How to add global CXX compiler flag to yocto build - compiler-flags

Question

It seems something obvious to me, but I couldn't find any solution. Suppose I want to add or change a compiler flag/option which applies to all yocto recipes. It is possible to add a global flag somewhere, without changing the recipes ?

Answer 1

You can add it to the machine configuration file.
The machine configuration file is in the board support layer, under conf/machine. It is named $MACHINE.conf, where MACHINE is defined in your local.conf.
Here are the ones in poky 1.4. Yours might be in a layer outside of poky.
> ls -1 meta-yocto-bsp/conf/machine/
atom-pc.conf
beagleboard.conf
mpc8315e-rdb.conf
routerstationpro.conf
> ls -1 meta/conf/machine/
include
qemuarm.conf
qemumips.conf
qemuppc.conf
qemux86-64.conf
qemux86.conf
Once you identify your board configuration file, add a line to the end to add to your C Flags:
TARGET_CFLAGS += " <my flags> "

Answer 2

You can add global compiler options for Yocto builds in poky/meta/conf/bitbake.conf. After adding options, check the bitbake environment using the command bitbake -e
cat poky/meta/conf/bitbake.conf
...
...
##################################################################
# Build flags and options.
##################################################################
export BUILD_CPPFLAGS = "-isystem${STAGING_INCDIR_NATIVE}"
BUILDSDK_CPPFLAGS = "-isystem${STAGING_INCDIR}"
export CPPFLAGS = "${TARGET_CPPFLAGS}"
export BUILD_CFLAGS = "${BUILD_CPPFLAGS} ${BUILD_OPTIMIZATION}"
BUILDSDK_CFLAGS = "${BUILDSDK_CPPFLAGS} ${BUILD_OPTIMIZATION}"
export CFLAGS = "${TARGET_CFLAGS}"
export TARGET_CFLAGS = "${TARGET_CPPFLAGS} ${SELECTED_OPTIMIZATION}"
export BUILD_CXXFLAGS = "${BUILD_CFLAGS}"
export CXXFLAGS = "${TARGET_CXXFLAGS}"
export TARGET_CXXFLAGS = "${TARGET_CFLAGS}"