gdb/

[deliverable/binutils-gdb.git] / gdb / amd64-linux-nat.c

/* Native-dependent code for GNU/Linux x86-64.

   Copyright (C) 2001-2012 Free Software Foundation, Inc.
   Contributed by Jiri Smid, SuSE Labs.

   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 "regcache.h"
#include "regset.h"
#include "linux-nat.h"
#include "amd64-linux-tdep.h"

#include "gdb_assert.h"
#include "gdb_string.h"
#include "elf/common.h"
#include <sys/uio.h>
#include <sys/ptrace.h>
#include <sys/debugreg.h>
#include <sys/syscall.h>
#include <sys/procfs.h>
#include <asm/prctl.h>
/* FIXME ezannoni-2003-07-09: we need <sys/reg.h> to be included after
   <asm/ptrace.h> because the latter redefines FS and GS for no apparent
   reason, and those definitions don't match the ones that libpthread_db
   uses, which come from <sys/reg.h>.  */
/* ezannoni-2003-07-09: I think this is fixed.  The extraneous defs have
   been removed from ptrace.h in the kernel.  However, better safe than
   sorry.  */
#include <asm/ptrace.h>
#include <sys/reg.h>
#include "gdb_proc_service.h"

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

#include "amd64-tdep.h"
#include "i386-linux-tdep.h"
#include "amd64-nat.h"
#include "i386-nat.h"
#include "i386-xstate.h"

#ifndef PTRACE_GETREGSET
#define PTRACE_GETREGSET	0x4204
#endif

#ifndef PTRACE_SETREGSET
#define PTRACE_SETREGSET	0x4205
#endif

/* Per-thread arch-specific data we want to keep.  */

struct arch_lwp_info
{
  /* Non-zero if our copy differs from what's recorded in the thread.  */
  int debug_registers_changed;
};

/* Does the current host support PTRACE_GETREGSET?  */
static int have_ptrace_getregset = -1;

/* Mapping between the general-purpose registers in GNU/Linux x86-64
   `struct user' format and GDB's register cache layout for GNU/Linux
   i386.

   Note that most GNU/Linux x86-64 registers are 64-bit, while the
   GNU/Linux i386 registers are all 32-bit, but since we're
   little-endian we get away with that.  */

/* From <sys/reg.h> on GNU/Linux i386.  */
static int amd64_linux_gregset32_reg_offset[] =
{
  RAX * 8, RCX * 8,		/* %eax, %ecx */
  RDX * 8, RBX * 8,		/* %edx, %ebx */
  RSP * 8, RBP * 8,		/* %esp, %ebp */
  RSI * 8, RDI * 8,		/* %esi, %edi */
  RIP * 8, EFLAGS * 8,		/* %eip, %eflags */
  CS * 8, SS * 8,		/* %cs, %ss */
  DS * 8, ES * 8,		/* %ds, %es */
  FS * 8, GS * 8,		/* %fs, %gs */
  -1, -1, -1, -1, -1, -1, -1, -1,
  -1, -1, -1, -1, -1, -1, -1, -1,
  -1, -1, -1, -1, -1, -1, -1, -1, -1,
  -1, -1, -1, -1, -1, -1, -1, -1,
  ORIG_RAX * 8			/* "orig_eax" */
};
\f

/* Transfering the general-purpose registers between GDB, inferiors
   and core files.  */

/* Fill GDB's register cache with the general-purpose register values
   in *GREGSETP.  */

void
supply_gregset (struct regcache *regcache, const elf_gregset_t *gregsetp)
{
  amd64_supply_native_gregset (regcache, gregsetp, -1);
}

/* Fill register REGNUM (if it is a general-purpose register) in
   *GREGSETP with the value in GDB's register cache.  If REGNUM is -1,
   do this for all registers.  */

void
fill_gregset (const struct regcache *regcache,
	      elf_gregset_t *gregsetp, int regnum)
{
  amd64_collect_native_gregset (regcache, gregsetp, regnum);
}

/* Transfering floating-point registers between GDB, inferiors and cores.  */

/* Fill GDB's register cache with the floating-point and SSE register
   values in *FPREGSETP.  */

void
supply_fpregset (struct regcache *regcache, const elf_fpregset_t *fpregsetp)
{
  amd64_supply_fxsave (regcache, -1, fpregsetp);
}

/* Fill register REGNUM (if it is a floating-point or SSE register) in
   *FPREGSETP with the value in GDB's register cache.  If REGNUM is
   -1, do this for all registers.  */

void
fill_fpregset (const struct regcache *regcache,
	       elf_fpregset_t *fpregsetp, int regnum)
{
  amd64_collect_fxsave (regcache, regnum, fpregsetp);
}
\f

/* Transferring arbitrary registers between GDB and inferior.  */

/* Fetch register REGNUM from the child process.  If REGNUM is -1, do
   this for all registers (including the floating point and SSE
   registers).  */

static void
amd64_linux_fetch_inferior_registers (struct target_ops *ops,
				      struct regcache *regcache, int regnum)
{
  struct gdbarch *gdbarch = get_regcache_arch (regcache);
  int tid;

  /* GNU/Linux LWP ID's are process ID's.  */
  tid = TIDGET (inferior_ptid);
  if (tid == 0)
    tid = PIDGET (inferior_ptid); /* Not a threaded program.  */

  if (regnum == -1 || amd64_native_gregset_supplies_p (gdbarch, regnum))
    {
      elf_gregset_t regs;

      if (ptrace (PTRACE_GETREGS, tid, 0, (long) &regs) < 0)
	perror_with_name (_("Couldn't get registers"));

      amd64_supply_native_gregset (regcache, &regs, -1);
      if (regnum != -1)
	return;
    }

  if (regnum == -1 || !amd64_native_gregset_supplies_p (gdbarch, regnum))
    {
      elf_fpregset_t fpregs;

      if (have_ptrace_getregset)
	{
	  char xstateregs[I386_XSTATE_MAX_SIZE];
	  struct iovec iov;

	  iov.iov_base = xstateregs;
	  iov.iov_len = sizeof (xstateregs);
	  if (ptrace (PTRACE_GETREGSET, tid,
		      (unsigned int) NT_X86_XSTATE, (long) &iov) < 0)
	    perror_with_name (_("Couldn't get extended state status"));

	  amd64_supply_xsave (regcache, -1, xstateregs);
	}
      else
	{
	  if (ptrace (PTRACE_GETFPREGS, tid, 0, (long) &fpregs) < 0)
	    perror_with_name (_("Couldn't get floating point status"));

	  amd64_supply_fxsave (regcache, -1, &fpregs);
	}
    }
}

/* Store register REGNUM back into the child process.  If REGNUM is
   -1, do this for all registers (including the floating-point and SSE
   registers).  */

static void
amd64_linux_store_inferior_registers (struct target_ops *ops,
				      struct regcache *regcache, int regnum)
{
  struct gdbarch *gdbarch = get_regcache_arch (regcache);
  int tid;

  /* GNU/Linux LWP ID's are process ID's.  */
  tid = TIDGET (inferior_ptid);
  if (tid == 0)
    tid = PIDGET (inferior_ptid); /* Not a threaded program.  */

  if (regnum == -1 || amd64_native_gregset_supplies_p (gdbarch, regnum))
    {
      elf_gregset_t regs;

      if (ptrace (PTRACE_GETREGS, tid, 0, (long) &regs) < 0)
	perror_with_name (_("Couldn't get registers"));

      amd64_collect_native_gregset (regcache, &regs, regnum);

      if (ptrace (PTRACE_SETREGS, tid, 0, (long) &regs) < 0)
	perror_with_name (_("Couldn't write registers"));

      if (regnum != -1)
	return;
    }

  if (regnum == -1 || !amd64_native_gregset_supplies_p (gdbarch, regnum))
    {
      elf_fpregset_t fpregs;

      if (have_ptrace_getregset)
	{
	  char xstateregs[I386_XSTATE_MAX_SIZE];
	  struct iovec iov;

	  iov.iov_base = xstateregs;
	  iov.iov_len = sizeof (xstateregs);
	  if (ptrace (PTRACE_GETREGSET, tid,
		      (unsigned int) NT_X86_XSTATE, (long) &iov) < 0)
	    perror_with_name (_("Couldn't get extended state status"));

	  amd64_collect_xsave (regcache, regnum, xstateregs, 0);

	  if (ptrace (PTRACE_SETREGSET, tid,
		      (unsigned int) NT_X86_XSTATE, (long) &iov) < 0)
	    perror_with_name (_("Couldn't write extended state status"));
	}
      else
	{
	  if (ptrace (PTRACE_GETFPREGS, tid, 0, (long) &fpregs) < 0)
	    perror_with_name (_("Couldn't get floating point status"));

	  amd64_collect_fxsave (regcache, regnum, &fpregs);

	  if (ptrace (PTRACE_SETFPREGS, tid, 0, (long) &fpregs) < 0)
	    perror_with_name (_("Couldn't write floating point status"));
	}
    }
}
\f
/* Support for debug registers.  */

static unsigned long
amd64_linux_dr_get (ptid_t ptid, int regnum)
{
  int tid;
  unsigned long value;

  tid = TIDGET (ptid);
  if (tid == 0)
    tid = PIDGET (ptid);

  errno = 0;
  value = ptrace (PTRACE_PEEKUSER, tid,
		  offsetof (struct user, u_debugreg[regnum]), 0);
  if (errno != 0)
    perror_with_name (_("Couldn't read debug register"));

  return value;
}

/* Set debug register REGNUM to VALUE in only the one LWP of PTID.  */

static void
amd64_linux_dr_set (ptid_t ptid, int regnum, unsigned long value)
{
  int tid;

  tid = TIDGET (ptid);
  if (tid == 0)
    tid = PIDGET (ptid);

  errno = 0;
  ptrace (PTRACE_POKEUSER, tid,
	  offsetof (struct user, u_debugreg[regnum]), value);
  if (errno != 0)
    perror_with_name (_("Couldn't write debug register"));
}

/* Return the inferior's debug register REGNUM.  */

static CORE_ADDR
amd64_linux_dr_get_addr (int regnum)
{
  /* DR6 and DR7 are retrieved with some other way.  */
  gdb_assert (DR_FIRSTADDR <= regnum && regnum <= DR_LASTADDR);

  return amd64_linux_dr_get (inferior_ptid, regnum);
}

/* Return the inferior's DR7 debug control register.  */

static unsigned long
amd64_linux_dr_get_control (void)
{
  return amd64_linux_dr_get (inferior_ptid, DR_CONTROL);
}

/* Get DR_STATUS from only the one LWP of INFERIOR_PTID.  */

static unsigned long
amd64_linux_dr_get_status (void)
{
  return amd64_linux_dr_get (inferior_ptid, DR_STATUS);
}

/* Callback for iterate_over_lwps.  Update the debug registers of
   LWP.  */

static int
update_debug_registers_callback (struct lwp_info *lwp, void *arg)
{
  if (lwp->arch_private == NULL)
    lwp->arch_private = XCNEW (struct arch_lwp_info);

  /* The actual update is done later just before resuming the lwp, we
     just mark that the registers need updating.  */
  lwp->arch_private->debug_registers_changed = 1;

  /* If the lwp isn't stopped, force it to momentarily pause, so we
     can update its debug registers.  */
  if (!lwp->stopped)
    linux_stop_lwp (lwp);

  /* Continue the iteration.  */
  return 0;
}

/* Set DR_CONTROL to CONTROL in all LWPs of the current inferior.  */

static void
amd64_linux_dr_set_control (unsigned long control)
{
  ptid_t pid_ptid = pid_to_ptid (ptid_get_pid (inferior_ptid));

  iterate_over_lwps (pid_ptid, update_debug_registers_callback, NULL);
}

/* Set address REGNUM (zero based) to ADDR in all LWPs of the current
   inferior.  */

static void
amd64_linux_dr_set_addr (int regnum, CORE_ADDR addr)
{
  ptid_t pid_ptid = pid_to_ptid (ptid_get_pid (inferior_ptid));

  gdb_assert (regnum >= 0 && regnum <= DR_LASTADDR - DR_FIRSTADDR);

  iterate_over_lwps (pid_ptid, update_debug_registers_callback, NULL);
}

/* Called when resuming a thread.
   If the debug regs have changed, update the thread's copies.  */

static void
amd64_linux_prepare_to_resume (struct lwp_info *lwp)
{
  int clear_status = 0;

  /* NULL means this is the main thread still going through the shell,
     or, no watchpoint has been set yet.  In that case, there's
     nothing to do.  */
  if (lwp->arch_private == NULL)
    return;

  if (lwp->arch_private->debug_registers_changed)
    {
      struct i386_debug_reg_state *state = i386_debug_reg_state ();
      int i;

      for (i = DR_FIRSTADDR; i <= DR_LASTADDR; i++)
	if (state->dr_ref_count[i] > 0)
	  {
	    amd64_linux_dr_set (lwp->ptid, i, state->dr_mirror[i]);

	    /* If we're setting a watchpoint, any change the inferior
	       had done itself to the debug registers needs to be
	       discarded, otherwise, i386_stopped_data_address can get
	       confused.  */
	    clear_status = 1;
	  }

      amd64_linux_dr_set (lwp->ptid, DR_CONTROL, state->dr_control_mirror);

      lwp->arch_private->debug_registers_changed = 0;
    }

  if (clear_status || lwp->stopped_by_watchpoint)
    amd64_linux_dr_set (lwp->ptid, DR_STATUS, 0);
}

static void
amd64_linux_new_thread (struct lwp_info *lp)
{
  struct arch_lwp_info *info = XCNEW (struct arch_lwp_info);

  info->debug_registers_changed = 1;

  lp->arch_private = info;
}
\f

/* This function is called by libthread_db as part of its handling of
   a request for a thread's local storage address.  */

ps_err_e
ps_get_thread_area (const struct ps_prochandle *ph,
                    lwpid_t lwpid, int idx, void **base)
{
  if (gdbarch_ptr_bit (target_gdbarch) == 32)
    {
      /* The full structure is found in <asm-i386/ldt.h>.  The second
	 integer is the LDT's base_address and that is used to locate
	 the thread's local storage.  See i386-linux-nat.c more
	 info.  */
      unsigned int desc[4];

      /* This code assumes that "int" is 32 bits and that
	 GET_THREAD_AREA returns no more than 4 int values.  */
      gdb_assert (sizeof (int) == 4);	
#ifndef PTRACE_GET_THREAD_AREA
#define PTRACE_GET_THREAD_AREA 25
#endif
      if  (ptrace (PTRACE_GET_THREAD_AREA, 
		   lwpid, (void *) (long) idx, (unsigned long) &desc) < 0)
	return PS_ERR;
      
      /* Extend the value to 64 bits.  Here it's assumed that a "long"
	 and a "void *" are the same.  */
      (*base) = (void *) (long) desc[1];
      return PS_OK;
    }
  else
    {
      /* This definition comes from prctl.h, but some kernels may not
         have it.  */
#ifndef PTRACE_ARCH_PRCTL
#define PTRACE_ARCH_PRCTL      30
#endif
      /* FIXME: ezannoni-2003-07-09 see comment above about include
	 file order.  We could be getting bogus values for these two.  */
      gdb_assert (FS < ELF_NGREG);
      gdb_assert (GS < ELF_NGREG);
      switch (idx)
	{
	case FS:
	  if (ptrace (PTRACE_ARCH_PRCTL, lwpid, base, ARCH_GET_FS) == 0)
	    return PS_OK;
	  break;
	case GS:
	  if (ptrace (PTRACE_ARCH_PRCTL, lwpid, base, ARCH_GET_GS) == 0)
	    return PS_OK;
	  break;
	default:                   /* Should not happen.  */
	  return PS_BADADDR;
	}
    }
  return PS_ERR;               /* ptrace failed.  */
}
\f

static void (*super_post_startup_inferior) (ptid_t ptid);

static void
amd64_linux_child_post_startup_inferior (ptid_t ptid)
{
  i386_cleanup_dregs ();
  super_post_startup_inferior (ptid);
}
\f

/* When GDB is built as a 64-bit application on linux, the
   PTRACE_GETSIGINFO data is always presented in 64-bit layout.  Since
   debugging a 32-bit inferior with a 64-bit GDB should look the same
   as debugging it with a 32-bit GDB, we do the 32-bit <-> 64-bit
   conversion in-place ourselves.  */

/* These types below (compat_*) define a siginfo type that is layout
   compatible with the siginfo type exported by the 32-bit userspace
   support.  */

typedef int compat_int_t;
typedef unsigned int compat_uptr_t;

typedef int compat_time_t;
typedef int compat_timer_t;
typedef int compat_clock_t;

struct compat_timeval
{
  compat_time_t tv_sec;
  int tv_usec;
};

typedef union compat_sigval
{
  compat_int_t sival_int;
  compat_uptr_t sival_ptr;
} compat_sigval_t;

typedef struct compat_siginfo
{
  int si_signo;
  int si_errno;
  int si_code;

  union
  {
    int _pad[((128 / sizeof (int)) - 3)];

    /* kill() */
    struct
    {
      unsigned int _pid;
      unsigned int _uid;
    } _kill;

    /* POSIX.1b timers */
    struct
    {
      compat_timer_t _tid;
      int _overrun;
      compat_sigval_t _sigval;
    } _timer;

    /* POSIX.1b signals */
    struct
    {
      unsigned int _pid;
      unsigned int _uid;
      compat_sigval_t _sigval;
    } _rt;

    /* SIGCHLD */
    struct
    {
      unsigned int _pid;
      unsigned int _uid;
      int _status;
      compat_clock_t _utime;
      compat_clock_t _stime;
    } _sigchld;

    /* SIGILL, SIGFPE, SIGSEGV, SIGBUS */
    struct
    {
      unsigned int _addr;
    } _sigfault;

    /* SIGPOLL */
    struct
    {
      int _band;
      int _fd;
    } _sigpoll;
  } _sifields;
} compat_siginfo_t;

#define cpt_si_pid _sifields._kill._pid
#define cpt_si_uid _sifields._kill._uid
#define cpt_si_timerid _sifields._timer._tid
#define cpt_si_overrun _sifields._timer._overrun
#define cpt_si_status _sifields._sigchld._status
#define cpt_si_utime _sifields._sigchld._utime
#define cpt_si_stime _sifields._sigchld._stime
#define cpt_si_ptr _sifields._rt._sigval.sival_ptr
#define cpt_si_addr _sifields._sigfault._addr
#define cpt_si_band _sifields._sigpoll._band
#define cpt_si_fd _sifields._sigpoll._fd

/* glibc at least up to 2.3.2 doesn't have si_timerid, si_overrun.
   In their place is si_timer1,si_timer2.  */
#ifndef si_timerid
#define si_timerid si_timer1
#endif
#ifndef si_overrun
#define si_overrun si_timer2
#endif

static void
compat_siginfo_from_siginfo (compat_siginfo_t *to, siginfo_t *from)
{
  memset (to, 0, sizeof (*to));

  to->si_signo = from->si_signo;
  to->si_errno = from->si_errno;
  to->si_code = from->si_code;

  if (to->si_code == SI_TIMER)
    {
      to->cpt_si_timerid = from->si_timerid;
      to->cpt_si_overrun = from->si_overrun;
      to->cpt_si_ptr = (intptr_t) from->si_ptr;
    }
  else if (to->si_code == SI_USER)
    {
      to->cpt_si_pid = from->si_pid;
      to->cpt_si_uid = from->si_uid;
    }
  else if (to->si_code < 0)
    {
      to->cpt_si_pid = from->si_pid;
      to->cpt_si_uid = from->si_uid;
      to->cpt_si_ptr = (intptr_t) from->si_ptr;
    }
  else
    {
      switch (to->si_signo)
	{
	case SIGCHLD:
	  to->cpt_si_pid = from->si_pid;
	  to->cpt_si_uid = from->si_uid;
	  to->cpt_si_status = from->si_status;
	  to->cpt_si_utime = from->si_utime;
	  to->cpt_si_stime = from->si_stime;
	  break;
	case SIGILL:
	case SIGFPE:
	case SIGSEGV:
	case SIGBUS:
	  to->cpt_si_addr = (intptr_t) from->si_addr;
	  break;
	case SIGPOLL:
	  to->cpt_si_band = from->si_band;
	  to->cpt_si_fd = from->si_fd;
	  break;
	default:
	  to->cpt_si_pid = from->si_pid;
	  to->cpt_si_uid = from->si_uid;
	  to->cpt_si_ptr = (intptr_t) from->si_ptr;
	  break;
	}
    }
}

static void
siginfo_from_compat_siginfo (siginfo_t *to, compat_siginfo_t *from)
{
  memset (to, 0, sizeof (*to));

  to->si_signo = from->si_signo;
  to->si_errno = from->si_errno;
  to->si_code = from->si_code;

  if (to->si_code == SI_TIMER)
    {
      to->si_timerid = from->cpt_si_timerid;
      to->si_overrun = from->cpt_si_overrun;
      to->si_ptr = (void *) (intptr_t) from->cpt_si_ptr;
    }
  else if (to->si_code == SI_USER)
    {
      to->si_pid = from->cpt_si_pid;
      to->si_uid = from->cpt_si_uid;
    }
  if (to->si_code < 0)
    {
      to->si_pid = from->cpt_si_pid;
      to->si_uid = from->cpt_si_uid;
      to->si_ptr = (void *) (intptr_t) from->cpt_si_ptr;
    }
  else
    {
      switch (to->si_signo)
	{
	case SIGCHLD:
	  to->si_pid = from->cpt_si_pid;
	  to->si_uid = from->cpt_si_uid;
	  to->si_status = from->cpt_si_status;
	  to->si_utime = from->cpt_si_utime;
	  to->si_stime = from->cpt_si_stime;
	  break;
	case SIGILL:
	case SIGFPE:
	case SIGSEGV:
	case SIGBUS:
	  to->si_addr = (void *) (intptr_t) from->cpt_si_addr;
	  break;
	case SIGPOLL:
	  to->si_band = from->cpt_si_band;
	  to->si_fd = from->cpt_si_fd;
	  break;
	default:
	  to->si_pid = from->cpt_si_pid;
	  to->si_uid = from->cpt_si_uid;
	  to->si_ptr = (void* ) (intptr_t) from->cpt_si_ptr;
	  break;
	}
    }
}

/* Convert a native/host siginfo object, into/from the siginfo in the
   layout of the inferiors' architecture.  Returns true if any
   conversion was done; false otherwise.  If DIRECTION is 1, then copy
   from INF to NATIVE.  If DIRECTION is 0, copy from NATIVE to
   INF.  */

static int
amd64_linux_siginfo_fixup (struct siginfo *native, gdb_byte *inf, int direction)
{
  /* Is the inferior 32-bit?  If so, then do fixup the siginfo
     object.  */
  if (gdbarch_addr_bit (get_frame_arch (get_current_frame ())) == 32)
    {
      gdb_assert (sizeof (struct siginfo) == sizeof (compat_siginfo_t));

      if (direction == 0)
	compat_siginfo_from_siginfo ((struct compat_siginfo *) inf, native);
      else
	siginfo_from_compat_siginfo (native, (struct compat_siginfo *) inf);

      return 1;
    }
  else
    return 0;
}

/* Get Linux/x86 target description from running target.

   Value of CS segment register:
     1. 64bit process: 0x33.
     2. 32bit process: 0x23.
 */

#define AMD64_LINUX_USER64_CS	0x33

static const struct target_desc *
amd64_linux_read_description (struct target_ops *ops)
{
  unsigned long cs;
  int tid;
  int is_64bit;
  static uint64_t xcr0;

  /* GNU/Linux LWP ID's are process ID's.  */
  tid = TIDGET (inferior_ptid);
  if (tid == 0)
    tid = PIDGET (inferior_ptid); /* Not a threaded program.  */

  /* Get CS register.  */
  errno = 0;
  cs = ptrace (PTRACE_PEEKUSER, tid,
	       offsetof (struct user_regs_struct, cs), 0);
  if (errno != 0)
    perror_with_name (_("Couldn't get CS register"));

  is_64bit = cs == AMD64_LINUX_USER64_CS;

  if (have_ptrace_getregset == -1)
    {
      uint64_t xstateregs[(I386_XSTATE_SSE_SIZE / sizeof (uint64_t))];
      struct iovec iov;

      iov.iov_base = xstateregs;
      iov.iov_len = sizeof (xstateregs);

      /* Check if PTRACE_GETREGSET works.  */
      if (ptrace (PTRACE_GETREGSET, tid,
		  (unsigned int) NT_X86_XSTATE, (long) &iov) < 0)
	have_ptrace_getregset = 0;
      else
	{
	  have_ptrace_getregset = 1;

	  /* Get XCR0 from XSAVE extended state.  */
	  xcr0 = xstateregs[(I386_LINUX_XSAVE_XCR0_OFFSET
			     / sizeof (uint64_t))];
	}
    }

  /* Check the native XCR0 only if PTRACE_GETREGSET is available.  */
  if (have_ptrace_getregset
      && (xcr0 & I386_XSTATE_AVX_MASK) == I386_XSTATE_AVX_MASK)
    {
      if (is_64bit)
	return tdesc_amd64_avx_linux;
      else
	return tdesc_i386_avx_linux;
    }
  else
    {
      if (is_64bit)
	return tdesc_amd64_linux;
      else
	return tdesc_i386_linux;
    }
}

/* Provide a prototype to silence -Wmissing-prototypes.  */
void _initialize_amd64_linux_nat (void);

void
_initialize_amd64_linux_nat (void)
{
  struct target_ops *t;

  amd64_native_gregset32_reg_offset = amd64_linux_gregset32_reg_offset;
  amd64_native_gregset32_num_regs = I386_LINUX_NUM_REGS;
  amd64_native_gregset64_reg_offset = amd64_linux_gregset_reg_offset;
  amd64_native_gregset64_num_regs = AMD64_LINUX_NUM_REGS;

  gdb_assert (ARRAY_SIZE (amd64_linux_gregset32_reg_offset)
	      == amd64_native_gregset32_num_regs);

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

  i386_use_watchpoints (t);

  i386_dr_low.set_control = amd64_linux_dr_set_control;
  i386_dr_low.set_addr = amd64_linux_dr_set_addr;
  i386_dr_low.get_addr = amd64_linux_dr_get_addr;
  i386_dr_low.get_status = amd64_linux_dr_get_status;
  i386_dr_low.get_control = amd64_linux_dr_get_control;
  i386_set_debug_register_length (8);

  /* Override the GNU/Linux inferior startup hook.  */
  super_post_startup_inferior = t->to_post_startup_inferior;
  t->to_post_startup_inferior = amd64_linux_child_post_startup_inferior;

  /* Add our register access methods.  */
  t->to_fetch_registers = amd64_linux_fetch_inferior_registers;
  t->to_store_registers = amd64_linux_store_inferior_registers;

  t->to_read_description = amd64_linux_read_description;

  /* Register the target.  */
  linux_nat_add_target (t);
  linux_nat_set_new_thread (t, amd64_linux_new_thread);
  linux_nat_set_siginfo_fixup (t, amd64_linux_siginfo_fixup);
  linux_nat_set_prepare_to_resume (t, amd64_linux_prepare_to_resume);
}