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 ?
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}"