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bpf: Add s390 testing documentation
This commits adds a document that explains how to test BPF in an s390 QEMU guest. Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Link: https://lore.kernel.org/bpf/20191029172916.36528-1-iii@linux.ibm.com
This commit is contained in:
Ilya Leoshkevich
Daniel Borkmann
parent
9ffccb7606
commit
7e07e7aec5
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@ -47,6 +47,15 @@ Program types
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prog_flow_dissector
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Testing BPF
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===========
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.. toctree::
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:maxdepth: 1
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s390
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.. Links:
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.. _Documentation/networking/filter.txt: ../networking/filter.txt
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.. _man-pages: https://www.kernel.org/doc/man-pages/
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@ -0,0 +1,205 @@
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===================
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Testing BPF on s390
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===================
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1. Introduction
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***************
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IBM Z are mainframe computers, which are descendants of IBM System/360 from
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year 1964. They are supported by the Linux kernel under the name "s390". This
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document describes how to test BPF in an s390 QEMU guest.
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2. One-time setup
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*****************
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The following is required to build and run the test suite:
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* s390 GCC
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* s390 development headers and libraries
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* Clang with BPF support
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* QEMU with s390 support
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* Disk image with s390 rootfs
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Debian supports installing compiler and libraries for s390 out of the box.
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Users of other distros may use debootstrap in order to set up a Debian chroot::
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sudo debootstrap \
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--variant=minbase \
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--include=sudo \
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testing \
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./s390-toolchain
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sudo mount --rbind /dev ./s390-toolchain/dev
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sudo mount --rbind /proc ./s390-toolchain/proc
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sudo mount --rbind /sys ./s390-toolchain/sys
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sudo chroot ./s390-toolchain
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Once on Debian, the build prerequisites can be installed as follows::
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sudo dpkg --add-architecture s390x
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sudo apt-get update
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sudo apt-get install \
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bc \
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bison \
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cmake \
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debootstrap \
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dwarves \
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flex \
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g++ \
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gcc \
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g++-s390x-linux-gnu \
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gcc-s390x-linux-gnu \
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gdb-multiarch \
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git \
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make \
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python3 \
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qemu-system-misc \
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qemu-utils \
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rsync \
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libcap-dev:s390x \
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libelf-dev:s390x \
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libncurses-dev
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Latest Clang targeting BPF can be installed as follows::
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git clone https://github.com/llvm/llvm-project.git
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ln -s ../../clang llvm-project/llvm/tools/
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mkdir llvm-project-build
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cd llvm-project-build
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cmake \
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-DLLVM_TARGETS_TO_BUILD=BPF \
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-DCMAKE_BUILD_TYPE=Release \
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-DCMAKE_INSTALL_PREFIX=/opt/clang-bpf \
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../llvm-project/llvm
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make
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sudo make install
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export PATH=/opt/clang-bpf/bin:$PATH
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The disk image can be prepared using a loopback mount and debootstrap::
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qemu-img create -f raw ./s390.img 1G
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sudo losetup -f ./s390.img
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sudo mkfs.ext4 /dev/loopX
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mkdir ./s390.rootfs
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sudo mount /dev/loopX ./s390.rootfs
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sudo debootstrap \
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--foreign \
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--arch=s390x \
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--variant=minbase \
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--include=" \
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iproute2, \
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iputils-ping, \
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isc-dhcp-client, \
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kmod, \
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libcap2, \
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libelf1, \
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netcat, \
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procps" \
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testing \
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./s390.rootfs
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sudo umount ./s390.rootfs
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sudo losetup -d /dev/loopX
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3. Compilation
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**************
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In addition to the usual Kconfig options required to run the BPF test suite, it
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is also helpful to select::
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CONFIG_NET_9P=y
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CONFIG_9P_FS=y
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CONFIG_NET_9P_VIRTIO=y
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CONFIG_VIRTIO_PCI=y
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as that would enable a very easy way to share files with the s390 virtual
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machine.
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Compiling kernel, modules and testsuite, as well as preparing gdb scripts to
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simplify debugging, can be done using the following commands::
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make ARCH=s390 CROSS_COMPILE=s390x-linux-gnu- menuconfig
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make ARCH=s390 CROSS_COMPILE=s390x-linux-gnu- bzImage modules scripts_gdb
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make ARCH=s390 CROSS_COMPILE=s390x-linux-gnu- \
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-C tools/testing/selftests \
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TARGETS=bpf \
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INSTALL_PATH=$PWD/tools/testing/selftests/kselftest_install \
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install
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4. Running the test suite
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*************************
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The virtual machine can be started as follows::
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qemu-system-s390x \
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-cpu max,zpci=on \
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-smp 2 \
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-m 4G \
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-kernel linux/arch/s390/boot/compressed/vmlinux \
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-drive file=./s390.img,if=virtio,format=raw \
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-nographic \
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-append 'root=/dev/vda rw console=ttyS1' \
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-virtfs local,path=./linux,security_model=none,mount_tag=linux \
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-object rng-random,filename=/dev/urandom,id=rng0 \
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-device virtio-rng-ccw,rng=rng0 \
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-netdev user,id=net0 \
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-device virtio-net-ccw,netdev=net0
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When using this on a real IBM Z, ``-enable-kvm`` may be added for better
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performance. When starting the virtual machine for the first time, disk image
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setup must be finalized using the following command::
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/debootstrap/debootstrap --second-stage
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Directory with the code built on the host as well as ``/proc`` and ``/sys``
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need to be mounted as follows::
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mkdir -p /linux
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mount -t 9p linux /linux
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mount -t proc proc /proc
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mount -t sysfs sys /sys
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After that, the test suite can be run using the following commands::
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cd /linux/tools/testing/selftests/kselftest_install
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./run_kselftest.sh
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As usual, tests can be also run individually::
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cd /linux/tools/testing/selftests/bpf
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./test_verifier
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5. Debugging
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************
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It is possible to debug the s390 kernel using QEMU GDB stub, which is activated
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by passing ``-s`` to QEMU.
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It is preferable to turn KASLR off, so that gdb would know where to find the
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kernel image in memory, by building the kernel with::
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RANDOMIZE_BASE=n
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GDB can then be attached using the following command::
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gdb-multiarch -ex 'target remote localhost:1234' ./vmlinux
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6. Network
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**********
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In case one needs to use the network in the virtual machine in order to e.g.
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install additional packages, it can be configured using::
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dhclient eth0
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7. Links
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********
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This document is a compilation of techniques, whose more comprehensive
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descriptions can be found by following these links:
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- `Debootstrap <https://wiki.debian.org/EmDebian/CrossDebootstrap>`_
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- `Multiarch <https://wiki.debian.org/Multiarch/HOWTO>`_
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- `Building LLVM <https://llvm.org/docs/CMake.html>`_
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- `Cross-compiling the kernel <https://wiki.gentoo.org/wiki/Embedded_Handbook/General/Cross-compiling_the_kernel>`_
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- `QEMU s390x Guest Support <https://wiki.qemu.org/Documentation/Platforms/S390X>`_
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- `Plan 9 folder sharing over Virtio <https://wiki.qemu.org/Documentation/9psetup>`_
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- `Using GDB with QEMU <https://wiki.osdev.org/Kernel_Debugging#Use_GDB_with_QEMU>`_
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