Hi,
I tried to build this environment, but it seems that it needs kvm
support. For me, it is very troublesome to prepare a kvm environment.
So could you please write this selftest?
Thanks,
Lonial Con
lonial con <kongln9170@xxxxxxxxx> 于2024年9月12日周四 21:31写道：
>
> Hi,
>
> I tried to build this environment, but it seems that it needs kvm support. For me, it is very troublesome to prepare a kvm environment. So could you please write this selftest?
>
> Thanks,
> Lonial Con
>
> Eduard Zingerman <eddyz87@xxxxxxxxx> 于2024年9月12日周四 12:31写道：
>>
>> On Thu, 2024-09-12 at 10:53 +0800, lonial con wrote:
>>
>> > I have never written a selftest before. I wrote a simple POC to
>> > demonstrate this bug. This POC can crash the Linux kernel 6.6.50. I
>> > think the ebpf code in the POC will be helpful for writing a
>> > selftest.
>>
>> Well all depends on how familiar you want to get with selftests
>> infrastructure :) Here is a promised intro. If you don't want to
>> bother, please let me know, I can write the selftest.
>> If you do want to bother, feel free to ask any questions.
>>
>> ***
>>
>> Please find a minimal recipe allowing to compile and run selftests in
>> a chroot at the bottom of this email. You would probably want to
>> adjust it, e.g. setup a user matching your local user inside chroot
>> and do a bind mount for sources directory etc.
>>
>> After setting up the environment you will have to write the test.
>>
>> BPF selftests reside in the following directory:
>> - tools/testing/selftests/bpf/
>>
>> Nowadays we mostly add selftests to test_progs executable and use
>> bpftool skeletons / libbpf to simplify maps and programs creation.
>>
>> The files located under prog_tests/ directory are compiled as host
>> programs, the files located under progs/ are compiled as BPF programs
>> (and libbpf skeletons are generated for these programs).
>> Skeletons generated for files from progs/ are used in tests declared
>> in prog_tests/.
>>
>> Your POC structure:
>> - sets up a few maps
>> - sets up data for ringbuf
>> - loads and runs BPF program
>>
>> You can look at a selftests that have similar structure, e.g.:
>> - tools/testing/selftests/bpf/prog_tests/ringbuf.c
>> - tools/testing/selftests/bpf/progs/test_ringbuf.c
>>
>> Interesting parts of the 'prog_tests/ringbuf.c':
>>
>> // this includes skeleton generated by bpftool
>> #include "test_ringbuf.lskel.h"
>>
>> static void ringbuf_subtest(void)
>> {
>> ...
>> // use generated methods to setup maps and programs
>> skel = test_ringbuf_lskel__open();
>> ...
>> err = test_ringbuf_lskel__load(skel);
>>
>> // you can do bpf_prog_run here as well
>> }
>>
>> // build system automatically wires up functions
>> // void test_*(void) as entry points for tests
>> // executed by test_progs binary
>> void test_ringbuf(void)
>> {
>> // needed for tests filtering, e.g. -t option for test_progs
>> if (test__start_subtest("ringbuf"))
>> ringbuf_subtest();
>> ...
>> }
>>
>>
>> *** chroot selftests build/run recipe follows ***
>>
>> # First, setup the bullseye chroot
>> sudo /usr/sbin/debootstrap --variant=buildd --arch=amd64 bullseye bullseye-chroot/ http://deb.debian.org/debian
>>
>> # provide {dev,proc} for chroot
>> sudo mount --rbind /dev ./bullseye-chroot/dev/
>> sudo mount --make-rslave ./bullseye-chroot/dev/
>> sudo mount -t proc proc ./bullseye-chroot/proc/
>>
>> # enter chroot
>> sudo chroot ./bullseye-chroot
>>
>> # Install build tools
>> apt install build-essential bc flex bison git libelf-dev libssl-dev \
>> docutils-common rsync curl zstd qemu-system-x86 sudo cmake \
>> libdw-dev lsb-release wget software-properties-common gnupg e2fsprogs
>>
>> # Install fresh clang-18 snapshot, the llvm.sh sets up some repos
>> curl https://apt.llvm.org/llvm.sh --output /tmp/llvm.sh
>> bash /tmp/llvm.sh 18
>> apt install clang-tools-18
>> ln -s /usr/bin/clang-18 /usr/bin/clang
>> ln -s /usr/bin/llvm-strip-18 /usr/bin/llvm-strip
>>
>> # that would be /root inside chroot
>> cd $HOME
>>
>> # Get and compile pahole, use instructions from:
>> # https://git.kernel.org/pub/scm/devel/pahole/pahole.git/about/
>> git clone https://git.kernel.org/pub/scm/devel/pahole/pahole.git
>> cd pahole
>> git submodule update --init --recursive
>> mkdir build
>> cd build
>> cmake -D__LIB=lib ..
>> make -j
>> # make it available system-wide
>> ln -s $(realpath pahole) /usr/local/bin/
>>
>> cd $HOME
>> git clone --depth=1 https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git
>>
>> # Run vmtests, this should download rootfs, build kernel and tests, run test_verifier
>> # vmtest.sh would ask for root password to mount rootfs image
>> cd bpf-next/tools/testing/selftests/bpf
>> ./vmtest.sh -- ./test_verifier
>>
>> # And now run test_progs
>> ./vmtest.sh -- ./test_progs
>>
>> # One can filter tests too
>> ./vmtest.sh -- ./test_progs -t ringbuf
>>
