diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog
index 8c995e316a..e10e1c6c47 100644
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,3 +1,11 @@
+2008-06-27  Pedro Alves  <pedro@codesourcery.com>
+
+	* lib/gdb.exp (gdb_saved_set_unbuffered_mode_obj): New global.
+	(gdb_compile): If target is *-*-cygwin* or *-*-mingw*, and we're
+	compiling an executable, link in an object that forces unbuffered
+	output.
+	* lib/set_unbuffered_mode.c: New file.
+
 2008-06-25  Jan Kratochvil  <jan.kratochvil@redhat.com>
 
 	* lib/gdb.exp (prepare_for_testing): Do not drop the OPTIONS argument.
diff --git a/gdb/testsuite/lib/gdb.exp b/gdb/testsuite/lib/gdb.exp
index e9b63f5711..72081a8db5 100644
--- a/gdb/testsuite/lib/gdb.exp
+++ b/gdb/testsuite/lib/gdb.exp
@@ -1536,11 +1536,18 @@ proc gdb_wrapper_init { args } {
     set gdb_wrapper_initialized 1
 }
 
+# Some targets need to always link a special object in.  Save its path here.
+global gdb_saved_set_unbuffered_mode_obj
+set gdb_saved_set_unbuffered_mode_obj ""
+
 proc gdb_compile {source dest type options} {
     global GDB_TESTCASE_OPTIONS;
     global gdb_wrapper_file;
     global gdb_wrapper_flags;
     global gdb_wrapper_initialized;
+    global srcdir
+    global objdir
+    global gdb_saved_set_unbuffered_mode_obj
 
     set outdir [file dirname $dest]
 
@@ -1627,6 +1634,44 @@ proc gdb_compile {source dest type options} {
 	set options [lreplace $options $nowarnings $nowarnings $flag]
     }
 
+    if { $type == "executable" } {
+	if { ([istarget "*-*-mingw*"]
+	      || [istarget "*-*-cygwin*"])} {
+	    # Force output to unbuffered mode, by linking in an object file
+	    # with a global contructor that calls setvbuf.
+	    #
+	    # Compile the special object seperatelly for two reasons:
+	    #  1) Insulate it from $options.
+	    #  2) Avoid compiling it for every gdb_compile invocation,
+	    #  which is time consuming, especially if we're remote
+	    #  host testing.
+	    #
+	    if { $gdb_saved_set_unbuffered_mode_obj == "" } {
+		verbose "compiling gdb_saved_set_unbuffered_obj"
+		set unbuf_src ${srcdir}/lib/set_unbuffered_mode.c
+		set unbuf_obj ${objdir}/set_unbuffered_mode.o
+
+		set result [gdb_compile "${unbuf_src}" "${unbuf_obj}" object {nowarnings}]
+		if { $result != "" } {
+		    return $result
+		}
+
+		set gdb_saved_set_unbuffered_mode_obj ${objdir}/set_unbuffered_mode_saved.o
+		# Link a copy of the output object, because the
+		# original may be automatically deleted.
+		remote_exec host "cp -f $unbuf_obj $gdb_saved_set_unbuffered_mode_obj"
+	    } else {
+		verbose "gdb_saved_set_unbuffered_obj already compiled"
+	    }
+
+	    # Rely on the internal knowledge that the global ctors are ran in
+	    # reverse link order.  In that case, we can use ldflags to
+	    # avoid copying the object file to the host multiple
+	    # times.
+	    lappend options "ldflags=$gdb_saved_set_unbuffered_mode_obj"
+	}
+    }
+
     set result [target_compile $source $dest $type $options];
 
     # Prune uninteresting compiler (and linker) output.
diff --git a/gdb/testsuite/lib/set_unbuffered_mode.c b/gdb/testsuite/lib/set_unbuffered_mode.c
new file mode 100644
index 0000000000..aa9180155e
--- /dev/null
+++ b/gdb/testsuite/lib/set_unbuffered_mode.c
@@ -0,0 +1,28 @@
+/* Copyright (C) 2008 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/>.  */
+
+/* Force outputs to unbuffered mode.  */
+
+#include <stdio.h>
+
+static int __gdb_set_unbuffered_output (void) __attribute__ ((constructor));
+static int
+__gdb_set_unbuffered_output (void)
+{
+  setvbuf (stdout, NULL, _IONBF, BUFSIZ);
+  setvbuf (stderr, NULL, _IONBF, BUFSIZ);
+}