diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 47a5fa5..be5669f 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,13 @@
+2014-06-23  Pedro Alves  <palves@redhat.com>
+
+	* amd64-linux-nat.c (amd64_linux_prepare_to_resume): Clear
+	DR_CONTROL before setting DR0..DR3.
+	* i386-linux-nat.c (i386_linux_prepare_to_resume): Likewise.
+	* nat/i386-dregs.c (i386_remove_aligned_watchpoint): Clear all
+	bits of DR_CONTROL related to the debug register slot being
+	disabled.  If all slots are vacant, clear local slowdown as well,
+	and assert DR_CONTROL is 0.
+
 2014-06-23  Siva Chandra Reddy  <sivachandra@google.com>
 
 	* python/lib/gdb/command/xmethods.py
diff --git a/gdb/gdbserver/ChangeLog b/gdb/gdbserver/ChangeLog
index 085677b..cd5aa0f 100644
--- a/gdb/gdbserver/ChangeLog
+++ b/gdb/gdbserver/ChangeLog
@@ -1,3 +1,8 @@
+2014-06-23  Pedro Alves  <palves@redhat.com>
+
+	* linux-x86-low.c (x86_linux_prepare_to_resume): Clear DR_CONTROL
+	before setting DR0..DR3.
+
 2014-06-20  Gary Benson  <gbenson@redhat.com>
 
 	* configure.ac (AC_REPLACE_FUNCS) <vasprintf, vsnprintf>: Removed.
diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog
index 57c5adc..2c8f159 100644
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2014-06-23  Pedro Alves  <palves@redhat.com>
+
+	* gdb.base/watchpoint-reuse-slot.c: New file.
+	* gdb.base/watchpoint-reuse-slot.exp: New file.
+
 2014-06-23  Siva Chandra Reddy  <sivachandra@google.com>
 
 	* gdb.python/py-xmethods.exp: Use "progspace" instead of the
diff --git a/gdb/amd64-linux-nat.c b/gdb/amd64-linux-nat.c
index 0cdc1f0..fa677c8 100644
--- a/gdb/amd64-linux-nat.c
+++ b/gdb/amd64-linux-nat.c
@@ -415,6 +415,11 @@ amd64_linux_prepare_to_resume (struct lwp_info *lwp)
 
 	 Ensure DR_CONTROL gets written as the very last register here.  */
 
+      /* Clear DR_CONTROL first.  In some cases, setting DR0-3 to a
+	 value that doesn't match what is enabled in DR_CONTROL
+	 results in EINVAL.  */
+      amd64_linux_dr_set (lwp->ptid, DR_CONTROL, 0);
+
       for (i = DR_FIRSTADDR; i <= DR_LASTADDR; i++)
 	if (state->dr_ref_count[i] > 0)
 	  {
@@ -427,7 +432,10 @@ amd64_linux_prepare_to_resume (struct lwp_info *lwp)
 	    clear_status = 1;
 	  }
 
-      amd64_linux_dr_set (lwp->ptid, DR_CONTROL, state->dr_control_mirror);
+      /* If DR_CONTROL is supposed to be zero, we've already set it
+	 above.  */
+      if (state->dr_control_mirror != 0)
+	amd64_linux_dr_set (lwp->ptid, DR_CONTROL, state->dr_control_mirror);
 
       lwp->arch_private->debug_registers_changed = 0;
     }
diff --git a/gdb/gdbserver/linux-x86-low.c b/gdb/gdbserver/linux-x86-low.c
index 94451da..9ba71e5 100644
--- a/gdb/gdbserver/linux-x86-low.c
+++ b/gdb/gdbserver/linux-x86-low.c
@@ -788,6 +788,8 @@ x86_linux_prepare_to_resume (struct lwp_info *lwp)
       struct i386_debug_reg_state *state
 	= &proc->private->arch_private->debug_reg_state;
 
+      x86_linux_dr_set (ptid, DR_CONTROL, 0);
+
       for (i = DR_FIRSTADDR; i <= DR_LASTADDR; i++)
 	if (state->dr_ref_count[i] > 0)
 	  {
@@ -800,7 +802,8 @@ x86_linux_prepare_to_resume (struct lwp_info *lwp)
 	    clear_status = 1;
 	  }
 
-      x86_linux_dr_set (ptid, DR_CONTROL, state->dr_control_mirror);
+      if (state->dr_control_mirror != 0)
+	x86_linux_dr_set (ptid, DR_CONTROL, state->dr_control_mirror);
 
       lwp->arch_private->debug_registers_changed = 0;
     }
diff --git a/gdb/i386-linux-nat.c b/gdb/i386-linux-nat.c
index 6667c17..ff96501 100644
--- a/gdb/i386-linux-nat.c
+++ b/gdb/i386-linux-nat.c
@@ -778,6 +778,8 @@ i386_linux_prepare_to_resume (struct lwp_info *lwp)
       /* See amd64_linux_prepare_to_resume for Linux kernel note on
 	 i386_linux_dr_set calls ordering.  */
 
+      i386_linux_dr_set (lwp->ptid, DR_CONTROL, 0);
+
       for (i = DR_FIRSTADDR; i <= DR_LASTADDR; i++)
 	if (state->dr_ref_count[i] > 0)
 	  {
@@ -790,7 +792,8 @@ i386_linux_prepare_to_resume (struct lwp_info *lwp)
 	    clear_status = 1;
 	  }
 
-      i386_linux_dr_set (lwp->ptid, DR_CONTROL, state->dr_control_mirror);
+      if (state->dr_control_mirror != 0)
+	i386_linux_dr_set (lwp->ptid, DR_CONTROL, state->dr_control_mirror);
 
       lwp->arch_private->debug_registers_changed = 0;
     }
diff --git a/gdb/nat/i386-dregs.c b/gdb/nat/i386-dregs.c
index 214616c..1fa5c19 100644
--- a/gdb/nat/i386-dregs.c
+++ b/gdb/nat/i386-dregs.c
@@ -348,6 +348,7 @@ i386_remove_aligned_watchpoint (struct i386_debug_reg_state *state,
 				CORE_ADDR addr, unsigned len_rw_bits)
 {
   int i, retval = -1;
+  int all_vacant = 1;
 
   ALL_DEBUG_REGISTERS (i)
     {
@@ -360,11 +361,30 @@ i386_remove_aligned_watchpoint (struct i386_debug_reg_state *state,
 	      /* Reset our mirror.  */
 	      state->dr_mirror[i] = 0;
 	      I386_DR_DISABLE (state, i);
+	      /* Even though not strictly necessary, clear out all
+		 bits in DR_CONTROL related to this debug register.
+		 Debug output is clearer when we don't have stale bits
+		 in place.  This also allows the assertion below.  */
+	      I386_DR_SET_RW_LEN (state, i, 0);
 	    }
 	  retval = 0;
 	}
+
+      if (!I386_DR_VACANT (state, i))
+	all_vacant = 0;
     }
 
+  if (all_vacant)
+    {
+      /* Even though not strictly necessary, clear out all of
+	 DR_CONTROL, so that when we have no debug registers in use,
+	 we end up with DR_CONTROL == 0.  The Linux support relies on
+	 this for an optimization.  Plus, it makes for clearer debug
+	 output.  */
+      state->dr_control_mirror &= ~DR_LOCAL_SLOWDOWN;
+
+      gdb_assert (state->dr_control_mirror == 0);
+    }
   return retval;
 }
 
diff --git a/gdb/testsuite/gdb.base/watchpoint-reuse-slot.c b/gdb/testsuite/gdb.base/watchpoint-reuse-slot.c
new file mode 100644
index 0000000..a5a8f5c
--- /dev/null
+++ b/gdb/testsuite/gdb.base/watchpoint-reuse-slot.c
@@ -0,0 +1,37 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2014 Free Software Foundation, Inc.
+
+   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/>.  */
+
+union aligned_buf
+{
+  char byte[12];
+
+  /* So that testing consistently starts on an aligned address.  */
+  unsigned long long force_align;
+};
+
+union aligned_buf buf;
+
+int
+main (void)
+{
+  volatile int i = 0;
+
+  /* Must be a single line.  */
+  for (i = 0; i < 100000; i++); /* stepi line */
+
+  return 0;
+}
diff --git a/gdb/testsuite/gdb.base/watchpoint-reuse-slot.exp b/gdb/testsuite/gdb.base/watchpoint-reuse-slot.exp
new file mode 100644
index 0000000..aa30398
--- /dev/null
+++ b/gdb/testsuite/gdb.base/watchpoint-reuse-slot.exp
@@ -0,0 +1,187 @@
+# Copyright 2014 Free Software Foundation, Inc.
+
+# 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/>.
+
+# Test alternating between watchpoint types, watching a sliding window
+# of addresses (thus alternating between aligned and unaligned
+# addresses).  Only a single watchpoint exists at any given time.  On
+# targets that only update the debug registers on resume, this
+# stresses the debug register setup code, both in GDB and in the
+# target/kernel as one watchpoint replaces the other in a single
+# operation.  (Note that we don't have any of these watchpoints
+# trigger.)
+
+if [target_info exists gdb,no_hardware_watchpoints] {
+    unsupported "no target support"
+    return
+}
+
+standard_testfile
+
+if {[prepare_for_testing "failed to prepare" $testfile $srcfile debug]} {
+    return -1
+}
+
+if ![runto_main] then {
+    fail "Can't run to main"
+    return 0
+}
+
+# The line we'll be stepping.
+set srcline [gdb_get_line_number "stepi line"]
+
+# The address the program is stopped at currently.
+set cur_addr ""
+
+# Get the current PC.
+
+proc get_pc {} {
+    global hex gdb_prompt
+
+    set addr ""
+    set test "get PC"
+    gdb_test_multiple "p /x \$pc" "$test" {
+	-re " = ($hex).*$gdb_prompt $" {
+	    set addr $expect_out(1,string)
+	    pass "$test"
+	}
+    }
+
+    return $addr
+}
+
+
+# Issue a stepi, and make sure the program advanced past the current
+# instruction (stored in the CUR_ADDR global).
+
+proc stepi {} {
+    global hex gdb_prompt cur_addr
+
+    set srcline "  for (i = 0; i < 100000; i++); /* stepi line */"
+    set test "stepi advanced"
+    gdb_test_multiple "stepi" $test {
+	-re "($hex).*[string_to_regexp $srcline]\r\n$gdb_prompt $" {
+	    set addr $expect_out(1,string)
+	    if {$addr != $cur_addr} {
+		pass $test
+	    } else {
+		fail $test
+	    }
+	    set cur_addr addr
+	}
+    }
+}
+
+gdb_breakpoint $srcline
+gdb_continue_to_breakpoint "stepi line"
+
+# The test tries various sequences of different types of watchpoints.
+# Probe for support first.
+
+# So we get an immediate warning/error if the target doesn't support a
+# given watchpoint type.
+gdb_test_no_output "set breakpoint always-inserted on"
+
+# The list of supported commands.  Below we'll probe for support and
+# add elements to this list.
+set cmds {}
+
+foreach cmd {"watch" "awatch" "rwatch"} {
+    set test $cmd
+    gdb_test_multiple "$cmd buf.byte\[0\]" $test {
+	-re "You may have requested too many.*$gdb_prompt $" {
+	    unsupported $test
+	}
+	-re "$gdb_prompt $" {
+	    pass $test
+	    lappend cmds $cmd
+	}
+    }
+
+   delete_breakpoints
+}
+
+set test "hbreak"
+gdb_test_multiple "hbreak main" $test {
+    -re "You may have requested too many.*$gdb_prompt $" {
+	pass $test
+    }
+    -re "$gdb_prompt $" {
+	pass $test
+	lappend cmds "hbreak"
+    }
+}
+
+delete_breakpoints
+
+set cur_addr [get_pc]
+
+# Watch WIDTH bytes at BASE + OFFSET.  CMD specifices the specific
+# type of watchpoint to use.  If CMD is "hbreak", WIDTH is ignored.
+
+proc watch_command {cmd base offset width} {
+    global srcfile srcline hex
+
+    if {$cmd == "hbreak"} {
+	set expr "*(buf.byte + $base + $offset)"
+	gdb_test "hbreak $expr" "Hardware assisted breakpoint \[0-9\]+ at $hex"
+    } elseif {$cmd == "watch"} {
+	set expr "*(buf.byte + $base + $offset)@$width"
+	gdb_test "$cmd $expr" \
+	    "Hardware watchpoint \[0-9\]+: [string_to_regexp $expr]"
+    } elseif {$cmd == "awatch"} {
+	set expr "*(buf.byte + $base + $offset)@$width"
+	gdb_test "$cmd $expr" \
+	    "Hardware access \\(read/write\\) watchpoint \[0-9\]+: [string_to_regexp $expr]"
+    } elseif {$cmd == "rwatch"} {
+	set expr "*(buf.byte + $base + $offset)@$width"
+	gdb_test "$cmd $expr" \
+	    "Hardware read watchpoint \[0-9\]+: [string_to_regexp $expr]"
+    }
+}
+
+# Run test proper.  See intro for description.
+
+foreach always_inserted {"off" "on" } {
+    gdb_test_no_output "set breakpoint always-inserted $always_inserted"
+    foreach cmd1 $cmds {
+	foreach cmd2 $cmds {
+	    for {set width 1} {$width < 4} {incr width} {
+
+		if {$cmd1 == "hbreak" && $cmd2 == "hbreak" && $width > 1} {
+		    # hbreak ignores WIDTH, no use testing more than
+		    # once.
+		    continue
+		}
+
+		for {set x 0} {$x < 4} {incr x} {
+		    set prefix "always-inserted $always_inserted: "
+		    append prefix "$cmd1 x $cmd2: "
+		    with_test_prefix "$prefix: width $width, iter $x" {
+			with_test_prefix "base + 0" {
+			    watch_command $cmd1 $x 0 $width
+			    stepi
+			    gdb_test_no_output "delete \$bpnum"
+			}
+			with_test_prefix "base + 1" {
+			    watch_command $cmd2 $x 1 $width
+			    stepi
+			    gdb_test_no_output "delete \$bpnum"
+			}
+		    }
+		}
+	    }
+	}
+    }
+}
