selftests: livepatch: Avoid running the tests if kernel-devel is missing

By checking if KDIR is a valid directory we can safely skip the tests if
kernel-devel isn't installed (default value of KDIR), or if KDIR
variable passed doesn't exists.

Reported-by: kernel test robot <[e-mail]>
Closes: https://lore.kernel.org/oe-kbuild-all/[e-mail]/
Signed-off-by: Marcos Paulo de Souza <[e-mail]>
Signed-off-by: Shuah Khan <[e-mail]>

tools/testing/selftests/livepatch/functions.sh

···
 	fi
 }
 
+# Check if we can compile the modules before loading them
+function has_kdir() {
+	if [ -z "$KDIR" ]; then
+		KDIR="/lib/modules/$(uname -r)/build"
+	fi
+
+	if [ ! -d "$KDIR" ]; then
+		echo "skip all tests: KDIR ($KDIR) not available to compile modules."
+		exit $ksft_skip
+	fi
+}
+
 # die(msg) - game over, man
 #	msg - dying words
 function die() {
···
 #		 the ftrace_enabled sysctl.
 function setup_config() {
 	is_root
+	has_kdir
 	push_config
 	set_dynamic_debug
 	set_ftrace_enabled 1

tools/testing/selftests/livepatch/test_modules/Makefile

···
 	test_klp_shadow_vars.o \
 	test_klp_syscall.o
 
+# Ensure that KDIR exists, otherwise skip the compilation
 modules:
+ifneq ("$(wildcard $(KDIR))", "")
 	$(Q)$(MAKE) -C $(KDIR) modules KBUILD_EXTMOD=$(TESTMODS_DIR)
+endif
 
+# Ensure that KDIR exists, otherwise skip the clean target
 clean:
+ifneq ("$(wildcard $(KDIR))", "")
 	$(Q)$(MAKE) -C $(KDIR) clean KBUILD_EXTMOD=$(TESTMODS_DIR)
+endif