avr and frame unwinding

["Theodore A. Roth" <troth@openavr.org>]

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Hi,

I've pretty much hit a wall on this, so I will have to ask for help
now.

The attached is what I have so far in my attempt to frame-ify
avr-tdep.c. As it stands, things kinda work. I can 'step' around a
program fine.

Things go wrong as soon as I try to 'next' over a function call, gdb
goes into an infinite loop. If I 'step' down into a function called
from main(), a backtrace never gets me back to main. Here's a dump of
the backtrace output (I'll forego the infinite loop output to save
some bandwidth 8-):

func1 () at tst.c:23
23          struct cc var = {0};        /* This uses memset()! */
(gdb) bt
#0  func1 () at tst.c:23
{ get_prev_frame (this_frame=0) { frame_id_p
(l={stack=0x8010f9,code=0xd0}) -> 1 }
{ frame_register_unwind (frame=0,regnum="PC",...) {
frame_register_unwind (frame=-1,regnum="PC",...) -> *optimizedp=0
*lvalp=2 *addrp=0x23 *bufferp=[fffffff0000000] }
-> *optimizedp=0 *lvalp=2 *addrp=0x23 *bufferp=[fffffff0000000] }
{ frame_pc_unwind (this_frame=0) -> 0xf0 }
->
{level=1,type=UNKNOWN_FRAME,unwind=<unknown>,pc=0xf0,id=<unknown>,func=<unknown>}
}
#1  0x000000f0 in func1 () at tst.c:22
{ get_prev_frame (this_frame=1) { get_frame_id (fi=1) {
frame_func_unwind (fi=0) -> 0xd0 }
Sending packet: $md0,27#96...Ack
Packet received:
cf92df92ef92ff920f931f93cf93df93cdb7deb726970fb6f894debf0fbecdbf86e0fe01319611
Sending packet: $mf7,11#98...Ack
Packet received: 928a95e9f719821a82ed80fe80cc24dd24
{ frame_register_unwind (frame=0,regnum="r28",...) Sending packet:
$m801100,1#f4...Ack
Packet received: 00
-> *optimizedp=0 *lvalp=1 *addrp=0x801100 *bufferp=[00] }
{ frame_register_unwind (frame=0,regnum="r29",...) Sending packet:
$m801101,1#f5...Ack
Packet received: 00
-> *optimizedp=0 *lvalp=1 *addrp=0x801101 *bufferp=[00] }
{ frame_id_eq
(l={stack=0x8010f9,code=0xd0},r={stack=0x80000e,code=0xd0}) -> 0 }
-> {stack=0x80000e,code=0xd0} }
{ frame_id_p (l={stack=0x80000e,code=0xd0}) -> 1 }
{ frame_id_inner
(l={stack=0x80000e,code=0xd0},r={stack=0x8010f9,code=0xd0}) -> 1 }
This frame inner-to next frame (corrupt stack?)
(gdb)


I'm pretty confused as to how frames are getting chained up and
unwound. I suspose that I'm not thinking about the the SP in the
proper manner in relation to the frames.

Could some kind soul lend me some insight?

Thanks.

Ted Roth

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/* Target-dependent code for Atmel AVR, for GDB.
   Copyright 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003
   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., 59 Temple Place - Suite 330,
   Boston, MA 02111-1307, USA.  */

/* Contributed by Theodore A. Roth, troth@openavr.org */

/* Portions of this file were taken from the original gdb-4.18 patch developed
   by Denis Chertykov, denisc@overta.ru */

#include "defs.h"
#include "frame.h"
#include "frame-unwind.h"
#include "frame-base.h"
#include "gdbcmd.h"
#include "gdbcore.h"
#include "inferior.h"
#include "symfile.h"
#include "arch-utils.h"
#include "regcache.h"
#include "gdb_string.h"

/* AVR Background:

   (AVR micros are pure Harvard Architecture processors.)

   The AVR family of microcontrollers have three distinctly different memory
   spaces: flash, sram and eeprom. The flash is 16 bits wide and is used for
   the most part to store program instructions. The sram is 8 bits wide and is
   used for the stack and the heap. Some devices lack sram and some can have
   an additional external sram added on as a peripheral.

   The eeprom is 8 bits wide and is used to store data when the device is
   powered down. Eeprom is not directly accessible, it can only be accessed
   via io-registers using a special algorithm. Accessing eeprom via gdb's
   remote serial protocol ('m' or 'M' packets) looks difficult to do and is
   not included at this time.

   [The eeprom could be read manually via ``x/b <eaddr + AVR_EMEM_START>'' or
   written using ``set {unsigned char}<eaddr + AVR_EMEM_START>''.  For this to
   work, the remote target must be able to handle eeprom accesses and perform
   the address translation.]

   All three memory spaces have physical addresses beginning at 0x0. In
   addition, the flash is addressed by gcc/binutils/gdb with respect to 8 bit
   bytes instead of the 16 bit wide words used by the real device for the
   Program Counter.

   In order for remote targets to work correctly, extra bits must be added to
   addresses before they are send to the target or received from the target
   via the remote serial protocol. The extra bits are the MSBs and are used to
   decode which memory space the address is referring to. */

#undef XMALLOC
#define XMALLOC(TYPE) ((TYPE*) xmalloc (sizeof (TYPE)))

#undef EXTRACT_INSN
#define EXTRACT_INSN(addr) extract_unsigned_integer(addr,2)

/* Constants: prefixed with AVR_ to avoid name space clashes */

enum
{
  AVR_REG_W = 24,
  AVR_REG_X = 26,
  AVR_REG_Y = 28,
  AVR_FP_REGNUM = 28,
  AVR_REG_Z = 30,

  AVR_SREG_REGNUM = 32,
  AVR_SP_REGNUM = 33,
  AVR_PC_REGNUM = 34,

  AVR_NUM_REGS = 32 + 1 /*SREG*/ + 1 /*SP*/ + 1 /*PC*/,
  AVR_NUM_REG_BYTES = 32 + 1 /*SREG*/ + 2 /*SP*/ + 4 /*PC*/,

  AVR_PC_REG_INDEX = 35,	/* index into array of registers */

  AVR_MAX_PROLOGUE_SIZE = 56,	/* bytes */

  /* Count of pushed registers. From r2 to r17 (inclusively), r28, r29 */
  AVR_MAX_PUSHES = 18,

  /* Number of the last pushed register. r17 for current avr-gcc */
  AVR_LAST_PUSHED_REGNUM = 17,

  /* FIXME: TRoth/2002-01-??: Can we shift all these memory masks left 8
     bits? Do these have to match the bfd vma values?. It sure would make
     things easier in the future if they didn't need to match.

     Note: I chose these values so as to be consistent with bfd vma
     addresses.

     TRoth/2002-04-08: There is already a conflict with very large programs
     in the mega128. The mega128 has 128K instruction bytes (64K words),
     thus the Most Significant Bit is 0x10000 which gets masked off my
     AVR_MEM_MASK.

     The problem manifests itself when trying to set a breakpoint in a
     function which resides in the upper half of the instruction space and
     thus requires a 17-bit address.

     For now, I've just removed the EEPROM mask and changed AVR_MEM_MASK
     from 0x00ff0000 to 0x00f00000. Eeprom is not accessible from gdb yet,
     but could be for some remote targets by just adding the correct offset
     to the address and letting the remote target handle the low-level
     details of actually accessing the eeprom. */

  AVR_IMEM_START = 0x00000000,	/* INSN memory */
  AVR_SMEM_START = 0x00800000,	/* SRAM memory */
#if 1
  /* No eeprom mask defined */
  AVR_MEM_MASK = 0x00f00000,	/* mask to determine memory space */
#else
  AVR_EMEM_START = 0x00810000,	/* EEPROM memory */
  AVR_MEM_MASK = 0x00ff0000,	/* mask to determine memory space */
#endif
};

/* Prologue types:

   NORMAL and CALL are the typical types (interchangeable with the
   -mcall-prologues gcc option.

   MAIN, INTR and SIG are invariant as far as I can tell.  */

enum {
    AVR_PROLOGUE_NONE,              /* No prologue */
    AVR_PROLOGUE_NORMAL,
    AVR_PROLOGUE_CALL,              /* -mcall-prologues */
    AVR_PROLOGUE_MAIN,
    AVR_PROLOGUE_INTR,              /* interrupt handler */
    AVR_PROLOGUE_SIG,               /* signal handler */
};

struct gdbarch_tdep
{
  /* FIXME: TRoth: is there anything to put here? */
  int foo;
};

/* Any function with a frame looks like this
   .......    <-SP POINTS HERE
   LOCALS1    <-FP POINTS HERE
   LOCALS0
   SAVED FP
   SAVED R3
   SAVED R2
   RET PC
   FIRST ARG
   SECOND ARG */

struct avr_unwind_cache
{
/*   CORE_ADDR return_pc; */
  /* The previous frame's inner most stack address.  Used as this
     frame ID's stack_addr.  */
  CORE_ADDR prev_sp;
  /* The frame's base, optionally used by the high-level debug info.  */
  CORE_ADDR base;
  int size;
  CORE_ADDR *saved_regs;
  /* How far the SP has been offset from the start of the stack frame (as
     defined by the previous frame's stack pointer).  */
  LONGEST sp_offset;
  int prologue_type;
  void **regs;
};

/* Lookup the name of a register given it's number. */

static const char *
avr_register_name (int regnum)
{
  static char *register_names[] = {
    "r0", "r1", "r2", "r3", "r4", "r5", "r6", "r7",
    "r8", "r9", "r10", "r11", "r12", "r13", "r14", "r15",
    "r16", "r17", "r18", "r19", "r20", "r21", "r22", "r23",
    "r24", "r25", "r26", "r27", "r28", "r29", "r30", "r31",
    "SREG", "SP", "PC"
  };

  if (regnum < 0)
    return NULL;
  if (regnum >= (sizeof (register_names) / sizeof (*register_names)))
    return NULL;
  return register_names[regnum];
}

/* Return the GDB type object for the "standard" data type
   of data in register N.  */

static struct type *
avr_register_type (struct gdbarch *gdbarch, int reg_nr)
{
  if (reg_nr == AVR_PC_REGNUM)
    return builtin_type_unsigned_long;
  if (reg_nr == AVR_SP_REGNUM)
    return builtin_type_void_data_ptr;
  else
    return builtin_type_uint8;
}

/* Instruction address checks and convertions. */

static CORE_ADDR
avr_make_iaddr (CORE_ADDR x)
{
  return ((x) | AVR_IMEM_START);
}

static int
avr_iaddr_p (CORE_ADDR x)
{
  return (((x) & AVR_MEM_MASK) == AVR_IMEM_START);
}

/* FIXME: TRoth: Really need to use a larger mask for instructions. Some
   devices are already up to 128KBytes of flash space.

   TRoth/2002-04-8: See comment above where AVR_IMEM_START is defined. */

static CORE_ADDR
avr_convert_iaddr_to_raw (CORE_ADDR x)
{
  return ((x) & 0xffffffff);
}

/* SRAM address checks and convertions. */

static CORE_ADDR
avr_make_saddr (CORE_ADDR x)
{
  return ((x) | AVR_SMEM_START);
}

static int
avr_saddr_p (CORE_ADDR x)
{
  return (((x) & AVR_MEM_MASK) == AVR_SMEM_START);
}

static CORE_ADDR
avr_convert_saddr_to_raw (CORE_ADDR x)
{
  return ((x) & 0xffffffff);
}

/* EEPROM address checks and convertions. I don't know if these will ever
   actually be used, but I've added them just the same. TRoth */

/* TRoth/2002-04-08: Commented out for now to allow fix for problem with large
   programs in the mega128. */

/*  static CORE_ADDR */
/*  avr_make_eaddr (CORE_ADDR x) */
/*  { */
/*    return ((x) | AVR_EMEM_START); */
/*  } */

/*  static int */
/*  avr_eaddr_p (CORE_ADDR x) */
/*  { */
/*    return (((x) & AVR_MEM_MASK) == AVR_EMEM_START); */
/*  } */

/*  static CORE_ADDR */
/*  avr_convert_eaddr_to_raw (CORE_ADDR x) */
/*  { */
/*    return ((x) & 0xffffffff); */
/*  } */

/* Convert from address to pointer and vice-versa. */

static void
avr_address_to_pointer (struct type *type, void *buf, CORE_ADDR addr)
{
  /* Is it a code address?  */
  if (TYPE_CODE (TYPE_TARGET_TYPE (type)) == TYPE_CODE_FUNC
      || TYPE_CODE (TYPE_TARGET_TYPE (type)) == TYPE_CODE_METHOD)
    {
      store_unsigned_integer (buf, TYPE_LENGTH (type),
			      avr_convert_iaddr_to_raw (addr));
    }
  else
    {
      /* Strip off any upper segment bits.  */
      store_unsigned_integer (buf, TYPE_LENGTH (type),
			      avr_convert_saddr_to_raw (addr));
    }
}

static CORE_ADDR
avr_pointer_to_address (struct type *type, const void *buf)
{
  CORE_ADDR addr = extract_unsigned_integer (buf, TYPE_LENGTH (type));

  if (TYPE_CODE_SPACE (TYPE_TARGET_TYPE (type)))
    {
      fprintf_unfiltered (gdb_stderr, "CODE_SPACE ---->> ptr->addr: 0x%lx\n",
			  addr);
      fprintf_unfiltered (gdb_stderr,
			  "+++ If you see this, please send me an "
                          "email <troth@openavr.org>\n");
    }

  /* Is it a code address?  */
  if (TYPE_CODE (TYPE_TARGET_TYPE (type)) == TYPE_CODE_FUNC
      || TYPE_CODE (TYPE_TARGET_TYPE (type)) == TYPE_CODE_METHOD
      || TYPE_CODE_SPACE (TYPE_TARGET_TYPE (type)))
    return avr_make_iaddr (addr);
  else
    return avr_make_saddr (addr);
}

static CORE_ADDR
avr_read_pc (ptid_t ptid)
{
  ptid_t save_ptid;
  CORE_ADDR pc;
  CORE_ADDR retval;

  save_ptid = inferior_ptid;
  inferior_ptid = ptid;
  pc = (int) read_register (AVR_PC_REGNUM);
  inferior_ptid = save_ptid;
  retval = avr_make_iaddr (pc);
  return retval;
}

static void
avr_write_pc (CORE_ADDR val, ptid_t ptid)
{
  ptid_t save_ptid;

  save_ptid = inferior_ptid;
  inferior_ptid = ptid;
  write_register (AVR_PC_REGNUM, avr_convert_iaddr_to_raw (val));
  inferior_ptid = save_ptid;
}

static CORE_ADDR
avr_read_sp (void)
{
  return (avr_make_saddr (read_register (AVR_SP_REGNUM)));
}

static void
avr_write_sp (CORE_ADDR val)
{
  write_register (AVR_SP_REGNUM, avr_convert_saddr_to_raw (val));
}

/* Translate a GDB virtual ADDR/LEN into a format the remote target
   understands.  Returns number of bytes that can be transfered
   starting at TARG_ADDR.  Return ZERO if no bytes can be transfered
   (segmentation fault).

   TRoth/2002-04-08: Could this be used to check for dereferencing an invalid
   pointer? */

static void
avr_remote_translate_xfer_address (struct gdbarch *gdbarch,
				   struct regcache *regcache,
				   CORE_ADDR memaddr, int nr_bytes,
				   CORE_ADDR *targ_addr, int *targ_len)
{
  long out_addr;
  long out_len;

  /* FIXME: TRoth: Do nothing for now. Will need to examine memaddr at this
     point and see if the high bit are set with the masks that we want. */

  *targ_addr = memaddr;
  *targ_len = nr_bytes;
}

/* Function pointers obtained from the target are half of what gdb expects so
   multiply by 2. */

static CORE_ADDR
avr_convert_from_func_ptr_addr (CORE_ADDR addr)
{
  return addr * 2;
}

/* Returns the return address for a dummy. */

static CORE_ADDR
avr_call_dummy_address (void)
{
  return entry_point_address ();
}

/* Function: avr_scan_prologue

   This function decodes an AVR function prologue to determine:
     1) the size of the stack frame
     2) which registers are saved on it
     3) the offsets of saved regs
   This information is stored in the avr_unwind_cache structure.

   Some devices lack the sbiw instruction, so on those replace this:
        sbiw    r28, XX
   with this:
        subi    r28,lo8(XX)
        sbci    r29,hi8(XX)

   A typical AVR function prologue with a frame pointer might look like this:
        push    rXX        ; saved regs
        ...
        push    r28
        push    r29
        in      r28,__SP_L__
        in      r29,__SP_H__
        sbiw    r28,<LOCALS_SIZE>
        in      __tmp_reg__,__SREG__
        cli
        out     __SP_L__,r28
        out     __SREG__,__tmp_reg__
        out     __SP_H__,r29

   A typical AVR function prologue without a frame pointer might look like
   this:
        push    rXX        ; saved regs
        ...

   A main function prologue looks like this:
        ldi     r28,lo8(<RAM_ADDR> - <LOCALS_SIZE>)
        ldi     r29,hi8(<RAM_ADDR> - <LOCALS_SIZE>)
        out     __SP_H__,r29
        out     __SP_L__,r28

   A signal handler prologue looks like this:
        push    __zero_reg__
        push    __tmp_reg__
        in      __tmp_reg__, __SREG__
        push    __tmp_reg__
        clr     __zero_reg__
        push    rXX             ; save registers r18:r27, r30:r31
        ...
        push    r28             ; save frame pointer
        push    r29
        in      r28, __SP_L__
        in      r29, __SP_H__
        sbiw    r28, <LOCALS_SIZE>
        out     __SP_H__, r29
        out     __SP_L__, r28
        
   A interrupt handler prologue looks like this:
        sei
        push    __zero_reg__
        push    __tmp_reg__
        in      __tmp_reg__, __SREG__
        push    __tmp_reg__
        clr     __zero_reg__
        push    rXX             ; save registers r18:r27, r30:r31
        ...
        push    r28             ; save frame pointer
        push    r29
        in      r28, __SP_L__
        in      r29, __SP_H__
        sbiw    r28, <LOCALS_SIZE>
        cli
        out     __SP_H__, r29
        sei     
        out     __SP_L__, r28

   A `-mcall-prologues' prologue looks like this (Note that the megas use a
   jmp instead of a rjmp, thus the prologue is one word larger since jmp is a
   32 bit insn and rjmp is a 16 bit insn):
        ldi     r26,lo8(<LOCALS_SIZE>)
        ldi     r27,hi8(<LOCALS_SIZE>)
        ldi     r30,pm_lo8(.L_foo_body)
        ldi     r31,pm_hi8(.L_foo_body)
        rjmp    __prologue_saves__+RRR
   .L_foo_body:  */

static CORE_ADDR
avr_scan_prologue (CORE_ADDR pc, struct avr_unwind_cache *info)
{
  int i;
  unsigned short insn;
  int scan_stage = 0;
  struct minimal_symbol *msymbol;
  unsigned char prologue[AVR_MAX_PROLOGUE_SIZE];
  int vpc = 0;

  read_memory (pc, prologue, AVR_MAX_PROLOGUE_SIZE);

  /* Scanning main()'s prologue
     ldi r28,lo8(<RAM_ADDR> - <LOCALS_SIZE>)
     ldi r29,hi8(<RAM_ADDR> - <LOCALS_SIZE>)
     out __SP_H__,r29
     out __SP_L__,r28 */

  if (1)
    {
      CORE_ADDR locals;
      unsigned char img[] = {
        0xde, 0xbf,		/* out __SP_H__,r29 */
        0xcd, 0xbf		/* out __SP_L__,r28 */
      };

      insn = EXTRACT_INSN (&prologue[vpc]);
      /* ldi r28,lo8(<RAM_ADDR> - <LOCALS_SIZE>) */
      if ((insn & 0xf0f0) == 0xe0c0)
        {
          locals = (insn & 0xf) | ((insn & 0x0f00) >> 4);
          insn = EXTRACT_INSN (&prologue[vpc + 2]);
          /* ldi r29,hi8(<RAM_ADDR> - <LOCALS_SIZE>) */
          if ((insn & 0xf0f0) == 0xe0d0)
            {
              locals |= ((insn & 0xf) | ((insn & 0x0f00) >> 4)) << 8;
              if (memcmp (prologue + vpc + 4, img, sizeof (img)) == 0)
                {
                  info->prologue_type = AVR_PROLOGUE_MAIN;
                  info->base = locals;
                  return pc + 4;
                }
            }
        }
    }

  /* Scanning `-mcall-prologues' prologue
     FIXME: mega prologue is a 12 bytes long */

  while (1)	/* Use while to avoid many goto's */
    {
      int loc_size;
      int body_addr;
      unsigned num_pushes;
      int pc_offset = 0;

      insn = EXTRACT_INSN (&prologue[vpc]);
      /* ldi r26,<LOCALS_SIZE> */
      if ((insn & 0xf0f0) != 0xe0a0)
	break;
      loc_size = (insn & 0xf) | ((insn & 0x0f00) >> 4);
      pc_offset += 2;

      insn = EXTRACT_INSN (&prologue[vpc + 2]);
      /* ldi r27,<LOCALS_SIZE> / 256 */
      if ((insn & 0xf0f0) != 0xe0b0)
	break;
      loc_size |= ((insn & 0xf) | ((insn & 0x0f00) >> 4)) << 8;
      pc_offset += 2;

      insn = EXTRACT_INSN (&prologue[vpc + 4]);
      /* ldi r30,pm_lo8(.L_foo_body) */
      if ((insn & 0xf0f0) != 0xe0e0)
	break;
      body_addr = (insn & 0xf) | ((insn & 0x0f00) >> 4);
      pc_offset += 2;

      insn = EXTRACT_INSN (&prologue[vpc + 6]);
      /* ldi r31,pm_hi8(.L_foo_body) */
      if ((insn & 0xf0f0) != 0xe0f0)
	break;
      body_addr |= ((insn & 0xf) | ((insn & 0x0f00) >> 4)) << 8;
      pc_offset += 2;

      msymbol = lookup_minimal_symbol ("__prologue_saves__", NULL, NULL);
      if (!msymbol)
	break;

      insn = EXTRACT_INSN (&prologue[vpc + 8]);
      /* rjmp __prologue_saves__+RRR */
      if ((insn & 0xf000) == 0xc000)
        {
          /* Extract PC relative offset from RJMP */
          i = (insn & 0xfff) | (insn & 0x800 ? (-1 ^ 0xfff) : 0);
          /* Convert offset to byte addressable mode */
          i *= 2;
          /* Destination address */
          i += pc_offset + pc + 10;

          if (body_addr != (pc + 10)/2)
            break;

          pc_offset += 2;
        }
      else if ((insn & 0xfe0e) == 0x940c)
        {
          /* Extract absolute PC address from JMP */
          i = (((insn & 0x1) | ((insn & 0x1f0) >> 3) << 16)
            | (EXTRACT_INSN (&prologue[vpc + 10]) & 0xffff));
          /* Convert address to byte addressable mode */
          i *= 2;

          if (body_addr != (pc + 12)/2)
            break;

          pc_offset += 4;
        }
      else
        break;

      /* Resolve offset (in words) from __prologue_saves__ symbol.
         Which is a pushes count in `-mcall-prologues' mode */
      num_pushes = AVR_MAX_PUSHES - (i - SYMBOL_VALUE_ADDRESS (msymbol)) / 2;

      if (num_pushes > AVR_MAX_PUSHES)
        {
          fprintf_unfiltered (gdb_stderr, "Num pushes too large: %d\n",
                              num_pushes);
          num_pushes = 0;
        }

      if (num_pushes)
	{
	  int from;

	  info->saved_regs[AVR_FP_REGNUM + 1] = num_pushes;
	  if (num_pushes >= 2)
	    info->saved_regs[AVR_FP_REGNUM] = num_pushes - 1;

	  i = 0;
	  for (from = AVR_LAST_PUSHED_REGNUM + 1 - (num_pushes - 2);
	       from <= AVR_LAST_PUSHED_REGNUM; ++from)
	    info->saved_regs [from] = ++i;
	}
      info->size = loc_size + num_pushes;
      info->prologue_type = AVR_PROLOGUE_CALL;

      return pc + pc_offset + num_pushes*2;
    }

  /* Scan for the beginning of the prologue for an interrupt or signal
     function */

  if (1)
    {
      unsigned char img[] = {
	0x78, 0x94,		/* sei */
	0x1f, 0x92,		/* push r1 */
	0x0f, 0x92,		/* push r0 */
	0x0f, 0xb6,		/* in r0,0x3f SREG */
	0x0f, 0x92,		/* push r0 */
	0x11, 0x24		/* clr r1 */
      };
      if (memcmp (prologue, img, sizeof (img)) == 0)
	{
	  vpc += sizeof (img);
	  info->saved_regs[0] = 2;
	  info->saved_regs[1] = 1;
	  info->size += 3;
	}
      else if (memcmp (img + 2, prologue, sizeof (img) - 2) == 0)
	{
	  vpc += sizeof (img) - 2;
	  info->saved_regs[0] = 2;
	  info->saved_regs[1] = 1;
	  info->size += 3;
	}
    }

  /* First stage of the prologue scanning.
     Scan pushes (saved registers) */

  for (; vpc < AVR_MAX_PROLOGUE_SIZE; vpc += 2)
    {
      insn = EXTRACT_INSN (&prologue[vpc]);
      if ((insn & 0xfe0f) == 0x920f)	/* push rXX */
	{
	  /* Bits 4-9 contain a mask for registers R0-R32. */
	  int regno = (insn & 0x1f0) >> 4;
	  info->size++;
	  info->saved_regs[regno] = info->size;
	  scan_stage = 1;
	}
      else
          break;
    }

  if (vpc >= AVR_MAX_PROLOGUE_SIZE)
     fprintf_unfiltered (gdb_stderr,
                         "Hit end of prologue while scanning pushes\n");

  /* Second stage of the prologue scanning.
     Scan:
     in r28,__SP_L__
     in r29,__SP_H__ */

  if (scan_stage == 1 && vpc < AVR_MAX_PROLOGUE_SIZE)
    {
      unsigned char img[] = {
	0xcd, 0xb7,		/* in r28,__SP_L__ */
	0xde, 0xb7		/* in r29,__SP_H__ */
      };
      unsigned short insn1;

      if (memcmp (prologue + vpc, img, sizeof (img)) == 0)
	{
	  vpc += 4;
	  scan_stage = 2;
	}
    }

  /* Third stage of the prologue scanning. (Really two stages)
     Scan for:
     sbiw r28,XX or subi r28,lo8(XX)
                    sbci r29,hi8(XX)
     in __tmp_reg__,__SREG__
     cli
     out __SP_H__,r29
     out __SREG__,__tmp_reg__
     out __SP_L__,r2* */

  if (scan_stage == 2 && vpc < AVR_MAX_PROLOGUE_SIZE)
    {
      int locals_size = 0;
      unsigned char img[] = {
	0x0f, 0xb6,		/* in r0,0x3f   ; store SREG in r0 */
	0xf8, 0x94,		/* cli */
	0xde, 0xbf,		/* out 0x3e,r29 ; SPH */
	0x0f, 0xbe,		/* out 0x3f,r0  ; SREG */
	0xcd, 0xbf		/* out 0x3d,r28 ; SPL */
      };
      unsigned char img_sig[] = {
	0xde, 0xbf,		/* out 0x3e,r29 ; SPH */
	0xcd, 0xbf		/* out 0x3d,r28 ; SPL */
      };
      unsigned char img_intr[] = {
	0xf8, 0x94,		/* cli */
	0xde, 0xbf,		/* out 0x3e,r29 ; SPH */
	0x78, 0x94,		/* sei */
	0xcd, 0xbf		/* out 0x3d,r28 ; SPL */
      };

      insn = EXTRACT_INSN (&prologue[vpc]);
      vpc += 2;
      if ((insn & 0xff30) == 0x9720)	/* sbiw r28,XXX */
	locals_size = (insn & 0xf) | ((insn & 0xc0) >> 2);
      else if ((insn & 0xf0f0) == 0x50c0)	/* subi r28,lo8(XX) */
	{
	  locals_size = (insn & 0xf) | ((insn & 0xf00) >> 4);
	  insn = EXTRACT_INSN (&prologue[vpc]);
	  vpc += 2;
	  locals_size += ((insn & 0xf) | ((insn & 0xf00) >> 4) << 8);
	}
      else
	return pc + vpc;

      /* Scan the last part of the prologue. */
      if (memcmp (prologue + vpc, img_sig, sizeof (img_sig)) == 0)
        {
          info->prologue_type = AVR_PROLOGUE_SIG;
          vpc += sizeof (img_sig);
        }
      else if (memcmp (prologue + vpc, img_intr, sizeof (img_intr)) == 0)
        {
          info->prologue_type = AVR_PROLOGUE_INTR;
          vpc += sizeof (img_intr);
        }
      if (memcmp (prologue + vpc, img, sizeof (img)) == 0)
        {
          info->prologue_type = AVR_PROLOGUE_NORMAL;
          vpc += sizeof (img);
        }

      info->size += locals_size;

      return pc + vpc;
    }

  /* If we got this far, we could not scan the prologue, so just return the pc
     of the frame. */

  return pc;
}

static CORE_ADDR
avr_skip_prologue (CORE_ADDR pc)
{
  CORE_ADDR func_addr, func_end;
  CORE_ADDR prologue_end = pc;

  /* See what the symbol table says */

  if (find_pc_partial_function (pc, NULL, &func_addr, &func_end))
    {
      struct symtab_and_line sal;
      struct avr_unwind_cache info = {0};
      CORE_ADDR saved_regs[AVR_NUM_REGS] = {0};

      info.saved_regs = saved_regs;

      /* Need to run the prologue scanner to figure out if the function has a
         prologue and possibly skip over moving data around some registers. */

      prologue_end = avr_scan_prologue (pc, &info);

      if (info.prologue_type != AVR_PROLOGUE_NONE)
        {
          sal = find_pc_line (func_addr, 0);

          if (sal.line != 0 && sal.end < func_end)
            return sal.end;
        }
    }

/* Either we didn't find the start of this function (nothing we can do),
   or there's no line info, or the line after the prologue is after
   the end of the function (there probably isn't a prologue). */

  return prologue_end;
}

static CORE_ADDR
avr_frame_address (struct frame_info *fi)
{
  return avr_make_saddr (get_frame_base (fi));
}

/* Not all avr devices support the BREAK insn. Those that don't should treat
   it as a NOP. Thus, it should be ok. Since the avr is currently a remote
   only target, this shouldn't be a problem (I hope). TRoth/2003-05-14  */

const unsigned char *
avr_breakpoint_from_pc (CORE_ADDR * pcptr, int *lenptr)
{
    static unsigned char avr_break_insn [] = { 0x98, 0x95 };
    *lenptr = sizeof (avr_break_insn);
    return avr_break_insn;
}

static void
avr_saved_regs_unwinder (struct frame_info *next_frame,
                         CORE_ADDR *this_saved_regs,
                         int regnum, int *optimizedp,
                         enum lval_type *lvalp, CORE_ADDR *addrp,
                         int *realnump, void *bufferp)
{
  if (this_saved_regs[regnum] != 0)
    {
      *optimizedp = 0;
      *lvalp = lval_memory;
      *addrp = this_saved_regs[regnum];
      *realnump = -1;
      if (bufferp != NULL)
        {
          /* Read the value in from memory.  */
          read_memory (this_saved_regs[regnum], bufferp,
                       register_size (current_gdbarch, regnum));
        }

      return;
    }

  /* No luck, assume this and the next frame have the same register
     value.  If a value is needed, pass the request on down the chain;
     otherwise just return an indication that the value is in the same
     register as the next frame.  */
  frame_register_unwind (next_frame, regnum, optimizedp, lvalp, addrp,
			 realnump, bufferp);
}

/* Put here the code to store, into fi->saved_regs, the addresses of
   the saved registers of frame described by FRAME_INFO.  This
   includes special registers such as pc and fp saved in special ways
   in the stack frame.  sp is even more special: the address we return
   for it IS the sp for the next frame. */

struct avr_unwind_cache *
avr_frame_unwind_cache (struct frame_info *next_frame,
                        void **this_prologue_cache)
{
  CORE_ADDR pc;
  ULONGEST prev_sp;
  ULONGEST this_base;
  struct avr_unwind_cache *info;
/*   ULONGEST return_pc; */
  int i;

  if ((*this_prologue_cache))
    return (*this_prologue_cache);

  info = FRAME_OBSTACK_ZALLOC (struct avr_unwind_cache);
  (*this_prologue_cache) = info;
  info->saved_regs = FRAME_OBSTACK_CALLOC (NUM_REGS, CORE_ADDR);

  info->size = 0;
  /* Return PC is either the first 2 bytes of the this frame or the last two
     bytes of the previsous frame. Not quite sure where the boundary is
     yet. */
/*   info->return_pc = 0; */
  info->sp_offset = 0;
  info->prologue_type = AVR_PROLOGUE_NONE;

  pc = frame_func_unwind (next_frame);

  avr_scan_prologue (pc, info);

  if (info->prologue_type != AVR_PROLOGUE_NONE)
    {
      ULONGEST high_base;       /* High byte of FP */

      /* The SP was moved to the FP.  This indicates that a new frame
         was created.  Get THIS frame's FP value by unwinding it from
         the next frame.  */
      frame_unwind_unsigned_register (next_frame, AVR_FP_REGNUM, &this_base);
      frame_unwind_unsigned_register (next_frame, AVR_FP_REGNUM+1, &high_base);
      this_base += (high_base << 8);
      
      /* The FP points at the last saved register.  Adjust the FP back
         to before the first saved register giving the SP.  */
      prev_sp = this_base + info->size;
    }
  else
    {
      /* Assume that the FP is this frame's SP but with that pushed
         stack space added back.  */
      frame_unwind_unsigned_register (next_frame, AVR_SP_REGNUM, &this_base);
      prev_sp = this_base + info->size;
    }

  info->base = avr_make_saddr (this_base);
  info->prev_sp = avr_make_saddr (prev_sp);

  /* Adjust all the saved registers so that they contain addresses and
     not offsets.  */
  for (i = 0; i < NUM_REGS - 1; i++)
    if (info->saved_regs[i])
      {
	info->saved_regs[i] = (info->prev_sp + info->saved_regs[i]);
      }

#if 0
  /* Calculate the return PC. Main has no return value on the stack, so ignore
     that case. */

  if (info->prologue_type != AVR_PROLOGUE_MAIN)
    {
      frame_unwind_unsigned_register (next_frame, AVR_SP_REGNUM, &return_pc);
      info->return_pc = avr_make_iaddr (return_pc);
    }
#endif

  return info;
}

static CORE_ADDR
avr_unwind_pc (struct gdbarch *gdbarch, struct frame_info *next_frame)
{
  ULONGEST pc;

  frame_unwind_unsigned_register (next_frame, AVR_PC_REGNUM, &pc);

  return avr_make_iaddr (pc);
}

/* Given a GDB frame, determine the address of the calling function's
   frame.  This will be used to create a new GDB frame struct.  */

static void
avr_frame_this_id (struct frame_info *next_frame,
                   void **this_prologue_cache,
                   struct frame_id *this_id)
{
  struct avr_unwind_cache *info
    = avr_frame_unwind_cache (next_frame, this_prologue_cache);
  CORE_ADDR base;
  CORE_ADDR func;
  struct frame_id id;

  /* The FUNC is easy.  */
  func = frame_func_unwind (next_frame);

  /* This is meant to halt the backtrace at "_start".  Make sure we
     don't halt it at a generic dummy frame. */
  if (inside_entry_file (func))
    return;

  /* Hopefully the prologue analysis either correctly determined the
     frame's base (which is the SP from the previous frame), or set
     that base to "NULL".  */
  base = info->prev_sp;
  if (base == 0)
    return;

  id = frame_id_build (base, func);

  /* Check that we're not going round in circles with the same frame
     ID (but avoid applying the test to sentinel frames which do go
     round in circles).  Can't use frame_id_eq() as that doesn't yet
     compare the frame's PC value.  */
  if (frame_relative_level (next_frame) >= 0
      && get_frame_type (next_frame) != DUMMY_FRAME
      && frame_id_eq (get_frame_id (next_frame), id))
    return;

  (*this_id) = id;
}

static void
avr_frame_prev_register (struct frame_info *next_frame,
			  void **this_prologue_cache,
			  int regnum, int *optimizedp,
			  enum lval_type *lvalp, CORE_ADDR *addrp,
			  int *realnump, void *bufferp)
{
  struct avr_unwind_cache *info
    = avr_frame_unwind_cache (next_frame, this_prologue_cache);

  avr_saved_regs_unwinder (next_frame, info->saved_regs, regnum, optimizedp,
                           lvalp, addrp, realnump, bufferp);
}

static const struct frame_unwind avr_frame_unwind = {
  NORMAL_FRAME,
  avr_frame_this_id,
  avr_frame_prev_register
};

const struct frame_unwind *
avr_frame_p (CORE_ADDR pc)
{
  return &avr_frame_unwind;
}

static CORE_ADDR
avr_frame_base_address (struct frame_info *next_frame, void **this_cache)
{
  struct avr_unwind_cache *info
    = avr_frame_unwind_cache (next_frame, this_cache);

  return info->base;
}

static const struct frame_base avr_frame_base = {
  &avr_frame_unwind,
  avr_frame_base_address,
  avr_frame_base_address,
  avr_frame_base_address
};

/* Assuming NEXT_FRAME->prev is a dummy, return the frame ID of that
   dummy frame.  The frame ID's base needs to match the TOS value
   saved by save_dummy_frame_tos(), and the PC match the dummy frame's
   breakpoint.  */

static struct frame_id
avr_unwind_dummy_id (struct gdbarch *gdbarch, struct frame_info *next_frame)
{
  ULONGEST base;

  frame_unwind_unsigned_register (next_frame, AVR_SP_REGNUM, &base);
  return frame_id_build (avr_make_saddr (base), frame_pc_unwind (next_frame));
}

/* Initialize the gdbarch structure for the AVR's. */

static struct gdbarch *
avr_gdbarch_init (struct gdbarch_info info, struct gdbarch_list *arches)
{
  struct gdbarch *gdbarch;
  struct gdbarch_tdep *tdep;

  /* Find a candidate among the list of pre-declared architectures. */
  arches = gdbarch_list_lookup_by_info (arches, &info);
  if (arches != NULL)
    return arches->gdbarch;

  /* None found, create a new architecture from the information provided. */
  tdep = XMALLOC (struct gdbarch_tdep);
  gdbarch = gdbarch_alloc (&info, tdep);

  /* If we ever need to differentiate the device types, do it here. */
  switch (info.bfd_arch_info->mach)
    {
    case bfd_mach_avr1:
    case bfd_mach_avr2:
    case bfd_mach_avr3:
    case bfd_mach_avr4:
    case bfd_mach_avr5:
      break;
    }

  set_gdbarch_short_bit (gdbarch, 2 * TARGET_CHAR_BIT);
  set_gdbarch_int_bit (gdbarch, 2 * TARGET_CHAR_BIT);
  set_gdbarch_long_bit (gdbarch, 4 * TARGET_CHAR_BIT);
  set_gdbarch_long_long_bit (gdbarch, 8 * TARGET_CHAR_BIT);
  set_gdbarch_ptr_bit (gdbarch, 2 * TARGET_CHAR_BIT);
  set_gdbarch_addr_bit (gdbarch, 4 * TARGET_CHAR_BIT);

  set_gdbarch_float_bit (gdbarch, 4 * TARGET_CHAR_BIT);
  set_gdbarch_double_bit (gdbarch, 4 * TARGET_CHAR_BIT);
  set_gdbarch_long_double_bit (gdbarch, 4 * TARGET_CHAR_BIT);

  set_gdbarch_float_format (gdbarch, &floatformat_ieee_single_little);
  set_gdbarch_double_format (gdbarch, &floatformat_ieee_single_little);
  set_gdbarch_long_double_format (gdbarch, &floatformat_ieee_single_little);

  set_gdbarch_read_pc (gdbarch, avr_read_pc);
  set_gdbarch_write_pc (gdbarch, avr_write_pc);
  set_gdbarch_read_sp (gdbarch, avr_read_sp);

  set_gdbarch_num_regs (gdbarch, AVR_NUM_REGS);

  set_gdbarch_sp_regnum (gdbarch, AVR_SP_REGNUM);
  set_gdbarch_pc_regnum (gdbarch, AVR_PC_REGNUM);

  set_gdbarch_register_name (gdbarch, avr_register_name);
  set_gdbarch_register_type (gdbarch, avr_register_type);

  set_gdbarch_print_insn (gdbarch, print_insn_avr);

  set_gdbarch_call_dummy_address (gdbarch, avr_call_dummy_address);

  set_gdbarch_address_to_pointer (gdbarch, avr_address_to_pointer);
  set_gdbarch_pointer_to_address (gdbarch, avr_pointer_to_address);

  set_gdbarch_use_struct_convention (gdbarch, generic_use_struct_convention);

  set_gdbarch_skip_prologue (gdbarch, avr_skip_prologue);
  set_gdbarch_inner_than (gdbarch, core_addr_lessthan);

  set_gdbarch_decr_pc_after_break (gdbarch, 0);
  set_gdbarch_breakpoint_from_pc (gdbarch, avr_breakpoint_from_pc);

  set_gdbarch_function_start_offset (gdbarch, 0);
  set_gdbarch_remote_translate_xfer_address (gdbarch,
					     avr_remote_translate_xfer_address);
  set_gdbarch_frame_args_skip (gdbarch, 0);
  set_gdbarch_frameless_function_invocation (gdbarch,
                                             frameless_look_for_prologue);
  set_gdbarch_frame_args_address (gdbarch, avr_frame_address);
  set_gdbarch_frame_locals_address (gdbarch, avr_frame_address);
  set_gdbarch_frame_num_args (gdbarch, frame_num_args_unknown);

  set_gdbarch_convert_from_func_ptr_addr (gdbarch,
					  avr_convert_from_func_ptr_addr);

  frame_unwind_append_predicate (gdbarch, avr_frame_p);
  frame_base_set_default (gdbarch, &avr_frame_base);

  set_gdbarch_unwind_dummy_id (gdbarch, avr_unwind_dummy_id);
  set_gdbarch_save_dummy_frame_tos (gdbarch, generic_save_dummy_frame_tos);

  set_gdbarch_unwind_pc (gdbarch, avr_unwind_pc);

  return gdbarch;
}

/* Send a query request to the avr remote target asking for values of the io
   registers. If args parameter is not NULL, then the user has requested info
   on a specific io register [This still needs implemented and is ignored for
   now]. The query string should be one of these forms:

   "Ravr.io_reg" -> reply is "NN" number of io registers

   "Ravr.io_reg:addr,len" where addr is first register and len is number of
   registers to be read. The reply should be "<NAME>,VV;" for each io register
   where, <NAME> is a string, and VV is the hex value of the register.

   All io registers are 8-bit. */

static void
avr_io_reg_read_command (char *args, int from_tty)
{
  int bufsiz = 0;
  char buf[400];
  char query[400];
  char *p;
  unsigned int nreg = 0;
  unsigned int val;
  int i, j, k, step;

/*    fprintf_unfiltered (gdb_stderr, "DEBUG: avr_io_reg_read_command " */
/*                        "(\"%s\", %d)\n", args, from_tty); */

  if (!current_target.to_query)
    {
      fprintf_unfiltered (gdb_stderr,
			  "ERR: info io_registers NOT supported by current "
                          "target\n");
      return;
    }

  /* Just get the maximum buffer size. */
  target_query ((int) 'R', 0, 0, &bufsiz);
  if (bufsiz > sizeof (buf))
    bufsiz = sizeof (buf);

  /* Find out how many io registers the target has. */
  strcpy (query, "avr.io_reg");
  target_query ((int) 'R', query, buf, &bufsiz);

  if (strncmp (buf, "", bufsiz) == 0)
    {
      fprintf_unfiltered (gdb_stderr,
			  "info io_registers NOT supported by target\n");
      return;
    }

  if (sscanf (buf, "%x", &nreg) != 1)
    {
      fprintf_unfiltered (gdb_stderr,
			  "Error fetching number of io registers\n");
      return;
    }

  reinitialize_more_filter ();

  printf_unfiltered ("Target has %u io registers:\n\n", nreg);

  /* only fetch up to 8 registers at a time to keep the buffer small */
  step = 8;

  for (i = 0; i < nreg; i += step)
    {
      /* how many registers this round? */
      j = step;
      if ((i+j) >= nreg)
        j = nreg - i;           /* last block is less than 8 registers */

      snprintf (query, sizeof (query) - 1, "avr.io_reg:%x,%x", i, j);
      target_query ((int) 'R', query, buf, &bufsiz);

      p = buf;
      for (k = i; k < (i + j); k++)
	{
	  if (sscanf (p, "%[^,],%x;", query, &val) == 2)
	    {
	      printf_filtered ("[%02x] %-15s : %02x\n", k, query, val);
	      while ((*p != ';') && (*p != '\0'))
		p++;
	      p++;		/* skip over ';' */
	      if (*p == '\0')
		break;
	    }
	}
    }
}

void
_initialize_avr_tdep (void)
{
  register_gdbarch_init (bfd_arch_avr, avr_gdbarch_init);

  /* Add a new command to allow the user to query the avr remote target for
     the values of the io space registers in a saner way than just using
     `x/NNNb ADDR`. */

  /* FIXME: TRoth/2002-02-18: This should probably be changed to 'info avr
     io_registers' to signify it is not available on other platforms. */

  add_cmd ("io_registers", class_info, avr_io_reg_read_command,
	   "query remote avr target for io space register values", &infolist);
}