diff --git a/config/makefiles/autotargets.mk b/config/makefiles/autotargets.mk
index 595729e65586..5d6daa5fd943 100644
--- a/config/makefiles/autotargets.mk
+++ b/config/makefiles/autotargets.mk
@@ -18,26 +18,54 @@ ifndef INCLUDED_AUTOTARGETS_MK #{
 MKDIR ?= mkdir -p
 TOUCH ?= touch
 
+# declare for local use, rules.mk may not have been loaded
+space = $(NULL) $(NULL)
+
 # Deps will be considered intermediate when used as a pre-requisite for
 # wildcard targets.  Inhibit their removal, mkdir -p is a standalone op.
 .PRECIOUS: %/.mkdir.done
 
-###########################################################################
-# Threadsafe directory creation
-# GENERATED_DIRS - Automated creation of these directories.
-# Squeeze '//' from the path, easily created by $(dir $(path))
-###########################################################################
-mkdir_deps =$(subst //,/,$(foreach dir,$(getargv),$(dir)/.mkdir.done))
+#########################
+##---]  FUNCTIONS  [---##
+#########################
+
+# Squeeze can be overzealous, restore root for abspath
+getPathPrefix =$(if $(filter /%,$(1)),/)
+
+# Squeeze '//' from the path, easily created by string functions
+_slashSqueeze =$(foreach val,$(getargv),$(call getPathPrefix,$(val))$(subst $(space),/,$(strip $(subst /,$(space),$(val)))))
+
+# Squeeze extraneous directory slashes from the path
+#  o protect embedded spaces within the path
+#  o replace //+ sequences with /
+slash_strip =\
+  $(strip \
+    $(subst <--[**]-->,$(space),\
+	$(call _slashSqueeze,\
+    $(subst $(space),<--[**]-->,$(1))\
+  )))
+
+# Extract directory path from a dependency file.
+mkdir_stem =$(foreach val,$(getargv),$(subst /.mkdir.done,$(NULL),$(val)))
+
+## Generate timestamp file for threadsafe directory creation
+mkdir_deps =$(foreach dir,$(getargv),$(call slash_strip,$(dir)/.mkdir.done))
+
+#######################
+##---]  TARGETS  [---##
+#######################
 
 %/.mkdir.done: # mkdir -p -p => mkdir -p
-	$(subst $(SPACE)-p,$(null),$(MKDIR)) -p $(dir $@)
+	$(subst $(space)-p,$(null),$(MKDIR)) -p $(dir $@)
 	@$(TOUCH) $@
 
 # A handful of makefiles are attempting "mkdir dot".  Likely not intended
 # or stale logic so add a stub target to handle the request and warn for now.
 .mkdir.done:
+ifndef NOWARN_AUTOTARGETS # {
 	@echo "WARNING: $(MKDIR) -dot- requested by $(MAKE) -C $(CURDIR) $(MAKECMDGOALS)"
 	@$(TOUCH) $@
+endif #}
 
 INCLUDED_AUTOTARGETS_MK = 1
 endif #}
diff --git a/config/makefiles/test/Makefile.in b/config/makefiles/test/Makefile.in
index 7462e2a4fe26..df8cfc258a0d 100644
--- a/config/makefiles/test/Makefile.in
+++ b/config/makefiles/test/Makefile.in
@@ -11,6 +11,7 @@ VPATH     = @srcdir@
 
 include $(DEPTH)/config/autoconf.mk
 
+USE_AUTOTARGETS_MK  = 1
 MAKEUTILS_UNIT_TEST = 1
 include $(topsrcdir)/config/makefiles/makeutils.mk
 
diff --git a/config/makefiles/test/check-autotargets.mk b/config/makefiles/test/check-autotargets.mk
index df10d4a918de..80c33060f685 100644
--- a/config/makefiles/test/check-autotargets.mk
+++ b/config/makefiles/test/check-autotargets.mk
@@ -8,8 +8,11 @@ ifdef VERBOSE
   $(warning loading test)
 endif
 
+space=$(null) $(null)
 GENERATED_DIRS = bogus # test data
 
+NOWARN_AUTOTARGETS = 1 # Unit test includes makefile twice.
+
 undefine USE_AUTOTARGETS_MK
 undefine INCLUDED_AUTOTARGETS_MK
 include $(topsrcdir)/config/makefiles/autotargets.mk
@@ -30,9 +33,54 @@ ifneq (bogus,$(findstring bogus,$(AUTO_DEPS)))
   $(error AUTO_DEPS=[$(AUTO_DEPS)] is not set correctly)
 endif
 
-path  = foo/bar.c
-exp = foo/.mkdir.done
-found = $(call mkdir_deps,$(dir $(path)))
+
+# relpath
+path  := foo/bar.c
+exp   := foo/.mkdir.done
+found := $(call mkdir_deps,$(dir $(path)))
 ifneq ($(exp),$(found))
   $(error mkdir_deps($(path))=$(exp) not set correctly [$(found)])
 endif
+
+# abspath
+path  := /foo//bar/
+exp   := /foo/bar/.mkdir.done
+found := $(call mkdir_deps,$(path))
+ifneq ($(exp),$(found))
+  $(error mkdir_deps($(path))=$(exp) not set correctly [$(found)])
+endif
+
+
+## verify strip_slash
+#####################
+
+path  := a/b//c///d////e/////
+exp   := a/b/c/d/e/.mkdir.done
+found := $(call mkdir_deps,$(path))
+ifneq ($(exp),$(found))
+  $(error mkdir_deps($(path))=$(exp) not set correctly [$(found)])
+endif
+
+
+## verify mkdir_stem()
+######################
+path  := verify/mkdir_stem
+pathD = $(call mkdir_deps,$(path))
+pathS = $(call mkdir_stem,$(pathD))
+exp   := $(path)
+
+ifeq ($(pathD),$(pathS))
+  $(error mkdir_deps and mkdir_stem should not match [$(pathD)])
+endif
+ifneq ($(pathS),$(exp))
+  $(error mkdir_stem=[$(pathS)] != exp=[$(exp)])
+endif
+
+
+## Verify embedded whitespace has been protected
+path  := a/b$(space)c//d
+exp   := a/b$(space)c/d
+found := $(call slash_strip,$(path))
+ifneq ($(exp),$(found))
+  $(error slash_strip($(path))=$(exp) not set correctly [$(found)])
+endif
diff --git a/js/src/config/makefiles/autotargets.mk b/js/src/config/makefiles/autotargets.mk
index 595729e65586..5d6daa5fd943 100644
--- a/js/src/config/makefiles/autotargets.mk
+++ b/js/src/config/makefiles/autotargets.mk
@@ -18,26 +18,54 @@ ifndef INCLUDED_AUTOTARGETS_MK #{
 MKDIR ?= mkdir -p
 TOUCH ?= touch
 
+# declare for local use, rules.mk may not have been loaded
+space = $(NULL) $(NULL)
+
 # Deps will be considered intermediate when used as a pre-requisite for
 # wildcard targets.  Inhibit their removal, mkdir -p is a standalone op.
 .PRECIOUS: %/.mkdir.done
 
-###########################################################################
-# Threadsafe directory creation
-# GENERATED_DIRS - Automated creation of these directories.
-# Squeeze '//' from the path, easily created by $(dir $(path))
-###########################################################################
-mkdir_deps =$(subst //,/,$(foreach dir,$(getargv),$(dir)/.mkdir.done))
+#########################
+##---]  FUNCTIONS  [---##
+#########################
+
+# Squeeze can be overzealous, restore root for abspath
+getPathPrefix =$(if $(filter /%,$(1)),/)
+
+# Squeeze '//' from the path, easily created by string functions
+_slashSqueeze =$(foreach val,$(getargv),$(call getPathPrefix,$(val))$(subst $(space),/,$(strip $(subst /,$(space),$(val)))))
+
+# Squeeze extraneous directory slashes from the path
+#  o protect embedded spaces within the path
+#  o replace //+ sequences with /
+slash_strip =\
+  $(strip \
+    $(subst <--[**]-->,$(space),\
+	$(call _slashSqueeze,\
+    $(subst $(space),<--[**]-->,$(1))\
+  )))
+
+# Extract directory path from a dependency file.
+mkdir_stem =$(foreach val,$(getargv),$(subst /.mkdir.done,$(NULL),$(val)))
+
+## Generate timestamp file for threadsafe directory creation
+mkdir_deps =$(foreach dir,$(getargv),$(call slash_strip,$(dir)/.mkdir.done))
+
+#######################
+##---]  TARGETS  [---##
+#######################
 
 %/.mkdir.done: # mkdir -p -p => mkdir -p
-	$(subst $(SPACE)-p,$(null),$(MKDIR)) -p $(dir $@)
+	$(subst $(space)-p,$(null),$(MKDIR)) -p $(dir $@)
 	@$(TOUCH) $@
 
 # A handful of makefiles are attempting "mkdir dot".  Likely not intended
 # or stale logic so add a stub target to handle the request and warn for now.
 .mkdir.done:
+ifndef NOWARN_AUTOTARGETS # {
 	@echo "WARNING: $(MKDIR) -dot- requested by $(MAKE) -C $(CURDIR) $(MAKECMDGOALS)"
 	@$(TOUCH) $@
+endif #}
 
 INCLUDED_AUTOTARGETS_MK = 1
 endif #}