diff --git a/Makefile b/Makefile
index 7f561ef954f29b..7aca399efae307 100644
--- a/Makefile
+++ b/Makefile
@@ -143,7 +143,8 @@ $(filter-out _all sub-make $(CURDIR)/Makefile, $(MAKECMDGOALS)) _all: sub-make
 
 # Invoke a second make in the output directory, passing relevant variables
 sub-make:
-	$(Q)$(MAKE) -C $(KBUILD_OUTPUT) KBUILD_SRC=$(CURDIR) \
+	$(Q)$(MAKE) -C $(KBUILD_OUTPUT) \
+	KBUILD_SRC=$(shell realpath --relative-to=$(KBUILD_OUTPUT) $(CURDIR)) \
 	-f $(CURDIR)/Makefile $(filter-out _all sub-make,$(MAKECMDGOALS))
 
 # Leave processing to above invocation of make
diff --git a/tools/lib/subcmd/Makefile b/tools/lib/subcmd/Makefile
index ed61fb3a46c08e..146ec9ec6737a6 100644
--- a/tools/lib/subcmd/Makefile
+++ b/tools/lib/subcmd/Makefile
@@ -33,6 +33,9 @@ ifneq ($(WERROR),0)
   CFLAGS += -Werror
 endif
 
+# Don't fail on fallthrough with newer GCCs.
+CFLAGS += -Wno-error=implicit-fallthrough
+
 CFLAGS += -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -D_GNU_SOURCE
 
 CFLAGS += -I$(srctree)/tools/include/