ExternalVendorCode/genode
1
0
Fork 0
mirror of https://github.com/genodelabs/genode.git synced 2025-01-18 02:40:08 +00:00
Code Issues Actions Packages Projects Releases Wiki Activity

New base-sel4 repository

Browse Source
This commit is contained in:
Norman Feske 2014-10-14 15:18:31 +02:00 committed by Christian Helmuth
parent a96243eebf
commit 456d81f517
7 changed files with 382 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

296
repos/base-sel4/doc/notes.txt Normal file
View File

@ -0,0 +1,296 @@
==========================================
Notes on porting Genode to the seL4 kernel
==========================================
Norman Feske
This document is a loose collection of notes about the exploration of the
seL4 and the port of the Genode system to this kernel. The seL4 kernel is
a modern microkernel jointly developed by NICTA and General Dynamics.
:[http://sel4.systems]:
Website of the seL4 project
A fresh Genode source-code repository
=====================================
Following the convention to host each kernel in its dedicated _base-<kernel>_
source repository, the seL4-specific code will go to _base-sel4_. This way,
we can cleanly hold the seL4-specific code apart from generic Genode code.
For the start, the new repository will contain three things: This notes
document at _doc/_, the port-description file for downloading the seL4
kernel _(ports/sel4.port)_ accompanied with the corresponding hash file
_(ports/sel4.hash)_, and a bunch of small tests _(src/test/sel4/)_
Since seL4 is hosted on GitHub, writing a port-description file is easy.
We can simply use _base-nova/ports/nova.port_ as a template and adapt it:
! LICENSE := GPLv2
! VERSION := git
! DOWNLOADS := sel4.git
!
! URL(sel4) := https://github.com/seL4/seL4.git
! # experimental branch
! REV(sel4) := b6fbb78cb1233aa8549ea3acb90524306f49a8d2
! DIR(sel4) := src/kernel/sel4
There are two branches of seL4. The master branch is the stable branch
that contains the formally verified version of the kernel. The experimental
branch contains features that are not yet ready to be included in the
master branch. Among those features are the support for virtualization.
To anticipate current developments of the seL4 community, I am going with
the experimental branch. For the ports file, I pick the commit ID of the
most recent commit of the experimental branch at the time of porting. Once,
the _ports/sel4.port_ file is in place, we can generate the matching
port hash as follows (from the base directory of the Genode source tree):
! # create an empty hash file
! touch repos/base-sel4/ports/sel4.hash
!
! # update the hash for the current version of the sel4.port file
! ./tool/ports/update_hash sel4
With the _sel4.port_ file in place, we can download the seL4 kernel via:
! ./tool/ports/prepare_port sel4
After invoking this command, the kernel source will be located at
_contrib/sel4-<hash>/src/kernel/sel4_.
Building the kernel for the first time
======================================
For getting acquainted with the code base, the README.md file provides a
good starting point. It seems to contain exactly the information that I need
at this point. As a first test, I am going to build the kernel for the pc99
platform using the Genode tool chain. According to the README, the following
command should work
! make TOOLPREFIX=/usr/local/genode-gcc/bin/genode-x86- \
! ARCH=ia32 PLAT=pc99
On the first attempt, the following error occurs:
! Traceback (most recent call last):
! File "./tools/invocation_header_gen.py", line 18, in <module>
! import tempita
! ImportError: No module named tempita
! make: *** [arch/api/invocation.h] Error 1
This problem could be easily solved by installing the 'python-tempita'
package. However, further down the road, the build process stops with
the following message:
! src/arch/ia32/kernel/boot_sys.c:75:26: error: ‘CONFIG_MAX_NUM_IOAPIC’ undeclared here (not in a function)
! src/plat/pc99/machine/hardware.c: In function ‘maskInterrupt’:
! src/plat/pc99/machine/hardware.c:36:9: error: implicit declaration of function ‘pic_mask_irq’ [-Werror=implicit-function-declaration]
! src/plat/pc99/machine/hardware.c:36:9: error: nested extern declaration of ‘pic_mask_irq’ [-Werror=nested-externs]
A 'grep' for 'MAX_NUM_IOAPIC' reveals that this definition is normally
generated by the kernel configuration program as there is a match in
_src/plat/pc99/Kconfig_. At this point, I am wondering if I am on the wrong
track altogether. On the seL4 download page, the kernel is mentioned as just
one of several "projects". But since it is the only one of the list of
projects that I am actually interested in, I wanted to focus on only this one.
But apparently, attempts to configure the kernel via 'make menuconfig' are not
supposed to work if checking out the repository in a free-standing fashion.
Sooner or later, I would have to look behind the curtain of the seL4 build
system. So why not now? Passing 'BUILD_VERBOSE=1 V=1' to 'make' is quite
helpful in this situation. A look into _include/config.h_ reveals that the
use of the autoconf-generated header _autoconf.h_ is optional. This is
nice. So I can leave the kernel-configuration magic out of the loop and just
manually specify the config definitions at the build command line. After
a few iterations, I came up with the following command-line arguments:
! make TOOLPREFIX=/usr/local/genode-gcc/bin/genode-x86- \
! ARCH=ia32 PLAT=pc99 BUILD_VERBOSE=1 V=1 \
! LDFLAGS+=-Wl,-melf_i386 \
! LDFLAGS+=-nostdlib \
! LDFLAGS+=-Wl,-nostdlib \
! CFLAGS+=-m32 \
! CONFIG_KERNEL_EXTRA_CPPFLAGS+=-DCONFIG_MAX_NUM_IOAPIC=1 \
! CONFIG_KERNEL_EXTRA_CPPFLAGS+=-DCONFIG_IRQ_IOAPIC=1
The 'CONFIG_IRQ_IOAPIC' flag is needed to specify whether the legacy PIC
or the IOPIC should be used. It is picked up by for conditionally compiling
the code of _src/plat/pc99/machine/hardware.c_.
As the result of the build process, we get a freshly baked 'kernel.elf'
file.
Of course, we don't want Genode users to manually build the kernel in this
way. So we add a "kernel" target to our _base-sel4_ repository. The kernel
target comes in the form of a _src/kernel/target.mk_ file and a library
_lib/mk/x86_32/kernel.mk_. The _target.mk_ file is just a pseudo target
with a dependency on the _kernel.mk_ library. There may be multiple versions
of the _kernel.mk_ library. The build-system configuration determines the
version that is used. E.g., when we set up the build directory for x86_32,
the _lib/mk/x86_32/kernel.mk_ one will be used. The _kernel.mk_ file looks
as follows:
! SEL4_DIR = $(call select_from_ports,sel4)/src/kernel/sel4
!
! ifeq ($(called_from_lib_mk),yes)
! all: build_kernel
! endif
!
! LINKER_OPT_PREFIX := -Wl,
!
! build_kernel:
! $(VERBOSE)$(MAKE) TOOLPREFIX=$(CROSS_DEV_PREFIX) \
! ARCH=ia32 PLAT=pc99 \
! LDFLAGS+=-nostdlib LDFLAGS+=-Wl,-nostdlib \
! $(addprefix LDFLAGS+=$(LINKER_OPT_PREFIX),$(LD_MARCH)) \
! $(addprefix CFLAGS+=,$(CC_MARCH)) \
! CONFIG_KERNEL_EXTRA_CPPFLAGS+=-DCONFIG_MAX_NUM_IOAPIC=1 \
! CONFIG_KERNEL_EXTRA_CPPFLAGS+=-DCONFIG_IRQ_IOAPIC=1 \
! SOURCE_ROOT=$(SEL4_DIR) -f$(SEL4_DIR)/Makefile
The pseudo target _base-sel4/src/kernel/target.mk_ exists merely for making
the result from the seL4 build directory visible in the install directory
_(bin/)_.
! TARGET = sel4
! LIBS = kernel
!
! $(INSTALL_DIR)/$(TARGET):
! $(VERBOSE)ln -sf $(LIB_CACHE_DIR)/kernel/kernel.elf $@
Genode's build system works in two stages. At the first (light-weight) stage,
it merely determines library dependencies. At the second stage, the actual
build steps are performed. The condition around the 'all' target ensures that
the 'build_kernel' target will be visited only at the second build stage with
the current working directory set to the library location and all build
variables (such as CROSS_DEV_PREFIX) defined. Fortunately, the seL4 build
system supports out-of-tree builds by defining the SOURCE_ROOT variable.
To test drive the kernel target, we first need to create Genode build
directory prepared for seL4. Later, we will add seL4 support to the regular
'create_builddir' tool. But for now, it suffices to create one manually:
# Create a new directory with an _etc/_ subdirectory.
# Add an _etc/specs.conf_ file with the following content:
! SPECS = sel4 x86_32
This tells the build system the so-called build specification.
# Add an _etc/build.conf_ file with the following content:
! GENODE_DIR := /path/to/your/genode.git
! BASE_DIR := $(GENODE_DIR)/repos/base
! REPOSITORIES := $(GENODE_DIR)/repos/base-sel4 \
! $(GENODE_DIR)/repos/base
! CONTRIB_DIR := $(GENODE_DIR)/contrib
GENODE_DIR must point to the root of Genode's source tree.
BASE_DIR is used by the build system to find the build-system scripts.
The CONTRIB_DIR is needed to enable the build system to find the location
of the seL4 source code. The 'REPOSITORIES' declaration lists all source
repositories that should be included in the build. Note that the order
is important. By listing 'base-sel4' before 'base', we allow 'base-sel4'
to override the content of the 'base' repository.
# Symlink the _<genode-dir>/too/builddir/build.mk_ file to a _Makefile_.
! ln -s <genode-dir>/tool/builddir/build.mk Makefile
With the build directory, we can trigger the kernel build via 'make kernel'.
The seL4 build process will be invoked from within the kernel library. Hence,
the library's directory _var/libcache/kernel_ will be used as the build
directory of the kernel.
Starting the kernel in Qemu
===========================
To test-drive the kernel, we need to create a bootable image including a boot
loader, the boot-loader configuration, and the kernel. To spare us the
manual work, Genode comes with a so-called run tool that automates this
procedure. We merely need to create run environment for seL4 to tweak the
run tool for this particular platform. The run environment for seL4 resides at
_base-sel4/run/env_. To create it, we can take inspiration from the run
environments of the other platforms such as NOVA. It comes down to
implementing the functions 'build_boot_image' and 'run_genode_until' according
to our needs. The former function contains the generation of the boot-loader
configuration, i.e., GRUB's _menu.lst_ file. At the current stage, we merely
load the seL4 ELF image as multi-boot kernel. For using the run tool for the
initial test, the following small run script at _base-sel4/run/test.run_ does
the trick:
! create_boot_directory
! build_boot_image ""
! append qemu_args " -nographic -m 64 "
! run_genode_until forever
To invoke it, all we have to do is issuing 'make run/test' from the build
directory. All we see, however, is, well, nothing.
Normally we would expect from the kernel to print a life sign when booting
up. This is suggested by a 'printf' in _arch/arm/kernel/boot.c_. So the lack
of output is most certainly a configuration issue. A look in
_include/plat/pc99/plat/machine/io.h_ indicates that 'kernel_putchar', which
is used as the back end of 'printf' _(src/machine/io.c)_ is compiled in only
if DEBUG mode is enabled. Adding 'DEBUG=1' to the sel4 build command (in our
_lib/mk/x86_32/kernel.mk_ file) enables this mode.
But enabling the DEBUG option comes with a strange surprise. The kernel build
would fail with the following error:
! kernel.o: In function `insert_dev_p_reg':
! kernel_final.c:(.boot.text+0x131a): undefined reference to `putchar'
The message is strange because the seL4 source code is void of any call to
'putchar'. It turned out that the compiler automatically turned a 'printf'
with a one-character string ("/n") into a call of 'putchar'. Fortunately,
this built-in heuristic can be disabled by passing '-fno-builtin-printf'
to the CFLAGS when compiling seL4. With this fix, we can successfully compile
the kernel in debug mode, boot it in Qemu, and observe the first life sign:
! Boot config: parsing cmdline '/sel4'
! Boot config: console_port of node #0 = 0x3f8
! Boot config: debug_port of node #0 = 0x3f8
! Boot config: max_num_nodes = 1
! Boot config: num_sh_frames = 0x0
! seL4 failed assertion '_ndks_end - _ndks_start <= NDKS_SIZE'
! at src/arch/ia32/kernel/boot_sys.c:424 in function try_boot_sys
The NDKS section apparently contains those parts of the image that should
always be mapped at the upper part of the virtual address space. The assertion
triggers because the section of the binary is larger (40900 bytes) than the
assumed limit NDKS_SIZE (12288 bytes). According to the linker script
_(src/plat/pc99/linker.lds)_, the section includes the kernel stack, the BSS,
and "COMMON" symbols. When looking at the list of those symbols using 'nm |
sort -n', the 'ksReadyQueues' symbol raises my eyebrows because it is quite
large (32768 bytes) compared to all others. This symbol belongs to an array,
which is dimensioned as CONFIG_NUM_DOMAINS * CONFIG_NUM_PRIORITIES. As we are
using the default configuration values of _include/config.h_,
CONFIG_NUM_DOMAINS is 16 and CONFIG_NUM_PRIORITIES is 256. Hence, the array
has 4096 entries with 8 bytes for each entry ('tcb_queue_t' with two
pointers). Interestingly, the default value of NUM_DOMAINS in the _Kconfig_ is
1, which would result in a much smaller 'ksReadyQueues' array. In fact,
passing the following argument to the kernel build fixes the assertion:
! CONFIG_KERNEL_EXTRA_CPPFLAGS+=-DCONFIG_NUM_DOMAINS=1
Now, the kernel bootstraps successfully, detects one CPU and tries to
obtain information about the boot modules, which we don't have provided yet.
Hence, the kernel backs out with the following message:
! Boot loader did not provide information about boot modules
! seL4 called fail at src/arch/ia32/kernel/boot_sys.c:711
! in function boot_sys, saying "boot_sys failed for some reason :(
Well, this is expected. So it is time to take the first baby step of providing
a root task to the system.
A root task for exercising the kernel interface
===============================================

28
repos/base-sel4/lib/mk/x86_32/kernel.mk Normal file
View File

@ -0,0 +1,28 @@
SEL4_DIR = $(call select_from_ports,sel4)/src/kernel/sel4
#
# Execute the kernel build only at the second build stage when we know
# about the complete build settings (e.g., the 'CROSS_DEV_PREFIX') and the
# current working directory is the library location.
#
ifeq ($(called_from_lib_mk),yes)
all: build_kernel
else
all:
endif
LINKER_OPT_PREFIX := -Wl,
build_kernel:
$(VERBOSE)$(MAKE) \
TOOLPREFIX=$(CROSS_DEV_PREFIX) \
ARCH=ia32 PLAT=pc99 DEBUG=1 V=1 \
LDFLAGS+=-nostdlib LDFLAGS+=-Wl,-nostdlib \
$(addprefix LDFLAGS+=$(LINKER_OPT_PREFIX),$(LD_MARCH)) \
CFLAGS+=-fno-builtin-printf \
$(addprefix CFLAGS+=,$(CC_MARCH)) \
CONFIG_KERNEL_EXTRA_CPPFLAGS+=-DCONFIG_MAX_NUM_IOAPIC=1 \
CONFIG_KERNEL_EXTRA_CPPFLAGS+=-DCONFIG_IRQ_IOAPIC=1 \
CONFIG_KERNEL_EXTRA_CPPFLAGS+=-DCONFIG_NUM_DOMAINS=1 \
SOURCE_ROOT=$(SEL4_DIR) -f$(SEL4_DIR)/Makefile

1
repos/base-sel4/ports/sel4.hash Normal file
View File

@ -0,0 +1 @@
c538b91d215024f21be14837192141004c9e3561

8
repos/base-sel4/ports/sel4.port Normal file
View File

@ -0,0 +1,8 @@
LICENSE := GPLv2
VERSION := git
DOWNLOADS := sel4.git
URL(sel4) := https://github.com/seL4/seL4.git
# experimental branch
REV(sel4) := b6fbb78cb1233aa8549ea3acb90524306f49a8d2
DIR(sel4) := src/kernel/sel4

7
repos/base-sel4/run/test.run Normal file
View File

@ -0,0 +1,7 @@
create_boot_directory
build_boot_image ""
append qemu_args " -nographic -m 64 "
run_genode_until forever

5
repos/base-sel4/src/kernel/target.mk Normal file
View File

@ -0,0 +1,5 @@
TARGET = sel4
LIBS = kernel
$(INSTALL_DIR)/$(TARGET):
$(VERBOSE)ln -sf $(LIB_CACHE_DIR)/kernel/kernel.elf $@

37
tool/run/boot_dir/sel4 Normal file
View File

@ -0,0 +1,37 @@
##
# Populate directory with binaries on seL4
#
proc run_boot_dir {binaries} {
#
# Collect contents of the ISO image
#
copy_and_strip_genode_binaries_to_run_dir $binaries
build { kernel }
exec cp bin/sel4 [run_dir]/sel4
if {[have_include "image/iso"] || [have_include "image/disk"]} {
#
# Install isolinux/GRUB files and bender
#
install_iso_bootloader_to_run_dir
#
# Generate GRUB config file
#
set fh [open "[run_dir]/boot/grub/menu.lst" "WRONLY CREAT TRUNC"]
puts $fh "timeout 0"
puts $fh "default 0"
puts $fh "\ntitle Genode on seL4"
puts $fh " kernel /sel4"
foreach binary $binaries {
if {$binary != "core"} {
puts $fh " module /genode/$binary" } }
close $fh
}
#
# Build image
#
run_image
}