Fix for tasks example to compile when using kernal5_8 feature

[murrayh]

When attempting to compile examples with Kernel v5.13, I was getting the following error

     Compiling example-probes v0.1.0 (/Work/fly-io-coding-challenge/36800/redbpf/examples/example-probes)
  warning: due to multiple output types requested, the explicitly specified output file name will be adapted for each output type
 warning: ignoring --out-dir flag due to -o flag

  error[E0609]: no field `__bindgen_anon_1` on type `bpf_iter_meta`
    --> examples/example-probes/src/tasks/main.rs:12:31
     |
  12 |     let seq_ptr = (*meta_ptr).__bindgen_anon_1.seq;
     |                               ^^^^^^^^^^^^^^^^ unknown field
     |
     = note: available fields are: `_address`

  For more information about this error, try `rustc --explain E0609`.
  warning: `example-probes` (bin "tasks") generated 2 warnings
  error: could not compile `example-probes` due to previous error; 2 warnings emitted

I was using the command:

cargo build --no-default-features --features llvm13,kernel5_8 --examples

This change allowed the tasks example to compile and execute for me -- although there may be a more appropriate fix?

[rhdxmr]

@murrayh what distro do you use? I wonder why struct bpf_iter_meta does not have the union field.

And #undef bpf_iter_meta does not work since bpf_iter_meta is not a macro defined constant.

[murrayh]

My host operating system is Pop OS

Linux pop-os 5.13.0-7620-generic #20~1634827117~21.04~874b071-Ubuntu SMP Fri Oct 29 15:06:55 UTC  x86_64 x86_64 x86_64 GNU/Linux

My docker container is Ubuntu 21

#
# docker build -f Dockerfile.muz-devenv -t muz-devenv --build-arg kernel_version=$(uname -r) .
#

FROM ubuntu:21.04

ARG kernel_version


# Essential setup

ENV DEBIAN_FRONTEND=noninteractive

RUN ln -fs /usr/share/zoneinfo/Australia/Melbourne /etc/localtime

RUN apt-get update \
    && apt-get install -y --no-install-recommends \
        ca-certificates \
        curl \
        gpg \
        gpg-agent \
        tzdata \
        wget \
        ;


# Rust with LLVM 13

RUN echo "deb http://apt.llvm.org/focal/ llvm-toolchain-focal-13 main" > /etc/apt/sources.list.d/llvm-toolchain.list
RUN echo "deb-src http://apt.llvm.org/focal/ llvm-toolchain-focal-13 main" >> /etc/apt/sources.list.d/llvm-toolchain.list
RUN wget -O - https://apt.llvm.org/llvm-snapshot.gpg.key | apt-key add -

RUN apt-get update \
    && apt-get install -y --no-install-recommends \
        build-essential \
        libclang-13-dev \
        libllvm13 \
        llvm-13 \
        llvm-13-dev \
        llvm-13-runtime \
        ;

ENV RUSTUP_HOME=/usr/local/rustup \
    CARGO_HOME=/usr/local/cargo \
    PATH=/usr/local/cargo/bin:$PATH

RUN curl https://sh.rustup.rs -sSf > rustup.sh \
    && sh rustup.sh -y \
          --default-toolchain stable \
          --profile minimal \
          --no-modify-path \
    && rustup component add rustfmt \
    && rustup --version \
    && cargo --version \
    && rustc --version \
    && cargo install bindgen \
    && chmod a+w -R $CARGO_HOME \
    && rm -f rustup.sh


# Dependencies required to build redBPF

RUN apt-get update \
    && apt-get install -y --no-install-recommends \
        bc \
        bison \
        clang-13 \
        flex \
        libelf-dev \
        libssl-dev \
        zlib1g-dev \
        ;

RUN /bin/bash -c " \
    set -e ; \
    KV=$kernel_version ; \
    KV=\${KV%%-*} ; \
    KV=\${KV%.0} ; \
    wget -O ./linux-\${KV}.tar.gz https://www.kernel.org/pub/linux/kernel/v5.x/linux-\${KV}.tar.gz ; \
    tar -xzf ./linux-\${KV}.tar.gz -C /usr/src/ ; \
    ls -l /usr/src/linux-\${KV}/ ; \
    rm ./linux-\${KV}.tar.gz ; \
    "
RUN make -C /usr/src/linux-* defconfig
RUN make -C /usr/src/linux-* prepare


# Handy developer utilities

RUN apt-get update \
    && apt-get install -y --no-install-recommends \
        ethtool \
        gitk \
        lsb-release \
        net-tools \
        sudo \
        vim \
        ;

RUN wget https://github.com/watchexec/watchexec/releases/download/cli-v1.17.1/watchexec-1.17.1-x86_64-unknown-linux-gnu.deb \
    && dpkg -i ./watchexec-1.17.1-x86_64-unknown-linux-gnu.deb \
    && rm ./watchexec-1.17.1-x86_64-unknown-linux-gnu.deb

RUN wget https://github.com/BurntSushi/ripgrep/releases/download/13.0.0/ripgrep_13.0.0_amd64.deb \
    && dpkg -i ./ripgrep_13.0.0_amd64.deb \
    && rm ./ripgrep_13.0.0_amd64.deb

I don't know why the bindings for struct bpf_iter_meta are generated incorrectly. I might be able to debug it, but I won't have time for that work for some weeks.

One thing I noticed is that gen_bindings.rs has probably 20 or 30 structs defined that only have the _address field as the only member -- they look obviously incorrect.

[rhdxmr]

I'm glad to see you use Pop!_OS. I had been a Pop!_OS user until two months ago. The distro was pre-installed on my System76 oryx pro laptop.

Anyway, did you build RedBPF in your ubuntu 21 docker container? And you probably specify KERNEL_SOURCE environment variable to the /usr/src/linux-${KV} when running the cargo build? Perhaps the ${KV} is different from the host's kernel version 5.13.0-7620-generic?

[murrayh]

Yes, ${KV} is 5.13.0 -- the original kernel source code which is different to Pop!_OS 5.13.0-7620-generic.

Intuitively though I would not expect this to impact the generation of bindings. Sure, if I try and link in the bindings and execute the application it might crash or do undefined things. But generating the rust <-> c bindings -- the running kernel shouldn't matter? Although If the kernel does expose some API introspection capabilities that would be some cool tech I would like to look into