kbuild: Create Makefile in output directory if != kernel tree

When building a kernel using the O= syntax to save output
files in a separate output directory now create a small Makefile in
that same dir.
This Makefile allow one to use make in the output directory without
the hassle of going back to the kernel source tree.
The O= option is added by this Makefile stub.
Please note that the Makefile silently overwrite an old one, so changes
will be lost if modified.
If there is a need to tweak a Makefile in the output directory it is recommended
to use the filename 'makefile', which GNU Make will try first.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>

1 files changed, 31 insertions, 0 deletions

diff --git a/scripts/mkmakefile b/scripts/mkmakefile
new file mode 100644
index 00000000000000..c4d621b30d0db1
--- /dev/null
+++ b/scripts/mkmakefile
@@ -0,0 +1,31 @@
+#!/bin/sh
+# Generates a small Makefile used in the root of the output
+# directory, to allow make to be started from there.
+# The Makefile also allow for more convinient build of external modules
+
+# Usage
+# $1 - Kernel src directory
+# $2 - Output directory
+# $3 - version
+# $4 - patchlevel
+
+
+cat << EOF
+# Automatically generated by $0: don't edit
+
+VERSION = $3
+PATCHLEVEL = $4
+
+KERNELSRC    := $1
+KERNELOUTPUT := $2
+
+MAKEFLAGS += --no-print-directory
+
+all:
+	\$(MAKE) -C \$(KERNELSRC) O=\$(KERNELOUTPUT)
+
+%::
+	\$(MAKE) -C \$(KERNELSRC) O=\$(KERNELOUTPUT) \$@
+
+EOF
+