build/core/pathmap.mk 文件定义了一个列表pathmap_INCL，列表中每项是"短名:路径"对。宏函数include-path-for将会使用这个列表，来通过短名获取相对于的路径，

如：$(call include-path-for,短名)

#

# A mapping from shorthand names to include directories.

# "短名: 路径"对列表pathmap_INCL

pathmap_INCL := \

bluedroid:system/bluetooth/bluedroid/include \

bluez-libs:external/bluez/libs/include \

bluez-utils:external/bluez/utils \

bootloader:bootable/bootloader/legacy/include \

corecg:external/skia/include/core \

dbus:external/dbus \

frameworks-base:frameworks/base/include \

graphics:external/skia/include/core \

libc:bionic/libc/include \

libdrm1:frameworks/base/media/libdrm/mobile1/include \

libdrm2:frameworks/base/media/libdrm/mobile2/include \

libhardware:hardware/libhardware/include \

libhardware_legacy:hardware/libhardware_legacy/include \

libhost:build/libs/host/include \

libm:bionic/libm/include \

libnativehelper:dalvik/libnativehelper/include \

libpagemap:system/extras/libpagemap/include \

libril:hardware/ril/include \

libstdc++:bionic/libstdc++/include \

libthread_db:bionic/libthread_db/include \

mkbootimg:system/core/mkbootimg \

recovery:bootable/recovery \

system-core:system/core/include

#

# Returns the path to the requested module's include directory,

# relative to the root of the source tree. Does not handle external

# modules.

#

# $(1): a list of modules (or other named entities) to find the includes for

#

define include-path-for

$(foreach n,$(1),$(patsubst $(n):%,%,$(filter $(n):%,$(pathmap_INCL))))

endef

上面的宏函数include-path-for使用了3个make内嵌函数：foreach，patsubst，filter。

foreach：

它是一个循环函数，类似于Linux的shell中的for语句，语法格式如下：

$(foreach VAR, LIST, TEXT)

include-path-for宏函数中：

VAR = n (是一个临时变量，只在foreach函数上下文中有效)

LIST = $(1) ( 是call include-path-for 时传递进来的参数，可以使很多空格隔开的字符串)

TEXT = $(patsubst $(n):%,%,$(filter $(n):%,$(pathmap_INCL))) (是每次循环时执行的表达式)

foreach函数和c语言中的如下格式的for循环类似：

for( int n, int i=0 ; i < number(LIST); i++)

{

n = LIST第一个字符串;

执行TEXT(引用n)表达式;

LIST丢掉第一个字符串

}

filter：

过滤函数，$(filter PATTERN…,TEXT)

过滤掉字串“TEXT”中所有不符合模式“PATTERN”的单词，保留所有符合此模式的单词。可以使用多个模式。模式中一般需要包含模式字符“%”。存在多个模式时，模式表达式之间使用空格分割。

sources := foo.c bar.c baz.s ugh.h

foo: $(sources)

cc $(filter %.c %.s,$(sources)) -o foo

返回值为“foo.c bar.c baz.s”。

$(filter $(n):%,$(pathmap_INCL)), 滤除掉pathmap_INCL列表中不属于以:隔开的字符串模式的字符串。