[deliverable/binutils-gdb.git] / gdb / arm-linux-nat.c

/* 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 "observer.h"
#include "gdbthread.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"

#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

#ifndef PTRACE_GETHBPREGS
#define PTRACE_GETHBPREGS 29
#define PTRACE_SETHBPREGS 30
#endif

/* 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
      && REG_VALID == regcache_register_status (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 (REG_VALID == regcache_register_status (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 (REG_VALID == regcache_register_status (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 (REG_VALID != regcache_register_status (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 (REG_VALID == regcache_register_status (regcache, regno))
        regcache_raw_collect (regcache, regno, (char *) &regs[regno]);
    }

  if (arm_apcs_32 && REG_VALID == regcache_register_status (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 (REG_VALID == regcache_register_status (regcache,
                                               regno + ARM_WR0_REGNUM))
      regcache_raw_collect (regcache, regno + ARM_WR0_REGNUM,
                            &regbuf[regno * 8]);

  for (regno = 0; regno < 2; regno++)
    if (REG_VALID == regcache_register_status (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 (REG_VALID == regcache_register_status (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;
      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;
          result = tdesc_arm_with_neon;
        }
      else if ((arm_hwcap & (HWCAP_VFPv3 | HWCAP_VFPv3D16)) == HWCAP_VFPv3)
        {
          arm_linux_vfp_register_count = 32;
          result = tdesc_arm_with_vfpv3;
        }
      else
        {
          arm_linux_vfp_register_count = 16;
          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;
}

/* Information describing the hardware breakpoint capabilities.  */
struct arm_linux_hwbp_cap
{
  gdb_byte arch;
  gdb_byte max_wp_length;
  gdb_byte wp_count;
  gdb_byte bp_count;
};

/* Get hold of the Hardware Breakpoint information for the target we are
   attached to.  Returns NULL if the kernel doesn't support Hardware 
   breakpoints at all, or a pointer to the information structure.  */
static const struct arm_linux_hwbp_cap *
arm_linux_get_hwbp_cap (void)
{
  /* The info structure we return.  */
  static struct arm_linux_hwbp_cap info;

  /* Is INFO in a good state?  -1 means that no attempt has been made to
     initialize INFO; 0 means an attempt has been made, but it failed; 1
     means INFO is in an initialized state.  */
  static int available = -1;

  if (available == -1)
    {
      int tid;
      unsigned int val;

      tid = GET_THREAD_ID (inferior_ptid);
      if (ptrace (PTRACE_GETHBPREGS, tid, 0, &val) < 0)
        available = 0;
      else
        {
          info.arch = (gdb_byte)((val >> 24) & 0xff);
          info.max_wp_length = (gdb_byte)((val >> 16) & 0xff);
          info.wp_count = (gdb_byte)((val >> 8) & 0xff);
          info.bp_count = (gdb_byte)(val & 0xff);
          available = (info.arch != 0);
        }
    }

  return available == 1 ? &info : NULL;
}

/* How many hardware breakpoints are available?  */
static int
arm_linux_get_hw_breakpoint_count (void)
{
  const struct arm_linux_hwbp_cap *cap = arm_linux_get_hwbp_cap ();
  return cap != NULL ? cap->bp_count : 0;
}

/* How many hardware watchpoints are available?  */
static int
arm_linux_get_hw_watchpoint_count (void)
{
  const struct arm_linux_hwbp_cap *cap = arm_linux_get_hwbp_cap ();
  return cap != NULL ? cap->wp_count : 0;
}

/* Have we got a free break-/watch-point available for use?  Returns -1 if
   there is not an appropriate resource available, otherwise returns 1.  */
static int
arm_linux_can_use_hw_breakpoint (int type, int cnt, int ot)
{
  if (type == bp_hardware_watchpoint || type == bp_read_watchpoint
      || type == bp_access_watchpoint || type == bp_watchpoint)
    {
      if (cnt + ot > arm_linux_get_hw_watchpoint_count ())
        return -1;
    }
  else if (type == bp_hardware_breakpoint)
    {
      if (cnt > arm_linux_get_hw_breakpoint_count ())
        return -1;
    }
  else
    gdb_assert (FALSE);

  return 1;
}

/* Enum describing the different types of ARM hardware break-/watch-points.  */
typedef enum
{
  arm_hwbp_break = 0,
  arm_hwbp_load = 1,
  arm_hwbp_store = 2,
  arm_hwbp_access = 3
} arm_hwbp_type;

/* Type describing an ARM Hardware Breakpoint Control register value.  */
typedef unsigned int arm_hwbp_control_t;

/* Structure used to keep track of hardware break-/watch-points.  */
struct arm_linux_hw_breakpoint
{
  /* Address to break on, or being watched.  */
  unsigned int address;
  /* Control register for break-/watch- point.  */
  arm_hwbp_control_t control;
};

/* Structure containing arrays of the break and watch points which are have
   active in each thread.

   The Linux ptrace interface to hardware break-/watch-points presents the 
   values in a vector centred around 0 (which is used fo generic information).
   Positive indicies refer to breakpoint addresses/control registers, negative
   indices to watchpoint addresses/control registers.

   The Linux vector is indexed as follows:
      -((i << 1) + 2): Control register for watchpoint i.
      -((i << 1) + 1): Address register for watchpoint i.
                    0: Information register.
       ((i << 1) + 1): Address register for breakpoint i.
       ((i << 1) + 2): Control register for breakpoint i.

   This structure is used as a per-thread cache of the state stored by the 
   kernel, so that we don't need to keep calling into the kernel to find a 
   free breakpoint.

   We treat break-/watch-points with their enable bit clear as being deleted.
   */
typedef struct arm_linux_thread_points
{
  /* Thread ID.  */
  int tid;
  /* Breakpoints for thread.  */
  struct arm_linux_hw_breakpoint *bpts;
  /* Watchpoint for threads.  */
  struct arm_linux_hw_breakpoint *wpts;
} *arm_linux_thread_points_p;
DEF_VEC_P (arm_linux_thread_points_p);

/* Vector of hardware breakpoints for each thread.  */
VEC(arm_linux_thread_points_p) *arm_threads = NULL;

/* Find the list of hardware break-/watch-points for a thread with id TID.
   If no list exists for TID we return NULL if ALLOC_NEW is 0, otherwise we
   create a new list and return that.  */
static struct arm_linux_thread_points *
arm_linux_find_breakpoints_by_tid (int tid, int alloc_new)
{
  int i;
  struct arm_linux_thread_points *t;

  for (i = 0; VEC_iterate (arm_linux_thread_points_p, arm_threads, i, t); ++i)
    {
      if (t->tid == tid)
        return t;
    }

  t = NULL;

  if (alloc_new)
    {
      t = xmalloc (sizeof (struct arm_linux_thread_points));
      t->tid = tid;
      t->bpts = xzalloc (arm_linux_get_hw_breakpoint_count ()
                         * sizeof (struct arm_linux_hw_breakpoint));
      t->wpts = xzalloc (arm_linux_get_hw_watchpoint_count ()
                         * sizeof (struct arm_linux_hw_breakpoint));
      VEC_safe_push (arm_linux_thread_points_p, arm_threads, t);
    }

  return t;
}

/* Initialize an ARM hardware break-/watch-point control register value.
   BYTE_ADDRESS_SELECT is the mask of bytes to trigger on; HWBP_TYPE is the 
   type of break-/watch-point; ENABLE indicates whether the point is enabled.
   */
static arm_hwbp_control_t 
arm_hwbp_control_initialize (unsigned byte_address_select,
                             arm_hwbp_type hwbp_type,
                             int enable)
{
  gdb_assert ((byte_address_select & ~0xffU) == 0);
  gdb_assert (hwbp_type != arm_hwbp_break 
              || ((byte_address_select & 0xfU) != 0));

  return (byte_address_select << 5) | (hwbp_type << 3) | (3 << 1) | enable;
}

/* Does the breakpoint control value CONTROL have the enable bit set?  */
static int
arm_hwbp_control_is_enabled (arm_hwbp_control_t control)
{
  return control & 0x1;
}

/* Change a breakpoint control word so that it is in the disabled state.  */
static arm_hwbp_control_t
arm_hwbp_control_disable (arm_hwbp_control_t control)
{
  return control & ~0x1;
}

/* Initialise the hardware breakpoint structure P.  The breakpoint will be
   enabled, and will point to the placed address of BP_TGT.  */
static void
arm_linux_hw_breakpoint_initialize (struct gdbarch *gdbarch,
                                    struct bp_target_info *bp_tgt,
                                    struct arm_linux_hw_breakpoint *p)
{
  unsigned mask;
  CORE_ADDR address = bp_tgt->placed_address;

  /* We have to create a mask for the control register which says which bits
     of the word pointed to by address to break on.  */
  if (arm_pc_is_thumb (gdbarch, address))
    mask = 0x3 << (address & 2);
  else
    mask = 0xf;

  p->address = (unsigned int) (address & ~3);
  p->control = arm_hwbp_control_initialize (mask, arm_hwbp_break, 1);
}

/* Get the ARM hardware breakpoint type from the RW value we're given when
   asked to set a watchpoint.  */
static arm_hwbp_type 
arm_linux_get_hwbp_type (int rw)
{
  if (rw == hw_read)
    return arm_hwbp_load;
  else if (rw == hw_write)
    return arm_hwbp_store;
  else
    return arm_hwbp_access;
}

/* Initialize the hardware breakpoint structure P for a watchpoint at ADDR
   to LEN.  The type of watchpoint is given in RW.  */
static void
arm_linux_hw_watchpoint_initialize (CORE_ADDR addr, int len, int rw,
                                    struct arm_linux_hw_breakpoint *p)
{
  const struct arm_linux_hwbp_cap *cap = arm_linux_get_hwbp_cap ();
  unsigned mask;

  gdb_assert (cap != NULL);
  gdb_assert (cap->max_wp_length != 0);

  mask = (1 << len) - 1;

  p->address = (unsigned int) addr;
  p->control = arm_hwbp_control_initialize (mask, 
                                            arm_linux_get_hwbp_type (rw), 1);
}

/* Are two break-/watch-points equal?  */
static int
arm_linux_hw_breakpoint_equal (const struct arm_linux_hw_breakpoint *p1,
                               const struct arm_linux_hw_breakpoint *p2)
{
  return p1->address == p2->address && p1->control == p2->control;
}

/* Insert the hardware breakpoint (WATCHPOINT = 0) or watchpoint (WATCHPOINT
   =1) BPT for thread TID.  */
static void
arm_linux_insert_hw_breakpoint1 (const struct arm_linux_hw_breakpoint* bpt, 
                                int tid, int watchpoint)
{
  struct arm_linux_thread_points *t = arm_linux_find_breakpoints_by_tid (tid, 1);
  gdb_byte count, i;
  struct arm_linux_hw_breakpoint* bpts;
  int dir;

  gdb_assert (t != NULL);

  if (watchpoint)
    {
      count = arm_linux_get_hw_watchpoint_count ();
      bpts = t->wpts;
      dir = -1;
    }
  else
    {
      count = arm_linux_get_hw_breakpoint_count ();
      bpts = t->bpts;
      dir = 1;
    }

  for (i = 0; i < count; ++i)
    if (!arm_hwbp_control_is_enabled (bpts[i].control))
      {
        errno = 0;
        if (ptrace (PTRACE_SETHBPREGS, tid, dir * ((i << 1) + 1), 
                    &bpt->address) < 0)
          perror_with_name (_("Unexpected error setting breakpoint address"));
        if (ptrace (PTRACE_SETHBPREGS, tid, dir * ((i << 1) + 2), 
                    &bpt->control) < 0)
          perror_with_name (_("Unexpected error setting breakpoint"));

        memcpy (bpts + i, bpt, sizeof (struct arm_linux_hw_breakpoint));
        break;
      }

  gdb_assert (i != count);
}

/* Remove the hardware breakpoint (WATCHPOINT = 0) or watchpoint
   (WATCHPOINT = 1) BPT for thread TID.  */
static void
arm_linux_remove_hw_breakpoint1 (const struct arm_linux_hw_breakpoint *bpt, 
                                 int tid, int watchpoint)
{
  struct arm_linux_thread_points *t = arm_linux_find_breakpoints_by_tid (tid, 0);
  gdb_byte count, i;
  struct arm_linux_hw_breakpoint *bpts;
  int dir;

  gdb_assert (t != NULL);

  if (watchpoint)
    {
      count = arm_linux_get_hw_watchpoint_count ();
      bpts = t->wpts;
      dir = -1;
    }
  else
    {
      count = arm_linux_get_hw_breakpoint_count ();
      bpts = t->bpts;
      dir = 1;
    }

  for (i = 0; i < count; ++i)
    if (arm_linux_hw_breakpoint_equal (bpt, bpts + i))
      {
        errno = 0;
        bpts[i].control = arm_hwbp_control_disable (bpts[i].control);
        if (ptrace (PTRACE_SETHBPREGS, tid, dir * ((i << 1) + 2), 
                    &bpts[i].control) < 0)
          perror_with_name (_("Unexpected error clearing breakpoint"));
        break;
      }

  gdb_assert (i != count);
}

/* Insert a Hardware breakpoint.  */
static int
arm_linux_insert_hw_breakpoint (struct gdbarch *gdbarch, 
                                struct bp_target_info *bp_tgt)
{
  struct lwp_info *lp;
  struct arm_linux_hw_breakpoint p;

  if (arm_linux_get_hw_breakpoint_count () == 0)
    return -1;

  arm_linux_hw_breakpoint_initialize (gdbarch, bp_tgt, &p);
  ALL_LWPS (lp)
    arm_linux_insert_hw_breakpoint1 (&p, TIDGET (lp->ptid), 0);

  return 0;
}

/* Remove a hardware breakpoint.  */
static int
arm_linux_remove_hw_breakpoint (struct gdbarch *gdbarch, 
                                struct bp_target_info *bp_tgt)
{
  struct lwp_info *lp;
  struct arm_linux_hw_breakpoint p;

  if (arm_linux_get_hw_breakpoint_count () == 0)
    return -1;

  arm_linux_hw_breakpoint_initialize (gdbarch, bp_tgt, &p);
  ALL_LWPS (lp)
    arm_linux_remove_hw_breakpoint1 (&p, TIDGET (lp->ptid), 0);

  return 0;
}

/* Are we able to use a hardware watchpoint for the LEN bytes starting at 
   ADDR?  */
static int
arm_linux_region_ok_for_hw_watchpoint (CORE_ADDR addr, int len)
{
  const struct arm_linux_hwbp_cap *cap = arm_linux_get_hwbp_cap ();
  CORE_ADDR max_wp_length, aligned_addr;

  /* Can not set watchpoints for zero or negative lengths.  */
  if (len <= 0)
    return 0;

  /* Need to be able to use the ptrace interface.  */
  if (cap == NULL || cap->wp_count == 0)
    return 0;

  /* Test that the range [ADDR, ADDR + LEN) fits into the largest address
     range covered by a watchpoint.  */
  max_wp_length = (CORE_ADDR)cap->max_wp_length;
  aligned_addr = addr & ~(max_wp_length - 1);

  if (aligned_addr + max_wp_length < addr + len)
    return 0;

  /* The current ptrace interface can only handle watchpoints that are a
     power of 2.  */
  if ((len & (len - 1)) != 0)
    return 0;

  /* All tests passed so we must be able to set a watchpoint.  */
  return 1;
}

/* Insert a Hardware breakpoint.  */
static int
arm_linux_insert_watchpoint (CORE_ADDR addr, int len, int rw,
                             struct expression *cond)
{
  struct lwp_info *lp;
  struct arm_linux_hw_breakpoint p;

  if (arm_linux_get_hw_watchpoint_count () == 0)
    return -1;

  arm_linux_hw_watchpoint_initialize (addr, len, rw, &p);
  ALL_LWPS (lp)
    arm_linux_insert_hw_breakpoint1 (&p, TIDGET (lp->ptid), 1);

  return 0;
}

/* Remove a hardware breakpoint.  */
static int
arm_linux_remove_watchpoint (CORE_ADDR addr, int len, int rw,
                             struct expression *cond)
{
  struct lwp_info *lp;
  struct arm_linux_hw_breakpoint p;

  if (arm_linux_get_hw_watchpoint_count () == 0)
    return -1;

  arm_linux_hw_watchpoint_initialize (addr, len, rw, &p);
  ALL_LWPS (lp)
    arm_linux_remove_hw_breakpoint1 (&p, TIDGET (lp->ptid), 1);

  return 0;
}

/* What was the data address the target was stopped on accessing.  */
static int
arm_linux_stopped_data_address (struct target_ops *target, CORE_ADDR *addr_p)
{
  struct siginfo *siginfo_p = linux_nat_get_siginfo (inferior_ptid);
  int slot = siginfo_p->si_errno;

  /* This must be a hardware breakpoint.  */
  if (siginfo_p->si_signo != SIGTRAP
      || (siginfo_p->si_code & 0xffff) != 0x0004 /* TRAP_HWBKPT */)
    return 0;

  /* We must be able to set hardware watchpoints.  */
  if (arm_linux_get_hw_watchpoint_count () == 0)
    return 0;

  /* If we are in a positive slot then we're looking at a breakpoint and not
     a watchpoint.  */
  if (slot >= 0)
    return 0;

  *addr_p = (CORE_ADDR) (uintptr_t) siginfo_p->si_addr;
  return 1;
}

/* Has the target been stopped by hitting a watchpoint?  */
static int
arm_linux_stopped_by_watchpoint (void)
{
  CORE_ADDR addr;
  return arm_linux_stopped_data_address (&current_target, &addr);
}

static int
arm_linux_watchpoint_addr_within_range (struct target_ops *target,
                                        CORE_ADDR addr,
                                        CORE_ADDR start, int length)
{
  return start <= addr && start + length - 1 >= addr;
}

/* Handle thread creation.  We need to copy the breakpoints and watchpoints
   in the parent thread to the child thread.  */
static void
arm_linux_new_thread (ptid_t ptid)
{
  int tid = TIDGET (ptid);
  const struct arm_linux_hwbp_cap *info = arm_linux_get_hwbp_cap ();

  if (info != NULL)
    {
      int i;
      struct arm_linux_thread_points *p;
      struct arm_linux_hw_breakpoint *bpts;

      if (VEC_empty (arm_linux_thread_points_p, arm_threads))
        return;

      /* Get a list of breakpoints from any thread. */
      p = VEC_last (arm_linux_thread_points_p, arm_threads);

      /* Copy that thread's breakpoints and watchpoints to the new thread. */
      for (i = 0; i < info->bp_count; i++)
        if (arm_hwbp_control_is_enabled (p->bpts[i].control))
          arm_linux_insert_hw_breakpoint1 (p->bpts + i, tid, 0);
      for (i = 0; i < info->wp_count; i++)
        if (arm_hwbp_control_is_enabled (p->wpts[i].control))
          arm_linux_insert_hw_breakpoint1 (p->wpts + i, tid, 1);
    }
}

/* Handle thread exit.  Tidy up the memory that has been allocated for the
   thread.  */
static void
arm_linux_thread_exit (struct thread_info *tp, int silent)
{
  const struct arm_linux_hwbp_cap *info = arm_linux_get_hwbp_cap ();

  if (info != NULL)
    {
      int i;
      int tid = TIDGET (tp->ptid);
      struct arm_linux_thread_points *t = NULL, *p;

      for (i = 0; 
           VEC_iterate (arm_linux_thread_points_p, arm_threads, i, p); i++)
        {
          if (p->tid == tid)
            {
              t = p;
              break;
            }
        }

      if (t == NULL)
        return;

      VEC_unordered_remove (arm_linux_thread_points_p, arm_threads, i);

      xfree (t->bpts);
      xfree (t->wpts);
      xfree (t);
    }
}

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;

  /* Add our hardware breakpoint and watchpoint implementation.  */
  t->to_can_use_hw_breakpoint = arm_linux_can_use_hw_breakpoint;
  t->to_insert_hw_breakpoint = arm_linux_insert_hw_breakpoint;
  t->to_remove_hw_breakpoint = arm_linux_remove_hw_breakpoint;
  t->to_region_ok_for_hw_watchpoint = arm_linux_region_ok_for_hw_watchpoint;
  t->to_insert_watchpoint = arm_linux_insert_watchpoint;
  t->to_remove_watchpoint = arm_linux_remove_watchpoint;
  t->to_stopped_by_watchpoint = arm_linux_stopped_by_watchpoint;
  t->to_stopped_data_address = arm_linux_stopped_data_address;
  t->to_watchpoint_addr_within_range = arm_linux_watchpoint_addr_within_range;

  t->to_read_description = arm_linux_read_description;

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

  /* Handle thread creation and exit */
  observer_attach_thread_exit (arm_linux_thread_exit);
  linux_nat_set_new_thread (t, arm_linux_new_thread);
}