[PATCH v2 1/8] selftests/mm: default KDIR to build directory

[Kevin Brodsky <kevin.brodsky@arm.com>]

KDIR currently defaults to the running kernel's modules directory
when building the page_frag module. The underlying assumption is
that most users build the kselftests in order to run them against
the system they're built on.

This assumption seems questionable, and there is no guarantee that
the module can actually be built against the running kernel.

Switch the default value of KDIR to the kernel's build directory,
i.e. $(O) if O= or KBUILD_OUTPUT= is used, and the source directory
otherwise. This seems like the least surprising option: the test
module is built against the kernel that has been previously built.

Note: we can't use $(top_srcdir) in mm/Makefile because it is only
defined once lib.mk is included.

Signed-off-by: Kevin Brodsky <kevin.brodsky@arm.com>
---
 tools/testing/selftests/mm/Makefile           | 2 +-
 tools/testing/selftests/mm/page_frag/Makefile | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/mm/Makefile b/tools/testing/selftests/mm/Makefile
index eaf9312097f7..bb93101e339e 100644
--- a/tools/testing/selftests/mm/Makefile
+++ b/tools/testing/selftests/mm/Makefile
@@ -44,7 +44,7 @@ LDLIBS = -lrt -lpthread -lm
 # warnings.
 CFLAGS += -U_FORTIFY_SOURCE
 
-KDIR ?= /lib/modules/$(shell uname -r)/build
+KDIR ?= $(if $(O),$(O),$(realpath ../../../..))
 ifneq (,$(wildcard $(KDIR)/Module.symvers))
 ifneq (,$(wildcard $(KDIR)/include/linux/page_frag_cache.h))
 TEST_GEN_MODS_DIR := page_frag
diff --git a/tools/testing/selftests/mm/page_frag/Makefile b/tools/testing/selftests/mm/page_frag/Makefile
index 8c8bb39ffa28..96e5f646e69b 100644
--- a/tools/testing/selftests/mm/page_frag/Makefile
+++ b/tools/testing/selftests/mm/page_frag/Makefile
@@ -1,5 +1,5 @@
 PAGE_FRAG_TEST_DIR := $(realpath $(dir $(abspath $(lastword $(MAKEFILE_LIST)))))
-KDIR ?= /lib/modules/$(shell uname -r)/build
+KDIR ?= $(if $(O),$(O),$(realpath ../../../../..))
 
 ifeq ($(V),1)
 Q =
-- 
2.51.2