diff --git a/functions.mk b/functions.mk
new file mode 100644
index 0000000000..51f6457016
--- /dev/null
+++ b/functions.mk
@@ -0,0 +1,7 @@
+# Utility function for recursively finding files, e.g.
+# ‘$(call rwildcard, path/to/dir, *.c *.h)’.
+rwildcard=$(foreach d,$(wildcard $1*),$(call rwildcard,$d/,$2) $(filter $(subst *,%,$2),$d))
+
+# Given a file name, produce the corresponding dependency file
+# (e.g. ‘foo/bar.o’ becomes ‘foo/.bar.o.dep’).
+filename-to-dep = $(dir $1).$(notdir $1).dep