Unified support for hardware breakpoints and watchpoints on

	x86 targets:

	* config/i386/nm-i386.h: New file.

	* config/i386/nm-i386.h: (i386_cleanup_dregs)
	(i386_insert_watchpoint, i386_remove_watchpoint)
	(i386_region_ok_for_watchpoint, i386_stopped_by_hwbp)
	(i386_stopped_data_address, i386_insert_hw_breakpoint)
	(i386_remove_hw_breakpoint): Declare prototypes.
	[I386_USE_GENERIC_WATCHPOINTS] (TARGET_CAN_USE_HARDWARE_WATCHPOINT):
	Define if not already defined.
	(TARGET_REGION_OK_FOR_HW_WATCHPOINT, HAVE_CONTINUABLE_WATCHPOINT)
	(STOPPED_BY_WATCHPOINT, target_stopped_data_address)
	(target_insert_watchpoint, target_remove_watchpoint)
	(target_insert_hw_breakpoint, target_remove_hw_breakpoint): Define
	to call the appropriate i386_* functions.

	* i386-nat.c: New file.

	* i386-nat.c (I386_DR_CONTROL_MASK, I386_DR_LOCAL_ENABLE)
	(I386_DR_GLOBAL_ENABLE, I386_DR_DISABLE, I386_DR_SET_RW_LEN)
	(I386_DR_GET_RW_LEN, I386_DR_WATCH_HIT): New macros.
	(dr_mirror, dr_status_mirror, dr_control_mirror, dr_ref_count)
	(maint_show_dr): New variables.
	(i386_cleanup_dregs, i386_show_dr, i386_length_and_rw_bits)
	(i386_insert_aligned_watchpoint, i386_remove_aligned_watchpoint)
	(i386_handle_nonaligned_watchpoint, i386_insert_watchpoint)
	(i386_remove_watchpoint, i386_region_ok_for_watchpoint)
	(i386_stopped_data_address, i386_stopped_by_hwbp)
	(i386_insert_hw_breakpoint, i386_remove_hw_breakpoint): New
	functions.
	(_initialize_i386_nat): New function.
	[I386_USE_GENERIC_WATCHPOINTS]: Add new	maint command
	`show-debug-regs', sets maint_show_dr to non-zero value and
	activates debugging print-outs in functions which insert, remove,
	and test watchpoints and hardware breakpoints.

	* Makefile.in (i386-nat.o): New target.
	(ALLDEPFILES): Add i386-nat.o.

1 files changed, 618 insertions, 0 deletions

diff --git a/gdb/i386-nat.c b/gdb/i386-nat.c
new file mode 100644
index 0000000..e250b1b
--- /dev/null
+++ b/gdb/i386-nat.c
@@ -0,0 +1,618 @@
+/* Intel x86 (a.k.a. ia32) native-dependent code.
+   Copyright (C) 2001 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.  */
+
+#include "defs.h"
+#include "breakpoint.h"
+#include "command.h"
+#include "gdbcmd.h"
+
+/* Support for hardware watchpoints and breakpoints using the x86
+   debug registers.
+
+   This provides several functions for inserting and removing
+   hardware-assisted breakpoints and watchpoints, testing if
+   one or more of the watchpoints triggerd and at what address,
+   checking whether a given region can be watched, etc.
+
+   A target which wants to use these functions should define
+   several macros, such as `target_insert_watchpoint' and
+   `target_stopped_data_address', listed in target.h, to call
+   the appropriate functions below.  It should also define
+   I386_USE_GENERIC_WATCHPOINTS in its tm.h file.
+
+   In addition, each target should provide several low-level
+   macros that will be called to insert watchpoints and hardware
+   breakpoints into the inferior, remove them, and check their
+   status.  These macros are:
+
+      I386_DR_LOW_SET_CONTROL  -- set the debug control (DR7)
+				  register to a given value
+
+      I386_DR_LOW_SET_ADDR     -- put an address into one debug
+				  register
+
+      I386_DR_LOW_RESET_ADDR   -- reset the address stored in
+				  one debug register
+
+      I386_DR_LOW_GET_STATUS   -- return the value of the debug
+				  status (DR6) register.
+
+   The functions below implement debug registers sharing by
+   reference counts, and allow to watch regions up to 16 bytes
+   long.  */
+
+#ifdef I386_USE_GENERIC_WATCHPOINTS
+
+/* Debug registers' indices.  */
+#define DR_NADDR		4  /* the number of debug address registers */
+#define DR_STATUS		6  /* index of debug status register (DR6) */
+#define DR_CONTROL		7  /* index of debug control register (DR7) */
+
+/* DR7 Debug Control register fields.  */
+
+/* How many bits to skip in DR7 to get to R/W and LEN fields.  */
+#define DR_CONTROL_SHIFT	16
+/* How many bits in DR7 per R/W and LEN field for each watchpoint.  */
+#define DR_CONTROL_SIZE		4
+
+/* Watchpoint/breakpoint read/write fields in DR7.  */
+#define DR_RW_EXECUTE		(0x0) /* break on instruction execution */
+#define DR_RW_WRITE		(0x1) /* break on data writes */
+#define DR_RW_READ		(0x3) /* break on data reads or writes */
+
+/* This is here for completeness.  No platform supports this
+   functionality yet (as of Mar-2001).  Note that the DE flag in the
+   CR4 register needs to be set to support this.  */
+#ifndef DR_RW_IORW
+#define DR_RW_IORW		(0x2) /* break on I/O reads or writes */
+#endif
+
+/* Watchpoint/breakpoint length fields in DR7.  The 2-bit left shift
+   is so we could OR this with the read/write field defined above.  */
+#define DR_LEN_1		(0x0 << 2) /* 1-byte region watch or breakpt */
+#define DR_LEN_2		(0x1 << 2) /* 2-byte region watch */
+#define DR_LEN_4		(0x3 << 2) /* 4-byte region watch */
+
+/* Local and Global Enable flags in DR7.
+
+   When the Local Enable flag is set, the breakpoint/watchpoint is
+   enabled only for the current task; the processor automatically
+   clears this flag on every task switch.  When the Global Enable
+   flag is set, the breakpoint/watchpoint is enabled for all tasks;
+   the processor never clears this flag.
+
+   Currently, all watchpoint are locally enabled.  If you need to
+   enable them globally, read the comment which pertains to this in
+   i386_insert_aligned_watchpoint below.  */
+#define DR_LOCAL_ENABLE_SHIFT	0   /* extra shift to the local enable bit */
+#define DR_GLOBAL_ENABLE_SHIFT	1   /* extra shift to the global enable bit */
+#define DR_ENABLE_SIZE		2   /* 2 enable bits per debug register */
+
+/* Local and global exact breakpoint enable flags (a.k.a. slowdown
+   flags).  These are only required on i386, to allow detection of the
+   exact instruction which caused a watchpoint to break; i486 and
+   later processors do that automatically.  We set these flags for
+   back compatibility.  */
+#define DR_LOCAL_SLOWDOWN	(0x100)
+#define DR_GLOBAL_SLOWDOWN	(0x200)
+
+/* Fields reserved by Intel.  This includes the GD (General Detect
+   Enable) flag, which causes a debug exception to be generated when a
+   MOV instruction accesses one of the debug registers.
+
+   FIXME: My Intel manual says we should use 0xF800, not 0xFC00.  */
+#define DR_CONTROL_RESERVED	(0xFC00)
+
+/* Auxiliary helper macros.  */
+
+/* A value that masks all fields in DR7 that are reserved by Intel.  */
+#define I386_DR_CONTROL_MASK		(~DR_CONTROL_RESERVED)
+
+/* The I'th debug register is vacant if its Local and Global Enable
+   bits are reset in the Debug Control register.  */
+#define I386_DR_VACANT(i) \
+  ((dr_control_mirror & (3 << (DR_ENABLE_SIZE * (i)))) == 0)
+
+/* Locally enable the break/watchpoint in the I'th debug register.  */
+#define I386_DR_LOCAL_ENABLE(i) \
+  dr_control_mirror |= (1 << (DR_LOCAL_ENABLE_SHIFT + DR_ENABLE_SIZE * (i)))
+
+/* Globally enable the break/watchpoint in the I'th debug register.  */
+#define I386_DR_GLOBAL_ENABLE(i) \
+  dr_control_mirror |= (1 << (DR_GLOBAL_ENABLE_SHIFT + DR_ENABLE_SIZE * (i)))
+
+/* Disable the break/watchpoint in the I'th debug register.  */
+#define I386_DR_DISABLE(i) \
+  dr_control_mirror &= ~(3 << (DR_ENABLE_SIZE * (i)))
+
+/* Set in DR7 the RW and LEN fields for the I'th debug register.  */
+#define I386_DR_SET_RW_LEN(i,rwlen) \
+  do { \
+    dr_control_mirror &= ~(0x0f << (DR_CONTROL_SHIFT+DR_CONTROL_SIZE*(i)));   \
+    dr_control_mirror |= ((rwlen) << (DR_CONTROL_SHIFT+DR_CONTROL_SIZE*(i))); \
+  } while (0)
+
+/* Get from DR7 the RW and LEN fields for the I'th debug register.  */
+#define I386_DR_GET_RW_LEN(i) \
+  ((dr_control_mirror >> (DR_CONTROL_SHIFT + DR_CONTROL_SIZE * (i))) & 0x0f)
+
+/* Did the watchpoint whose address is in the I'th register break?  */
+#define I386_DR_WATCH_HIT(i)	(dr_status_mirror & (1 << (i)))
+
+/* A macro to loop over all debug registers.  */
+#define ALL_DEBUG_REGISTERS(i)	for (i = 0; i < DR_NADDR; i++)
+
+/* Mirror the inferior's DRi registers.  We keep the status and
+   control registers separated because they don't hold addresses.  */
+static CORE_ADDR dr_mirror[DR_NADDR];
+static unsigned	 dr_status_mirror, dr_control_mirror;
+
+/* Reference counts for each debug register.  */
+static int	 dr_ref_count[DR_NADDR];
+
+/* Whether or not to print the mirrored debug registers.  */
+static int	 maint_show_dr;
+
+/* Types of operations supported by i386_handle_nonaligned_watchpoint.  */
+typedef enum { WP_INSERT, WP_REMOVE, WP_COUNT } i386_wp_op_t;
+
+/* Internal functions.  */
+
+/* Return the value of a 4-bit field for DR7 suitable for watching a
+   region of LEN bytes for accesses of type TYPE.  LEN is assumed
+   to have the value of 1, 2, or 4.  */
+static unsigned i386_length_and_rw_bits (int len, enum target_hw_bp_type type);
+
+/* Insert a watchpoint at address ADDR, which is assumed to be aligned
+   according to the length of the region to watch.  LEN_RW_BITS is the
+   value of the bit-field from DR7 which describes the length and
+   access type of the region to be watched by this watchpoint.  Return
+   0 on success, -1 on failure.  */
+static int i386_insert_aligned_watchpoint (CORE_ADDR addr,
+					   unsigned len_rw_bits);
+
+/* Remove a watchpoint at address ADDR, which is assumed to be aligned
+   according to the length of the region to watch.  LEN_RW_BITS is the
+   value of the bits from DR7 which describes the length and access
+   type of the region watched by this watchpoint.  Return 0 on
+   success, -1 on failure.  */
+static int i386_remove_aligned_watchpoint (CORE_ADDR addr,
+					   unsigned len_rw_bits);
+
+/* Insert or remove a (possibly non-aligned) watchpoint, or count the
+   number of debug registers required to watch a region at address
+   ADDR whose length is LEN for accesses of type TYPE.  Return 0 on
+   successful insertion or removal, a positive number when queried
+   about the number of registers, or -1 on failure.  If WHAT is not
+   a valid value, bombs through internal_error.  */
+static int i386_handle_nonaligned_watchpoint (i386_wp_op_t what,
+					      CORE_ADDR addr, int len,
+					      enum target_hw_bp_type type);
+
+/* Implementation.  */
+
+/* Clear the reference counts and forget everything we knew about
+   the debug registers.  */
+void
+i386_cleanup_dregs (void)
+{
+  int i;
+
+  ALL_DEBUG_REGISTERS(i)
+    {
+      dr_mirror[i] = 0;
+      dr_ref_count[i] = 0;
+    }
+  dr_control_mirror = 0;
+  dr_status_mirror  = 0;
+}
+
+/* Print the values of the mirrored debug registers.
+   This is called when maint_show_dr is non-zero.  To set that
+   up, type "maint show-debug-regs" at GDB's prompt.  */
+static void
+i386_show_dr (const char *func, CORE_ADDR addr,
+	      int len, enum target_hw_bp_type type)
+{
+  int i;
+
+  puts_unfiltered (func);
+  if (addr || len)
+    printf_unfiltered (" (addr=%lx, len=%d, type=%s)",
+		       /* This code is for ia32, so casting CORE_ADDR
+			  to unsigned long should be okay.  */
+		       (unsigned long)addr, len,
+		       type == hw_write ? "data-write"
+		       : (type == hw_read ? "data-read"
+			  : (type == hw_access ? "data-read/write"
+			     : (type == hw_execute ? "instruction-execute"
+				/* FIXME: if/when I/O read/write
+				   watchpoints are supported, add them
+				   here.  */
+				: "??unknown??"))));
+  puts_unfiltered (":\n");
+  printf_unfiltered ("\tCONTROL (DR7): %08x          STATUS (DR6): %08x\n",
+		     dr_control_mirror, dr_status_mirror);
+  ALL_DEBUG_REGISTERS(i)
+    {
+      printf_unfiltered ("\tDR%d: addr=%08lx, ref.count=%d  DR%d: addr=%08lx, ref.count=%d\n",
+			 i, dr_mirror[i], dr_ref_count[i],
+			 i+1, dr_mirror[i+1], dr_ref_count[i+1]);
+      i++;
+    }
+}
+
+/* Return the value of a 4-bit field for DR7 suitable for watching a
+   region of LEN bytes for accesses of type TYPE.  LEN is assumed
+   to have the value of 1, 2, or 4.  */
+static unsigned
+i386_length_and_rw_bits (int len, enum target_hw_bp_type type)
+{
+  unsigned rw;
+
+  switch (type)
+    {
+      case hw_execute:
+	rw = DR_RW_EXECUTE;
+	break;
+      case hw_write:
+	rw = DR_RW_WRITE;
+	break;
+      case hw_read:	 /* x86 doesn't support data-read watchpoints */
+      case hw_access:
+	rw = DR_RW_READ;
+	break;
+#if 0
+      case hw_io_access: /* not yet supported */
+	rw = DR_RW_IORW;
+	break;
+#endif
+      default:
+	internal_error (__FILE__, __LINE__, "\
+Invalid hw breakpoint type %d in i386_length_and_rw_bits.\n", (int)type);
+    }
+
+  switch (len)
+    {
+      case 4:
+	return (DR_LEN_4 | rw);
+      case 2:
+	return (DR_LEN_2 | rw);
+      case 1:
+	return (DR_LEN_1 | rw);
+      default:
+	internal_error (__FILE__, __LINE__, "\
+Invalid hw breakpoint length %d in i386_length_and_rw_bits.\n", len);
+    }
+}
+
+/* Insert a watchpoint at address ADDR, which is assumed to be aligned
+   according to the length of the region to watch.  LEN_RW_BITS is the
+   value of the bits from DR7 which describes the length and access
+   type of the region to be watched by this watchpoint.  Return 0 on
+   success, -1 on failure.  */
+static int
+i386_insert_aligned_watchpoint (CORE_ADDR addr, unsigned len_rw_bits)
+{
+  int i;
+
+  /* First, look for an occupied debug register with the same address
+     and the same RW and LEN definitions.  If we find one, we can
+     reuse it for this watchpoint as well (and save a register).  */
+  ALL_DEBUG_REGISTERS(i)
+    {
+      if (!I386_DR_VACANT (i)
+	  && dr_mirror[i] == addr
+	  && I386_DR_GET_RW_LEN (i) == len_rw_bits)
+	{
+	  dr_ref_count[i]++;
+	  return 0;
+	}
+    }
+
+  /* Next, look for a vacant debug register.  */
+  ALL_DEBUG_REGISTERS(i)
+    {
+      if (I386_DR_VACANT (i))
+	break;
+    }
+
+  /* No more debug registers!  */
+  if (i >= DR_NADDR)
+    return -1;
+
+  /* Now set up the register I to watch our region.  */
+
+  /* Record the info in our local mirrored array.  */
+  dr_mirror[i] = addr;
+  dr_ref_count[i] = 1;
+  I386_DR_SET_RW_LEN (i, len_rw_bits);
+  /* Note: we only enable the watchpoint locally, i.e. in the current
+     task.  Currently, no x86 target allows or supports global
+     watchpoints; however, if any target would want that in the
+     future, GDB should probably provide a command to control whether
+     to enable watchpoints globally or locally, and the code below
+     should use global or local enable and slow-down flags as
+     appropriate.  */
+  I386_DR_LOCAL_ENABLE (i);
+  dr_control_mirror |= DR_LOCAL_SLOWDOWN;
+  dr_control_mirror &= I386_DR_CONTROL_MASK;
+
+  /* Finally, actually pass the info to the inferior.  */
+  I386_DR_LOW_SET_CONTROL (dr_control_mirror);
+  I386_DR_LOW_SET_ADDR (i, addr);
+
+  return 0;
+}
+
+/* Remove a watchpoint at address ADDR, which is assumed to be aligned
+   according to the length of the region to watch.  LEN_RW_BITS is the
+   value of the bits from DR7 which describes the length and access
+   type of the region watched by this watchpoint.  Return 0 on
+   success, -1 on failure.  */
+static int
+i386_remove_aligned_watchpoint (CORE_ADDR addr, unsigned len_rw_bits)
+{
+  int i, retval = -1;
+
+  ALL_DEBUG_REGISTERS(i)
+    {
+      if (!I386_DR_VACANT (i)
+	  && dr_mirror[i] == addr
+	  && I386_DR_GET_RW_LEN (i) == len_rw_bits)
+	{
+	  if (--dr_ref_count[i] == 0) /* no longer in use? */
+	    {
+	      /* Reset our mirror.  */
+	      dr_mirror[i] = 0;
+	      I386_DR_DISABLE (i);
+	      /* Reset it in the inferior.  */
+	      I386_DR_LOW_RESET_ADDR (i);
+	      I386_DR_LOW_SET_CONTROL (dr_control_mirror);
+	    }
+	  retval = 0;
+	}
+    }
+
+  return retval;
+}
+
+/* Insert or remove a (possibly non-aligned) watchpoint, or count the
+   number of debug registers required to watch a region at address
+   ADDR whose length is LEN for accesses of type TYPE.  Return 0 on
+   successful insertion or removal, a positive number when queried
+   about the number of registers, or -1 on failure.  If WHAT is not
+   a valid value, bombs through internal_error.  */
+static int
+i386_handle_nonaligned_watchpoint (i386_wp_op_t what, CORE_ADDR addr, int len,
+				   enum target_hw_bp_type type)
+{
+  int align;
+  int size;
+  int rv = 0, status = 0;
+
+  static int size_try_array[4][4] =
+  {
+    { 1, 1, 1, 1 },		/* trying size one */
+    { 2, 1, 2, 1 },		/* trying size two */
+    { 2, 1, 2, 1 },		/* trying size three */
+    { 4, 1, 2, 1 }		/* trying size four */
+  };
+
+  while (len > 0)
+    {
+      align = addr % 4;
+      /* Four is the maximum length an x86 debug register can watch.  */
+      size = size_try_array[len > 4 ? 3 : len - 1][align];
+      if (what == WP_COUNT)
+	/* size_try_array[] is defined so that each iteration through
+	   the loop is guaranteed to produce an address and a size
+	   that can be watched with a single debug register.  Thus,
+	   for counting the registers required to watch a region, we
+	   simply need to increment the count on each iteration.  */
+	rv++;
+      else
+	{
+	  unsigned len_rw = i386_length_and_rw_bits (size, type);
+
+	  if (what == WP_INSERT)
+	    status = i386_insert_aligned_watchpoint (addr, len_rw);
+	  else if (what == WP_REMOVE)
+	    status = i386_remove_aligned_watchpoint (addr, len_rw);
+	  else
+	    internal_error (__FILE__, __LINE__, "\
+Invalid value %d of operation in i386_handle_nonaligned_watchpoint.\n",
+			    (int)what);
+	  /* We keep the loop going even after a failure, because some
+	     of the other aligned watchpoints might still succeed
+	     (e.g. if they watch addresses that are already watched,
+	     in which case we just increment the reference counts of
+	     occupied debug registers).  If we break out of the loop
+	     too early, we could cause those addresses watched by
+	     other watchpoints to be disabled when breakpoint.c reacts
+	     to our failure to insert this watchpoint and tries to
+	     remove it.  */
+	  if (status)
+	    rv = status;
+	}
+      addr += size;
+      len -= size;
+    }
+  return rv;
+}
+
+/* Insert a watchpoint to watch a memory region which starts at
+   address ADDR and whose length is LEN bytes.  Watch memory accesses
+   of the type TYPE.  Return 0 on success, -1 on failure.  */
+int
+i386_insert_watchpoint (CORE_ADDR addr, int len, int type)
+{
+  int retval;
+
+  if (len == 3 || len > 4 || addr % len != 0)
+    retval = i386_handle_nonaligned_watchpoint (WP_INSERT, addr, len, type);
+  else
+    {
+      unsigned len_rw = i386_length_and_rw_bits (len, type);
+
+      retval = i386_insert_aligned_watchpoint (addr, len_rw);
+    }
+
+  if (maint_show_dr)
+    i386_show_dr ("insert_watchpoint", addr, len, type);
+
+  return retval;
+}
+
+/* Remove a watchpoint that watched the memory region which starts at
+   address ADDR, whose length is LEN bytes, and for accesses of the
+   type TYPE.  Return 0 on success, -1 on failure.  */
+int
+i386_remove_watchpoint (CORE_ADDR addr, int len, int type)
+{
+  int retval;
+
+  if (len == 3 || len > 4 || addr % len != 0)
+    retval = i386_handle_nonaligned_watchpoint (WP_REMOVE, addr, len, type);
+  else
+    {
+      unsigned len_rw = i386_length_and_rw_bits (len, type);
+
+      retval = i386_remove_aligned_watchpoint (addr, len_rw);
+    }
+
+  if (maint_show_dr)
+    i386_show_dr ("remove_watchpoint", addr, len, type);
+
+  return retval;
+}
+
+/* Return non-zero if we can watch a memory region that starts at
+   address ADDR and whose length is LEN bytes.  */
+int
+i386_region_ok_for_watchpoint (CORE_ADDR addr, int len)
+{
+  /* Compute how many aligned watchpoints we would need to cover this
+     region.  */
+  int nregs = i386_handle_nonaligned_watchpoint (WP_COUNT, addr, len,
+						 hw_write);
+
+  return nregs <= DR_NADDR ? 1 : 0;
+}
+
+/* If the inferior has some watchpoint that triggered, return the
+   address associated with that watchpoint.  Otherwise, return
+   zero.  */
+CORE_ADDR
+i386_stopped_data_address (void)
+{
+  int i;
+  CORE_ADDR ret = 0;
+
+  dr_status_mirror = I386_DR_LOW_GET_STATUS ();
+
+  ALL_DEBUG_REGISTERS(i)
+    {
+      if (I386_DR_WATCH_HIT (i)
+	  /* This second condition makes sure DRi is set up for a data
+	     watchpoint, not a hardware breakpoint.  The reason is
+	     that GDB doesn't call the target_stopped_data_address
+	     method except for data watchpoints.  In other words, I'm
+	     being paranoiac.  */
+	  && I386_DR_GET_RW_LEN (i) != 0)
+	{
+	  ret = dr_mirror[i];
+	  if (maint_show_dr)
+	    i386_show_dr ("watchpoint_hit", ret, -1, hw_write);
+	}
+    }
+  if (maint_show_dr && ret == 0)
+    i386_show_dr ("stopped_data_addr", 0, 0, hw_write);
+
+  return ret;
+}
+
+/* Return non-zero if the inferior has some break/watchpoint that
+   triggered.  */
+int
+i386_stopped_by_hwbp (void)
+{
+  int i;
+
+  dr_status_mirror = I386_DR_LOW_GET_STATUS ();
+  if (maint_show_dr)
+    i386_show_dr ("stopped_by_hwbp", 0, 0, hw_execute);
+
+  ALL_DEBUG_REGISTERS(i)
+    {
+      if (I386_DR_WATCH_HIT (i))
+	return 1;
+    }
+
+  return 0;
+}
+
+/* Insert a hardware-assisted breakpoint at address ADDR.  SHADOW is
+   unused.  Return 0 on success, EBUSY on failure.  */
+int
+i386_insert_hw_breakpoint (CORE_ADDR addr, void *shadow)
+{
+  unsigned len_rw = i386_length_and_rw_bits (1, hw_execute);
+  int retval = i386_insert_aligned_watchpoint (addr, len_rw) ? EBUSY : 0;
+
+  if (maint_show_dr)
+    i386_show_dr ("insert_hwbp", addr, 1, hw_execute);
+
+  return retval;
+}
+
+/* Remove a hardware-assisted breakpoint at address ADDR.  SHADOW is
+   unused.  Return 0 on success, -1 on failure.  */
+int
+i386_remove_hw_breakpoint (CORE_ADDR addr, void *shadow)
+{
+  unsigned len_rw = i386_length_and_rw_bits (1, hw_execute);
+  int retval = i386_remove_aligned_watchpoint (addr, len_rw);
+
+  if (maint_show_dr)
+    i386_show_dr ("remove_hwbp", addr, 1, hw_execute);
+
+  return retval;
+}
+
+#endif /* I386_USE_GENERIC_WATCHPOINTS */
+
+
+void
+_initialize_i386_nat (void)
+{
+#ifdef I386_USE_GENERIC_WATCHPOINTS
+  /* A maintenance command to enable printing the internal DRi mirror
+     variables.  */
+  add_set_cmd ("show-debug-regs", class_maintenance,
+	       var_boolean, (char *) &maint_show_dr,
+	       "\
+Set whether to show variables that mirror the x86 debug registers.\n\
+Use \"on\" to enable, \"off\" to disable.\n\
+If enabled, the debug registers values are shown when GDB inserts\n\
+or removes a hardware breakpoint or watchpoint, and when the inferior\n\
+triggers a breakpoint or watchpoint.", &maintenancelist);
+#endif
+}