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127 lines
6.9 KiB
Plaintext
127 lines
6.9 KiB
Plaintext
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=================
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Genode tool chain
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=================
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The Genode OS framework depends on the GNU C++ compiler and tool chain. As
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most GNU compilers shipped with standard Linux distributions include
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distro-specific patches and configurations, these tools do not meet Genode's
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special requirements (e.g., thread-local storage configuration). Therefore,
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there exists a special tool chain adapted to the specific requirements of
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Genode.
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Recommended development platform
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################################
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We use recent [https://www.ubuntu.com/ - Ubuntu] LTS releases on our
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development hosts. Hence, Genode should always build without trouble on these
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platforms.
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Unified tool chain
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##################
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Starting with Genode version 11.11, there is a unified tool chain for all base
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platforms and supported CPU architectures (x86_32, x86_64, ARM, and RISC-V). For
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Genode development, we highly recommend the use of the official Genode tool
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chain. It can be obtained in two ways: as pre-compiled binaries or manually
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compiled:
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:Pre-compiled:
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Our pre-compiled tool chain is runnable on Linux x86_32 and x86_64. The
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archives for both versions will be extracted to '/usr/local/genode-gcc'. To
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extract the archive, use the following command:
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! sudo tar xPfj genode-toolchain-<version>-<arch>.tar.bz2
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The use of the 'P' option ensures that the tool chain will be installed at
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the correct absolute path '/usr/local/genode-gcc' where the build system
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expects it to reside by default. Please note, Genode OS Framework releases
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require a Genode tool chain with an equal or next smaller version number.
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[https://sourceforge.net/projects/genode/files/genode-toolchain/ - Download the pre-compiled tool chain...]
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:Compile from source:
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For those of you who prefer compiling the tool chain from source, we provide
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a tool for downloading, building, and installing the Genode tool chain. You
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find the tool in Genode's source tree at 'tool/tool_chain'. For usage
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instructions, just start the tool without arguments.
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In both cases, the Genode tool chain will be installed to '/usr/local/genode-gcc'.
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All tools are prefixed with 'genode-x86-', 'genode-arm-', or 'genode-riscv-'
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respectively such that it is safe to add the installation directory to our
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'PATH' variable (optional). The Genode tool chain will be used by the Genode
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build system by default. If you desire to use a different tool chain, create a
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file called 'tools.conf' in the 'etc/' subdirectory of your build directory
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where you can define the tool-chain prefix to be used:
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! CROSS_DEV_PREFIX = /path/to/your/custom/tool_chain/your-x86-
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However, we recommend you to stick with the official Genode tool chain. If you
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see a valid reason not to use it, please contact us (e.g., via the mailing
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list).
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Background information - Why do we need a special tool chain?
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#############################################################
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Early on in the genesis of Genode, we introduced a custom tool chain to
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overcome several problems inherent to the use of standard tool chains installed
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on Linux host platforms.
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First, GCC and binutils versions vary a lot between different Linux systems.
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Testing the Genode code with all those different tool chains and constantly
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adapting the code to the peculiarities of certain tool-chain versions is
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infeasible and annoying. Second, Linux tool chains use certain features that
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stand in the way when building low-level system components. For example, the
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'-fstack-protector' option is enabled by default on some Linux distributions.
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Hence, we have to turn it off when building Genode. However, some tool chains
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lack this option. So the attempt to turn it off produces an error. The most
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important problem with Linux tool chains is the dependency of their respective
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GCC support libraries on the glibc. When not using a Linux glibc, as the case
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with Genode, this leads to manifold problems, most of them subtle and extremely
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hard to debug. For example, the support libraries expect the Linux way of
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implementing thread-local storage (using segment registers on x86_32). This
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code will simply crash on other kernels. Another example is the use of certain
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C-library functions, which are not available on Genode. Hence, Genode provides
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custom implementations of those functions (in the 'cxx' library).
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Unfortunately, the set of functions used varies across tool-chain versions. For
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these reasons, we introduced a custom configured tool chain where we mitigated
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those problems by pinning the tools to certain versions and tweaking the
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compiler configuration to our needs (i.e., preventing the use of Linux TLS).
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That said, the use a our custom configured tool chain was not free from
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problems either. In particular, the script for creating the tool chain relied
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on a libc being present on the host system. The header files of the libc would
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be used to build the GCC support libraries. This introduced two problems. When
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adding Genode's libc to the picture, which is based on FreeBSD's C library, the
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expectations of the GCC support libraries did not match 100% with the semantics
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implemented by Genode's libc (e.g., the handling of 'errno' differs). The
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second problem is the limitation that the tool chain could only be built for
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the platform that corresponds to the host. For example, on a Linux-x86_32
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system, it was not possible to build a x86_64 or ARM tool chain. For this
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reason we used the ARM tool chains provided by CodeSourcery.
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With Genode 11.11, we addressed the root of the tool-chain problem by
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completely decoupling the Genode tool chain from the host system that is used
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to build it. The most important step was the removal of GCC's dependency on
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a C library, which is normally needed to build the GCC support libraries. We
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were able to remove the libc dependency by sneaking-in a small custom libc stub
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into the GCC build process. This stub comes in the form of the single header
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file 'tool/libgcc_libc_stub.h' and brings along all type definitions and
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function declarations expected by the support-library code. Furthermore, we
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removed all GNU-specific heuristics from the tool chain. Technically, the
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Genode tool chain is a bare-metal tool chain. But in contrast to existing
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bare-metal tool chains, C++ is fully supported.
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With the libc dependency out of the way, we are now free to build the tool
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chain for arbitrary architectures, which brings us two immediate benefits. We
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do no longer have to rely on the CodeSourcery tool chain for ARM. There is now
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a 'genode-arm' tool chain using the same compiler configuration as used on x86.
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The second benefit is the use of multiarch libs on the x86 platform. The
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genode-x86 tool chain can be used for both x86_32 and x86_64 as build target,
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the latter being the default.
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Since we introduced GDB support into Genode, we added GDB in addition to GCC
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and binutils to the Genode tool chain. The version is supposed to match the one
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expected by Genode's GDB facility, avoiding potential problems with mismatching
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protocols between GDB monitor and GDB.
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