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Release notes for the Genode OS Framework 9.02
Genode Labs
Whereas the focus of the previous release 8.11 was the refinement of
Genode's base API and the creation of the infrastructure needed to build
real-world applications, the release 9.02 is focused on functional
enhancements in two directions. The first direction is broadening the
number of possible base platforms for the framework. At present, most
microkernels bring along a custom user land, which is closely tied to the
particular kernel. Our vision is to establish Genode as a common ground for
developing applications, protocol stacks, and device drivers in such a way
that the software becomes easily portable among different kernels. This
release makes Genode available on the L4ka::Pistachio kernel. Hence,
software developed with the Genode API can now run unmodified on
Linux/x86, L4/Fiasco, and L4ka::Pistachio. In the second direction, we
are steadily advancing the functionality available on top of Genode. With
this release, we introduce a basic networking facility and support for
native Qt4 applications as major new features. Thanks to Genode's
portability, these features become automatically available on all
supported base platforms.
Our original plan for the release 9.02 also comprised the support of a
Linux-on-Genode (para-)virtualization solution. Initially, we intended to
make [ - L4Linux] available on
the L4/Fiasco version of Genode. However, we identified several downsides
with this approach. Apparently, the development of the officially available
version of L4/Fiasco has become slow and long-known issues remain unfixed.
L4Linux, however, is closely tied to L4/Fiasco and the L4 environment. For
us at Genode Labs, maintaining both a custom port of L4Linux for Genode
and L4/Fiasco by ourself in addition to developing Genode is unfeasible.
In contrast, the Pistachio kernel features more advanced options for
virtualization ([ - Afterburner]
and VT support) that we want to explore. Furthermore, there exists another
version of L4Linux called OKLinux for the OKL4 kernel developed at
[ - OK-Labs], which is very interesting as well.
Therefore, we decided against an ad-hoc solution and deferred this feature
to the next release. [http:/about/road-map - See our updated road map...]
Major new Features
Genode on L4ka::Pistachio
From the very beginning, the base API of the Genode OS Framework was
designed for portability. We put a lot of effort into finding API
abstractions that are both implementable on a wide range of kernels and as
close to the hardware as possible to keep the abstraction overhead low. For
this reason, we developed the framework in parallel for the Linux kernel and
the L4/Fiasco kernel. To validate our claim that Genode is highly portable,
Julian Stecklina ported the framework to another member of the L4 family,
namely the [ - L4ka::Pistachio kernel].
This high-performance kernel implements the latest official L4 API called
L4.x2 and has a number of advanced features such as multi-processor support
and virtualization support.
After Julian successfully created the first Pistachio version of Genode,
we successively refined his work and conducted further unifications among
the platform-dependent code for the different kernels. The result of this
effort is included in this release and comes in the form of the
'base-pistachio' source-code repository.
;Interesting technical notes:
* The IRQ handling on Pistachio is slightly different from L4/Fiasco.
On L4/Fiasco, an IRQ becomes unmasked only when the user-level IRQ
handler thread blocks for an IRQ by issuing an IPC call to the
kernel's corresponding IRQ thread. In contrast, Pistachio unmasks an
IRQ as soon as the user-level IRQ handler associates itself with an
IRQ. Thus, an IRQ message may occur not only when the user-level IRQ
handler blocks for any IRQ but anytime. In particular, IRQ messages
may interfere with the IRQ handler's IPC communication with other
threads. To ensure that IRQ messages do only occur when expecting
them, we lazily associate the IRQ handler thread to the IRQ the
first time we wait for an IRQ and issue an unmasking IPC call
subsequent times.
* Genode provides a mechanism for gracefully destructing threads that
are in a blocking state, for example waiting for an IPC message.
Such a thread may hold locks or other resources that would not
get properly freed when just killing the thread by force. Therefore,
Genode provides a way to issue the cancellation of a blocking
operation by another thread (e.g., the thread calling the destructor).
Once, a blocking operation got canceled, a C++ exception
('Blocking_canceled') is raised such the thread can fall back into
a defined state and then be destructed. On L4ka::Pistachio, we use
Pistachio's pager-exchange-registers feature in combination with
the user-defined UTCB handle for cancelling blocking operations and
detecting cancellations. The interesting code bits can be found in
'src/base/ipc/', 'src/base/lock/',
'src/core/', and in the Pistachio-specific
timer-service implementation.
* During the refinement of the Pistachio version, we were able to further
generalize code that was previously specific for L4/Fiasco and
L4ka::Pistachio respectively. Now, the platform-specific code comprises
less than 3,000 lines of code (LOC) for L4/Pistachio, circa 2,000 LOC
for L4/Fiasco, and circa 1,000 LOC for Linux. Hence, we expect that
porting the framework to further kernels is possible at reasonable
engineering costs.
:Current limitations:
* The current version does not use superpages (4M mappings) because we
experienced problems with mapping 4K pages out of 4M pages. This is an
issue that we like to investigate further because using 4M mappings
would improve the boot time and reduce the kernel-memory usage.
* Currently, we use a simple sleeping spinlock for synchronization, which
is not optimal for several reasons. There are no fairness guarantees,
the spinning consumes CPU time, and threads that got blocked in the
contention case are woken up at the coarse granularity of the kernel's
timer tick, which is typically one millisecond.
* Nested RM sessions as introduced as an experimental feature in the
Genode release 8.11 are not yet supported.
:Further details:
You can find further technical details and usage instructions at this
dedicated [ - page].
Qt4 on Genode
The minimalism of the Genode OS Framework with regard to its code
complexity raised the question of whether this framework is feasible
for hosting real-world applications and widely used runtime environments.
Christian Prochaska took the challenge to port Trolltech's Qt4 application
framework, which serves as the basis for the popular KDE desktop, to Genode.
Because Christian started his work more than a year ago at a time when no
C library was available on Genode, several intermediate steps were needed.
The first step was the integration of the Qt4 tools such as the meta-object
compiler (moc) and resource compiler properly into the our build systion.
With the tools in place, the Linux version of Genode came to an advantage.
In this environment, a Genode application is able to use glibc functionality.
So the problem of a missing C library could be deferred and Christian was
able to focus on interfacing Qt with the existing Genode services such as
the Nitpicker GUI sever. Next, the glibc dependencies were successively
replaced by custom implementations or simple dummy stubs. Thereby, all
needed functionalities such as timed semaphores and thread-local storage
had to be mapped to existing Genode API calls. Once, all glibc dependencies
had been dissolved, Qt could be compiled for the L4/Fiasco version.
Since a C library has become available in Genode 8.11, we were able to
replace Christian's intermediate stub codes with a real C library. We also
utilize recently added features of Genode such as its alarm framework to
simplify the Qt4 port. Furthermore, we were able to remove all
platform-specific bits such that the Qt4 port has now become completely
generic with regard to the underlying kernel. Qt4 can be executed on Linux,
L4/Fiasco, and L4ka::Pistachio without any changes. Figure [qt4_screenshot]
shows a screenshot of Qt's Tetrix example running side-by-side with native
Genode applications.
[image qt4_screenshot]
:Current state:
* The Qt4 port comes in the form of a source-code repository, which contains
all Qt source codes, and some example programs such as Tetrix. You can
download the Qt4 repository as a separate archive at the download page of
the Genode release 9.2. For the next release, we plan to separate the
Genode-specific parts from Qt original code and make the Genode-specific
parts a regular component of the Genode main line.
* The Qt4 port consists of Qt's Core library, GUI library, Script library,
XML library, and the UI tools library. Other libraries such as Webkit
are not ported yet.
* This first version of Qt4 on Genode is not to be considered as stable.
There are several known issues yet to be addressed. In particular,
the 'QEventDispatcher' is still work in progress and not fully stabilized.
* Because, we use to statically link programs, the binaries of Qt
applications are exceedingly large. For example the Tetrix binary is
100MB including debug information and 11MB in the stripped form. For
employing Qt on Genode at a larger scale, Genode should be enhanced with
shared-library support.
With Genode 8.11, we introduced the Device-Driver-Environment Kit (DDE Kit)
API, which is a C API specifically designed for implementing and porting
device drivers written in plain C. We have now complemented DDE Kit with an
environment for executing Linux device drivers natively on Genode. This
library is called 'dde_linux26' and contained in our new 'linux_drivers'
source-code repository. The environment consists of several parts, which
correspond to the different sub systems of the Linux kernel 2.6, such as
'arch', 'drivers', 'kernel'.
The first class of device-drivers supported by DDE Linux 2.6 is networking.
At the current stage, the DDE Linux network library comprises general
network-device infrastructure as well as an exemplary driver for the PCnet32
network device.
Based on this library, we have created a basic TCP/IP test utilizing the
uIP stack, which uses the DDE Linux network library as back end. The test
program implements a basic web server displaying uIP packet statistics.
When executed on Qemu, you can use your host's web browser to connect to
the web server running on Genode:
For booting Genode on L4/Fiasco with the web-server demo, use a GRUB
entry in your 'menu.lst' file as follows.
! title Genode: DDE Linux 2.6 NET on L4/Fiasco
! kernel /fiasco/bootstrap -maxmem=64 -modaddr=0x02000000
! module /fiasco/fiasco -nokd -serial -serial_esc
! module /fiasco/sigma0
! module /genode/core
! module /genode/init
! module /config
! module /genode/timer
! module /genode/pci_drv
! module /genode/test-dde_linux26_net
The first four lines are L4/Fiasco specific. When using L4ka::Pistachio,
the 'menu.lst' entry looks like this:
! title Genode: DDE Linux 2.6 NET on L4/Pistachio
! kernel /pistachio/kickstart
! module /pistachio/x86-kernel
! module /pistachio/sigma0
! module /genode/core
! module /genode/init
! module /config
! module /genode/timer
! module /genode/pci_drv
! module /genode/test-dde_linux26_net
The web-server test requires the PCI bus driver and the timer service.
Therefore, the 'config' file for Genode's init should have following
! <config>
! <start>
! <filename>timer</filename>
! <ram_quota>512K</ram_quota>
! </start>
! <start>
! <filename>pci_drv</filename>
! <ram_quota>512K</ram_quota>
! </start>
! <start>
! <filename>test-dde_linux26_net</filename>
! <ram_quota>16M</ram_quota>
! </start>
! </config>
Now, its time to create an ISO image from all files specified in
the GRUB configuration. For this, the new utility 'tool/create_iso'
becomes handy. The ISO image can then be booted on Qemu using the
following arguments:
! qemu -m 64 -serial stdio -no-kqemu -cdrom <iso-image> \
! -net nic,model=pcnet -net user -redir tcp:5555::80
The '-redir' argument tells qemu to redirect TCP connections with
localhost:5555 to the guest OS at port 80. After having booted
up Genode on Qemu, you can use your host's web browser to access
the web server:
! firefox http://localhost:5555
:Notes about using the TAP version:
* Preparations
* You must be permitted to sudo and have installed the tunctl
utility. Under Debian/Ubuntu execute
! sudo apt-get install uml-utilities
* Create TAP device
! TAPDEV=$(sudo tunctl -b -u $USER)
! sudo /sbin/ifconfig $TAPDEV
* setup DHCP server on $TAPDEV and
* Run qemu
! qemu -m 64 -serial stdio -no-kqemu -cdrom dde.iso \
! -net nic,model=pcnet \
! -net tap,ifname=$TAPDEV,script=no,downscript=no
* Ping
* Cleanup
* Stop DHCP server
* Remove TAP device
! sudo tunctl -d $TAPDEV
Operating-system services and libraries
C Runtime
We have replaced the 'malloc' implementation of the original FreeBSD C
library with a custom implementation, which relies on Genode's 'Heap' as
allocator. The FreeBSD libc reserves a default memory pool of 1MB, which
is no problem on FreeBSD because virtual memory is backed lazily with
physical pages on demand. On Genode however, we immediately account the
allocated memory, which implicates high quota requirements even for
applications that use little memory. In contrast, Genode's heap allocates
and accounts its backing store in relatively small chunks of a few KB.
Therefore, the quota accounting for applications is much more in line with
the actual memory usage. Furthermore, our custom 'malloc' implementation
has the additional benefit of being thread safe.
* Added i386-specific parts of gen lib, in particular longjmp, setjmp.
Device-Driver-Environment Kit
* The DDE Kit uses our alarm framework (located in the 'os' repository) now
rather than its own event-scheduler implementation formerly called 'Tick'.
* We refined the DDE Kit API and reduced the number of custom types. For
example, we removed the custom 'dde_kit_lock_t' and using
'struct dde_kit_lock' instead, and replaced 'dde_kit_thread_t' with
'struct dde_kit_thread'.
Because of the apparent stabilization of the DDE Kit API, we have now added
this API to Genode's official API reference.
[ - See the documentation of the DDE Kit API...]
PS/2 input driver
We improved the PS/2 keyboard driver by adding missing scan-code translations
for the scan code set 1, in particular the cursor keys.
Launchpad configuration
Launchpad is a graphical application for interactively starting and killing
programs. It is used for the default demonstration of Genode. By default,
launchpad displays a preconfigured list of programs and their respective
default memory quotas. The user can tweak the memory quota for each entry
with mouse and then start a program by clicking on its name. As an
alternative to using the default list, you can now define the list manually
by supplying a configuration to Launchpad. The following example tells
launchpad to display a list of two launcher entries:
! <launcher>
! <filename>sdl_pathfind</filename>
! <ram_quota>10M</ram_quota>
! </launcher>
! <launcher>
! <filename>liquid_fb</filename>
! <ram_quota>10M</ram_quota>
! </launcher>
To use this configuration for a Launchpad started via init, you can simply
insert the launchpad configuration into the '<start>' node of the launchpad
entry in init's 'config' file.
Platform-specific changes
* Raise 'Blocking_canceled' exceptions on canceled IPC calls
32-bit Linux
* We continued dissolving the dependency of Genode from the glibc by using
a custom 'getenv' implementation used during process creation.
* By default, we compile now with '-nostdinc' and explicitly specify
'/usr/include' as include search directory only when needed. Previously,
a Genode application, which included a host include file by mistake, has
not raised any compilation error when compiled for the Linux version of
Genode. Now, all Genode platforms behave equally with regard to include
search directories.
* We enforce using the actual compiler's C++ support libraries rather than
the default libraries installed on the host.
Tools and build infrastructure
Official tool chain
At the download section of our website, we used to provide a crosstool-based
tool chain as pre-compiled binaries. Since we got several requests about
how to build such a tool chain from scratch, we created custom utility for
downloading, building, and installing the official Genode tool chain. You
can find the utility at 'tool/tool_chain'. For usage instructions, just
start 'tool_chain' without arguments. Because this utility is a plain script,
you can follow and verify each step that we use for creating the Genode tool
chain. Currently, this official tool chain is based on binutils 2.18 and
gcc 4.2.4.
As an alternative to installing the tool chain from source, we also
provide pre-compiled binaries at the download section of our website.
[ - Visit our tool-chain download website...]
For the Linux version of Genode, we still use the host's default gcc
as tool chain. This way, we spare the hassle of downloading and installing
a custom tool chain for somebody who wants to give Genode a quick try.
With this is mind, we have fixes several small issues with gcc 4.3.2:
* Fixed dependency generation for gcc-4.3.2. Older version of gcc used to
append a '.o' dependency at the target of '.d'-files. However, gcc-4.3.2
seems to handle the option '-MT' differently, resulting in a rule that
contains only the '.d' as target. Now, we explicitly specify both the
'.o' file and the '.d' file as target. Consequently, on older gcc
versions, the '.o' file appears twice but that is no problem.
* Fixed assembler issue with the 'fnstsw' instruction in the C library.
This instruction does not accept eax but only ax as argument.
Build-directory creation tool
We added a rule for creating a pre-configured build directory for the
Pistachio version to our build-directory creation tool
('tool/builddir/create_builddir'). Furthermore, we changed the default
build configuration such that the official Genode tool chain is used for
L4/Fiasco and L4ka::Pistachio.
Build system
* Improved clean rule - visit each target directory only once
* Stop the build process on the first error by default, for continuing
the build process depite of an error, you can use the '-i' argument
of make.
* Compiler flags can now be set specific for compiling C and C++ sources.
This is needed because both variants allow different sets of warning
options. The new variables are called 'CC_CXX_OPT' and 'CC_C_OPT'.
ISO image creation tool
We have created a convenient front end for 'genisoimage', which we
use for testing Genode on Qemu. You can find this ISO-image-creation
tool at 'tool/create_iso'. For usage instructions, simply start the
tool without arguments.