Genode tool chain

The Genode OS framework depends on the GNU C++ compiler and tool chain. As most GNU compilers shipped with standard Linux distributions include distro-specific patches and configurations, these tools do not meet Genode's special requirements (e.g., thread-local storage configuration). Therefore, there exists a special tool chain adapted to the specific requirements of Genode.

Recommended development platform

We currently use Ubuntu 12.04 LTS on servers and client machines. Hence, Genode should always build without trouble on these platforms.

Unified tool chain

Starting with Genode version 11.11, there is a unified tool chain for all base platforms and supported CPU architectures (x86_32, x86_64, and ARM). For Genode development, we highly recommend the use of the official Genode tool chain. It can be obtained in two ways: as pre-compiled binaries or manually compiled:

Pre-compiled

Our pre-compiled tool chain is runnable on Linux x86_32 and x86_64. The archives for both versions will be extracted to /usr/local/genode-gcc. To extract the archive, use the following command:

 sudo tar xPfj genode-toolchain-<version>-<arch>.tar.bz2

The use of the P option ensures that the tool chain will be installed at the correct absolute path /usr/local/genode-gcc where the build system expects it to reside by default. Download the pre-compiled tool chain...

Compile from source

For those of you who prefer compiling the tool chain from source, we provide a tool for downloading, building, and installing the Genode tool chain. You find the tool in Genode's source tree at tool/tool_chain. For usage instructions, just start the tool without arguments.

In both cases, the tool chain will be installed to /usr/local/genode-gcc. All tools are prefixed with genode-x86- or genode-arm- respectively such that it is safe to add the installation directory to our PATH variable (optional). The Genode tool chain will be used by the Genode build system by default. If you desire to use a different tool chain, create a file called tools.conf in the etc/ subdirectory of your build directory where you can define the tool-chain prefix to be used:

 CROSS_DEV_PREFIX = /path/to/your/custom/tool_chain/your-x86-

However, we recommend you to stick with the official Genode tool chain. If you see a valid reason not to use it, please contact us (e.g., via the mailing list).

Background information - Why do we need a special tool chain?

Early on in the genesis of Genode, we introduced a custom tool chain to overcome several problems inherent to the use of standard tool chains installed on Linux host platforms.

First, GCC and binutils versions vary a lot between different Linux systems. Testing the Genode code with all those different tool chains and constantly adapting the code to the peculiarities of certain tool-chain versions is infeasible and annoying. Second, Linux tool chains use certain features that stand in the way when building low-level system components. For example, the -fstack-protector option is enabled by default on some Linux distributions. Hence, we have to turn it off when building Genode. However, some tool chains lack this option. So the attempt to turn it off produces an error. The most important problem with Linux tool chains is the dependency of their respective GCC support libraries on the glibc. When not using a Linux glibc, as the case with Genode, this leads to manifold problems, most of them subtle and extremely hard to debug. For example, the support libraries expect the Linux way of implementing thread-local storage (using segment registers on x86_32). This code will simply crash on other kernels. Another example is the use of certain C-library functions, which are not available on Genode. Hence, Genode provides custom implementations of those functions (in the cxx library). Unfortunately, the set of functions used varies across tool-chain versions. For these reasons, we introduced a custom configured tool chain where we mitigated those problems by pinning the tools to certain versions and tweaking the compiler configuration to our needs (i.e., preventing the use of Linux TLS).

That said, the use a our custom configured tool chain was not free from problems either. In particular, the script for creating the tool chain relied on a libc being present on the host system. The header files of the libc would be used to build the GCC support libraries. This introduced two problems. When adding Genode's libc to the picture, which is based on FreeBSD's C library, the expectations of the GCC support libraries did not match 100% with the semantics implemented by Genode's libc (e.g., the handling of errno differs). The second problem is the limitation that the tool chain could only be built for the platform that corresponds to the host. For example, on a Linux-x86_32 system, it was not possible to build a x86_64 or ARM tool chain. For this reason we used the ARM tool chains provided by CodeSourcery.

With Genode 11.11, we addressed the root of the tool-chain problem by completely decoupling the Genode tool chain from the host system that is used to build it. The most important step was the removal of GCC's dependency on a C library, which is normally needed to build the GCC support libraries. We were able to remove the libc dependency by sneaking-in a small custom libc stub into the GCC build process. This stub comes in the form of the single header file tool/libgcc_libc_stub.h and brings along all type definitions and function declarations expected by the support-library code. Furthermore, we removed all GNU-specific heuristics from the tool chain. Technically, the Genode tool chain is a bare-metal tool chain. But in contrast to existing bare-metal tool chains, C++ is fully supported.

With the libc dependency out of the way, we are now free to build the tool chain for arbitrary architectures, which brings us two immediate benefits. We do no longer have to rely on the CodeSourcery tool chain for ARM. There is now a genode-arm tool chain using the same compiler configuration as used on x86. The second benefit is the use of multiarch libs on the x86 platform. The genode-x86 tool chain can be used for both x86_32 and x86_64 as build target, the latter being the default.

Since we introduced GDB support into Genode, we added GDB in addition to GCC and binutils to the Genode tool chain. The version is supposed to match the one expected by Genode's GDB facility, avoiding potential problems with mismatching protocols between GDB monitor and GDB.