/* Get previous frame state for an existing frame state.
   Copyright (C) 2016 The Qt Company Ltd.
   Copyright (C) 2024 CIP United Inc.
   This file is part of elfutils.

   This file is free software; you can redistribute it and/or modify
   it under the terms of either

     * the GNU Lesser General Public License as published by the Free
       Software Foundation; either version 3 of the License, or (at
       your option) any later version

   or

     * 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

   or both in parallel, as here.

   elfutils 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 copies of the GNU General Public License and
   the GNU Lesser General Public License along with this program.  If
   not, see <http://www.gnu.org/licenses/>.  */

#ifdef HAVE_CONFIG_H
# include <config.h>
#endif

#define BACKEND mips_
#define SP_REG 29
#define FP_REG 30
#define LR_REG 31
#define FP_OFFSET 0
#define LR_OFFSET 8
#define SP_OFFSET 16

#include "libebl_CPU.h"

/* There was no CFI. Maybe we happen to have a frame pointer and can unwind from that?  */

bool
EBLHOOK(unwind) (Ebl *ebl __attribute__ ((unused)), Dwarf_Addr pc __attribute__ ((unused)),
		 ebl_tid_registers_t *setfunc, ebl_tid_registers_get_t *getfunc,
		 ebl_pid_memory_read_t *readfunc, void *arg,
		 bool *signal_framep __attribute__ ((unused)))
{
  Dwarf_Word fp, lr, sp;

  if (!getfunc(LR_REG, 1, &lr, arg))
    return false;

  if (lr == 0 || !setfunc(-1, 1, &lr, arg))
    return false;

  if (!getfunc(FP_REG, 1, &fp, arg))
    fp = 0;

  if (!getfunc(SP_REG, 1, &sp, arg))
    sp = 0;

  Dwarf_Word newLr, newFp, newSp;

  if (!readfunc(fp + LR_OFFSET, &newLr, arg))
    newLr = 0;

  if (!readfunc(fp + FP_OFFSET, &newFp, arg))
    newFp = 0;

  newSp = fp + SP_OFFSET;

  // These are not fatal if they don't work. They will just prevent unwinding at the next frame.
  setfunc(LR_REG, 1, &newLr, arg);
  setfunc(FP_REG, 1, &newFp, arg);
  setfunc(SP_REG, 1, &newSp, arg);

  // If the fp is invalid, we might still have a valid lr.
  // But if the fp is valid, then the stack should be moving in the right direction.
  return fp == 0 || newSp > sp;
}
