning("Hit heuristic-fence-post without finding");
                
                warning("enclosing function for address 0x%x", pc);
                if (!blurb_printed)
                  {
                    printf_filtered ("\
This warning occurs if you are debugging a function without any symbols\n\
(for example, in a stripped executable).  In that case, you may wish to\n\
increase the size of the search with the `set heuristic-fence-post' command.\n\
\n\
Otherwise, you told GDB there was a function where there isn't one, or\n\
(more likely) you have encountered a bug in GDB.\n");
                    blurb_printed = 1;
                  }
              }

            return 0; 
          }
        else if (ABOUT_TO_RETURN(start_pc))
            break;

    start_pc += 8; /* skip return, and its delay slot */
#if 0
    /* skip nops (usually 1) 0 - is this */
    while (start_pc < pc && read_memory_integer (start_pc, 4) == 0)
        start_pc += 4;
#endif
    return start_pc;
}

static mips_extra_func_info_t
heuristic_proc_desc(start_pc, limit_pc, next_frame)
    CORE_ADDR start_pc, limit_pc;
    FRAME next_frame;
{
    CORE_ADDR sp = next_frame ? next_frame->frame : read_register (SP_REGNUM);
    CORE_ADDR cur_pc;
    int frame_size;
    int has_frame_reg = 0;
    int reg30; /* Value of $r30. Used by gcc for frame-pointer */
    unsigned long reg_mask = 0;

    if (start_pc == 0) return NULL;
    bzero(&temp_proc_desc, sizeof(temp_proc_desc));
    bzero(&temp_saved_regs, sizeof(struct frame_saved_regs));
    PROC_LOW_ADDR(&temp_proc_desc) = start_pc;

    if (start_pc + 200 < limit_pc) limit_pc = start_pc + 200;
  restart:
    frame_size = 0;
    for (cur_pc = start_pc; cur_pc < limit_pc; cur_pc += 4) {
        char buf[4];
        unsigned long word;
        int status;

        status = read_memory_nobpt (cur_pc, buf, 4); 
        if (status) memory_error (status, cur_pc);
        word = extract_unsigned_integer (buf, 4);

        if ((word & 0xFFFF0000) == 0x27bd0000) /* addiu $sp,$sp,-i */
            frame_size += (-word) & 0xFFFF;
        else if ((word & 0xFFFF0000) == 0x23bd0000) /* addu $sp,$sp,-i */
            frame_size += (-word) & 0xFFFF;
        else if ((word & 0xFFE00000) == 0xafa00000) { /* sw reg,offset($sp) */
            int reg = (word & 0x001F0000) >> 16;
            reg_mask |= 1 << reg;
            temp_saved_regs.regs[reg] = sp + (short)word;
        }
        else if ((word & 0xFFFF0000) == 0x27be0000) { /* addiu $30,$sp,size */
            if ((unsigned short)word != frame_size)
                reg30 = sp + (unsigned short)word;
            else if (!has_frame_reg) {
                int alloca_adjust;
                has_frame_reg = 1;
                reg30 = read_next_frame_reg(next_frame, 30);
                alloca_adjust = reg30 - (sp + (unsigned short)word);
                if (alloca_adjust > 0) {
                    /* FP > SP + frame_size. This may be because
                    /* of an alloca or somethings similar.
                     * Fix sp to "pre-alloca" value, and try again.
                     */
                    sp += alloca_adjust;
                    goto restart;
                }
            }
        }
        else if ((word & 0xFFE00000) == 0xafc00000) { /* sw reg,offset($30) */
            int reg = (word & 0x001F0000) >> 16;
            reg_mask |= 1 << reg;
            temp_saved_regs.regs[reg] = reg30 + (short)word;
        }
    }
    if (has_frame_reg) {
        PROC_FRAME_REG(&temp_proc_desc) = 30;
        PROC_FRAME_OFFSET(&temp_proc_desc) = 0;
    }
    else {
        PROC_FRAME_REG(&temp_proc_desc) = SP_REGNUM;
        PROC_FRAME_OFFSET(&temp_proc_desc) = frame_size;
    }
    PROC_REG_MASK(&temp_proc_desc) = reg_mask;
    PROC_PC_REG(&temp_proc_desc) = RA_REGNUM;
    return &temp_proc_desc;
}

static mips_extra_func_info_t
find_proc_desc(pc, next_frame)
    CORE_ADDR pc;
    FRAME next_frame;
{
  mips_extra_func_info_t proc_desc;
  struct block *b = block_for_pc(pc);
  struct symbol *sym;
  CORE_ADDR startaddr;

  find_pc_partial_function (pc, NULL, &startaddr, NULL);
  if (b == NULL)
    sym = NULL;
  else
    {
      if (startaddr > BLOCK_START (b))
        /* This is the "pathological" case referred to in a comment in
           print_frame_info.  It might be better to move this check into
           symbol reading.  */
        sym = NULL;
      else
        sym = lookup_symbol (MIPS_EFI_SYMBOL_NAME, b, LABEL_NAMESPACE,
                             0, NULL);
    }

  if (sym)
    {
        /* IF this is the topmost frame AND
         * (this proc does not have debugging information OR
         * the PC is in the procedure prologue)
         * THEN create a "heuristic" proc_desc (by analyzing
         * the actual code) to replace the "official" proc_desc.
         */
        proc_desc = (mips_extra_func_info_t)SYMBOL_VALUE(sym);
        if (next_frame == NULL) {
            struct symtab_and_line val;
            struct symbol *proc_symbol =
                PROC_DESC_IS_DUMMY(proc_desc) ? 0 : PROC_SYMBOL(proc_desc);

            if (proc_symbol) {
                val = find_pc_line (BLOCK_START
                                    (SYMBOL_BLOCK_VALUE(proc_symbol)),
                                    0);
                val.pc = val.end ? val.end : pc;
            }
            if (!proc_symbol || pc < val.pc) {
                mips_extra_func_info_t found_heuristic =
                    heuristic_proc_desc(PROC_LOW_ADDR(proc_desc),
                                        pc, next_frame);
                if (found_heuristic) proc_desc = found_heuristic;
            }
        }
    }
  else
    {
      /* Is linked_proc_desc_table really necessary?  It only seems to be used
         by procedure call dummys.  However, the procedures being called ought
         to have their own proc_descs, and even if they don't,
         heuristic_proc_desc knows how to create them! */

      register struct linked_proc_info *link;
      for (link = linked_proc_desc_table; link; link = link->next)
          if (PROC_LOW_ADDR(&link->info) <= pc
              && PROC_HIGH_ADDR(&link->info) > pc)
              return &link->info;

      if (startaddr == 0)
        startaddr = heuristic_proc_start (pc);

      proc_desc =
        heuristic_proc_desc (startaddr, pc, next_frame);
    }
  return proc_desc;
}

mips_extra_func_info_t cached_proc_desc;

FRAME_ADDR
mips_frame_chain(frame)
    FRAME frame;
{
    mips_extra_func_info_t proc_desc;
    CORE_ADDR saved_pc = FRAME_SAVED_PC(frame);

    if (saved_pc == 0 || inside_entry_file (saved_pc))
      return 0;

    proc_desc = find_proc_desc(saved_pc, frame);
    if (!proc_desc)
      return 0;

    cached_proc_desc = proc_desc;
    return read_next_frame_reg(frame, PROC_FRAME_REG(proc_desc))
      + PROC_FRAME_OFFSET(proc_desc);
}

void
init_extra_frame_info(fci)
     struct frame_info *fci;
{
  extern struct obstack frame_cache_obstack;
  /* Use proc_desc calculated in frame_chain */
  mips_extra_func_info_t proc_desc =
    fci->next ? cached_proc_desc : find_proc_desc(fci->pc, fci->next);

  fci->saved_regs = (struct frame_saved_regs*)
    obstack_alloc (&frame_cache_obstack, sizeof(struct frame_saved_regs));
  memset (fci->saved_regs, 0, sizeof (struct frame_saved_regs));
  fci->proc_desc =
    proc_desc == &temp_proc_desc ? 0 : proc_desc;
  if (proc_desc)
    {
      int ireg;
      CORE_ADDR reg_position;
      unsigned long mask;
      /* r0 bit means kernel trap */
      int kernel_trap = PROC_REG_MASK(proc_desc) & 1;

      /* Fixup frame-pointer - only needed for top frame */
      /* This may not be quite right, if proc has a real frame register */
      if (fci->pc == PROC_LOW_ADDR(proc_desc) && !PROC_DESC_IS_DUMMY(proc_desc))
        fci->frame = read_register (SP_REGNUM);
      else
        fci->frame = READ_FRAME_REG(fci, PROC_FRAME_REG(proc_desc))
                      + PROC_FRAME_OFFSET(proc_desc);

      /* If this is the innermost frame, and we are still in the
         prologue (loosely defined), then the registers may not have
         been saved yet.  */
      if (fci->next == NULL
          && !PROC_DESC_IS_DUMMY(proc_desc)
          && mips_in_lenient_prologue (PROC_LOW_ADDR (proc_desc), fci->pc))
        {
          /* Can't just say that the registers are not saved, because they
             might get clobbered halfway through the prologue.
             heuristic_proc_desc already has the right code to figure out
             exactly what has been saved, so use it.  As far as I know we
             could be doing this (as we do on the 68k, for example)
             regardless of whether we are in the prologue; I'm leaving in
             the check for being in the prologue only out of conservatism
             (I'm not sure whether heuristic_proc_desc handles all cases,
             for example).

             This stuff is ugly (and getting uglier by the minute).  Probably
             the best way to clean it up is to ignore the proc_desc's from
             the symbols altogher, and get all the information we need by
             examining the prologue (provided we can make the prologue
             examining code good enough to get all the cases...).  */
          proc_desc =
            heuristic_proc_desc (PROC_LOW_ADDR (proc_desc),
                                 fci->pc,
                                 fci->next);
        }

      if (proc_desc == &temp_proc_desc)
        *fci->saved_regs = temp_saved_regs;
      else
        {
          /* find which general-purpose registers were saved */
          reg_position = fci->frame + PROC_REG_OFFSET(proc_desc);
          mask = kernel_trap ? 0xFFFFFFFF : PROC_REG_MASK(proc_desc);
          for (ireg= 31; mask; --ireg, mask <<= 1)
            if (mask & 0x80000000)
              {
                fci->saved_regs->regs[ireg] = reg_position;
                reg_position -= 4;
              }
          /* find which floating-point registers were saved */
          reg_position = fci->frame + PROC_FREG_OFFSET(proc_desc);

          /* The freg_offset points to where the first *double* register
             is saved.  So skip to the high-order word. */
          reg_position += 4;
          mask = kernel_trap ? 0xFFFFFFFF : PROC_FREG_MASK(proc_desc);
          for (ireg = 31; mask; --ireg, mask <<= 1)
            if (mask & 0x80000000)
              {
                fci->saved_regs->regs[FP0_REGNUM+ireg] = reg_position;
                reg_position -= 4;
              }
        }

      /* hack: if argument regs are saved, guess these contain args */
      if ((PROC_REG_MASK(proc_desc) & 0xF0) == 0) fci->num_args = -1;
      else if ((PROC_REG_MASK(proc_desc) & 0x80) == 0) fci->num_args = 4;
      else if ((PROC_REG_MASK(proc_desc) & 0x40) == 0) fci->num_args = 3;
      else if ((PROC_REG_MASK(proc_desc) & 0x20) == 0) fci->num_args = 2;
      else if ((PROC_REG_MASK(proc_desc) & 0x10) == 0) fci->num_args = 1;

      fci->saved_regs->regs[PC_REGNUM] = fci->saved_regs->regs[RA_REGNUM];
    }
}

/* MIPS stack frames are almost impenetrable.  When execution stops,
   we basically have to look at symbol information for the function
   that we stopped in, which tells us *which* register (if any) is
   the base of the frame pointer, and what offset from that register
   the frame itself is at.  

   This presents a problem when trying to examine a stack in memory
   (that isn't executing at the moment), using the "frame" command.  We
   don't have a PC, nor do we have any registers except SP.

   This routine takes two arguments, SP and PC, and tries to make the
   cached frames look as if these two arguments defined a frame on the
   cache.  This allows the rest of info frame to extract the important
   arguments without difficulty.  */

FRAME
setup_arbitrary_frame (argc, argv)
     int argc;
     FRAME_ADDR *argv;
{
  if (argc != 2)
    error ("MIPS frame specifications require two arguments: sp and pc");

  return create_new_frame (argv[0], argv[1]);
}


CORE_ADDR
mips_push_arguments(nargs, args, sp, struct_return, struct_addr)
  int nargs;
  value *args;
  CORE_ADDR sp;
  int struct_return;
  CORE_ADDR struct_addr;
{
  CORE_ADDR buf;
  register i;
  int accumulate_size = struct_return ? 4 : 0;
  struct mips_arg { char *contents; int len; int offset; };
  struct mips_arg *mips_args =
      (struct mips_arg*)alloca(nargs * sizeof(struct mips_arg));
  register struct mips_arg *m_arg;
  for (i = 0, m_arg = mips_args; i < nargs; i++, m_arg++) {
    extern value value_arg_coerce();
    value arg = value_arg_coerce (args[i]);
    m_arg->len = TYPE_LENGTH (VALUE_TYPE (arg));
    /* This entire mips-specific routine is because doubles must be aligned
     * on 8-byte boundaries. It still isn't quite right, because MIPS decided
     * to align 'struct {int a, b}' on 4-byte boundaries (even though this
     * breaks their varargs implementation...). A correct solution
     * requires an simulation of gcc's 'alignof' (and use of 'alignof'
     * in stdarg.h/varargs.h).
     */
    if (m_arg->len > 4) accumulate_size = (accumulate_size + 7) & -8;
    m_arg->offset = accumulate_size;
    accumulate_size = (accumulate_size + m_arg->len + 3) & -4;
    m_arg->contents = VALUE_CONTENTS(arg);
  }
  accumulate_size = (accumulate_size + 7) & (-8);
  if (accumulate_size < 16) accumulate_size = 16; 
  sp -= accumulate_size;
  for (i = nargs; m_arg--, --i >= 0; )
    write_memory(sp + m_arg->offset, m_arg->contents, m_arg->len);
  if (struct_return) {
    buf = struct_addr;
    write_memory(sp, (char *)&buf, sizeof(CORE_ADDR));
  }
  return sp;
}

/* MASK(i,j) == (1<<i) + (1<<(i+1)) + ... + (1<<j)). Assume i<=j<31. */
#define MASK(i,j) ((1 << (j)+1)-1 ^ (1 << (i))-1)

void
mips_push_dummy_frame()
{
  int ireg;
  struct linked_proc_info *link = (struct linked_proc_info*)
      xmalloc(sizeof(struct linked_proc_info));
  mips_extra_func_info_t proc_desc = &link->info;
  CORE_ADDR sp = read_register (SP_REGNUM);
  CORE_ADDR save_address;
  REGISTER_TYPE buffer;
  link->next = linked_proc_desc_table;
  linked_proc_desc_table = link;
#define PUSH_FP_REGNUM 16 /* must be a register preserved across calls */
#define GEN_REG_SAVE_MASK MASK(1,16)|MASK(24,28)|(1<<31)
#define GEN_REG_SAVE_COUNT 22
#define FLOAT_REG_SAVE_MASK MASK(0,19)
#define FLOAT_REG_SAVE_COUNT 20
#define SPECIAL_REG_SAVE_COUNT 4
  /*
   * The registers we must save are all those not preserved across
   * procedure calls. Dest_Reg (see tm-mips.h) must also be saved.
   * In addition, we must save the PC, and PUSH_FP_REGNUM.
   * (Ideally, we should also save MDLO/-HI and FP Control/Status reg.)
   *
   * Dummy frame layout:
   *  (high memory)
   *    Saved PC
   *    Saved MMHI, MMLO, FPC_CSR
   *    Saved R31
   *    Saved R28
   *    ...
   *    Saved R1
   *    Saved D18 (i.e. F19, F18)
   *    ...
   *    Saved D0 (i.e. F1, F0)
   *    CALL_DUMMY (subroutine stub; see tm-mips.h)
   *    Parameter build area (not yet implemented)
   *  (low memory)
   */
  PROC_REG_MASK(proc_desc) = GEN_REG_SAVE_MASK;
  PROC_FREG_MASK(proc_desc) = mips_fpu ? FLOAT_REG_SAVE_MASK : 0;
  PROC_REG_OFFSET(proc_desc) = /* offset of (Saved R31) from FP */
      -sizeof(long) - 4 * SPECIAL_REG_SAVE_COUNT;
  PROC_FREG_OFFSET(proc_desc) = /* offset of (Saved D18) from FP */
      -sizeof(double) - 4 * (SPECIAL_REG_SAVE_COUNT + GEN_REG_SAVE_COUNT);
  /* save general registers */
  save_address = sp + PROC_REG_OFFSET(proc_desc);
  for (ireg = 32; --ireg >= 0; )
    if (PROC_REG_MASK(proc_desc) & (1 << ireg))
      {
        buffer = read_register (ireg);
        write_memory (save_address, (char *)&buffer, sizeof(REGISTER_TYPE));
        save_address -= 4;
      }
  /* save floating-points registers starting with high order word */
  save_address = sp + PROC_FREG_OFFSET(proc_desc) + 4;
  for (ireg = 32; --ireg >= 0; )
    if (PROC_FREG_MASK(proc_desc) & (1 << ireg))
      {
        buffer = read_register (ireg + FP0_REGNUM);
        write_memory (save_address, (char *)&buffer, 4);
        save_address -= 4;
      }
  write_register (PUSH_FP_REGNUM, sp);
  PROC_FRAME_REG(proc_desc) = PUSH_FP_REGNUM;
  PROC_FRAME_OFFSET(proc_desc) = 0;
  buffer = read_register (PC_REGNUM);
  write_memory (sp - 4, (char *)&buffer, sizeof(REGISTER_TYPE));
  buffer = read_register (HI_REGNUM);
  write_memory (sp - 8, (char *)&buffer, sizeof(REGISTER_TYPE));
  buffer = read_register (LO_REGNUM);
  write_memory (sp - 12, (char *)&buffer, sizeof(REGISTER_TYPE));
  buffer = read_register (mips_fpu ? FCRCS_REGNUM : ZERO_REGNUM);
  write_memory (sp - 16, (char *)&buffer, sizeof(REGISTER_TYPE));
  sp -= 4 * (GEN_REG_SAVE_COUNT
             + (mips_fpu ? FLOAT_REG_SAVE_COUNT : 0)
             + SPECIAL_REG_SAVE_COUNT);
  write_register (SP_REGNUM, sp);
  PROC_LOW_ADDR(proc_desc) = sp - CALL_DUMMY_SIZE + CALL_DUMMY_START_OFFSET;
  PROC_HIGH_ADDR(proc_desc) = sp;
  SET_PROC_DESC_IS_DUMMY(proc_desc);
  PROC_PC_REG(proc_desc) = RA_REGNUM;
}

void
mips_pop_frame()
{
  register int regnum;
  FRAME frame = get_current_frame ();
  CORE_ADDR new_sp = frame->frame;

  mips_extra_func_info_t proc_desc = frame->proc_desc;

  write_register (PC_REGNUM, FRAME_SAVED_PC(frame));
  if (proc_desc)
    {
      for (regnum = 32; --regnum >= 0; )
        if (PROC_REG_MASK(proc_desc) & (1 << regnum))
          write_register (regnum,
                          read_memory_integer (frame->saved_regs->regs[regnum],
                                               4));
      for (regnum = 32; --regnum >= 0; )
        if (PROC_FREG_MASK(proc_desc) & (1 << regnum))
          write_register (regnum + FP0_REGNUM,
                          read_memory_integer (frame->saved_regs->regs[regnum + FP0_REGNUM], 4));
    }
  write_register (SP_REGNUM, new_sp);
  flush_cached_frames ();
  /* We let mips_init_extra_frame_info figure out the frame pointer */
  set_current_frame (create_new_frame (0, read_pc ()));

  if (PROC_DESC_IS_DUMMY(proc_desc))
    {
      struct linked_proc_info *pi_ptr, *prev_ptr;

      for (pi_ptr = linked_proc_desc_table, prev_ptr = NULL;
           pi_ptr != NULL;
           prev_ptr = pi_ptr, pi_ptr = pi_ptr->next)
        {
          if (&pi_ptr->info == proc_desc)
            break;
        }

      if (pi_ptr == NULL)
        error ("Can't locate dummy extra frame info\n");

      if (prev_ptr != NULL)
        prev_ptr->next = pi_ptr->next;
      else
        linked_proc_desc_table = pi_ptr->next;

      free (pi_ptr);

      write_register (HI_REGNUM, read_memory_integer(new_sp - 8, 4));
      write_register (LO_REGNUM, read_memory_integer(new_sp - 12, 4));
      if (mips_fpu)
        write_register (FCRCS_REGNUM, read_memory_integer(new_sp - 16, 4));
    }
}

static void
mips_print_register (regnum, all)
     int regnum, all;
{
  unsigned char raw_buffer[MAX_REGISTER_RAW_SIZE];
  REGISTER_TYPE val;

  /* Get the data in raw format.  */
  if (read_relative_register_raw_bytes (regnum, raw_buffer))
    {
      printf_filtered ("%s: [Invalid]", reg_names[regnum]);
      return;
    }

  /* If an even floating pointer register, also print as double. */
  if (regnum >= FP0_REGNUM && regnum < FP0_REGNUM+32
      && !((regnum-FP0_REGNUM) & 1)) {
    char dbuffer[MAX_REGISTER_RAW_SIZE]; 

    read_relative_register_raw_bytes (regnum, dbuffer);
    read_relative_register_raw_bytes (regnum+1, dbuffer+4);
#ifdef REGISTER_CONVERT_TO_TYPE
    REGISTER_CONVERT_TO_TYPE(regnum, builtin_type_double, dbuffer);
#endif
    printf_filtered ("(d%d: ", regnum-FP0_REGNUM);
    val_print (builtin_type_double, dbuffer, 0,
               stdout, 0, 1, 0, Val_pretty_default);
    printf_filtered ("); ");
  }
  fputs_filtered (reg_names[regnum], stdout);

  /* The problem with printing numeric register names (r26, etc.) is that
     the user can't use them on input.  Probably the best solution is to
     fix it so that either the numeric or the funky (a2, etc.) names
     are accepted on input.  */
  if (regnum < 32)
    printf_filtered ("(r%d): ", regnum);
  else
    printf_filtered (": ");

  /* If virtual format is floating, print it that way.  */
  if (TYPE_CODE (REGISTER_VIRTUAL_TYPE (regnum)) == TYPE_CODE_FLT
      && ! INVALID_FLOAT (raw_buffer, REGISTER_VIRTUAL_SIZE(regnum))) {
    val_print (REGISTER_VIRTUAL_TYPE (regnum), raw_buffer, 0,
               stdout, 0, 1, 0, Val_pretty_default);
  }
  /* Else print as integer in hex.  */
  else
    {
      long val;

      val = extract_signed_integer (raw_buffer,
                                    REGISTER_RAW_SIZE (regnum));

      if (val == 0)
        printf_filtered ("0");
      else if (all)
        /* FIXME: We should be printing this in a fixed field width, so that
           registers line up.  */
        printf_filtered (local_hex_format(), val);
      else
        printf_filtered ("%s=%d", local_hex_string(val), val);
    }
}

/* Replacement for generic do_registers_info.  */
void
mips_do_registers_info (regnum, fpregs)
     int regnum;
     int fpregs;
{
  if (regnum != -1) {
      mips_print_register (regnum, 0);
      printf_filtered ("\n");
  }
  else {
      for (regnum = 0; regnum < NUM_REGS; ) {
          if ((!fpregs) && regnum >= FP0_REGNUM && regnum <= FCRIR_REGNUM) {
            regnum++;
            continue;
          }
          mips_print_register (regnum, 1);
          regnum++;
          if ((regnum & 3) == 0 || regnum == NUM_REGS)
              printf_filtered (";\n");
          else
              printf_filtered ("; ");
      }
  }
}
/* Return number of args passed to a frame. described by FIP.
   Can return -1, meaning no way to tell.  */

int
mips_frame_num_args(fip)
        FRAME fip;
{
#if 0
        struct chain_info_t *p;

        p = mips_find_cached_frame(FRAME_FP(fip));
        if (p->valid)
                return p->the_info.numargs;
#endif
        return -1;
}
\f
/* Does this instruction involve use of a delay slot?  */
static int
is_delayed (insn)
     unsigned long insn;
{
  int i;
  for (i = 0; i < NUMOPCODES; ++i)
    if (mips_opcodes[i].pinfo != INSN_MACRO
        && (insn & mips_opcodes[i].mask) == mips_opcodes[i].match)
      break;
  return i < NUMOPCODES && (mips_opcodes[i].pinfo & ANY_DELAY);
}

/* To skip prologues, I use this predicate.  Returns either PC itself
   if the code at PC does not look like a function prologue; otherwise
   returns an address that (if we're lucky) follows the prologue.  If
   LENIENT, then we must skip everything which is involved in setting
   up the frame (it's OK to skip more, just so long as we don't skip
   anything which might clobber the registers which are being saved.
   We must skip more in the case where part of the prologue is in the
   delay slot of a non-prologue instruction).  */

CORE_ADDR
mips_skip_prologue (pc, lenient)
     CORE_ADDR pc;
     int lenient;
{
    struct symbol *f;
    struct block *b;
    unsigned long inst;
    int offset;
    int seen_sp_adjust = 0;

    /* Skip the typical prologue instructions. These are the stack adjustment
       instruction and the instructions that save registers on the stack
       or in the gcc frame.  */
    for (offset = 0; offset < 100; offset += 4)
      {
        char buf[4];
        int status;

        status = read_memory_nobpt (pc + offset, buf, 4);
        if (status)
          memory_error (status, pc + offset);
        inst = extract_unsigned_integer (buf, 4);

        if (lenient && is_delayed (inst))
          continue;

        if ((inst & 0xffff0000) == 0x27bd0000)  /* addiu $sp,$sp,offset */
            seen_sp_adjust = 1;
        else if ((inst & 0xFFE00000) == 0xAFA00000 && (inst & 0x001F0000))
            continue;                           /* sw reg,n($sp) */
                                                /* reg != $zero */
        else if ((inst & 0xFFE00000) == 0xE7A00000) /* swc1 freg,n($sp) */
            continue;
        else if ((inst & 0xF3E00000) == 0xA3C00000 && (inst & 0x001F0000))
                                                /* sx reg,n($s8) */
            continue;                           /* reg != $zero */
        else if (inst == 0x03A0F021)            /* move $s8,$sp */
            continue;
        else if ((inst & 0xFF9F07FF) == 0x00800021) /* move reg,$a0-$a3 */
            continue;
        else
            break;
    }
    return pc + offset;

/* FIXME schauer. The following code seems no longer necessary if we
   always skip the typical prologue instructions.  */

#if 0
    if (seen_sp_adjust)
      return pc + offset;

    /* Well, it looks like a frameless. Let's make sure.
       Note that we are not called on the current PC,
       but on the function`s start PC, and I have definitely
       seen optimized code that adjusts the SP quite later */
    b = block_for_pc(pc);
    if (!b) return pc;

    f = lookup_symbol(MIPS_EFI_SYMBOL_NAME, b, LABEL_NAMESPACE, 0, NULL);
    if (!f) return pc;
    /* Ideally, I would like to use the adjusted info
       from mips_frame_info(), but for all practical
       purposes it will not matter (and it would require
       a different definition of SKIP_PROLOGUE())

       Actually, it would not hurt to skip the storing
       of arguments on the stack as well. */
    if (((mips_extra_func_info_t)SYMBOL_VALUE(f))->pdr.frameoffset)
        return pc + 4;

    return pc;
#endif
}

/* Is address PC in the prologue (loosely defined) for function at
   STARTADDR?  */

static int
mips_in_lenient_prologue (startaddr, pc)
     CORE_ADDR startaddr;
     CORE_ADDR pc;
{
  CORE_ADDR end_prologue = mips_skip_prologue (startaddr, 1);
  return pc >= startaddr && pc < end_prologue;
}

/* Given a return value in `regbuf' with a type `valtype', 
   extract and copy its value into `valbuf'.  */
void
mips_extract_return_value (valtype, regbuf, valbuf)
    struct type *valtype;
    char regbuf[REGISTER_BYTES];
    char *valbuf;
{
  int regnum;
  
  regnum = TYPE_CODE (valtype) == TYPE_CODE_FLT && mips_fpu ? FP0_REGNUM : 2;

  memcpy (valbuf, regbuf + REGISTER_BYTE (regnum), TYPE_LENGTH (valtype));
#ifdef REGISTER_CONVERT_TO_TYPE
  REGISTER_CONVERT_TO_TYPE(regnum, valtype, valbuf);
#endif
}

/* Given a return value in `regbuf' with a type `valtype', 
   write it's value into the appropriate register.  */
void
mips_store_return_value (valtype, valbuf)
    struct type *valtype;
    char *valbuf;
{
  int regnum;
  char raw_buffer[MAX_REGISTER_RAW_SIZE];
  
  regnum = TYPE_CODE (valtype) == TYPE_CODE_FLT && mips_fpu ? FP0_REGNUM : 2;
  memcpy(raw_buffer, valbuf, TYPE_LENGTH (valtype));

#ifdef REGISTER_CONVERT_FROM_TYPE
  REGISTER_CONVERT_FROM_TYPE(regnum, valtype, raw_buffer);
#endif

  write_register_bytes(REGISTER_BYTE (regnum), raw_buffer, TYPE_LENGTH (valtype));
}

/* Let the user turn off floating point and set the fence post for
   heuristic_proc_start.  */

void
_initialize_mips_tdep ()
{
  add_show_from_set
    (add_set_cmd ("mipsfpu", class_support, var_boolean,
                  (char *) &mips_fpu,
                  "Set use of floating point coprocessor.\n\
Turn off to avoid using floating point instructions when calling functions\n\
or dealing with return values.", &setlist),
     &showlist);

  add_show_from_set
    (add_set_cmd ("heuristic-fence-post", class_support, var_uinteger,
                  (char *) &heuristic_fence_post,
                  "\
Set the distance searched for the start of a function.\n\
If you are debugging a stripped executable, GDB needs to search through the\n\
program for the start of a function.  This command sets the distance of the\n\
search.  The only need to set it is when debugging a stripped executable.",
                  &setlist),
     &showlist);
}