[PATCH] kbuild: add workaround for Debian make-kpkg

From: Masahiro Yamada
Date: Wed Mar 06 2019 - 11:01:29 EST

Since commit 3812b8c5c5d5 ("kbuild: make -r/-R effective in top
Makefile for old Make versions"), make-kpkg is not working.

make-kpkg directly includes the top Makefile of Linux kernel, and
appends some debian_* targets.


# Include the kernel makefile
override dot-config := 1
include Makefile
dot-config := 1

I did not know the kernel Makefile was used in that way, and it is
hard to guarantee the behavior when the kernel Makefile is included
by another Makefile from a different project.

Looks like Debian Stretch stopped providing make-kpkg (except PowerPC).
Maybe it is obsolete and being replaced with 'make deb-pkg' etc.
but still widely used.

This commit adds a workaround; if the top Makefile is included by
another Makefile, skip sub-make in order to make the main part visible.
'MAKEFLAGS += -rR' does not become effective for GNU Make < 4.0, but
Debian/Ubuntu is already using newer versions.

The effect of this commit:

Debian 8 (Jessie) : Fixed
Debian 9 (Stretch) : make-kpkg (kernel-package) is not provided
Ubuntu 14.04 LTS : NOT Fixed
Ubuntu 16.04 LTS : Fixed
Ubuntu 18.04 LTS : Fixed

This commit cannot fix Ubuntu 14.04 because it installs GNU Make 3.81,
but its support will end in Apr 2019, which is before the Linux v5.1

I added warning so that nobody would try to include the top Makefile.

Fixes: 3812b8c5c5d5 ("kbuild: make -r/-R effective in top Makefile for old Make versions")
Reported-by: Liz Zhang <lizzha@xxxxxxxxxxxxx>
Signed-off-by: Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx>
Tested-by: Lili Deng <v-lide@xxxxxxxxxxxxx>

Makefile | 10 ++++++++++
1 file changed, 10 insertions(+)

diff --git a/Makefile b/Makefile
index ef4b32c..925d870 100644
--- a/Makefile
+++ b/Makefile
@@ -31,6 +31,16 @@ _all:
# descending is started. They are now explicitly listed as the
# prepare rule.

+# Ugly workaround for Debian make-kpkg:
+# make-kpkg directly includes the top Makefile of Linux kernel. In such a case,
+# skip sub-make to support debian_* targets in ruleset/kernel_version.mk, but
+# displays warning to discourage such abusage.
+ifneq ($(word 2, $(MAKEFILE_LIST)),)
+$(warning Do not include top Makefile of Linux Kernel)
+sub-make-done := 1
ifneq ($(sub-make-done),1)

# Do not use make's built-in rules and variables