Overview
Sometime it could be convenient to generate FreeBSD binaries on the Linux host. Just a few examples:
- CI/CD deployment with a compilation check on the Linux Containers. It is especially the case for the SaaS environments where you are not able to select another OS (or it is not supported by the vendor)
- Ability to automatically generate binaries for the all supported platforms with a minimal cost/efforts.
- Using single docker or other linux-specific technology to cover all platforms.
I am using osxcross without any problem to generate OSX binaries, so decided to do the same with FreeBSD. This article shows how to do this and will provide some automated examples.
Using GCC
Most of the articles in the net i found are recommending to use GCC, which is default compiler on Linux distributions. GCC supports cross-compilation natively, but to achieve this you need to build entire kit from scratch.
Short overview of the process:
- Compile install latest binutils with
--target=x86_64-pc-freebsd10configure argument. - Get FreeBSD libs/includes and install them to the buildroot location
- Compile and install GMP with
--host=x86_64-pc-freebsd10configure argument. - Compile and install MPC with
--host=x86_64-pc-freebsd10configure argument. - Finally compile GCC, you will have to specify sysroot path and all the libs location. Also you will have to manually define
#define HAVE_ALIGNED_ALLOC 1due to bug in the GCC autoconf scripts.
I created Dockerfile with all steps mentioned. GCC natively supporting only libstdc++ which is not available on the FreeBSD. Below is an example:
root@96de1e64fff1:/# /opt/cross-freebsd/bin/x86_64-pc-freebsd10-c++ -o helo helo.cpp root@96de1e64fff1:/# file helo helo: ELF 64-bit LSB executable, x86-64, version 1 (FreeBSD), dynamically linked, interpreter /libexec/ld-elf.so.1, for FreeBSD 10.3, not stripped root@96de1e64fff1:/# readelf -d helo|grep NEEDED 0x0000000000000001 (NEEDED) Shared library: [libstdc++.so.6] 0x0000000000000001 (NEEDED) Shared library: [libm.so.5] 0x0000000000000001 (NEEDED) Shared library: [libgcc_s.so.1] 0x0000000000000001 (NEEDED) Shared library: [libc.so.7]
You can override this by overriding this using compiler/linker flags:
root@96de1e64fff1:/# /opt/cross-freebsd/bin/x86_64-pc-freebsd10-c++ -std=c++11 -I/opt/cross-freebsd/x86_64-pc-freebsd10/usr/include/c++/v1 -nostdinc++ -nodefaultlibs -lc++ -lm -lc -lgcc_s -lgcc -o helo helo.cpp root@96de1e64fff1:/# readelf -d helo|grep NEEDED 0x0000000000000001 (NEEDED) Shared library: [libc++.so.1] 0x0000000000000001 (NEEDED) Shared library: [libcxxrt.so.1] 0x0000000000000001 (NEEDED) Shared library: [libm.so.5] 0x0000000000000001 (NEEDED) Shared library: [libc.so.7] 0x0000000000000001 (NEEDED) Shared library: [libgcc_s.so.1]
Some comments on the commandline:
-std=c++11 -nostdinc++needed to avoid errors on libc++ headers-nodefaultlibs -lc++ -lm -lc -lgcc_s -lgccwill tell gcc to not use with a predefined libraries but to use libc++ instead.
Problems with GCC cross-build:
- Entire build chain need to be built from scratch. Not a big issue if you are using containers, but still takes some time to maintain it.
- Natively only
libstdc++is supported which is now not part of the FreeBSD installation. To workaround this you can provide it with your code or to build static. It is possible to uselibc++instead but this required a lot of custom flags and may not work reliable. - Natively FreeBSD is not using gcc (with only exception of some ports), so behavior of the resulted code may be different due to some compiler differences.
Using Clang
After all i decided to take another approach. Clang is now (starting from FreeBSD 10) default compiler, as well as libc++ is used instead of libstdc++. Great news is that clang already supports cross-compilation without need to completely recompile entire toolset. I been able to get working FreeBSD binaries on default Ubuntu LTS buildhost.
Below is a part of the Dockerfile to fetch required headers and libraries, install them to /opt/cross-freebsd-10 and fix broken links:
# Get FreeBSD libs/headers, extract and fix broken links
RUN cd /tmp && wget http://ftp.plusline.de/FreeBSD/releases/amd64/10.4-RELEASE/base.txz \
&& mkdir -p /opt/cross-freebsd-10 \
&& cd /opt/cross-freebsd-10 \
&& tar -xf /tmp/base.txz ./lib/ ./usr/lib/ ./usr/include/ \
&& cd /opt/cross-freebsd-10/usr/lib \
&& find . -xtype l|xargs ls -l|grep ' /lib/' \
| awk '{print "ln -sf /opt/cross-freebsd-10"$11 " " $9}' \
| /bin/sh && \
rm -f /tmp/base.txz
Now it is possible to create FreeBSD binaries using additional compiler flags: -target x86_64-unknown-freebsd10.0 --sysroot=/opt/cross-freebsd-10/
E.g.
root@4f9b820ae1c9:/# clang++ -target x86_64-unknown-freebsd10.0 --sysroot=/opt/cross-freebsd-10/ -o helo helo.cpp root@4f9b820ae1c9:/# file helo helo: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically linked, interpreter /libexec/ld-elf.so.1, for FreeBSD 10.4, not stripped
Resulted binary will run on FreeBSD host only.
Lets check dependencies:
root@4f9b820ae1c9:/# readelf -d helo|grep NEEDED 0x0000000000000001 (NEEDED) Shared library: [libc++.so.1] 0x0000000000000001 (NEEDED) Shared library: [libcxxrt.so.1] 0x0000000000000001 (NEEDED) Shared library: [libm.so.5] 0x0000000000000001 (NEEDED) Shared library: [libgcc_s.so.1] 0x0000000000000001 (NEEDED) Shared library: [libc.so.7]
As we could see dependencies are fine and matching normal FreeBSD 10.4 installation. Of course you may have many buildroots to simplify multiply targets.
Conclusion
It was found that both GCC and CLANG are able to cross-compile to FreeBSD using Linux host. However, CLANG require less efforts for this, mostly due to implemented -target switch and natively supported libc++ used by the FreeBSD project. I think it is better to use it for this task, with only exception if your source code has some strict GCC dependencies.
I implemented cross compilation to the FreeBSD as part of the CircleCI tests for the smartomontools project. I am planning to play with other targets (ARM, PPC) as well.
. Next thing is to define devices available on the board: button (GPIO-0), and DHT21 sensor (GPIO-14). Additionally i defined dummy device, which will be later used in the rules engine:
. Additionally you will have to create virtual devices (using virtual switch) in the DomoticZ for the Temperature + Humidity sensor and the switch. ID in devices section should match one from DomoticZ. Also you may want to setup syslogd ip to see logs from the device when not using serial. This is important, because in my case DHT sensor was not working properly when powered from TTL converter (properly not enough current) but its not possible to use serial when 220V is connected.
