I feel like I must be doing something fundamentally wrong. I created a recipe based on a cmake project. Compiling the project using the toolchain yocto created is as simple as running cmake then make but it fails to compile using a recipe:
SUMMARY = "Opendnp3 is the de facto reference implementation of IEEE-1815 (DNP3)"
DESCRIPTION = "Opendnp3 is a portable, scalable, and rigorously tested implementation of the DNP3 (www.dnp.org) protocol stack written in C++11. The library is designed for high-performance applications like many concurrent TCP sessions or huge device simulations. It also embeds very nicely on Linux."
HOMEPAGE = "https://www.automatak.com/opendnp3"
SECTION = "libs"
DEPENDS = "asio"
LICENSE = "Apache-2.0"
LIC_FILES_CHKSUM = "file://NOTICE;md5=9788d3abe6c9401d72fdb3717de33e6a"
SRCREV = "e00ff31b837821064e5208c15866a9d46f8777b1"
SRC_URI = "git://github.com/automatak/dnp3;branch=2.0.x"
S = "${WORKDIR}/git"
inherit cmake
EXTRA_OECMAKE += ""
Problem is I think that the CXXFLAGS used for g++ don't appear to be consistent with the CXXFLAGS defined by the toolchain's environment. Mainly --sysroot is missing and g++ fails to find standard c++ headers (ex: cstdint).
I partially fixed the issue by overriding do_configure from cmake.bbclas simply by removing -DCMAKE_TOOLCHAIN_FILE=${WORKDIR}/toolchain.cmake. As a matter of fact CXXFLAGS are defined by toolchain.cmake as:
-march=armv7-a -mfpu=neon -mfloat-abi=hard -mcpu=cortex-a8 --sysroot=/home/star/moxa-build/tmp/work/cortexa8hf-neon-poky-linux-gnueabi/dnp3/2.2.0-r0/recipe-sysroot -O2 -pipe -g -feliminate-unused-debug-types -fdebug-prefix-map=/home/star/moxa-build/tmp/work/cortexa8hf-neon-poky-linux-gnueabi/dnp3/2.2.0-r0=/usr/src/debug/dnp3/2.2.0-r0 -fdebug-prefix-map=/home/star/moxa-build/tmp/work/cortexa8hf-neon-poky-linux-gnueabi/dnp3/2.2.0-r0/recipe-sysroot-native= -fdebug-prefix-map=/home/star/moxa-build/tmp/work/cortexa8hf-neon-poky-linux-gnueabi/dnp3/2.2.0-r0/recipe-sysroot= -fvisibility-inlines-hidden -march=armv7-a -mfpu=neon -mfloat-abi=hard -mcpu=cortex-a8 --sysroot=/home/star/moxa-build/tmp/work/cortexa8hf-neon-poky-linux-gnueabi/dnp3/2.2.0-r0/recipe-sysroot
So sysroot is defined (twice actually) as:
/home/star/moxa-build/tmp/work/cortexa8hf-neon-poky-linux-gnueabi/dnp3/2.2.0-r0/recipe-sysroot
but doesn't end up in the Makefile generated by cmake so I guess that something in toolchain.cmake makes the project's cmake configuration go south.
Turns out it was a cmake issue with the project itself. There was a merry mix-up between C and CXX flags in one of the included .cmake configuration file. I'll submit a pull request to the maintainer. CXXFLAGS being handled differently between the SDK (included directly in th CXX command) and by bitbake explained why it worked with the SDK (still not quite sure why it worked without toolchain.cmake though).
Thanks.
--sysroot is missing from CXXFLAGS because yocto stuffs it in the CXX variable itself. Note that alongside the sysroots directory yocto will have an environment-setup-XXX file which you should source. That's where all the sysroot stuff comes from.