====== Variables ======

==== Auto override ====
<code make>
# Create an automatic OVERRIDE for everything under src/
AUTO_OVERRIDES = $(notdir $(wildcard $(BR2_EXTERNAL)/src/*)))
do_override = $(1)_OVERRIDE_SRCDIR = $(BR2_EXTERNAL)/src/$(2)
$(foreach override,$(AUTO_OVERRIDES),\
        $(eval $(call do_override,$(call UPPERCASE,$(override)),$(override))))

#(this snippet is licensed GPLv2+). 
#by Arnout Vandecappelle (Essensium/Mind) 
</code>

==== Variables ====
| **$(@D)** | which contains the directory in which the package source code has been uncompressed. |
| **$(FOO_DIR)** | same as **$(@D)** |
| **$(FOO_PKGDIR)** | contains the path to the directory containing the foo.mk and Config.in files.|
| **$(HOST_DIR)** | |
| **$(STAGING_DIR)** | |
| **$(TARGET_DIR)** | |


==== Cross compilation ====
Variables are defined in //buildroot/package/Makefile.in//

| **$(TARGET_CC)**  | cross compiler gcc binary (i.e.: TARGET_CC=/home/user/project/out/host/usr/bin/ccache /home/user/project/out/host/usr/bin/arm-linux-gcc) |
| **$(TARGET_AR) | 
| $(TARGET_AS) | 
| $(TARGET_CPP) |
| $(TARGET_CXX) | 
| _FC _LD _NM | _RANLIB | _READELF | _OBJCOPY | 
| _OBJDUMP** |
| **$(TARGET_CC_NOCCACHE)** |
| **$(TARGET_CXX_NOCCACHE)** |

| **$(TARGET_CFLAGS)** | (i.e: TARGET_CFLAGS=-D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64  -pipe -Os -g2) |
| **$(TARGET_CPPFLAGS)** |
| **$(TARGET_CXXFLAGS)** |
| **$(TARGET_LDFLAGS)** |

| **$(TARGET_MAKE_ENV)** | env which has to be set for cross compilation. 
It overrides search path, to get cross compiler first. (i.e:PATH="/home/user/project/out/host/bin:/home/user/project/out/host/ ...) |
| $(TARGET_DIR) | device root filesystem (i.e: needed for installing packages into $(TARGET_DIR)/usr/bin)|
| $(STAGING_DIR) | development target root filesystem (contains all needed libraries to build other packages, contains debug info and not stripped binary)|

Additional variables (not needed in normal use)
| **$(CCACHE)** | full path to ccache binary or empty (i.e: CCACHE=/home/user/project/out/host/usr/bin/ccache) |
| **$(TARGET_CROSS)** | prefix with full path to cross compiler (i.e: TARGET_CROSS=/home/user/project/out/host/usr/bin/arm-linux-) |
| **$(ABI)** | gnueabi[hf] eabi[hf] |
| **$(GNU_TARGET_NAME)** | GNU_TARGET_NAME=arm-buildroot-linux-uclibcgnueabi |


=== Example ===
<code>
################################################################################
#
# genromfs
#
################################################################################

GENROMFS_VERSION = 0.5.2
GENROMFS_SITE = http://downloads.sourceforge.net/project/romfs/genromfs/$(GENROMFS_VERSION)
GENROMFS_LICENSE = GPLv2+
GENROMFS_LICENSE_FILES = COPYING

define GENROMFS_BUILD_CMDS
        $(TARGET_MAKE_ENV) $(MAKE) -C $(@D) \
                CC="$(TARGET_CC)" \
                CFLAGS="$(TARGET_CFLAGS)" \
                LDFLAGS="$(TARGET_LDFLAGS)"
endef

define GENROMFS_INSTALL_TARGET_CMDS
        $(TARGET_MAKE_ENV) $(MAKE) -C $(@D) PREFIX=$(TARGET_DIR) install
endef

define HOST_GENROMFS_BUILD_CMDS
        $(HOST_MAKE_ENV) $(MAKE) -C $(@D)
endef

define HOST_GENROMFS_INSTALL_CMDS
        $(HOST_MAKE_ENV) $(MAKE) -C $(@D) PREFIX=$(HOST_DIR) install
endef

$(eval $(generic-package))
$(eval $(host-generic-package))
</code>

=== LUA ===
<code>
LUAPOSIX_CONF_OPTS = --libdir="/usr/lib/lua/$(LUAINTERPRETER_ABIVER)" --datarootdir="/usr/share/lua/$(LUAINTERPRETER_ABIVER)"
</code>

<code>
define LUAEXPATUTILS_INSTALL_TARGET_CMDS
$(INSTALL) -m 0644 -D $(@D)/lua/doc.lua >$(TARGET_DIR)/usr/share/lua/$(LUAINTERPRETER_ABIVER)/lxp/doc.lua
endef
</code>

<code makefile>
define LUA_MSGPACK_NATIVE_BUILD_CMDS
        $(TARGET_CC) $(TARGET_CFLAGS) -fPIC -shared -o $(@D)/msgpack.so $(@D)/mp.c
endef

define LUA_MSGPACK_NATIVE_INSTALL_TARGET_CMDS
        $(INSTALL) -m 755 -D $(@D)/msgpack.so \
                $(TARGET_DIR)/usr/lib/lua/$(LUAINTERPRETER_ABIVER)/msgpack.so
endef

$(eval $(generic-package))
</code>