Overriding Build Options

Some packages might require overriding certain build options because we are cross compiling.

The build system allows for several entries under Advanced configuration options (for developers) > Kernel extra CFLAGS and Advanced configuration options (for developers) > Target Options which will pass the defined flags onto the kernel and packages respectively.

CONFIGURE_VARS

1. Override ac_cv_* variables that are normally set during autoconf ./configure phase.
2. override pkgconfig configure vars

Example: Some packages check for features (header files) and do not offer -enable/-with or -disable/-without configure options (to be written into _ARGS). Search for the configure variable in config.log and preset it in CONFIGURE_VARS.

      CONFIGURE_VARS += \
              ac_cv_header_regex_h=no

CONFIGURE_ARGS

1. Add options/test after ./configure

Looking into config.log can help

Available compiler flags are handled in rules.mk

TARGET_CFLAGS:=$(TARGET_OPTIMIZATION)$(if $(CONFIG_DEBUG), -g3) $(EXTRA_OPTIMIZATION)
TARGET_CXXFLAGS = $(TARGET_CFLAGS)
TARGET_ASFLAGS_DEFAULT = $(TARGET_CFLAGS)
TARGET_ASFLAGS = $(TARGET_ASFLAGS_DEFAULT)
TARGET_CPPFLAGS:=-I$(STAGING_DIR)/usr/include -I$(STAGING_DIR)/include
TARGET_LDFLAGS:=-L$(STAGING_DIR)/usr/lib -L$(STAGING_DIR)/lib

Typically you should only add additional options to compile flags.

TARGET_CFLAGS+= -Wall

Example: Support multiple library versions via .../usr/lib/libname-v1/ or .../usr/lib/libname-v2/ and select them.

BUG CXXFLAGS can contain wrong options because GCC/G++ accept different ones.

MAKE_VARS in include/package-defaults.mk

MAKE_VARS = \
        CFLAGS="$(TARGET_CFLAGS) $(EXTRA_CFLAGS) $(TARGET_CPPFLAGS) $(EXTRA_CPPFLAGS)" \
        CXXFLAGS="$(TARGET_CXXFLAGS) $(EXTRA_CXXFLAGS) $(TARGET_CPPFLAGS) $(EXTRA_CPPFLAGS)" \
        LDFLAGS="$(TARGET_LDFLAGS) $(EXTRA_LDFLAGS)"

MAKE_FLAGS

MAKE_FLAGS = \
        $(TARGET_CONFIGURE_OPTS) \
        CROSS="$(TARGET_CROSS)" \
        ARCH="$(ARCH)"

include/cmake.mk

CMAKE_OPTIONS

CMAKE_HOST_OPTIONS

SCONS_VARS are set in include/scons.mk

SCONS_VARS = \
        CC="$(TARGET_CC_NOCACHE)" \
        CXX="$(TARGET_CXX_NOCACHE)" \
        CFLAGS="$(TARGET_CFLAGS) $(EXTRA_CFLAGS)" \
        CXXFLAGS="$(TARGET_CFLAGS) $(EXTRA_CFLAGS)" \
        CPPFLAGS="$(TARGET_CPPFLAGS) $(EXTRA_CPPFLAGS)" \
        LDFLAGS="$(TARGET_LDFLAGS) $(EXTRA_LDFLAGS)" \
        DESTDIR="$(PKG_INSTALL_DIR)"

SCONS_OPTIONS have no default set.

scons is only used by a few packages: iotivity smartsnmpd