[PATCH] kunit: Fix 'hooks.o' build by recursing into kunit

[David Gow <davidgow@google.com>]

KUnit's 'hooks.o' file need to be built-in whenever KUnit is enabled
(even if CONFIG_KUNIT=m). We'd previously attemtped to do this by adding
'kunit/hooks.o' to obj-y in lib/Makefile, but this caused hooks.c to be
rebuilt even when it was unchanged.

Instead, always recurse into lib/kunit using obj-y when KUnit is
enabled, and add the hooks there.

Fixes: 7170b7ed6acb ("kunit: Add "hooks" to call into KUnit when it's built as a module").
Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/linux-kselftest/CAHk-=wiEf7irTKwPJ0jTMOF3CS-13UXmF6Fns3wuWpOZ_wGyZQ@mail.gmail.com/
Signed-off-by: David Gow <davidgow@google.com>
---

I like this way of handling the makefiles much better. I had tried it
when originally writing the hooks patch and not managed to get it
working. Not sure what's changed now, but it works in all of the usual
cases (CONFIG_KUNIT={n,y,m}, kunit.py run, etc).

Linus, Shuah: Let me know if you want this to go via the KUnit branch,
or if you just want to apply it directly and get rid of the annoyances
ASAP.

---
 lib/Makefile       | 12 ++++--------
 lib/kunit/Makefile |  2 +-
 2 files changed, 5 insertions(+), 9 deletions(-)

diff --git a/lib/Makefile b/lib/Makefile
index 469be6240523..baf2821f7a00 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -127,14 +127,10 @@ CFLAGS_test_fpu.o += $(FPU_CFLAGS)
 
 obj-$(CONFIG_TEST_LIVEPATCH) += livepatch/
 
-obj-$(CONFIG_KUNIT) += kunit/
-# Include the KUnit hooks unconditionally. They'll compile to nothing if
-# CONFIG_KUNIT=n, otherwise will be a small table of static data (static key,
-# function pointers) which need to be built-in even when KUnit is a module.
-ifeq ($(CONFIG_KUNIT), m)
-obj-y += kunit/hooks.o
-else
-obj-$(CONFIG_KUNIT) += kunit/hooks.o
+# Some KUnit files (hooks.o) need to be built-in even when KUnit is a module,
+# so we can't just use obj-$(CONFIG_KUNIT).
+ifdef CONFIG_KUNIT
+obj-y += kunit/
 endif
 
 ifeq ($(CONFIG_DEBUG_KOBJECT),y)
diff --git a/lib/kunit/Makefile b/lib/kunit/Makefile
index da665cd4ea12..cb417f504996 100644
--- a/lib/kunit/Makefile
+++ b/lib/kunit/Makefile
@@ -13,7 +13,7 @@ kunit-objs +=				debugfs.o
 endif
 
 # KUnit 'hooks' are built-in even when KUnit is built as a module.
-lib-y +=				hooks.o
+obj-y +=				hooks.o
 
 obj-$(CONFIG_KUNIT_TEST) +=		kunit-test.o
 
-- 
2.39.2.637.g21b0678d19-goog