Build all binaries with PIE

PIE (position independent executable) adds security to executables
by composing them entirely of position-independent code (PIC. The
.so libraries already build with -fPIC. This adds -fPIE which is
the equivalent to -fPIC, but for executables. This for allows Exec
Shield to use address space layout randomization to prevent attackers
from knowing where existing executable code is during a security
attack using exploits that rely on knowing the offset of the
executable code in the binary, such as return-to-libc attacks.

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>

m4/virt-compile-pie.m4

@@ -0,0 +1,30 @@
+dnl
+dnl Check for support for position independent executables
+dnl
+dnl Copyright (C) 2013 Red Hat, Inc.
+dnl
+dnl This library is free software; you can redistribute it and/or
+dnl modify it under the terms of the GNU Lesser General Public
+dnl License as published by the Free Software Foundation; either
+dnl version 2.1 of the License, or (at your option) any later version.
+dnl
+dnl This library is distributed in the hope that it will be useful,
+dnl but WITHOUT ANY WARRANTY; without even the implied warranty of
+dnl MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+dnl Lesser General Public License for more details.
+dnl
+dnl You should have received a copy of the GNU Lesser General Public
+dnl License along with this library.  If not, see
+dnl <http://www.gnu.org/licenses/>.
+dnl
+
+AC_DEFUN([LIBVIRT_COMPILE_PIE],[
+    PIE_CFLAGS=
+    PIE_LDFLAGS=
+    gl_COMPILER_OPTION_IF([-fPIE -DPIE], [
+        PIE_CFLAGS="-fPIE -DPIE"
+        PIE_LDFLAGS="-pie"
+    ])
+    AC_SUBST([PIE_CFLAGS])
+    AC_SUBST([PIE_LDFLAGS])
+])