diff --git a/rules.mak b/rules.mak
index 65a1b9695b..49edb9bf07 100644
--- a/rules.mak
+++ b/rules.mak
@@ -106,6 +106,17 @@ leqv = $(if $(filter $(call lnot,$1),$(call lnot,$2)),y,n)
 # Logical if: like make's $(if) but with an leqv-like test
 lif = $(if $(subst n,,$1),$2,$3)
 
+# String testing functions: inputs to these can be any string;
+# the output is always either "y" or "n". Leading and trailing whitespace
+# is ignored when comparing strings.
+# String equality
+eq = $(if $(subst $2,,$1)$(subst $1,,$2),n,y)
+# String inequality
+ne = $(if $(subst $2,,$1)$(subst $1,,$2),y,n)
+# Emptiness/non-emptiness tests:
+isempty = $(if $1,n,y)
+notempty = $(if $1,y,n)
+
 # Generate files with tracetool
 TRACETOOL=$(PYTHON) $(SRC_PATH)/scripts/tracetool.py