/* GNU/Linux on ARM native support.
   Copyright (C) 1999, 2000, 2001, 2002, 2004, 2005, 2006, 2007, 2008, 2009,
   2010, 2011 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 3 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, see <http://www.gnu.org/licenses/>.  */

#include "defs.h"
#include "inferior.h"
#include "gdbcore.h"
#include "gdb_string.h"
#include "regcache.h"
#include "target.h"
#include "linux-nat.h"
#include "target-descriptions.h"
#include "auxv.h"

#include "arm-tdep.h"
#include "arm-linux-tdep.h"

#include <elf/common.h>
#include <sys/user.h>
#include <sys/ptrace.h>
#include <sys/utsname.h>
#include <sys/procfs.h>

/* Prototypes for supply_gregset etc.  */
#include "gregset.h"

/* Defines ps_err_e, struct ps_prochandle.  */
#include "gdb_proc_service.h"

#include "features/arm-with-iwmmxt.c"
#include "features/arm-with-vfpv2.c"
#include "features/arm-with-vfpv3.c"
#include "features/arm-with-neon.c"

#ifndef PTRACE_GET_THREAD_AREA
#define PTRACE_GET_THREAD_AREA 22
#endif

#ifndef PTRACE_GETWMMXREGS
#define PTRACE_GETWMMXREGS 18
#define PTRACE_SETWMMXREGS 19
#endif

#ifndef PTRACE_GETVFPREGS
#define PTRACE_GETVFPREGS 27
#define PTRACE_SETVFPREGS 28
#endif

/* These are in <asm/elf.h> in current kernels.  */
#define HWCAP_VFP       64
#define HWCAP_IWMMXT    512
#define HWCAP_NEON      4096
#define HWCAP_VFPv3     8192
#define HWCAP_VFPv3D16  16384

/* A flag for whether the WMMX registers are available.  */
static int arm_linux_has_wmmx_registers;

/* The number of 64-bit VFP registers we have (expect this to be 0,
   16, or 32).  */
static int arm_linux_vfp_register_count;

extern int arm_apcs_32;

/* The following variables are used to determine the version of the
   underlying GNU/Linux operating system.  Examples:

   GNU/Linux 2.0.35             GNU/Linux 2.2.12
   os_version = 0x00020023      os_version = 0x0002020c
   os_major = 2                 os_major = 2
   os_minor = 0                 os_minor = 2
   os_release = 35              os_release = 12

   Note: os_version = (os_major << 16) | (os_minor << 8) | os_release

   These are initialized using get_linux_version() from
   _initialize_arm_linux_nat().  */

static unsigned int os_version, os_major, os_minor, os_release;

/* On GNU/Linux, threads are implemented as pseudo-processes, in which
   case we may be tracing more than one process at a time.  In that
   case, inferior_ptid will contain the main process ID and the
   individual thread (process) ID.  get_thread_id () is used to get
   the thread id if it's available, and the process id otherwise.  */

int
get_thread_id (ptid_t ptid)
{
  int tid = TIDGET (ptid);
  if (0 == tid)
    tid = PIDGET (ptid);
  return tid;
}

#define GET_THREAD_ID(PTID)	get_thread_id (PTID)

/* Get the value of a particular register from the floating point
   state of the process and store it into regcache.  */

static void
fetch_fpregister (struct regcache *regcache, int regno)
{
  int ret, tid;
  gdb_byte fp[ARM_LINUX_SIZEOF_NWFPE];
  
  /* Get the thread id for the ptrace call.  */
  tid = GET_THREAD_ID (inferior_ptid);

  /* Read the floating point state.  */
  ret = ptrace (PT_GETFPREGS, tid, 0, fp);
  if (ret < 0)
    {
      warning (_("Unable to fetch floating point register."));
      return;
    }

  /* Fetch fpsr.  */
  if (ARM_FPS_REGNUM == regno)
    regcache_raw_supply (regcache, ARM_FPS_REGNUM,
			 fp + NWFPE_FPSR_OFFSET);

  /* Fetch the floating point register.  */
  if (regno >= ARM_F0_REGNUM && regno <= ARM_F7_REGNUM)
    supply_nwfpe_register (regcache, regno, fp);
}

/* Get the whole floating point state of the process and store it
   into regcache.  */

static void
fetch_fpregs (struct regcache *regcache)
{
  int ret, regno, tid;
  gdb_byte fp[ARM_LINUX_SIZEOF_NWFPE];

  /* Get the thread id for the ptrace call.  */
  tid = GET_THREAD_ID (inferior_ptid);
  
  /* Read the floating point state.  */
  ret = ptrace (PT_GETFPREGS, tid, 0, fp);
  if (ret < 0)
    {
      warning (_("Unable to fetch the floating point registers."));
      return;
    }

  /* Fetch fpsr.  */
  regcache_raw_supply (regcache, ARM_FPS_REGNUM,
		       fp + NWFPE_FPSR_OFFSET);

  /* Fetch the floating point registers.  */
  for (regno = ARM_F0_REGNUM; regno <= ARM_F7_REGNUM; regno++)
    supply_nwfpe_register (regcache, regno, fp);
}

/* Save a particular register into the floating point state of the
   process using the contents from regcache.  */

static void
store_fpregister (const struct regcache *regcache, int regno)
{
  int ret, tid;
  gdb_byte fp[ARM_LINUX_SIZEOF_NWFPE];

  /* Get the thread id for the ptrace call.  */
  tid = GET_THREAD_ID (inferior_ptid);
  
  /* Read the floating point state.  */
  ret = ptrace (PT_GETFPREGS, tid, 0, fp);
  if (ret < 0)
    {
      warning (_("Unable to fetch the floating point registers."));
      return;
    }

  /* Store fpsr.  */
  if (ARM_FPS_REGNUM == regno && regcache_valid_p (regcache, ARM_FPS_REGNUM))
    regcache_raw_collect (regcache, ARM_FPS_REGNUM, fp + NWFPE_FPSR_OFFSET);

  /* Store the floating point register.  */
  if (regno >= ARM_F0_REGNUM && regno <= ARM_F7_REGNUM)
    collect_nwfpe_register (regcache, regno, fp);

  ret = ptrace (PTRACE_SETFPREGS, tid, 0, fp);
  if (ret < 0)
    {
      warning (_("Unable to store floating point register."));
      return;
    }
}

/* Save the whole floating point state of the process using
   the contents from regcache.  */

static void
store_fpregs (const struct regcache *regcache)
{
  int ret, regno, tid;
  gdb_byte fp[ARM_LINUX_SIZEOF_NWFPE];

  /* Get the thread id for the ptrace call.  */
  tid = GET_THREAD_ID (inferior_ptid);
  
  /* Read the floating point state.  */
  ret = ptrace (PT_GETFPREGS, tid, 0, fp);
  if (ret < 0)
    {
      warning (_("Unable to fetch the floating point registers."));
      return;
    }

  /* Store fpsr.  */
  if (regcache_valid_p (regcache, ARM_FPS_REGNUM))
    regcache_raw_collect (regcache, ARM_FPS_REGNUM, fp + NWFPE_FPSR_OFFSET);

  /* Store the floating point registers.  */
  for (regno = ARM_F0_REGNUM; regno <= ARM_F7_REGNUM; regno++)
    if (regcache_valid_p (regcache, regno))
      collect_nwfpe_register (regcache, regno, fp);

  ret = ptrace (PTRACE_SETFPREGS, tid, 0, fp);
  if (ret < 0)
    {
      warning (_("Unable to store floating point registers."));
      return;
    }
}

/* Fetch a general register of the process and store into
   regcache.  */

static void
fetch_register (struct regcache *regcache, int regno)
{
  int ret, tid;
  elf_gregset_t regs;

  /* Get the thread id for the ptrace call.  */
  tid = GET_THREAD_ID (inferior_ptid);
  
  ret = ptrace (PTRACE_GETREGS, tid, 0, &regs);
  if (ret < 0)
    {
      warning (_("Unable to fetch general register."));
      return;
    }

  if (regno >= ARM_A1_REGNUM && regno < ARM_PC_REGNUM)
    regcache_raw_supply (regcache, regno, (char *) &regs[regno]);

  if (ARM_PS_REGNUM == regno)
    {
      if (arm_apcs_32)
        regcache_raw_supply (regcache, ARM_PS_REGNUM,
			     (char *) &regs[ARM_CPSR_GREGNUM]);
      else
        regcache_raw_supply (regcache, ARM_PS_REGNUM,
			     (char *) &regs[ARM_PC_REGNUM]);
    }
    
  if (ARM_PC_REGNUM == regno)
    { 
      regs[ARM_PC_REGNUM] = gdbarch_addr_bits_remove
			      (get_regcache_arch (regcache),
			       regs[ARM_PC_REGNUM]);
      regcache_raw_supply (regcache, ARM_PC_REGNUM,
			   (char *) &regs[ARM_PC_REGNUM]);
    }
}

/* Fetch all general registers of the process and store into
   regcache.  */

static void
fetch_regs (struct regcache *regcache)
{
  int ret, regno, tid;
  elf_gregset_t regs;

  /* Get the thread id for the ptrace call.  */
  tid = GET_THREAD_ID (inferior_ptid);
  
  ret = ptrace (PTRACE_GETREGS, tid, 0, &regs);
  if (ret < 0)
    {
      warning (_("Unable to fetch general registers."));
      return;
    }

  for (regno = ARM_A1_REGNUM; regno < ARM_PC_REGNUM; regno++)
    regcache_raw_supply (regcache, regno, (char *) &regs[regno]);

  if (arm_apcs_32)
    regcache_raw_supply (regcache, ARM_PS_REGNUM,
			 (char *) &regs[ARM_CPSR_GREGNUM]);
  else
    regcache_raw_supply (regcache, ARM_PS_REGNUM,
			 (char *) &regs[ARM_PC_REGNUM]);

  regs[ARM_PC_REGNUM] = gdbarch_addr_bits_remove
			  (get_regcache_arch (regcache), regs[ARM_PC_REGNUM]);
  regcache_raw_supply (regcache, ARM_PC_REGNUM,
		       (char *) &regs[ARM_PC_REGNUM]);
}

/* Store all general registers of the process from the values in
   regcache.  */

static void
store_register (const struct regcache *regcache, int regno)
{
  int ret, tid;
  elf_gregset_t regs;
  
  if (!regcache_valid_p (regcache, regno))
    return;

  /* Get the thread id for the ptrace call.  */
  tid = GET_THREAD_ID (inferior_ptid);
  
  /* Get the general registers from the process.  */
  ret = ptrace (PTRACE_GETREGS, tid, 0, &regs);
  if (ret < 0)
    {
      warning (_("Unable to fetch general registers."));
      return;
    }

  if (regno >= ARM_A1_REGNUM && regno <= ARM_PC_REGNUM)
    regcache_raw_collect (regcache, regno, (char *) &regs[regno]);
  else if (arm_apcs_32 && regno == ARM_PS_REGNUM)
    regcache_raw_collect (regcache, regno,
			 (char *) &regs[ARM_CPSR_GREGNUM]);
  else if (!arm_apcs_32 && regno == ARM_PS_REGNUM)
    regcache_raw_collect (regcache, ARM_PC_REGNUM,
			 (char *) &regs[ARM_PC_REGNUM]);

  ret = ptrace (PTRACE_SETREGS, tid, 0, &regs);
  if (ret < 0)
    {
      warning (_("Unable to store general register."));
      return;
    }
}

static void
store_regs (const struct regcache *regcache)
{
  int ret, regno, tid;
  elf_gregset_t regs;

  /* Get the thread id for the ptrace call.  */
  tid = GET_THREAD_ID (inferior_ptid);
  
  /* Fetch the general registers.  */
  ret = ptrace (PTRACE_GETREGS, tid, 0, &regs);
  if (ret < 0)
    {
      warning (_("Unable to fetch general registers."));
      return;
    }

  for (regno = ARM_A1_REGNUM; regno <= ARM_PC_REGNUM; regno++)
    {
      if (regcache_valid_p (regcache, regno))
	regcache_raw_collect (regcache, regno, (char *) &regs[regno]);
    }

  if (arm_apcs_32 && regcache_valid_p (regcache, ARM_PS_REGNUM))
    regcache_raw_collect (regcache, ARM_PS_REGNUM,
			 (char *) &regs[ARM_CPSR_GREGNUM]);

  ret = ptrace (PTRACE_SETREGS, tid, 0, &regs);

  if (ret < 0)
    {
      warning (_("Unable to store general registers."));
      return;
    }
}

/* Fetch all WMMX registers of the process and store into
   regcache.  */

#define IWMMXT_REGS_SIZE (16 * 8 + 6 * 4)

static void
fetch_wmmx_regs (struct regcache *regcache)
{
  char regbuf[IWMMXT_REGS_SIZE];
  int ret, regno, tid;

  /* Get the thread id for the ptrace call.  */
  tid = GET_THREAD_ID (inferior_ptid);

  ret = ptrace (PTRACE_GETWMMXREGS, tid, 0, regbuf);
  if (ret < 0)
    {
      warning (_("Unable to fetch WMMX registers."));
      return;
    }

  for (regno = 0; regno < 16; regno++)
    regcache_raw_supply (regcache, regno + ARM_WR0_REGNUM,
			 &regbuf[regno * 8]);

  for (regno = 0; regno < 2; regno++)
    regcache_raw_supply (regcache, regno + ARM_WCSSF_REGNUM,
			 &regbuf[16 * 8 + regno * 4]);

  for (regno = 0; regno < 4; regno++)
    regcache_raw_supply (regcache, regno + ARM_WCGR0_REGNUM,
			 &regbuf[16 * 8 + 2 * 4 + regno * 4]);
}

static void
store_wmmx_regs (const struct regcache *regcache)
{
  char regbuf[IWMMXT_REGS_SIZE];
  int ret, regno, tid;

  /* Get the thread id for the ptrace call.  */
  tid = GET_THREAD_ID (inferior_ptid);

  ret = ptrace (PTRACE_GETWMMXREGS, tid, 0, regbuf);
  if (ret < 0)
    {
      warning (_("Unable to fetch WMMX registers."));
      return;
    }

  for (regno = 0; regno < 16; regno++)
    if (regcache_valid_p (regcache, regno + ARM_WR0_REGNUM))
      regcache_raw_collect (regcache, regno + ARM_WR0_REGNUM,
			    &regbuf[regno * 8]);

  for (regno = 0; regno < 2; regno++)
    if (regcache_valid_p (regcache, regno + ARM_WCSSF_REGNUM))
      regcache_raw_collect (regcache, regno + ARM_WCSSF_REGNUM,
			    &regbuf[16 * 8 + regno * 4]);

  for (regno = 0; regno < 4; regno++)
    if (regcache_valid_p (regcache, regno + ARM_WCGR0_REGNUM))
      regcache_raw_collect (regcache, regno + ARM_WCGR0_REGNUM,
			    &regbuf[16 * 8 + 2 * 4 + regno * 4]);

  ret = ptrace (PTRACE_SETWMMXREGS, tid, 0, regbuf);

  if (ret < 0)
    {
      warning (_("Unable to store WMMX registers."));
      return;
    }
}

/* Fetch and store VFP Registers.  The kernel object has space for 32
   64-bit registers, and the FPSCR.  This is even when on a VFPv2 or
   VFPv3D16 target.  */
#define VFP_REGS_SIZE (32 * 8 + 4)

static void
fetch_vfp_regs (struct regcache *regcache)
{
  char regbuf[VFP_REGS_SIZE];
  int ret, regno, tid;

  /* Get the thread id for the ptrace call.  */
  tid = GET_THREAD_ID (inferior_ptid);

  ret = ptrace (PTRACE_GETVFPREGS, tid, 0, regbuf);
  if (ret < 0)
    {
      warning (_("Unable to fetch VFP registers."));
      return;
    }

  for (regno = 0; regno < arm_linux_vfp_register_count; regno++)
    regcache_raw_supply (regcache, regno + ARM_D0_REGNUM,
			 (char *) regbuf + regno * 8);

  regcache_raw_supply (regcache, ARM_FPSCR_REGNUM,
		       (char *) regbuf + 32 * 8);
}

static void
store_vfp_regs (const struct regcache *regcache)
{
  char regbuf[VFP_REGS_SIZE];
  int ret, regno, tid;

  /* Get the thread id for the ptrace call.  */
  tid = GET_THREAD_ID (inferior_ptid);

  ret = ptrace (PTRACE_GETVFPREGS, tid, 0, regbuf);
  if (ret < 0)
    {
      warning (_("Unable to fetch VFP registers (for update)."));
      return;
    }

  for (regno = 0; regno < arm_linux_vfp_register_count; regno++)
    regcache_raw_collect (regcache, regno + ARM_D0_REGNUM,
			  (char *) regbuf + regno * 8);

  regcache_raw_collect (regcache, ARM_FPSCR_REGNUM,
			(char *) regbuf + 32 * 8);

  ret = ptrace (PTRACE_SETVFPREGS, tid, 0, regbuf);

  if (ret < 0)
    {
      warning (_("Unable to store VFP registers."));
      return;
    }
}

/* Fetch registers from the child process.  Fetch all registers if
   regno == -1, otherwise fetch all general registers or all floating
   point registers depending upon the value of regno.  */

static void
arm_linux_fetch_inferior_registers (struct target_ops *ops,
				    struct regcache *regcache, int regno)
{
  if (-1 == regno)
    {
      fetch_regs (regcache);
      fetch_fpregs (regcache);
      if (arm_linux_has_wmmx_registers)
	fetch_wmmx_regs (regcache);
      if (arm_linux_vfp_register_count > 0)
	fetch_vfp_regs (regcache);
    }
  else 
    {
      if (regno < ARM_F0_REGNUM || regno == ARM_PS_REGNUM)
        fetch_register (regcache, regno);
      else if (regno >= ARM_F0_REGNUM && regno <= ARM_FPS_REGNUM)
        fetch_fpregister (regcache, regno);
      else if (arm_linux_has_wmmx_registers
	       && regno >= ARM_WR0_REGNUM && regno <= ARM_WCGR7_REGNUM)
	fetch_wmmx_regs (regcache);
      else if (arm_linux_vfp_register_count > 0
	       && regno >= ARM_D0_REGNUM
	       && regno <= ARM_D0_REGNUM + arm_linux_vfp_register_count)
	fetch_vfp_regs (regcache);
    }
}

/* Store registers back into the inferior.  Store all registers if
   regno == -1, otherwise store all general registers or all floating
   point registers depending upon the value of regno.  */

static void
arm_linux_store_inferior_registers (struct target_ops *ops,
				    struct regcache *regcache, int regno)
{
  if (-1 == regno)
    {
      store_regs (regcache);
      store_fpregs (regcache);
      if (arm_linux_has_wmmx_registers)
	store_wmmx_regs (regcache);
      if (arm_linux_vfp_register_count > 0)
	store_vfp_regs (regcache);
    }
  else
    {
      if (regno < ARM_F0_REGNUM || regno == ARM_PS_REGNUM)
        store_register (regcache, regno);
      else if ((regno >= ARM_F0_REGNUM) && (regno <= ARM_FPS_REGNUM))
        store_fpregister (regcache, regno);
      else if (arm_linux_has_wmmx_registers
	       && regno >= ARM_WR0_REGNUM && regno <= ARM_WCGR7_REGNUM)
	store_wmmx_regs (regcache);
      else if (arm_linux_vfp_register_count > 0
	       && regno >= ARM_D0_REGNUM
	       && regno <= ARM_D0_REGNUM + arm_linux_vfp_register_count)
	store_vfp_regs (regcache);
    }
}

/* Wrapper functions for the standard regset handling, used by
   thread debugging.  */

void
fill_gregset (const struct regcache *regcache,	
	      gdb_gregset_t *gregsetp, int regno)
{
  arm_linux_collect_gregset (NULL, regcache, regno, gregsetp, 0);
}

void
supply_gregset (struct regcache *regcache, const gdb_gregset_t *gregsetp)
{
  arm_linux_supply_gregset (NULL, regcache, -1, gregsetp, 0);
}

void
fill_fpregset (const struct regcache *regcache,
	       gdb_fpregset_t *fpregsetp, int regno)
{
  arm_linux_collect_nwfpe (NULL, regcache, regno, fpregsetp, 0);
}

/* Fill GDB's register array with the floating-point register values
   in *fpregsetp.  */

void
supply_fpregset (struct regcache *regcache, const gdb_fpregset_t *fpregsetp)
{
  arm_linux_supply_nwfpe (NULL, regcache, -1, fpregsetp, 0);
}

/* Fetch the thread-local storage pointer for libthread_db.  */

ps_err_e
ps_get_thread_area (const struct ps_prochandle *ph,
                    lwpid_t lwpid, int idx, void **base)
{
  if (ptrace (PTRACE_GET_THREAD_AREA, lwpid, NULL, base) != 0)
    return PS_ERR;

  /* IDX is the bias from the thread pointer to the beginning of the
     thread descriptor.  It has to be subtracted due to implementation
     quirks in libthread_db.  */
  *base = (void *) ((char *)*base - idx);

  return PS_OK;
}

static unsigned int
get_linux_version (unsigned int *vmajor,
		   unsigned int *vminor,
		   unsigned int *vrelease)
{
  struct utsname info;
  char *pmajor, *pminor, *prelease, *tail;

  if (-1 == uname (&info))
    {
      warning (_("Unable to determine GNU/Linux version."));
      return -1;
    }

  pmajor = strtok (info.release, ".");
  pminor = strtok (NULL, ".");
  prelease = strtok (NULL, ".");

  *vmajor = (unsigned int) strtoul (pmajor, &tail, 0);
  *vminor = (unsigned int) strtoul (pminor, &tail, 0);
  *vrelease = (unsigned int) strtoul (prelease, &tail, 0);

  return ((*vmajor << 16) | (*vminor << 8) | *vrelease);
}

static const struct target_desc *
arm_linux_read_description (struct target_ops *ops)
{
  CORE_ADDR arm_hwcap = 0;
  arm_linux_has_wmmx_registers = 0;
  arm_linux_vfp_register_count = 0;

  if (target_auxv_search (ops, AT_HWCAP, &arm_hwcap) != 1)
    {
      return NULL;
    }

  if (arm_hwcap & HWCAP_IWMMXT)
    {
      arm_linux_has_wmmx_registers = 1;
      if (tdesc_arm_with_iwmmxt == NULL)
	initialize_tdesc_arm_with_iwmmxt ();
      return tdesc_arm_with_iwmmxt;
    }

  if (arm_hwcap & HWCAP_VFP)
    {
      int pid;
      char *buf;
      const struct target_desc * result = NULL;

      /* NEON implies VFPv3-D32 or no-VFP unit.  Say that we only support
	 Neon with VFPv3-D32.  */
      if (arm_hwcap & HWCAP_NEON)
	{
	  arm_linux_vfp_register_count = 32;
	  if (tdesc_arm_with_neon == NULL)
	    initialize_tdesc_arm_with_neon ();
	  result = tdesc_arm_with_neon;
	}
      else if ((arm_hwcap & (HWCAP_VFPv3 | HWCAP_VFPv3D16)) == HWCAP_VFPv3)
	{
	  arm_linux_vfp_register_count = 32;
	  if (tdesc_arm_with_vfpv3 == NULL)
	    initialize_tdesc_arm_with_vfpv3 ();
	  result = tdesc_arm_with_vfpv3;
	}
      else
	{
	  arm_linux_vfp_register_count = 16;
	  if (tdesc_arm_with_vfpv2 == NULL)
	    initialize_tdesc_arm_with_vfpv2 ();
	  result = tdesc_arm_with_vfpv2;
	}

      /* Now make sure that the kernel supports reading these
	 registers.  Support was added in 2.6.30.  */
      pid = GET_LWP (inferior_ptid);
      errno = 0;
      buf = alloca (VFP_REGS_SIZE);
      if (ptrace (PTRACE_GETVFPREGS, pid, 0, buf) < 0
	  && errno == EIO)
	result = NULL;

      return result;
    }

  return NULL;
}

void _initialize_arm_linux_nat (void);

void
_initialize_arm_linux_nat (void)
{
  struct target_ops *t;

  os_version = get_linux_version (&os_major, &os_minor, &os_release);

  /* Fill in the generic GNU/Linux methods.  */
  t = linux_target ();

  /* Add our register access methods.  */
  t->to_fetch_registers = arm_linux_fetch_inferior_registers;
  t->to_store_registers = arm_linux_store_inferior_registers;

  t->to_read_description = arm_linux_read_description;

  /* Register the target.  */
  linux_nat_add_target (t);
}