I want to inject memory errors on my system to check whether RAS/EDAC system really works and logs errors on my memory (during boot or any runtime). I came across with many tools but I don't know which one to actually trust. The machine I want to test is a Sandy Bridge machine running Linux kernel 5.15.0-58-generic version. Specificially, I want to test my system with Einj tool (https://docs.kernel.org/firmware-guide/acpi/apei/einj.html). Although I followed the earlier steps in the link (BIOS supports Einj, CONFIG_DEBUG_FS, CONFIG_ACPI_APEI, CONFIG_ACPI_APEI_EINJ config parameters are set on my kernel), the files mentioned in the document: /sys/kernel/debug/apei/einj etc. are not present. How can I proceed with this tool? Or is there a better way/tool to inject memory errors to check the EDAC subsystem?
I am trying to build minimal kernel under 1 Mb with Buildroot. It is intended for small board with qspi memory and basic functionality, ethernet, usb, spi, and some GPIO's. Basic terminal access via ssh and UART.
My first thoughts are if it is even possible to modify kernel .config via linux-menuconfig to reach this size.
Also if it is possible to identify the redundant parts without deep knowledge about kernel architecture and exclude them from compilation.
If someone can direct me to good direction how to solve this problem or even specify some tools and ways how to do it would be very helpful.
Thank you!
If you have working build root for your board, than, it's better to continue to work with it. Technic for disabling kernel options should be the same. In the article he reached ~0,7MB uImage with lost a lot of functionality (p40). He started with minimal (bare) config (p27) and add blocks of configs. So instead of identify the redundant parts you can build smallest possible uImage you can boot. Than add to it more options: ext2, serial and so on. Actually this work require a lot of testing. And you probably brake dependencies.
Kernel configs (working and new one) could be compared using diff -Naur, so you can see what changed.
Offtopic:
Looks like yocto officially supported by altera. here are instructions how to build altera-image-minimal. If you fine with it size, than use it and don't spend time on minimizing uImage. If you need extra packages installed into it, than you can ease extend it.
And here are instructions about building Angstrom (yocto based distribution). You can create you custom image based on console-image-minimal.
I use Angstrom in production. Must say, it was really hard to use it first time.
Whether or not you build the kernel with buildroot is not really relevant. The important thing is to configure it so it fits in 1MB. When you build the kernel from buildroot, you can do that with make linux-menuconfig, as you mention.
That said, getting a kernel under 1MB will be quite hard. Biff once did this for an x86-based platform, bifferboard. But that was without networking or USB.
You can refer to the kernel size tuning guide, which has links to some patches to reduce the size. But it's not been updated in a couple of years.
I'm complety new to this but I finally got around to building a Linux kernel so far so good. I am following a guide here:
A10-OLinuXino-LIME
My problem/concern is now I am in a .config menu and I've been searching online to no avail to determine what does it mean by a modularizes features verse includes, like should I switch to if I want those features to be there?
Any help or advice would be greatly appreciated it! I'm primarily doing this to include WiFi usb drivers I will be needing.
It depends on what system you run this kernel. If it's an embedded system, then you will probably be more concerned about memory benefits. In RAM you can win about several Kbytes per module. For the devices are not represented in the system/hardware, it then has a sense to put some drivers on Modules. Some modules can be taking more time when the kernel starts, and it is probably better to load them later, when the system is running.
You will probably be concerned about disk space, if you put some stuff Compiled-in so you can have a benefit because you don't need to have a module loading utility.
Have a look at this thread as well
I'm primarily doing this to include WiFi usb drivers I will be needing.
Its not necessary to build the complete kernel unless to build a USB WiFi driver. All you need is the kernel headers installed. From make menuconfig select the module you want to build, choose M, save the .config. This will build a module which can be loaded, instead of getting compiled as a part of the vmlinux image.
I am compiling my own Linux kernel and userland tools for a PXE environment meant for cloning and reimaging. Right now, I'm sticking to a specific kernel version and using preconfigured .config's for building the Linux kernel.
I need to change from using preconfigured .config's to automatically generating the default configuration for the specified architecture, and then enabling all ethernet, ATA, SATA, and SCSI drivers.
The reason I want to do this is:
Updating the kernel means updating the preconfigured .config's, which takes too much time to manually do. The way I'm doing it now is using menuconfig, enabling the options I need, and saving the resulting .config to my repository.
I know the kernel I'm building is missing some drivers because I've encountered some PC's that were not able to mount the NFS share because Linux could not find an ethernet device (which I've verified by booting an Ubuntu CD, which did find the ethernet device). I want an automated way of building any Linux kernel version that will guarantee that ALL drivers I need are pulled in.
Using a distribution's configuration pulls in too many unnecessary drivers and features for my purposes. It lengthens the kernel build time from 10-15 mintues to an hour or more, and the resulting image is too big.
Does anyone know how to write a Bash script to accomplish this?
Have you considered using a text editor to modify the .config file.
Then you can modify it using search and replace.
Plus, there are other choices for configuring the kernel than the menu-driven "menuconfig".
How do the Linux kernel developers test their code locally and after they have it committed? Do they use some kind of unit testing and build automation? Test plans?
The Linux kernel has a heavy emphasis on community testing.
Typically, any developer will test their own code before submitting, and quite often they will be using a development version of the kernel from Linus, or one of the other unstable/development trees for a project relevant to their work. This means they are often testing both their changes and other people's changes.
There tends not to be much in the way of formal test plans, but extra testing may be asked for before features are merged into upstream trees.
As Dean pointed out, there's also some automated testing: The Linux Test Project and the kernel Autotest (good overview).
Developers will often also write automated tests targeted to test their change, but I'm not sure there's a (often used) mechanism to centrally collect these ad hoc tests.
It depends a lot on which area of the kernel is being changed of course - the testing you'd do for a new network driver is quite different to the testing you'd do when replacing the core scheduling algorithm.
Naturally, the kernel itself and its parts are tested prior to the release, but these tests cover only the basic functionality. There are some testing systems which perform testing of Linux Kernel:
The Linux Test Project (LTP) delivers test suites to the open source community that validate the reliability and stability of Linux. The LTP test suite contains a collection of tools for testing the Linux kernel and related features.
Autotest—a framework for fully automated testing. It is designed primarily to test the Linux kernel, though it is useful for many other purposes such as qualifying new hardware, virtualization testing, and other general user space program testing under Linux platforms. It's an open-source project under the GPL and is used and developed by a number of organizations, including Google, IBM, Red Hat, and many others.
Also there are certification systems developed by some major GNU/Linux distribution companies. These systems usually check complete GNU/Linux distributions for compatibility with hardware. There are certification systems developed by Novell, Red Hat, Oracle, Canonical, and Google.
There are also systems for dynamic analysis of the Linux kernel:
Kmemleak is a memory leak detector included in the Linux kernel. It provides a way of detecting possible kernel memory leaks in a way similar to a tracing garbage collector with the difference that the orphan objects are not freed, but only reported via /sys/kernel/debug/kmemleak.
Kmemcheck traps every read and write to memory that was allocated dynamically (i.e., with kmalloc()). If a memory address is read that has not previously been written to, a message is printed to the kernel log. It is also is a part of the Linux kernel.
Fault Injection Framework (included in the Linux kernel) allows for infusing errors and exceptions into an application's logic to achieve a higher coverage and fault tolerance of the system.
How do the Linux kernel developers test their code locally and after they have it committed?
Do they use some kind of unit testing and build automation?
In the classic sense of words, no.
For example, Ingo Molnar is running the following workload:
build a new kernel with a random set of configuration options
boot into it
go to 1
Every build fail, boot fail, bug or runtime warning is dealt with. 24/7. Multiply by several boxes, and one can uncover quite a lot of problems.
Test plans?
No.
There may be a misunderstanding that there is a central testing facility, but there is none. Everyone does what he/she wants.
In-tree tools
A good way to find test tools in the kernel is to:
make help and read all targets
look under tools/testing
In v4.0, this leads me to:
kselftest under tools/testing/selftests. Run with make kselftest. Must be running built kernel already. See also: Documentation/kselftest.txt , https://kselftest.wiki.kernel.org/
ktest under tools/testing/ktest. See also: http://elinux.org/Ktest , http://www.slideshare.net/satorutakeuchi18/kernel-auto-testbyktest
Static analysers section of make help, which contains targets like:
checkstack: Perl: what does checkstack.pl in linux source do?
coccicheck for Coccinelle (mentioned by askb)
Kernel CI
https://kernelci.org/ is a project that aims to make kernel testing more automated and visible.
It appears to do only build and boot tests (TODO how to test automatically that boot worked Source should be at https://github.com/kernelci/).
Linaro seems to be the main maintainer of the project, with contributions from many big companies: https://kernelci.org/sponsors/
Linaro Lava
http://www.linaro.org/initiatives/lava/ looks like a CI system with focus on development board bringup and the Linux kernel.
ARM LISA
https://github.com/ARM-software/lisa
Not sure what it does in detail, but it is by ARM and Apache Licensed, so likely worth a look.
Demo: https://www.youtube.com/watch?v=yXZzzUEngiU
Step debuggers
Not really unit testing, but may help once your tests start failing:
QEMU + GDB: https://stackoverflow.com/a/42316607/895245
KGDB: https://stackoverflow.com/a/44226360/895245
My own QEMU + Buildroot + Python setup
I also started a setup focused on ease of development, but I ended up adding some simple testing capabilities to it as well: https://github.com/cirosantilli/linux-kernel-module-cheat/tree/8217e5508782827320209644dcbaf9a6b3141724#test-this-repo
I haven't analyzed all the other setups in great detail, and they likely do much more than mine, however I believe that my setup is very easy to get started with quickly because it has a lot of documentation and automation.
It’s not very easy to automate kernel testing. Most Linux developers do the testing on their own, much like adobriyan mentioned.
However, there are a few things that help with debugging the Linux Kernel:
kexec: A system call that allows you to put another kernel into memory and reboot without going back to the BIOS, and if it fails, reboot back.
dmesg: Definitely the place to look for information about what happened during the kernel boot and whether it works/doesn't work.
Kernel Instrumentation: In addition to printk's (and an option called 'CONFIG_PRINTK_TIME' which allows you to see (to microsecond accuracy) when the kernel output what), the kernel configuration allows you to turn on a lot of tracers that enable them to debug what is happening.
Then, developers usually have others review their patches. Once the patches are reviewed locally and seen not to interfere with anything else, and the patches are tested to work with the latest kernel from Linus without breaking anything, the patches are pushed upstream.
Here's a nice video detailing the process a patch goes through before it is integrated into the kernel.
In addition to the other answers, this emphasise more on the functionality testing, hardware certification testing and performance testing the Linux kernel.
A lot of testing actually happen through scripts, static code analysis tools, code reviews, etc. which is very efficient in catching bugs, which would otherwise break something in the application.
Sparse – An open-source tool designed to find faults in the Linux kernel.
Coccinelle is another program does matching and transformation engine which provides the language SmPL (Semantic Patch Language) for specifying desired matches and transformations in C code.
checkpatch.pl and other scripts - coding style issues can be found in the file Documentation/CodingStyle in the kernel source tree. The important thing to remember when reading it is not that this style is somehow better than any other style, just that it is consistent. This helps developers easily find and fix coding style issues. The script scripts/checkpatch.pl in the kernel source tree has been developed for it. This script can point out problems easily, and should always be run by a developer on their changes, instead of having a reviewer waste their time by pointing out problems later on.
There are also:
MMTests which is collection of benchmarks and scripts to analyze the results.
Trinity which is Linux system call fuzz tester.
Also the LTP pages at SourceForge are quite outdated and the project has moved to GitHub.
I would imagine they use virtualization to do quick tests. It could be something like QEMU, VirtualBox or Xen, and some scripts to perform configurations and automated tests.
Automated testing is probably done by trying either many random configurations or a few specific ones (if they are working with a specific issue). Linux has a lot of low-level tools (such as dmesg) to monitor and log debug data from the kernel, so I imagine that is used as well.
As far as I know, there is an automatically performance regression check tool (named lkp/0 day) running/funding by the Intel. It will test each valid patch sent to the mailing list and check the scores changed from different microbenchmarks such as hackbench, fio, unixbench, netperf, etc.
Once there is a performance regression/improvement, a corresponding report will be sent directly to the patch author and a Cc related maintainers.
LTP and Memtests are generally preferred tools.
adobriyan mentioned Ingo's loop of random configuration build testing. That is pretty much now covered by the 0-day test bot (aka kbuild test bot). A nice article about the infrastructure is presented here: Kernel Build/boot testing
The idea behind this set-up is to notify the developers ASAP so that they can rectify the errors soon enough (before the patches make it into Linus' tree in some cases as the kbuild infrastructure also tests against maintainer's subsystem trees).
Once after contributors submit their patch files and after making a merge request, Linux gatekeepers are checking the patch by integrating and reviewing it. Once it succeeds, they will merge the patch into the relevant branch and a make new version release.
The Linux Test Project is the main source which provides test scenarios (test cases) to run against the kernel after applying patches. This may take around 2 ~ 4 hours, and it depends.
Please note regarding the file system of the selected kernel is going to test against.
Example: ext4 generates different results against ext3 and so on.
Kernel Testing procedure.
Get latest kernel source from the repository (The Linux Kernel Archives or GitHub)
Apply the patch file (using a diff tool)
Build the new kernel.
Test against test procedures in LTP (Linux Test Project)
I had done Linux kernel compilation and done some modifications for Android (Android 6.0 (Marshmallow) and Android 7.0 (Nougat)) in which I use Linux version 3. I cross-compiled it on a Linux system, debugged the errors manually and then ran its boot image file in Android and checked if it was going in a loop-hole or not. If it runs perfect then it means it is compiled perfectly according to system requirements.
For MotoG kernel Compilation
Note: The Linux kernel will change according to requirements which depend on system hardware