add the configure option to enable the stack protector (on by default)

configure.ac

@@ -69,6 +69,19 @@ AC_PATH_PROG([VARNISHTEST], [varnishtest], [],
 AC_PATH_PROG([VARNISHD], [varnishd], [],
     [$LIBVARNISHAPI_SBINDIR:$LIBVARNISHAPI_BINDIR:$PATH])
 
+# --enable-stack-protector
+AC_ARG_ENABLE(stack-protector,
+       AS_HELP_STRING([--enable-stack-protector],[enable stack protector (default is YES)]),
+       [],
+       [enable_stack_protector=yes])
+
+if test "x$enable_stack_protector" != "xno"; then
+	AX_CHECK_COMPILE_FLAG([-fstack-protector],
+		AX_CHECK_LINK_FLAG([-fstack-protector],
+			[CFLAGS="${CFLAGS} -fstack-protector"], [], []),
+		[], [])
+fi
+
 AC_CONFIG_FILES([
 	Makefile
 	src/Makefile

src/vmod_blobcode.vcc

@@ -297,17 +297,18 @@ The VMOD allocates memory in various ways for new blobs and
 strings. The ``blob`` object and its methods allocate memory from the
 heap, and hence they are only limited by available virtual memory.
 
-The ``encode()`` and ``decode()`` functions allocate Varnish
-workspace.  If these functions are failing, as indicated by "out of
-space" messages in the Varnish log (with the ``VCL_Error`` tag), then
-you will need to increase the varnishd parameters ``workspace_client``
-and/or ``workspace_backend``.
-
-The ``transcode()`` function also allocates workspace for the string
-that it returns, and it allocates space on the stack for a temporary
-BLOB. If this function causes stack overflow, you may need to increase
-the stack size for the varnishd process, for example with ``ulimit
--s``.
+The ``encode()``, ``decode()`` and ``transcode()`` functions allocate
+Varnish workspace.  If these functions are failing, as indicated by
+"out of space" messages in the Varnish log (with the ``VCL_Error``
+tag), then you will need to increase the varnishd parameters
+``workspace_client`` and/or ``workspace_backend``.
+
+The ``transcode()`` function also allocates space on the stack for a
+temporary BLOB. If this function causes stack overflow, you may need
+to increase the stack size for the varnishd process, for example with
+``ulimit -s``. By default, the VMOD is built with the stack protector
+enabled (compile option ``-fstack-protector``), but it can be disabled
+with the ``./configure`` option ``--disable-stack-protector``.
 
 AUTHORS
 =======