diff --git a/common/core.mk b/common/core.mk
new file mode 100644
index 0000000..e5264b0
--- /dev/null
+++ b/common/core.mk
@@ -0,0 +1,56 @@
+#
+# Copyright (C) 2018 The Android Open Source Project
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+# Only use ANDROID_BUILD_SHELL to wrap around bash.
+# DO NOT use other shells such as zsh.
+ifdef ANDROID_BUILD_SHELL
+SHELL := $(ANDROID_BUILD_SHELL)
+else
+# Use bash, not whatever shell somebody has installed as /bin/sh
+# This is repeated from main.mk, since envsetup.sh runs this file
+# directly.
+SHELL := /bin/bash
+endif
+
+# Utility variables.
+empty :=
+space := $(empty) $(empty)
+comma := ,
+# Note that make will eat the newline just before endef.
+define newline
+
+
+endef
+# The pound character "#"
+define pound
+#
+endef
+# Unfortunately you can't simply define backslash as \ or \\.
+backslash := \a
+backslash := $(patsubst %a,%,$(backslash))
+
+# Prevent accidentally changing these variables
+.KATI_READONLY := SHELL empty space comma newline pound backslash
+
+# Basic warning/error wrappers. These will be redefined to include the local
+# module information when reading Android.mk files.
+define pretty-warning
+$(warning $(1))
+endef
+
+define pretty-error
+$(error $(1))
+endef
diff --git a/common/math.mk b/common/math.mk
new file mode 100644
index 0000000..ac3151e
--- /dev/null
+++ b/common/math.mk
@@ -0,0 +1,270 @@
+#
+# Copyright (C) 2017 The Android Open Source Project
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+###########################################################
+# Basic math functions for non-negative integers <= 100
+#
+# (SDK versions for example)
+###########################################################
+__MATH_POS_NUMBERS :=  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19 20 \
+                      21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 \
+                      41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 \
+                      61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 \
+                      81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100
+__MATH_NUMBERS := 0 $(__MATH_POS_NUMBERS)
+
+math-error = $(call pretty-error,$(1))
+math-expect :=
+math-expect-true :=
+math-expect :=
+math-expect-error :=
+
+# Run the math tests with:
+#  make -f ${ANDROID_BUILD_TOP}/build/make/core/math.mk RUN_MATH_TESTS=true
+#  $(get_build_var CKATI) -f ${ANDROID_BUILD_TOP}//build/make/core/math.mk RUN_MATH_TESTS=true
+ifdef RUN_MATH_TESTS
+  MATH_TEST_FAILURE :=
+  MATH_TEST_ERROR :=
+  math-error = $(if $(MATH_TEST_ERROR),,$(eval MATH_TEST_ERROR:=$(1)))
+  define math-expect
+    $(eval got:=$$$1) \
+    $(if $(subst $(got),,$(2))$(subst $(2),,$(got))$(MATH_TEST_ERROR), \
+      $(if $(MATH_TEST_ERROR),$(warning $(MATH_TEST_ERROR)),$(warning $$$1 '$(got)' != '$(2)')) \
+      $(eval MATH_TEST_FAILURE := true)) \
+    $(eval MATH_TEST_ERROR :=) \
+    $(eval got:=)
+  endef
+  math-expect-true = $(call math-expect,$(1),true)
+  math-expect-false = $(call math-expect,$(1),)
+
+  define math-expect-error
+    $(eval got:=$$$1) \
+    $(if $(subst $(MATH_TEST_ERROR),,$(2))$(subst $(2),,$(MATH_TEST_ERROR)), \
+      $(warning '$(MATH_TEST_ERROR)' != '$(2)') \
+      $(eval MATH_TEST_FAILURE := true)) \
+    $(eval MATH_TEST_ERROR :=) \
+    $(eval got:=)
+  endef
+endif
+
+# Returns true if $(1) is a non-negative integer <= 100, otherwise returns nothing.
+define math_is_number
+$(strip \
+  $(if $(1),,$(call math-error,Argument missing)) \
+  $(if $(word 2,$(1)),$(call math-error,Multiple words in a single argument: $(1))) \
+  $(if $(filter $(1),$(__MATH_NUMBERS)),true))
+endef
+
+define math_is_zero
+$(strip \
+  $(if $(word 2,$(1)),$(call math-error,Multiple words in a single argument: $(1))) \
+  $(if $(filter 0,$(1)),true))
+endef
+
+$(call math-expect-true,(call math_is_number,0))
+$(call math-expect-true,(call math_is_number,2))
+$(call math-expect-false,(call math_is_number,foo))
+$(call math-expect-false,(call math_is_number,-1))
+$(call math-expect-error,(call math_is_number,1 2),Multiple words in a single argument: 1 2)
+$(call math-expect-error,(call math_is_number,no 2),Multiple words in a single argument: no 2)
+
+$(call math-expect-true,(call math_is_zero,0))
+$(call math-expect-false,(call math_is_zero,1))
+$(call math-expect-false,(call math_is_zero,foo))
+$(call math-expect-error,(call math_is_zero,1 2),Multiple words in a single argument: 1 2)
+$(call math-expect-error,(call math_is_zero,no 2),Multiple words in a single argument: no 2)
+
+define _math_check_valid
+$(if $(call math_is_number,$(1)),,$(call math-error,Only non-negative integers <= 100 are supported (not $(1))))
+endef
+
+$(call math-expect,(call _math_check_valid,0))
+$(call math-expect,(call _math_check_valid,1))
+$(call math-expect,(call _math_check_valid,100))
+$(call math-expect-error,(call _math_check_valid,-1),Only non-negative integers <= 100 are supported (not -1))
+$(call math-expect-error,(call _math_check_valid,101),Only non-negative integers <= 100 are supported (not 101))
+$(call math-expect-error,(call _math_check_valid,),Argument missing)
+$(call math-expect-error,(call _math_check_valid,1 2),Multiple words in a single argument: 1 2)
+
+# return a list containing integers ranging from [$(1),$(2)]
+define int_range_list
+$(strip \
+  $(call _math_check_valid,$(1))$(call _math_check_valid,$(2)) \
+  $(if $(call math_is_zero,$(1)),0)\
+  $(wordlist $(if $(call math_is_zero,$(1)),1,$(1)),$(2),$(__MATH_POS_NUMBERS)))
+endef
+
+$(call math-expect,(call int_range_list,0,1),0 1)
+$(call math-expect,(call int_range_list,1,1),1)
+$(call math-expect,(call int_range_list,1,2),1 2)
+$(call math-expect,(call int_range_list,2,1),)
+$(call math-expect-error,(call int_range_list,1,101),Only non-negative integers <= 100 are supported (not 101))
+
+
+# Returns the greater of $1 or $2.
+# If $1 or $2 is not a positive integer <= 100, then an error is generated.
+define math_max
+$(strip $(call _math_check_valid,$(1)) $(call _math_check_valid,$(2)) \
+  $(lastword $(filter $(1) $(2),$(__MATH_NUMBERS))))
+endef
+
+$(call math-expect-error,(call math_max),Argument missing)
+$(call math-expect-error,(call math_max,1),Argument missing)
+$(call math-expect-error,(call math_max,1 2,3),Multiple words in a single argument: 1 2)
+$(call math-expect,(call math_max,0,1),1)
+$(call math-expect,(call math_max,1,0),1)
+$(call math-expect,(call math_max,1,1),1)
+$(call math-expect,(call math_max,5,42),42)
+$(call math-expect,(call math_max,42,5),42)
+
+define math_gt_or_eq
+$(if $(filter $(1),$(call math_max,$(1),$(2))),true)
+endef
+
+define math_lt
+$(if $(call math_gt_or_eq,$(1),$(2)),,true)
+endef
+
+$(call math-expect-true,(call math_gt_or_eq, 2, 1))
+$(call math-expect-true,(call math_gt_or_eq, 1, 1))
+$(call math-expect-false,(call math_gt_or_eq, 1, 2))
+
+# $1 is the variable name to increment
+define inc_and_print
+$(strip $(eval $(1) := $($(1)) .)$(words $($(1))))
+endef
+
+ifdef RUN_MATH_TESTS
+a :=
+$(call math-expect,(call inc_and_print,a),1)
+$(call math-expect,(call inc_and_print,a),2)
+$(call math-expect,(call inc_and_print,a),3)
+$(call math-expect,(call inc_and_print,a),4)
+endif
+
+# Returns the words in $2 that are numbers and are less than $1
+define numbers_less_than
+$(strip \
+  $(foreach n,$2, \
+    $(if $(call math_is_number,$(n)), \
+      $(if $(call math_lt,$(n),$(1)), \
+        $(n)))))
+endef
+
+$(call math-expect,(call numbers_less_than,0,0 1 2 3),)
+$(call math-expect,(call numbers_less_than,1,0 2 1 3),0)
+$(call math-expect,(call numbers_less_than,2,0 2 1 3),0 1)
+$(call math-expect,(call numbers_less_than,3,0 2 1 3),0 2 1)
+$(call math-expect,(call numbers_less_than,4,0 2 1 3),0 2 1 3)
+$(call math-expect,(call numbers_less_than,3,0 2 1 3 2),0 2 1 2)
+
+_INT_LIMIT_WORDS := $(foreach a,x x,$(foreach b,x x x x x x x x x x x x x x x x,\
+  $(foreach c,x x x x x x x x x x x x x x x x,x x x x x x x x x x x x x x x x)))
+
+define _int_encode
+$(if $(filter $(words x $(_INT_LIMIT_WORDS)),$(words $(wordlist 1,$(1),x $(_INT_LIMIT_WORDS)))),\
+  $(call math-error,integer greater than $(words $(_INT_LIMIT_WORDS)) is not supported!),\
+    $(wordlist 1,$(1),$(_INT_LIMIT_WORDS)))
+endef
+
+# _int_max returns the maximum of the two arguments
+# input: two (x) lists; output: one (x) list
+# integer cannot be passed in directly. It has to be converted using _int_encode.
+define _int_max
+$(subst xx,x,$(join $(1),$(2)))
+endef
+
+# first argument is greater than second argument
+# output: non-empty if true
+# integer cannot be passed in directly. It has to be converted using _int_encode.
+define _int_greater-than
+$(filter-out $(words $(2)),$(words $(call _int_max,$(1),$(2))))
+endef
+
+# first argument equals to second argument
+# output: non-empty if true
+# integer cannot be passed in directly. It has to be converted using _int_encode.
+define _int_equal
+$(filter $(words $(1)),$(words $(2)))
+endef
+
+# first argument is greater than or equal to second argument
+# output: non-empty if true
+# integer cannot be passed in directly. It has to be converted using _int_encode.
+define _int_greater-or-equal
+$(call _int_greater-than,$(1),$(2))$(call _int_equal,$(1),$(2))
+endef
+
+define int_plus
+$(words $(call _int_encode,$(1)) $(call _int_encode,$(2)))
+endef
+
+$(call math-expect,(call int_plus,0,0),0)
+$(call math-expect,(call int_plus,0,1),1)
+$(call math-expect,(call int_plus,1,0),1)
+$(call math-expect,(call int_plus,1,100),101)
+$(call math-expect,(call int_plus,100,100),200)
+
+define int_subtract
+$(strip \
+  $(if $(call _int_greater-or-equal,$(call _int_encode,$(1)),$(call _int_encode,$(2))),\
+  $(words $(filter-out xx,$(join $(call _int_encode,$(1)),$(call _int_encode,$(2))))),\
+    $(call math-error,subtract underflow $(1) - $(2))))
+endef
+
+$(call math-expect,(call int_subtract,0,0),0)
+$(call math-expect,(call int_subtract,1,0),1)
+$(call math-expect,(call int_subtract,1,1),0)
+$(call math-expect,(call int_subtract,100,1),99)
+$(call math-expect,(call int_subtract,200,100),100)
+$(call math-expect-error,(call int_subtract,0,1),subtract underflow 0 - 1)
+
+define int_multiply
+$(words $(foreach a,$(call _int_encode,$(1)),$(call _int_encode,$(2))))
+endef
+
+$(call math-expect,(call int_multiply,0,0),0)
+$(call math-expect,(call int_multiply,1,0),0)
+$(call math-expect,(call int_multiply,1,1),1)
+$(call math-expect,(call int_multiply,100,1),100)
+$(call math-expect,(call int_multiply,1,100),100)
+$(call math-expect,(call int_multiply,4,100),400)
+$(call math-expect,(call int_multiply,100,4),400)
+
+define int_divide
+$(if $(filter 0,$(2)),$(call math-error,division by zero is not allowed!),$(strip \
+  $(if $(call _int_greater-or-equal,$(call _int_encode,$(1)),$(call _int_encode,$(2))), \
+    $(call int_plus,$(call int_divide,$(call int_subtract,$(1),$(2)),$(2)),1),0)))
+endef
+
+$(call math-expect,(call int_divide,1,1),1)
+$(call math-expect,(call int_divide,200,1),200)
+$(call math-expect,(call int_divide,200,3),66)
+$(call math-expect,(call int_divide,1,2),0)
+$(call math-expect-error,(call int_divide,0,0),division by zero is not allowed!)
+$(call math-expect-error,(call int_divide,1,0),division by zero is not allowed!)
+
+ifdef RUN_MATH_TESTS
+  ifdef MATH_TEST_FAILURE
+    math-tests:
+	@echo FAIL
+	@false
+  else
+    math-tests:
+	@echo PASS
+  endif
+  .PHONY: math-tests
+endif
diff --git a/common/strings.mk b/common/strings.mk
new file mode 100644
index 0000000..ce6d6fb
--- /dev/null
+++ b/common/strings.mk
@@ -0,0 +1,117 @@
+#
+# Copyright (C) 2018 The Android Open Source Project
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+###########################################################
+## Convert to lower case without requiring a shell, which isn't cacheable.
+##
+## $(1): string
+###########################################################
+to-lower=$(subst A,a,$(subst B,b,$(subst C,c,$(subst D,d,$(subst E,e,$(subst F,f,$(subst G,g,$(subst H,h,$(subst I,i,$(subst J,j,$(subst K,k,$(subst L,l,$(subst M,m,$(subst N,n,$(subst O,o,$(subst P,p,$(subst Q,q,$(subst R,r,$(subst S,s,$(subst T,t,$(subst U,u,$(subst V,v,$(subst W,w,$(subst X,x,$(subst Y,y,$(subst Z,z,$1))))))))))))))))))))))))))
+
+###########################################################
+## Convert to upper case without requiring a shell, which isn't cacheable.
+##
+## $(1): string
+###########################################################
+to-upper=$(subst a,A,$(subst b,B,$(subst c,C,$(subst d,D,$(subst e,E,$(subst f,F,$(subst g,G,$(subst h,H,$(subst i,I,$(subst j,J,$(subst k,K,$(subst l,L,$(subst m,M,$(subst n,N,$(subst o,O,$(subst p,P,$(subst q,Q,$(subst r,R,$(subst s,S,$(subst t,T,$(subst u,U,$(subst v,V,$(subst w,W,$(subst x,X,$(subst y,Y,$(subst z,Z,$1))))))))))))))))))))))))))
+
+# Sanity-check to-lower and to-upper
+lower := abcdefghijklmnopqrstuvwxyz-_
+upper := ABCDEFGHIJKLMNOPQRSTUVWXYZ-_
+
+ifneq ($(lower),$(call to-lower,$(upper)))
+  $(error to-lower sanity check failure)
+endif
+
+ifneq ($(upper),$(call to-upper,$(lower)))
+  $(error to-upper sanity check failure)
+endif
+
+lower :=
+upper :=
+
+###########################################################
+## Returns true if $(1) and $(2) are equal.  Returns
+## the empty string if they are not equal.
+###########################################################
+define streq
+$(strip $(if $(strip $(1)),\
+  $(if $(strip $(2)),\
+    $(if $(filter-out __,_$(subst $(strip $(1)),,$(strip $(2)))$(subst $(strip $(2)),,$(strip $(1)))_),,true), \
+    ),\
+  $(if $(strip $(2)),\
+    ,\
+    true)\
+ ))
+endef
+
+###########################################################
+## Convert "a b c" into "a:b:c"
+###########################################################
+define normalize-path-list
+$(subst $(space),:,$(strip $(1)))
+endef
+
+###########################################################
+## Convert "a b c" into "a,b,c"
+###########################################################
+define normalize-comma-list
+$(subst $(space),$(comma),$(strip $(1)))
+endef
+
+###########################################################
+## Read the word out of a colon-separated list of words.
+## This has the same behavior as the built-in function
+## $(word n,str).
+##
+## The individual words may not contain spaces.
+##
+## $(1): 1 based index
+## $(2): value of the form a:b:c...
+###########################################################
+
+define word-colon
+$(word $(1),$(subst :,$(space),$(2)))
+endef
+
+###########################################################
+## Convert "a=b c= d e = f" into "a=b c=d e=f"
+##
+## $(1): list to collapse
+## $(2): if set, separator word; usually "=", ":", or ":="
+##       Defaults to "=" if not set.
+###########################################################
+
+define collapse-pairs
+$(eval _cpSEP := $(strip $(if $(2),$(2),=)))\
+$(strip $(subst $(space)$(_cpSEP)$(space),$(_cpSEP),$(strip \
+    $(subst $(_cpSEP), $(_cpSEP) ,$(1)))$(space)))
+endef
+
+###########################################################
+## Given a list of pairs, if multiple pairs have the same
+## first components, keep only the first pair.
+##
+## $(1): list of pairs
+## $(2): the separator word, such as ":", "=", etc.
+define uniq-pairs-by-first-component
+$(eval _upbfc_fc_set :=)\
+$(strip $(foreach w,$(1), $(eval _first := $(word 1,$(subst $(2),$(space),$(w))))\
+    $(if $(filter $(_upbfc_fc_set),$(_first)),,$(w)\
+        $(eval _upbfc_fc_set += $(_first)))))\
+$(eval _upbfc_fc_set :=)\
+$(eval _first:=)
+endef