I was configuring rpi-3.8.y (raspbian kernel on 3.8.y branch) using menuconfig and came across the following,
Will selecting a PREEMPT-ible kernel (choice #3) cross-compile a real-time one ?
No.
The closest thing you'll get to real-time with Linux is PREEMPT_RT, which is an out-of-tree patch set, and clearly not present in whatever kernel sources you're building.
Related
I am writing a recipe for a package which needs to be aware of the underlying machine's microarchitecture. In other words, I would like a string such as aarch64 or arm64 for a 64-bit Arm system, and x86_64 for a 64-bit Intel system.
So far, I have identified:
MACHINE - This seems to be whatever the meta-* layer author decides to name their machine and may contain the architecture, it may not. For example, beaglebone is no use.
MACHINE_ARCH - This seems to be close to what I'm looking for. However, taking this BSP layer as an example, and doing a quick search, it doesn't seem as though this variable is set anywhere. Only read from in a few packages.
TUNE_PKGARCH - May be the best bet so far. But, what format is this variable in? What architecture naming conventions are used? Also, the aforementioned BSP layer, again, doesn't seem to set this anywhere.
I would have thought that knowing the machine architecture in a well-defined format is important, but it doesn't seem to be so simple. Any advice?
I'm accustomed to doing this with uname -m (Windows fans can use the output of SET processor), so for me in Yocto it ends up being a toss-up:
According to the Mega-Manual entry for TARGET_ARCH:
TARGET_ARCH
The target machine's architecture. The OpenEmbedded build system supports many
architectures. Here is an example list of architectures supported. This list is by
no means complete as the architecture is configurable:
arm
i586
x86_64
powerpc
powerpc64
mips
mipsel
uname -m is a bit better since you get subarchitectural information as well. From the machines I have access to at this moment:
Intel-based Nuc build system: x86_64
ARM embedded system: armv7l
Raspberry Pi 4B: aarch64
I have found that the GNU automake (native) and libtool (available for target) packages compute a useful variable named UNAME_MACHINE_ARCH. If you are using libtool already or are willing to take it on just for the purpose of having this done for you :-#), you can solve this way. Look in the built tree for files named config.guess.
You may be able to get by more generically than libtool by using Yocto BUILD_ARCH:
BUILD_ARCH
Specifies the architecture of the build host (e.g. i686). The OpenEmbedded build
system sets the value of BUILD_ARCH from the machine name reported by the uname
command.
So play with these and make your own choice depending on your project's circumstances.
I'm trying to port Android 11 to my board(odroid-n2) and I'm confused about how I can build an board specific kernel module and ramdisk. Could I get some help about this?
Recently, to solve kernel fragmentation, it seems AOSP is splitting kernel into two different block.
(1) GKI(Generic Kernel Image)
(2) Vendor specific kernel
For GKI, I think I can use an image from ci.android.com.
For Vendor specific portion(Related to vendor_boot partition),
is there specific flow for this? or something to refer?
I'm referring to {android kernel}/common/build.config.db845c for case-study, I don't understand why 'gki_defconfig + db845c_gki.fragment' should be combined to one to generate configruation for kernel build. I think we only build kernel module for vendor specific portion.
*) For android docs, I'm referring to the followings.
https://source.android.com/setup/build/building-kernels
https://source.android.com/devices/architecture/kernel/generic-kernel-image
Indeed, with GKI (Generic Kernel Image), generic parts and vendor parts are separated. As of today, that distinction is quite clear: vmlinux is GKI and any module (*.ko) is vendor. That might change in the future if GKI modules show to be useful. Then there could be GKI (Kernel+Modules) + Vendor Modules.
The whole build process is quite new as well and still evolving with this quite fundamental change to how Android kernels are developed. Historically, device kernels and modules were build in one logical step and compatibility was ensured by the combined build. Now there is a shift towards a world where we can cleanly build the kernel and the modules entirely separate without overlap. It is likely to get much easier in the future to build vendor modules without having to build too much of the GKI kernel at the same time. Yet, the way the build currently works, it is easier to set up as it is.
Android 11 introduced the concept of "compliance" for GKI based kernels. That means a shipped kernel is ABI compatible to the GKI kernel. In theory that means that you could literally swap out the kernel that you have and replace it with a build from ci.android.com. Note, a compatible kernel can have significant (ABI compatible) patches that the GKI does not have. So, while compatible, it might not lead to the same experience.
Android 12 enables devices to be launched with signed boot images containing the GKI kernel. Since the Kernel<>Module ABI of those kernels is kept stable, this also allows independent updates of GKI kernel and vendor modules.
When you refer to the db845c build config, yes, this looks a bit confusing. This is a full blown config and the build indeed produces an (ABI compatible!) kernel and the vendor specific modules. The fragment can be considered a patch to the gki_defconfig in the sense that it does not change the core kernel, but enables the required modules.
For the final release, the kernel image from this build will be replaced by the GKI kernel image. But for development, the kernel that comes out of this build is perfectly fine to use.
In practice it helps downstream projects to develop core kernel features and modules at the same time, though changes for modules and kernel need to go into different repositories (db845c being an exception here a reference board).
To somewhat answer your question on how to build the db845c kernel, ci.android.com also provides the build log along with the artifacts to download. For the android12-5.10 branch and the target kernel_db845c, a recent build can be found here. The build.log states at the beginning the instructions to reproduce this:
$ BUILD_CONFIG=common/build.config.db845c build/build.sh
This is the relevant step based on the general instructions on source.android.com - building kernels.
I have a custom board with imx6dl chip and peripherals. I have compiled u-boot, zImage and rootfs from examples provided by manufacturer. But when i try to build yocto from git repo with latests releases, it fails to run (some drivers not working, board is loading and display interface, but touchscreen is not working for ex.),
Is there any way to include precompiled binaries zImage, u-boot and device table to bitbake recipes? I'm very new to yocto project, and only need to get bootable image with working drivers and qt5.
If you have a working boot chain (e.g. u-boot, kernel and device tree) that you have built out-of-yocto, then you might try building a rootfs only. This requires two main settings, to be made in your local.conf to get started. Please don't firget that this is just a starting point, and it is highly advised to get the kernel/bootloader build sorted out really soon.
PREFERRED_PROVIDER_virtual/kernel = "linux-dummy to have no kernel being built, and something like MACHINE="qemuarm" to set up an armv7 build on poky later than version 3.0. The core-image-minimal target should at least be enough to drop you in a shell for starters, and then you can proceed from there.
Additionally, it might be qorth asking the board vendor or the yocto community (#yocto on the freenode server) if they know about a proper BSP layer. FSL things are quite nicely supported these days, and if your board is closely related to one of the well-known ones, you've got a high chance that meta-freescale just does the trick nicely.
Addition:
#Martin pointed out the mention of Qemu is misleading. This is just the easiest way to make Yocto build a userland for the armv7-architecture which the imx6dl is based on. The resulting root filesystem should be sufficiently compatible to get started, before moving on to more tuned MACHINE configuration.
I'm using Yocto project to build a linux kernel image following these steps:
https://www.at91.com/linux4sam/bin/view/Linux4SAM/Sama5d27Som1EKMainPage
For some reasons I just want to reduce my Image size so I can flash it on QSPI 8 Mega octet memory. I have tried to reduce the size of my rootFS, I have removed some packages that I found in .manifest file and some Distro features. But I did not find how can I modify the kernel size which size is fixed ( 4.2 Mega octet ).
I think that when I can remove some drivers that I don't need the kernel size will be reduced.
I just want to know how can I find what drivers are built in my image and where can I find them ? and later how can I delete the ones that I don't need ?
Thank you.
if you check the .config file that was generated for your BSP, it will show what drivers (and other things) were built into your kernel (check for the 'y' on all the options).
Such file should be somewhere in:
tmp/work//linux-yocto//linux-*-build/.config
Sorry that I can't give you the exact location, but it literally depends on what BSP/MACHINE you are building for.
Also, if you want to modify such configuration, you can call:
$ bitbake -c menuconfig virtual/kernel
that will bring up the menuconfig ncurses interface, in which you can not only see what is installed but also modify what you need.
I followed the instructions given in the link: http://blog.avirtualhome.com/how-to-compile-a-new-ubuntu-11-04-natty-kernel/ for building a custom kernel and booting it. Everything works fine, except that when building it, I used the option skipmodule=true (as given in this link), so I guess the modules are not built for this kernel. So I have two questions:
How do I build only the modules for my flavor, now that I have the rest of the kernel built? 'make modules' will build it for generic flavor only, if I'm not wrong.
Also does it require me to build the entire kernel source, 'fakeroot debian/rules binary-i5' (i5 is my custom falvor), each time I make a change to one of my modules?
Thanks.
1) To build a linux kernel module for a specific kernel from the module source directory do:
make -C {path-to-kernel-source} M=`pwd` modules
The -C option tells is used to point to the kernel source tree where it finds the kernel's top-level Makefile. The M=`pwd` option points it to the module source directory, where it builds the 'modules' target.
2) Nope, its not necessary to build the source kernel. Either having the kernel source tree or the kernel headers suffice.