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===============================================
Release notes for the Genode OS Framework 10.08
===============================================
Genode Labs
The Genode project is back with the feature-packed release 10.08, set out to
bring device support of the Genode OS Framework to the next level. Our road
map hinted at two particular spots of activity, introducing wireless networking
and enabling hardware-accelerated graphics. To pursue the first goal, we pushed
the boundaries of our Linux device driver environment by porting Madwifi to
Genode. When it comes to hardware-accelerated graphics, today the Gallium3D
protocol stack and the corresponding GEM GPU drivers are the state of the art
on Linux and other UNIX-like operating systems. With the current release, we
make this powerful graphics architecture available on Genode, including
support for hardware-accelerated 3D graphics on Intel GMA GPUs. But we haven't
stopped with our device-driver related activities here as we introduce a new
ATAPI driver accommodated with an ISO9660 file-system implementation, and we
largely revisited our existing driver base.
Apart from device-driver support, two major features of the release are the
upgrade of the Qt4 framework from version 4.5.2 to version 4.6.3 alongside with
many performance and stability improvements, and the added support for dynamic
linking on ARM platforms with both the OKL4 and Codezero kernels.
Gallium3D and Intel's Graphics Execution Manager
################################################
Gallium3D is the most modern and most actively developed open-source software
stack regarding hardware-accelerated graphics. It is mainly deployed on
Linux but it has been ported to other operating systems such as the BSD family,
OpenSolaris, AROS, and now Genode. In the following, we will first provide
a little background about Gallium3D followed by a rough overview on how its
components fit into Genode.
Gallium3D was designed to displace the long-evolved but inherently insecure
direct rendering infrastructure on Linux. With DRI, each application that uses
hardware-accelerated graphics has unlimited access to the GPU and its resources
such as the frame buffer. To allow multiple applications to use the GPU in a
time-shared manner, those applications have to behave cooperatively. There is a
central service, the DRM driver in the kernel, orchestrating the applications
in such a way that well-behaved applications use distinct GPU resources such as memory
and contexts, and so come along nicely. However, there are no effective measures
against misbehaving applications. A further consequence of this architecture
is the multitude of vendor-specific protocol implementations. Because each
application contains an instance of the GPU driver accessing the broad hardware
interface of the graphics device, each vendor happened to take a different route
for translating graphics APIs such as OpenGL to the actual device interface.
Consequently, the code basis for graphics protocol stacks has become extremely
complex and fragmented. In contrast, the designers of Gallium3D set out to
modularize the protocol stack such that generic code is easy to use by different
vendors and the vendor-specific portion of the protocol stack stays as small as
possible, thereby lowering the costs for new-device support in the future.
In contrast to DRI, a Gallium-based application does not operate directly on
the GPU device. Instead, it uses a higher-level abstraction, namely buffer
objects for holding data operated on by the GPU. Buffer objects can contain
pixels, geometry data, and GPU command streams. The latter type of buffer
object can be issued for execution to perform actual GPU operations. The
buffer-object interface is provided by a central service called graphics
execution manager (GEM) normally residing in the kernel. GEM arbitrates the
allocation of buffer objects, manages cache coherency between GPU and CPU, and
passes buffers objects containing GPU command streams scheduled for execution to the
graphics device.
The high-complexity Gallium3D protocol stack is instantiated for each
application and acts as a client of the (relatively) low-complexity GEM.
Provided that the GPU command stream assembled by a Gallium3D application
cannot subvert the operation of GEM, this architecture removes the complex
protocol stack from the trusted computing base. Only the low-complexity GEM
service must be trusted with regard to security, robustness, and the absence
of GPU-based inter-application crosstalk. In contrast to DRI, Gallium3D is
perfectly in line with the architecturally principles of Genode. On Linux, the
Gallium3D stack communicates with GEM via 'ioctl' operations on the '/dev/drm/'
device interface. In the context of Genode, GEM should be executed as a
user-level device driver and resource multiplexer providing the GEM operations
as a GPU session interface by the means of RPC and shared memory. Each
Gallium3D application connects to the GPU server and operates on a GPU session.
The puzzle pieces of Mesa/Gallium3D
===================================
Gallium3D is part of the Mesa OpenGL library. It comes as a set of modules
consisting of state trackers (API implementations such as OpenGL),
drivers (translating generic graphics commands into device-specific command
streams), winsys (the glue between a window system and the Gallium3D
application), and a large library of utilities. Most of the code is
independent from the actual GPU device as well as the operating-system.
On Genode, Mesa-7.8.1 has been incorporated into the 'libports' repository.
However, we only use the Gallium3D-related parts of Mesa on Genode. For
example, the port does not make use of the Mesa swrast facility for
software-based rendering. It rather relies on the Gallium3D softpipe driver.
When built, all generic Gallium3D-related parts of Mesa are linked into the
single 'gallium.lib.so' library.
The following figure gives an overview of how the components of the graphics
software stack relate to each other. The components are described in the
following.
[image gallium3d]
EGL driver
~~~~~~~~~~
EGL is an OS-agnostic API for managing rendering buffers. The implementation
of this API is OS-specific because, among other things, it cares about the
interaction of the application with the native windowing system such that the
result of GPU-based rendering can be displayed in the GUI. EGL also plays a special
role among the Gallium state trackers because it is used by other state trackers.
The window-system-specific code is called EGL driver. Mesa-7.8.1 comes with
EGL drivers for the X window system and the Linux kernel-mode-switching
interface. For Genode, we have added a new EGL driver that uses Genode's
'Framebuffer_session' interface as back end. It is located at
'libports/src/lib/egl'. Because the EGL driver is GPU-independent, it is
part of 'gallium.lib.so'. The following screenshot shows the EGL driver
in action.
[image gallium_softpipe_screen]
Gallium i915 GPU driver
~~~~~~~~~~~~~~~~~~~~~~~
We picked Intel's GMA as the first series of supported GPUs because they
are well documented and GEM has been implemented first for Intel GPUs.
There are two Gallium3D drivers for Intel GPUs called i915 and i965.
Currently, we have ported the i915 driver that supports the following GPU
models: i915 G/GM, i945 G/GM/GME, G33G, Q33G, and Q35G. On Genode, the Gallium3D
GPU driver comes in the form of a shared library called 'gallium-i915.lib.so'.
Is gets dynamically loaded by the EGL driver using 'dlopen'. If the EGL
driver fails to load the 'gallium-i915.lib.so' driver, it falls back
to the softpipe driver compiled into 'gallium.lib.so'.
Because there is no build dependency to this shared library, we created a
pseudo build target at 'libports/src/lib/gallium/i915' for the sole purpose of
building this library as a side effect.
On Linux, the code contained in 'gallium-i915.lib.so' communicates with the '/dev/drm/'
device interface. However, the interaction with the device is not performed
directly but via a library called 'libdrm'.
libdrm
~~~~~~
The DRM library is a convenient front end to the '/dev/drm/' device. At
first glance, replacing this library with a Genode-specific implementation
seems natural. However, because 'libdrm' is not only a mere wrapper around the 'ioctl'
interface of the device but also contains a substantial amount of program logic
and device heuristics, we decided to reuse this library unmodified and go for
the 'ioctl' interface as a hook to connect Gallium3D with GEM. Hence, 'libdrm'
has become part of the 'libports' repository alongside Mesa. Ultimately,
'libdrm' translates all requests coming from 'gallium-i915.lib.so' to
(GPU-specific) 'ioctl' and 'mmap' operations on the '/dev/drm/' device. On
Genode, there is no such device. In fact, there are no device nodes at all.
Instead, we use our libc plugin mechanism to redirect operations on this
specific device file to a dedicated libc plugin. When 'libdrm' opens '/dev/drm/', the
libc plugin located at 'src/lib/libdrm/' takes over the responsibility of the
returned file descriptor. Therefore all file operations on this file handle are
handed over to the plugin. This is the point where we can transparently
incorporate RPC communication to the GEM service. For now, however, we do not
have RPC stub code yet. Instead, we link the GEM code directly into
'gallium-i915.lib.so'. This allows us to implement the GEM-related 'ioctl'
operations by calling GEM code directly. For the interaction between
'libdrm' and GEM, we added a preliminary 'Gpu_driver' interface located at
'os/include/gpu/'.
Graphics execution manager
~~~~~~~~~~~~~~~~~~~~~~~~~~
GEM is normally part of the Linux kernel and dispatches (a subset of)
operations on '/dev/drm/'. We use the Intel-specific GEM code taken from
Linux-2.6.34. This code relies on the Intel-AGP subsystem to manage the GPU's
graphics translation table. Therefore, we had to port the Intel-AGP sub system
as well. Because GEM is a relatively new feature of the Linux kernel, we
decided to not use our Linux device driver environment (currently based on the
kernel version 2.6.20) for our porting work but rather went for the creation
of a driver-specific Linux emulation environment. The code is part of the
'linux_drivers' repository and located at 'src/drivers/gpu/'. The 'contrib/'
subdirectory contains unmodified Linux code, the 'i915' subdirectory contains
the implementation of the 'Gpu_driver' interface and code for emulating Linux
interfaces in a way that the 'contrib/' code behaves like in its natural
execution environment.
Building an OpenGL application
==============================
As an example on how to build an OpenGL application on Genode, the 'libports'
repository provides a slightly modified version of the famous Gears demo.
You can find the code under 'libports/app/eglgears/'.
Prior building the application, make sure that you have issued 'make
prepare' for the 'mesa' and 'libdrm' libraries. In the root of the 'libports'
repository, issue the following commands to download the upstream source
codes for these libraries and to integrate them with the Genode build system:
! make prepare PKG=mesa
! make prepare PKG=libdrm
After having added 'libc' and 'libports' to the 'REPOSITORIES' declaration
of your '<build-dir>/etc/build.conf', you can building 'eglgears' via
'make app/eglgears'. The build process will create the 'eglgears' executable
alongside with 'gallium.lib.so'. You can start 'eglgears' using a plain
framebuffer such as 'vesa_drv'. The EGL driver included in 'gallium.lib.so'
will try to load a shared library called 'gallium-i915.lib.so' and, if not
present, revert to the softpipe driver.
If you want to give the hardware-accelerated version a spin, you will
need to build 'gallium-i915.lib.so'. The driver is only built when
the build 'SPECS' variable contains the keyword 'i915'. Simply add the
following line to your '<build-dir>/etc/specs.conf' file:
! SPECS += i915
Currently, the GEM (contained in the 'linux_drivers' repository') is
linked to 'gallium-i915.lib.so'. Hence, the 'linux_drivers' repository
must be specified in your 'build.conf'. The Gallium driver is built
as a side effect of building a pseudo target via:
! make lib/gallium
If you add the resulting 'gallium-i915.lib.so' to core's ROM service,
the EGL driver will attempt to use the hardware driver.
Current limitations
===================
At the current stage, Gallium3D on Genode is able to run the Gears
demo using Intel GMA GPUs. However, the work done so far must be
regarded as the first of several steps towards a complete solution.
Let us highlight the most important limitations and construction
sites:
* Both GEM and the Gallium3D protocol stack are executed as part of
a single process, accessing the GPU exclusively. Until we have
separated GEM from Gallium3D, only a single GPU-using application
can run at a time.
* Even though a Gallium3D application is able to use the GPU for
3D rendering, the EGL driver relies on CPU-based blitting
in order to transfer the rendering result to the screen.
* Interrupt-based synchronization has not been implemented yet. The
GPU is expected to be faster than the CPU. For this reason,
the EGL driver waits for 5 ms after each rendered frame.
Proper vblank handling is desired.
* On some platforms, we observed pixel artifacts, which
we attribute to cache coherency issues.
* Resource deallocation within the GEM driver has not been implemented
yet. Therefore, we expect that the current version is not suited for
highly dynamic applications.
* The 'eglgears' demo runs fine with resolutions up to 800x600
but we observed unstable behaviour with higher resolutions.
Despite of these limitations, the first version of Gallium3D on
Genode showcases that a subsystem as comprehensive as Gallium3D
plus GEM can be natively executed on Genode.
Operating-system services and libraries
#######################################
Init configuration concept
==========================
The previous release 10.05 introduced a new configuration concept that enables
the specification of mandatory access-control rules among flexible ways to
route service requests throughout the system. With the current release, this
concept is used by default. We have adapted all example configurations to the
new format, polished the new init implementation, and moved it from
'os/src/init/experimental/' to 'os/src/init/'. The old init variant is still
available at 'os/src/init/traditional/' but it is scheduled to be removed with
the next release 10.11.
The description of the configuration concept and the XML format is provided by
the document "Configuring the init process of Genode" located at
'os/doc/init.txt'.
Block session interface
=======================
The block session interface extends Genode's range of device-class interfaces by
a general-purpose interface to access block devices. It is based on the
packet-stream framework, using a single TX-stream to transmit block requests
to the server-side. Clients are free to request read/write operations on
several sequent blocks at once. Services implementing the server-side of the
block-session interface can choose an appropriate block size and the kind of
block-operation they support (e.g., read-only device). The new block session
interface is located at 'os/include/block_session/'.
ROM-loop block device
=====================
Based on the new block session interface, we implemented a service, which
provides a rom-file as read-only block-device. Linux users might know this
kind of service under the term "loop device". The following configuration
snippet shows how the file provided by a rom-session can be used as block
device:
! <config>
! ...
! <start name="rom_loopdev">
! <resource name="RAM" quantum="1M"/>
! <provides><service name="Block"/></provides>
! <config>
! <filename>livecd.iso</filename>
! </config>
! </config>
C runtime enhancements
======================
Both 'libc' and 'libm' are now built as *shared objects*, reducing the memory
footprint for scenarios with multiple libc-using applications. When starting
programs that use the libc, make sure to have 'libc.lib.so' and 'libm.lib.so'
available as files at the ROM service.
Motivated by our work on Gallium3D and libdrm, we extended the libc *plugin*
*interface* with the support of 'ioctl' and 'mmap'. This change enables us to
install custom handlers of those libc calls for a specific file. In the
particular case, libdrm performs 'ioctl' and 'mmap' calls referring to the
'/dev/drm' device interface. Now, we can supply a libc plugin specific for a
single file.
The update of Qt4 from version 4.5.2 to version 4.6.3 required refinements
of 'clock_gettime()', 'sysctl()', and 'getpagesize()'. Those functions
are still dummy stubs but with a meaningful behaviour from Qt4's perspective.
DDE Kit
=======
During our various device-driver activities, we improved the DDE Kit support
library for device-driver developments. The revised handling of I/O memory
resources now allows multiple requests of the same resource to support, e.g.,
multiple Linux 'ioremap()' calls. The I/O memory-mapping type is configurable
as uncached or write-combined, and DDE Kit automatically keeps track of
virtual-to-physical address mappings. Also, DDE Kit now provides 64-bit integer
types and a proper 'size_t'.
Dynamic linker
==============
In order to support shared libraries on ARM platforms, we added EABI support to
the dynamic linker and Genode's build-system environment. Thus shared libraries
are now supported on Codezero and OKL4 GTA01 targets. This also includes C++
exception handling.
Additionally, we implemented libc's dynamic linking interface ('dlfcn.h') and are
now able to support dynamic loading of libraries by applications via 'dlopen'
and friends.
Device drivers
##############
New ATAPI driver
================
With version 10.08, Genode provides a port of the low level ATA/ATPI driver
available from [http://ata-atapi.com]. Currently, the driver supports ATAPI
devices only and is implemented as a block-interface server (see Section
[Block session interface]). By default, the driver tries to take advantage of
the device's DMA engine but it can also operate in PIO mode as a fall-back
solution.
New wireless networking driver
==============================
According to our roadmap, we introduce initial support for wireless networking.
Based on DDE Linux 2.6, a port of the madwifi driver (version 0.9.4) is now
available for Genode. This driver supports widely used wifi-cards containing an
Atheros chipset (namely: 5210, 5211, 5212).
Due to the fact that part of the madwifi-project's contribution is binary code
in uuencoded form containing mandatory copyright headers, you need a 'uudecode'
binary installed on your system if you like to compile the madwifi driver for
Genode. If you're using Ubuntu/Debian or one of its derivates as your
development environment, you might install the necessary application via:
! sudo aptitude install sharutils
! emerge sharutils (on Gentoo)
This first wireless networking driver is in experimental stage and doesn't
support any form of encryption and authentication on the ieee80211 layer. So
you can only use it in conjunction with an unprotected access-point.
To set an appropriate ESSID you can tweak the driver's configuration, like in
the following example:
! <config>
! ...
! <start name="madwifi_drv">
! <resource name="RAM" quantum="2M"/>
! <provides><service name="Nic"/></provides>
! <config>
! <essid>My_access_point</essid>
! </config>
! </config>
When started, the 'madwifi_drv' announces a "Nic" session usable by the
lwIP stack.
PCI driver
==========
We enhanced the PCI bus scanning facility of our PCI driver with regard to
multi-function devices and added an accessor function for the physical
bus-device-function (BDF) ID.
VESA driver
===========
To support a wider range of graphics cards, we revised the VESA driver and
support more peculiarities of VBE implementations. Some of these are: unaligned
I/O port accesses, dependency on the physical BDF of PCI devices, support for
all flavours of PCI configuration space accesses.
PS/2 input driver
=================
Even after long years of intensive use, the PS/2 driver is sometimes good for a
surprise, which prompted us to improve the keyboard scan code and mouse button
handling. The driver fully supports scan code set 1 and 2 keyboards and copes
with oddities like "fake shift" events and "yet another scan code for Pause".
Timer
=====
The current release corrects a shortcoming of our timer driver on Pistachio and
Fiasco. Timing on these platforms is now more accurate.
Paravirtualized Linux
#####################
Based on the new block-session interface, we implemented a new stub driver
for OKLinux that enables the usage of a block-session device within Linux.
Thereby, the old stub driver that provided a ROM file as block device
is no longer needed and will be removed with the next release. A ROM file
can now be supplied to Linux via the new ROM loop service.
Protocol stacks and libraries
#############################
lwIP
====
Tweaking the configuration of the lightweight IP stack to better fit Genode's
application needs lead to a considerable improvement with respect to network
performance.
ISO9660 file system
===================
ISO9660 is the standard file system used on data CD/DVD medias. With the ATAPI
driver ready, we implemented ISO9660 support on top of the this driver. The
'iso9660' server implements the ROM-session interface and can be used by any
ROM connection. In order to take advantage of this new feature, we exploit
Genode's new configuration concept and route the client's ROM service
request to the ISO9660 server.
Configuration file snippet:
! <start name="atapi_drv">
! <resource name="RAM" quantum="1M" />
! <provides><service name="Block" /></provides>
! </start>
! <start name="iso9660">
! <resource name="RAM" quantum="10M" />
! <provides><service name="ROM" /></provides>
! </start>
! <start name="iso-client">
! <resource name="RAM" quantum="1M" />
! <route>
! <service name="ROM"><child name="iso9660"/></service>
! <any-service><parent /><any-child/></any-service>
! </route>
! </start>
:Limitations:
The memory necessary to read a file from the ATAPI driver into memory is
currently accounted on behalf of the ISO9660 server, not for the client side.
Because of this limitation, it becomes necessary to equip the ISO server with
a sufficient memory quota.
The 'Ecma-119' standard requires support for 8.3 upper-case file names only.
Because of this limitation, a number of unapproved ISO 9660 extensions have
evolved (eg. Joliet, Rock Ridge). Since we don't see using 8.3 file names within
Genode as an option, we added Rock Ridge extension support to the ISO 9660
server. Please make sure that your ISO-creation tool supports the Rock Ridge
extension and enable it during ISO creation.
Qt4.6.3
=======
We updated our port of the Qt4 framework from version 4.5.2 to version 4.6.3.
Thereby, we changed the way of how the source code is organized. Previously, we
maintained copies of modified files within the 'qt4' repository. Now, we
keep those changes in the form of patches, which get applied to the 'contrib'
code when 'make prepare' is issued within the 'qt4' repository. This change
significantly reduces the size of the 'qt4' repository. We applied the same
approach to the port of the Arora browser. Furthermore, the performance and
stability of Qt4 and Webkit in particular have received a lot of attention,
resulting in a much improved Arora browsing experience.
Platform-specific changes
#########################
OKL4
====
With the current release, we have started to maintain a few patches of the
official version of the OKL4v2 kernel. The patches are located at
'base-okl4/patches' and have the following purpose:
:'syscall_pic.patch':
The original distribution of the OKL4 kernel comes with x86 syscall bindings
that use absolute addressing modes. Therefore, code using L4 syscalls
cannot be compiled as position-independent code (gcc option '-fPIC').
Unfortunately, shared libraries must be compiled as position independent
because the location of such a library's text segment is not known at
compile time. Consequently, OKL4 syscalls cannot be issued by shared
libraries, which is a severe limitation. The patch fixes the problem
by changing all OKL4 syscall bindings and removing PIC-incompatible
addressing modes. It does not affect the functionality of the kernel.
:'eabi_build.patch':
The build system of the orignal OKL4 distribution is not prepared to
compile ARM EABI binaries as generated by modern tool chains such as the
Codesourcery GCC. The patch applies the needed changes to the OKL4 build
infrastructure.
Pistachio
=========
Similar to the situation with the OKL4 kernel, we need to patch the Pistachio
system-call bindings to enable syscalls from shared libraries. The
corresponding patch is located at 'base-pistachio/patches' and is known to work
with Pistachio revision 'r782:57124b75c67c'. Without applying this patch, the
linker generates text relocation infos, which result in a run-time error of the
'ldso' on the attempt to modify the read-only text segment of a shared library.
Codezero
========
Because we enhanced our dynamic linker to support ARM EABI, shared libraries
are now fully usable with the Codezero kernel.
Tools and build system
######################
Unified tool chain for building ARM targets
===========================================
With the previous versions of Genode,
we took the approach to use the tool chains of the respective kernel
to build Genode targets. For example, we used to rely on NICTA's ARM cross compiler
(based on gcc-3.4) for building Genode for the OKL4/gta01 platform.
Genode on Codezero, however, used the Codesourcery tool chain. We identified this approach as
a dead end because we would need to support modern tool chains alongside
ancient tool chains that are no longer used in practice. For accommodating
the latter, we had to introduce special workarounds and make compromises.
Therefore, we changed Genode to officially support one modern reference
tool chain to build all ARM-specific targets both on OKL4 and Codezero.
Currently, we use the Codesourcery tool chain version 2009q3-67, which
is available here:
:Codesourcery ARM EABI tool chain:
[http://www.codesourcery.com/sgpp/lite/arm/portal/release1039]
Because the original OKL4v2 distribution does not support modern ARM EABI tool
chains, it cannot be used out of the box anymore. But you can find a patch
to enable ARM EABI for OKL4v2 at 'base-okl4/patches/'.
Build system
============
* We changed the build system to link all shared libraries with
the '--whole-archive' option.
* All libraries are now built as position-independent code (compiler
option '-fPIC') by default. It is possible to explicitly disable
'-fPIC' by adding 'CC_OPT_PIC=' to the library description file.
* To ease the integration of third-party code into the Genode build
system, we have added a mechanism for setting source-file-specific
compiler options. Compiler arguments for a single file such as
'main.cc' can be assigned by setting the build variable 'CC_OPT_main'.