From 50012bd4384ca8fff92c12b9d7d25ad0872f6dd3 Mon Sep 17 00:00:00 2001
From: Ben Hutchings <benh@debian.org>
Date: Mon, 26 Apr 2021 18:27:16 +0200
Subject: [PATCH] kbuild: Abort build if SUBDIRS used

Forwarded: not-needed
Bug-Debian: https://bugs.debian.org/987575

DKMS and module-assistant both build OOT modules as root.  If they
build an old OOT module that still use SUBDIRS this causes Kbuild
to try building a full kernel, which obviously fails but not before
deleting files from the installed headers package.

To avoid such mishaps, detect this situation and abort the build.

The error message is based on that used in commit 0126be38d988
"kbuild: announce removal of SUBDIRS if used".

Gbp-Pq: Topic debian
Gbp-Pq: Name kbuild-abort-build-if-subdirs-used.patch
---
 Makefile | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/Makefile b/Makefile
index 39b86ee2f7b..29b2d114b13 100644
--- a/Makefile
+++ b/Makefile
@@ -225,6 +225,18 @@ ifeq ("$(origin M)", "command line")
   KBUILD_EXTMOD := $(M)
 endif
 
+# Old syntax make ... SUBDIRS=$PWD should be rejected to avoid mishaps
+# (see Debian bugs #982334, #987575)
+ifndef KBUILD_EXTMOD
+  ifdef SUBDIRS
+    $(warning =============== ERROR ==============)
+    $(warning 'SUBDIRS' was removed in Linux 5.3)
+    $(warning Use 'M=' or 'KBUILD_EXTMOD=' instead)
+    $(warning ====================================)
+    $(error .)
+  endif
+endif
+
 $(if $(word 2, $(KBUILD_EXTMOD)), \
 	$(error building multiple external modules is not supported))
 
-- 
2.30.2