better document new --make-target= option

defaults/config.sh

@@ -3,7 +3,11 @@
 # Arch-specific options that normally shouldn't be changed.
 #
 KERNEL_MAKE_DIRECTIVE="bzImage"
-KERNEL_MAKE_DIRECTIVE_OVERRIDE="--INVALID--"
+# since "" is allowed (this will translate in `make `, which is nice
+# for xen-based kernels, the default value of
+# KERNEL_MAKE_DIRECTIVE_OVERRIDE cannot be ""
+DEFAULT_KERNEL_MAKE_DIRECTIVE_OVERRIDE="--INVALID--"
+KERNEL_MAKE_DIRECTIVE_OVERRIDE="${DEFAULT_KERNEL_MAKE_DIRECTIVE_OVERRIDE}"
 KERNEL_MAKE_DIRECTIVE_2=""
 KERNEL_BINARY="arch/i386/boot/bzImage"
 KERNEL_BINARY_OVERRIDE=""

doc/genkernel.8.txt

@@ -190,7 +190,9 @@ LOW-LEVEL COMPILATION OPTIONS
     GNU Make to use for the kernel compilation.
 
 *--kernel-target*=<t>::
-    Override default make target (bzImage)
+    Override default make target (bzImage), note that values
+    like --kernel-target= are also valid (useful for Xen
+    based kernel sources)
 
 *--kernel-binary*=<path>::
     Override default kernel binary path (arch/foo/boot/bar)

gen_compile.sh

@@ -297,7 +297,7 @@ compile_kernel() {
 		gen_die "KERNEL_MAKE undefined - I don't know how to compile a kernel for this arch!"
 	cd ${KERNEL_DIR}
 	local kernel_make_directive="${KERNEL_MAKE_DIRECTIVE}"
-	if [ "${KERNEL_MAKE_DIRECTIVE_OVERRIDE}" != "--INVALID--" ]; then
+	if [ "${KERNEL_MAKE_DIRECTIVE_OVERRIDE}" != "${DEFAULT_KERNEL_MAKE_DIRECTIVE_OVERRIDE}" ]; then
 		kernel_make_directive="${KERNEL_MAKE_DIRECTIVE_OVERRIDE}"
 	fi
 	print_info 1 "        >> Compiling ${KV} ${kernel_make_directive/_install/ [ install ]/}..."