rbpf/src/lib.rs

// SPDX-License-Identifier: (Apache-2.0 OR MIT)
// Derived from uBPF <https://github.com/iovisor/ubpf>
// Copyright 2016 6WIND S.A. <quentin.monnet@6wind.com>
// Copyright 2023 Isovalent, Inc. <quentin@isovalent.com>

//! Virtual machine and JIT compiler for eBPF programs.
#![doc(
    html_logo_url = "https://raw.githubusercontent.com/qmonnet/rbpf/main/misc/rbpf.png",
    html_favicon_url = "https://raw.githubusercontent.com/qmonnet/rbpf/main/misc/rbpf.ico"
)]
// Test examples from README.md as part as doc tests.
#![doc = include_str!("../README.md")]
// Configures the crate to be `no_std` when `std` feature is disabled.
#![cfg_attr(not(feature = "std"), no_std)]

extern crate byteorder;
extern crate combine;
extern crate log;
#[cfg(feature = "std")]
extern crate time;

#[cfg(not(feature = "std"))]
extern crate alloc;

#[cfg(feature = "cranelift")]
extern crate cranelift_codegen;
#[cfg(feature = "cranelift")]
extern crate cranelift_frontend;
#[cfg(feature = "cranelift")]
extern crate cranelift_jit;
#[cfg(feature = "cranelift")]
extern crate cranelift_module;
#[cfg(feature = "cranelift")]
extern crate cranelift_native;

use crate::lib::*;
use byteorder::{ByteOrder, LittleEndian};

mod asm_parser;
pub mod assembler;
#[cfg(feature = "cranelift")]
mod cranelift;
pub mod disassembler;
pub mod ebpf;
pub mod helpers;
pub mod insn_builder;
mod interpreter;
#[cfg(all(not(windows), feature = "std"))]
mod jit;
#[cfg(not(feature = "std"))]
mod no_std_error;
mod verifier;

/// Reexports all the types needed from the `std`, `core`, and `alloc`
/// crates. This avoids elaborate import wrangling having to happen in every
/// module. Inspired by the design used in `serde`.
pub mod lib {
    mod core {
        #[cfg(not(feature = "std"))]
        pub use core::*;
        #[cfg(feature = "std")]
        pub use std::*;
    }

    pub use self::core::convert::TryInto;
    pub use self::core::mem;
    pub use self::core::mem::ManuallyDrop;
    pub use self::core::ptr;

    pub use self::core::f64;

    #[cfg(feature = "std")]
    pub use std::println;

    #[cfg(not(feature = "std"))]
    pub use alloc::vec;
    #[cfg(not(feature = "std"))]
    pub use alloc::vec::Vec;
    #[cfg(feature = "std")]
    pub use std::vec::Vec;

    #[cfg(not(feature = "std"))]
    pub use alloc::string::{String, ToString};
    #[cfg(feature = "std")]
    pub use std::string::{String, ToString};

    // In no_std we cannot use randomness for hashing, thus we need to use
    // BTree-based implementations of Maps and Sets. The cranelift module uses
    // BTrees by default, hence we need to expose it twice here.
    #[cfg(not(feature = "std"))]
    pub use alloc::collections::{BTreeMap as HashMap, BTreeMap, BTreeSet as HashSet, BTreeSet};
    #[cfg(feature = "std")]
    pub use std::collections::{BTreeMap, HashMap, HashSet};

    /// In no_std we use a custom implementation of the error which acts as a
    /// replacement for the io Error.
    #[cfg(not(feature = "std"))]
    pub use crate::no_std_error::{Error, ErrorKind};
    #[cfg(feature = "std")]
    pub use std::io::{Error, ErrorKind};

    #[cfg(not(feature = "std"))]
    pub use alloc::format;
}

/// eBPF verification function that returns an error if the program does not meet its requirements.
///
/// Some examples of things the verifier may reject the program for:
///
///   - Program does not terminate.
///   - Unknown instructions.
///   - Bad formed instruction.
///   - Unknown eBPF helper index.
pub type Verifier = fn(prog: &[u8]) -> Result<(), Error>;

/// eBPF helper function.
pub type Helper = fn(u64, u64, u64, u64, u64) -> u64;

// A metadata buffer with two offset indications. It can be used in one kind of eBPF VM to simulate
// the use of a metadata buffer each time the program is executed, without the user having to
// actually handle it. The offsets are used to tell the VM where in the buffer the pointers to
// packet data start and end should be stored each time the program is run on a new packet.
struct MetaBuff {
    data_offset: usize,
    data_end_offset: usize,
    buffer: Vec<u8>,
}

/// A virtual machine to run eBPF program. This kind of VM is used for programs expecting to work
/// on a metadata buffer containing pointers to packet data.
///
/// # Examples
///
/// ```
/// let prog = &[
///     0x79, 0x11, 0x08, 0x00, 0x00, 0x00, 0x00, 0x00, // Load mem from mbuff at offset 8 into R1.
///     0x69, 0x10, 0x02, 0x00, 0x00, 0x00, 0x00, 0x00, // ldhx r1[2], r0
///     0x95, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00  // exit
/// ];
/// let mem = &mut [
///     0xaa, 0xbb, 0x11, 0x22, 0xcc, 0xdd
/// ];
///
/// // Just for the example we create our metadata buffer from scratch, and we store the pointers
/// // to packet data start and end in it.
/// let mut mbuff = [0u8; 32];
/// unsafe {
///     let mut data     = mbuff.as_ptr().offset(8)  as *mut u64;
///     let mut data_end = mbuff.as_ptr().offset(24) as *mut u64;
///     *data     = mem.as_ptr() as u64;
///     *data_end = mem.as_ptr() as u64 + mem.len() as u64;
/// }
///
/// // Instantiate a VM.
/// let mut vm = rbpf::EbpfVmMbuff::new(Some(prog)).unwrap();
///
/// // Provide both a reference to the packet data, and to the metadata buffer.
/// let res = vm.execute_program(mem, &mut mbuff).unwrap();
/// assert_eq!(res, 0x2211);
/// ```
pub struct EbpfVmMbuff<'a> {
    prog: Option<&'a [u8]>,
    verifier: Verifier,
    #[cfg(all(not(windows), feature = "std"))]
    jit: Option<jit::JitMemory<'a>>,
    #[cfg(feature = "cranelift")]
    cranelift_prog: Option<cranelift::CraneliftProgram>,
    helpers: HashMap<u32, ebpf::Helper>,
    allowed_memory: HashSet<u64>,
}

impl<'a> EbpfVmMbuff<'a> {
    /// Create a new virtual machine instance, and load an eBPF program into that instance.
    /// When attempting to load the program, it passes through a simple verifier.
    ///
    /// # Examples
    ///
    /// ```
    /// let prog = &[
    ///     0x79, 0x11, 0x08, 0x00, 0x00, 0x00, 0x00, 0x00, // Load mem from mbuff into R1.
    ///     0x69, 0x10, 0x02, 0x00, 0x00, 0x00, 0x00, 0x00, // ldhx r1[2], r0
    ///     0x95, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00  // exit
    /// ];
    ///
    /// // Instantiate a VM.
    /// let mut vm = rbpf::EbpfVmMbuff::new(Some(prog)).unwrap();
    /// ```
    pub fn new(prog: Option<&'a [u8]>) -> Result<EbpfVmMbuff<'a>, Error> {
        if let Some(prog) = prog {
            verifier::check(prog)?;
        }

        Ok(EbpfVmMbuff {
            prog,
            verifier: verifier::check,
            #[cfg(all(not(windows), feature = "std"))]
            jit: None,
            #[cfg(feature = "cranelift")]
            cranelift_prog: None,
            helpers: HashMap::new(),
            allowed_memory: HashSet::new(),
        })
    }

    /// Load a new eBPF program into the virtual machine instance.
    ///
    /// # Examples
    ///
    /// ```
    /// let prog1 = &[
    ///     0xb7, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // mov r0, 0
    ///     0x95, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00  // exit
    /// ];
    /// let prog2 = &[
    ///     0x79, 0x11, 0x08, 0x00, 0x00, 0x00, 0x00, 0x00, // Load mem from mbuff into R1.
    ///     0x69, 0x10, 0x02, 0x00, 0x00, 0x00, 0x00, 0x00, // ldhx r1[2], r0
    ///     0x95, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00  // exit
    /// ];
    ///
    /// // Instantiate a VM.
    /// let mut vm = rbpf::EbpfVmMbuff::new(Some(prog1)).unwrap();
    /// vm.set_program(prog2).unwrap();
    /// ```
    pub fn set_program(&mut self, prog: &'a [u8]) -> Result<(), Error> {
        (self.verifier)(prog)?;
        self.prog = Some(prog);
        Ok(())
    }

    /// Set a new verifier function. The function should return an `Error` if the program should be
    /// rejected by the virtual machine. If a program has been loaded to the VM already, the
    /// verifier is immediately run.
    ///
    /// # Examples
    ///
    /// ```
    /// use rbpf::lib::{Error, ErrorKind};
    /// use rbpf::ebpf;
    ///
    /// // Define a simple verifier function.
    /// fn verifier(prog: &[u8]) -> Result<(), Error> {
    ///     let last_insn = ebpf::get_insn(prog, (prog.len() / ebpf::INSN_SIZE) - 1);
    ///     if last_insn.opc != ebpf::EXIT {
    ///         return Err(Error::new(ErrorKind::Other,
    ///                    "[Verifier] Error: program does not end with “EXIT” instruction"));
    ///     }
    ///     Ok(())
    /// }
    ///
    /// let prog1 = &[
    ///     0xb7, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // mov r0, 0
    ///     0x95, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00  // exit
    /// ];
    ///
    /// // Instantiate a VM.
    /// let mut vm = rbpf::EbpfVmMbuff::new(Some(prog1)).unwrap();
    /// // Change the verifier.
    /// vm.set_verifier(verifier).unwrap();
    /// ```
    pub fn set_verifier(&mut self, verifier: Verifier) -> Result<(), Error> {
        if let Some(prog) = self.prog {
            verifier(prog)?;
        }
        self.verifier = verifier;
        Ok(())
    }

    /// Register a built-in or user-defined helper function in order to use it later from within
    /// the eBPF program. The helper is registered into a hashmap, so the `key` can be any `u32`.
    ///
    /// If using JIT-compiled eBPF programs, be sure to register all helpers before compiling the
    /// program. You should be able to change registered helpers after compiling, but not to add
    /// new ones (i.e. with new keys).
    ///
    /// # Examples
    ///
    /// ```
    /// use rbpf::helpers;
    ///
    /// // This program was compiled with clang, from a C program containing the following single
    /// // instruction: `return bpf_trace_printk("foo %c %c %c\n", 10, 1, 2, 3);`
    /// let prog = &[
    ///     0x18, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // load 0 as u64 into r1 (That would be
    ///     0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // replaced by tc by the address of
    ///                                                     // the format string, in the .map
    ///                                                     // section of the ELF file).
    ///     0xb7, 0x02, 0x00, 0x00, 0x0a, 0x00, 0x00, 0x00, // mov r2, 10
    ///     0xb7, 0x03, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, // mov r3, 1
    ///     0xb7, 0x04, 0x00, 0x00, 0x02, 0x00, 0x00, 0x00, // mov r4, 2
    ///     0xb7, 0x05, 0x00, 0x00, 0x03, 0x00, 0x00, 0x00, // mov r5, 3
    ///     0x85, 0x00, 0x00, 0x00, 0x06, 0x00, 0x00, 0x00, // call helper with key 6
    ///     0x95, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00  // exit
    /// ];
    ///
    /// // Instantiate a VM.
    /// let mut vm = rbpf::EbpfVmMbuff::new(Some(prog)).unwrap();
    ///
    /// // Register a helper.
    /// // On running the program this helper will print the content of registers r3, r4 and r5 to
    /// // standard output.
    /// # #[cfg(feature = "std")]
    /// vm.register_helper(6, helpers::bpf_trace_printf).unwrap();
    /// ```
    pub fn register_helper(&mut self, key: u32, function: Helper) -> Result<(), Error> {
        self.helpers.insert(key, function);
        Ok(())
    }

    /// Register a set of addresses that the eBPF program is allowed to load and store.
    ///
    /// When using certain helpers, typically map lookups, the Linux kernel will return pointers
    /// to structs that the eBPF program needs to interact with. By default rbpf only allows the
    /// program to interact with its stack, the memory buffer and the program itself, making it
    /// impossible to supply functional implementations of these helpers.
    /// This option allows you to pass in a list of addresses that rbpf will allow the program
    /// to load and store to. Given Rust's memory model you will always know these addresses up
    /// front when implementing the helpers.
    ///
    /// Each invocation of this method will append to the set of allowed addresses.
    ///
    /// # Examples
    ///
    /// ```
    /// use std::iter::FromIterator;
    /// use std::ptr::addr_of;
    ///
    /// struct MapValue {
    ///     data: u8
    /// }
    /// static VALUE: MapValue = MapValue { data: 1 };
    ///
    /// let prog = &[
    ///     0xb7, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // mov r0, 0
    ///     0x95, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00  // exit
    /// ];
    ///
    /// // Instantiate a VM.
    /// let mut vm = rbpf::EbpfVmMbuff::new(Some(prog)).unwrap();
    /// let start = addr_of!(VALUE) as u64;
    /// let addrs = Vec::from_iter(start..start+size_of::<MapValue>() as u64);
    /// vm.register_allowed_memory(&addrs);
    /// ```
    pub fn register_allowed_memory(&mut self, addrs: &[u64]) {
        for i in addrs {
            self.allowed_memory.insert(*i);
        }
    }

    /// Execute the program loaded, with the given packet data and metadata buffer.
    ///
    /// If the program is made to be compatible with Linux kernel, it is expected to load the
    /// address of the beginning and of the end of the memory area used for packet data from the
    /// metadata buffer, at some appointed offsets. It is up to the user to ensure that these
    /// pointers are correctly stored in the buffer.
    ///
    /// # Examples
    ///
    /// ```
    /// let prog = &[
    ///     0x79, 0x11, 0x08, 0x00, 0x00, 0x00, 0x00, 0x00, // Load mem from mbuff into R1.
    ///     0x69, 0x10, 0x02, 0x00, 0x00, 0x00, 0x00, 0x00, // ldhx r1[2], r0
    ///     0x95, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00  // exit
    /// ];
    /// let mem = &mut [
    ///     0xaa, 0xbb, 0x11, 0x22, 0xcc, 0xdd
    /// ];
    ///
    /// // Just for the example we create our metadata buffer from scratch, and we store the
    /// // pointers to packet data start and end in it.
    /// let mut mbuff = [0u8; 32];
    /// unsafe {
    ///     let mut data     = mbuff.as_ptr().offset(8)  as *mut u64;
    ///     let mut data_end = mbuff.as_ptr().offset(24) as *mut u64;
    ///     *data     = mem.as_ptr() as u64;
    ///     *data_end = mem.as_ptr() as u64 + mem.len() as u64;
    /// }
    ///
    /// // Instantiate a VM.
    /// let mut vm = rbpf::EbpfVmMbuff::new(Some(prog)).unwrap();
    ///
    /// // Provide both a reference to the packet data, and to the metadata buffer.
    /// let res = vm.execute_program(mem, &mut mbuff).unwrap();
    /// assert_eq!(res, 0x2211);
    /// ```
    pub fn execute_program(&self, mem: &[u8], mbuff: &[u8]) -> Result<u64, Error> {
        interpreter::execute_program(self.prog, mem, mbuff, &self.helpers, &self.allowed_memory)
    }

    /// JIT-compile the loaded program. No argument required for this.
    ///
    /// If using helper functions, be sure to register them into the VM before calling this
    /// function.
    ///
    /// # Examples
    ///
    /// ```
    /// let prog = &[
    ///     0x79, 0x11, 0x08, 0x00, 0x00, 0x00, 0x00, 0x00, // Load mem from mbuff into R1.
    ///     0x69, 0x10, 0x02, 0x00, 0x00, 0x00, 0x00, 0x00, // ldhx r1[2], r0
    ///     0x95, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00  // exit
    /// ];
    ///
    /// // Instantiate a VM.
    /// let mut vm = rbpf::EbpfVmMbuff::new(Some(prog)).unwrap();
    ///
    /// vm.jit_compile();
    /// ```
    #[cfg(all(not(windows), feature = "std"))]
    pub fn jit_compile(&mut self) -> Result<(), Error> {
        let prog = match self.prog {
            Some(prog) => prog,
            None => Err(Error::new(
                ErrorKind::Other,
                "Error: No program set, call prog_set() to load one",
            ))?,
        };
        self.jit = Some(jit::JitMemory::new(prog, &self.helpers, true, false)?);
        Ok(())
    }

    /// Execute the previously JIT-compiled program, with the given packet data and metadata
    /// buffer, in a manner very similar to `execute_program()`.
    ///
    /// If the program is made to be compatible with Linux kernel, it is expected to load the
    /// address of the beginning and of the end of the memory area used for packet data from the
    /// metadata buffer, at some appointed offsets. It is up to the user to ensure that these
    /// pointers are correctly stored in the buffer.
    ///
    /// # Safety
    ///
    /// **WARNING:** JIT-compiled assembly code is not safe, in particular there is no runtime
    /// check for memory access; so if the eBPF program attempts erroneous accesses, this may end
    /// very bad (program may segfault). It may be wise to check that the program works with the
    /// interpreter before running the JIT-compiled version of it.
    ///
    /// For this reason the function should be called from within an `unsafe` bloc.
    ///
    /// # Examples
    ///
    /// ```
    /// let prog = &[
    ///     0x79, 0x11, 0x08, 0x00, 0x00, 0x00, 0x00, 0x00, // Load mem from mbuff into r1.
    ///     0x69, 0x10, 0x02, 0x00, 0x00, 0x00, 0x00, 0x00, // ldhx r1[2], r0
    ///     0x95, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00  // exit
    /// ];
    /// let mem = &mut [
    ///     0xaa, 0xbb, 0x11, 0x22, 0xcc, 0xdd
    /// ];
    ///
    /// // Just for the example we create our metadata buffer from scratch, and we store the
    /// // pointers to packet data start and end in it.
    /// let mut mbuff = [0u8; 32];
    /// unsafe {
    ///     let mut data     = mbuff.as_ptr().offset(8)  as *mut u64;
    ///     let mut data_end = mbuff.as_ptr().offset(24) as *mut u64;
    ///     *data     = mem.as_ptr() as u64;
    ///     *data_end = mem.as_ptr() as u64 + mem.len() as u64;
    /// }
    ///
    /// // Instantiate a VM.
    /// let mut vm = rbpf::EbpfVmMbuff::new(Some(prog)).unwrap();
    ///
    /// # #[cfg(all(not(windows), feature = "std"))]
    /// vm.jit_compile();
    ///
    /// // Provide both a reference to the packet data, and to the metadata buffer.
    /// # #[cfg(all(not(windows), feature = "std"))]
    /// unsafe {
    ///     let res = vm.execute_program_jit(mem, &mut mbuff).unwrap();
    ///     assert_eq!(res, 0x2211);
    /// }
    /// ```
    #[cfg(all(not(windows), feature = "std"))]
    pub unsafe fn execute_program_jit(
        &self,
        mem: &mut [u8],
        mbuff: &'a mut [u8],
    ) -> Result<u64, Error> {
        // If packet data is empty, do not send the address of an empty slice; send a null pointer
        //  as first argument instead, as this is uBPF's behavior (empty packet should not happen
        //  in the kernel; anyway the verifier would prevent the use of uninitialized registers).
        //  See `mul_loop` test.
        let mem_ptr = match mem.len() {
            0 => std::ptr::null_mut(),
            _ => mem.as_ptr() as *mut u8,
        };
        // The last two arguments are not used in this function. They would be used if there was a
        // need to indicate to the JIT at which offset in the mbuff mem_ptr and mem_ptr + mem.len()
        // should be stored; this is what happens with struct EbpfVmFixedMbuff.
        match &self.jit {
            Some(jit) => Ok(jit.get_prog()(
                mbuff.as_ptr() as *mut u8,
                mbuff.len(),
                mem_ptr,
                mem.len(),
                0,
                0,
            )),
            None => Err(Error::new(
                ErrorKind::Other,
                "Error: program has not been JIT-compiled",
            )),
        }
    }

    /// Compile the loaded program using the Cranelift JIT.
    ///
    /// If using helper functions, be sure to register them into the VM before calling this
    /// function.
    ///
    /// # Examples
    ///
    /// ```
    /// let prog = &[
    ///     0x79, 0x11, 0x08, 0x00, 0x00, 0x00, 0x00, 0x00, // Load mem from mbuff into R1.
    ///     0x69, 0x10, 0x02, 0x00, 0x00, 0x00, 0x00, 0x00, // ldhx r1[2], r0
    ///     0x95, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00  // exit
    /// ];
    ///
    /// // Instantiate a VM.
    /// let mut vm = rbpf::EbpfVmMbuff::new(Some(prog)).unwrap();
    ///
    /// vm.cranelift_compile();
    /// ```
    #[cfg(feature = "cranelift")]
    pub fn cranelift_compile(&mut self) -> Result<(), Error> {
        use crate::cranelift::CraneliftCompiler;

        let prog = match self.prog {
            Some(prog) => prog,
            None => Err(Error::new(
                ErrorKind::Other,
                "Error: No program set, call prog_set() to load one",
            ))?,
        };

        let compiler = CraneliftCompiler::new(self.helpers.clone());
        let program = compiler.compile_function(prog)?;

        self.cranelift_prog = Some(program);
        Ok(())
    }

    /// Execute the previously compiled program, with the given packet data and metadata
    /// buffer, in a manner very similar to `execute_program()`.
    ///
    /// If the program is made to be compatible with Linux kernel, it is expected to load the
    /// address of the beginning and of the end of the memory area used for packet data from the
    /// metadata buffer, at some appointed offsets. It is up to the user to ensure that these
    /// pointers are correctly stored in the buffer.
    ///
    ///
    /// # Examples
    ///
    /// ```
    /// let prog = &[
    ///     0x79, 0x11, 0x08, 0x00, 0x00, 0x00, 0x00, 0x00, // Load mem from mbuff into r1.
    ///     0x69, 0x10, 0x02, 0x00, 0x00, 0x00, 0x00, 0x00, // ldhx r1[2], r0
    ///     0x95, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00  // exit
    /// ];
    /// let mem = &mut [
    ///     0xaa, 0xbb, 0x11, 0x22, 0xcc, 0xdd
    /// ];
    ///
    /// // Just for the example we create our metadata buffer from scratch, and we store the
    /// // pointers to packet data start and end in it.
    /// let mut mbuff = [0u8; 32];
    /// unsafe {
    ///     let mut data     = mbuff.as_ptr().offset(8)  as *mut u64;
    ///     let mut data_end = mbuff.as_ptr().offset(24) as *mut u64;
    ///     *data     = mem.as_ptr() as u64;
    ///     *data_end = mem.as_ptr() as u64 + mem.len() as u64;
    /// }
    ///
    /// // Instantiate a VM.
    /// let mut vm = rbpf::EbpfVmMbuff::new(Some(prog)).unwrap();
    ///
    /// vm.cranelift_compile();
    ///
    /// // Provide both a reference to the packet data, and to the metadata buffer.
    /// let res = vm.execute_program_cranelift(mem, &mut mbuff).unwrap();
    /// assert_eq!(res, 0x2211);
    /// ```
    #[cfg(feature = "cranelift")]
    pub fn execute_program_cranelift(
        &self,
        mem: &mut [u8],
        mbuff: &'a mut [u8],
    ) -> Result<u64, Error> {
        // If packet data is empty, do not send the address of an empty slice; send a null pointer
        //  as first argument instead, as this is uBPF's behavior (empty packet should not happen
        //  in the kernel; anyway the verifier would prevent the use of uninitialized registers).
        //  See `mul_loop` test.
        let mem_ptr = match mem.len() {
            0 => ptr::null_mut(),
            _ => mem.as_ptr() as *mut u8,
        };

        // The last two arguments are not used in this function. They would be used if there was a
        // need to indicate to the JIT at which offset in the mbuff mem_ptr and mem_ptr + mem.len()
        // should be stored; this is what happens with struct EbpfVmFixedMbuff.
        match &self.cranelift_prog {
            Some(prog) => {
                Ok(prog.execute(mem_ptr, mem.len(), mbuff.as_ptr() as *mut u8, mbuff.len()))
            }
            None => Err(Error::new(
                ErrorKind::Other,
                "Error: program has not been compiled with cranelift",
            )),
        }
    }
}

/// A virtual machine to run eBPF program. This kind of VM is used for programs expecting to work
/// on a metadata buffer containing pointers to packet data, but it internally handles the buffer
/// so as to save the effort to manually handle the metadata buffer for the user.
///
/// This struct implements a static internal buffer that is passed to the program. The user has to
/// indicate the offset values at which the eBPF program expects to find the start and the end of
/// packet data in the buffer. On calling the `execute_program()` or `execute_program_jit()` functions, the
/// struct automatically updates the addresses in this static buffer, at the appointed offsets, for
/// the start and the end of the packet data the program is called upon.
///
/// # Examples
///
/// This was compiled with clang from the following program, in C:
///
/// ```c
/// #include <linux/bpf.h>
/// #include "path/to/linux/samples/bpf/bpf_helpers.h"
///
/// SEC(".classifier")
/// int classifier(struct __sk_buff *skb)
/// {
///   void *data = (void *)(long)skb->data;
///   void *data_end = (void *)(long)skb->data_end;
///
///   // Check program is long enough.
///   if (data + 5 > data_end)
///     return 0;
///
///   return *((char *)data + 5);
/// }
/// ```
///
/// Some small modifications have been brought to have it work, see comments.
///
/// ```
/// let prog = &[
///     0xb7, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // mov r0, 0
///     // Here opcode 0x61 had to be replace by 0x79 so as to load a 8-bytes long address.
///     // Also, offset 0x4c had to be replace with e.g. 0x40 so as to prevent the two pointers
///     // from overlapping in the buffer.
///     0x79, 0x12, 0x40, 0x00, 0x00, 0x00, 0x00, 0x00, // load pointer to mem from r1[0x40] to r2
///     0x07, 0x02, 0x00, 0x00, 0x05, 0x00, 0x00, 0x00, // add r2, 5
///     // Here opcode 0x61 had to be replace by 0x79 so as to load a 8-bytes long address.
///     0x79, 0x11, 0x50, 0x00, 0x00, 0x00, 0x00, 0x00, // load ptr to mem_end from r1[0x50] to r1
///     0x2d, 0x12, 0x03, 0x00, 0x00, 0x00, 0x00, 0x00, // if r2 > r1 skip 3 instructions
///     0x71, 0x20, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // load r2 (= *(mem + 5)) into r0
///     0x67, 0x00, 0x00, 0x00, 0x38, 0x00, 0x00, 0x00, // r0 >>= 56
///     0xc7, 0x00, 0x00, 0x00, 0x38, 0x00, 0x00, 0x00, // r0 <<= 56 (arsh) extend byte sign to u64
///     0x95, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00  // exit
/// ];
/// let mem1 = &mut [
///     0xaa, 0xbb, 0x11, 0x22, 0xcc, 0xdd
/// ];
/// let mem2 = &mut [
///     0xaa, 0xbb, 0x11, 0x22, 0xcc, 0x27
/// ];
///
/// // Instantiate a VM. Note that we provide the start and end offsets for mem pointers.
/// let mut vm = rbpf::EbpfVmFixedMbuff::new(Some(prog), 0x40, 0x50).unwrap();
///
/// // Provide only a reference to the packet data. We do not manage the metadata buffer.
/// let res = vm.execute_program(mem1).unwrap();
/// assert_eq!(res, 0xffffffffffffffdd);
///
/// let res = vm.execute_program(mem2).unwrap();
/// assert_eq!(res, 0x27);
/// ```
pub struct EbpfVmFixedMbuff<'a> {
    parent: EbpfVmMbuff<'a>,
    mbuff: MetaBuff,
}

impl<'a> EbpfVmFixedMbuff<'a> {
    /// Create a new virtual machine instance, and load an eBPF program into that instance.
    /// When attempting to load the program, it passes through a simple verifier.
    ///
    /// # Examples
    ///
    /// ```
    /// let prog = &[
    ///     0xb7, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // mov r0, 0
    ///     0x79, 0x12, 0x40, 0x00, 0x00, 0x00, 0x00, 0x00, // load mem from r1[0x40] to r2
    ///     0x07, 0x02, 0x00, 0x00, 0x05, 0x00, 0x00, 0x00, // add r2, 5
    ///     0x79, 0x11, 0x50, 0x00, 0x00, 0x00, 0x00, 0x00, // load mem_end from r1[0x50] to r1
    ///     0x2d, 0x12, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, // if r2 > r1 skip 3 instructions
    ///     0x71, 0x20, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // load r2 (= *(mem + 5)) into r0
    ///     0x95, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00  // exit
    /// ];
    ///
    /// // Instantiate a VM. Note that we provide the start and end offsets for mem pointers.
    /// let mut vm = rbpf::EbpfVmFixedMbuff::new(Some(prog), 0x40, 0x50).unwrap();
    /// ```
    pub fn new(
        prog: Option<&'a [u8]>,
        data_offset: usize,
        data_end_offset: usize,
    ) -> Result<EbpfVmFixedMbuff<'a>, Error> {
        let parent = EbpfVmMbuff::new(prog)?;
        let get_buff_len = |x: usize, y: usize| if x >= y { x + 8 } else { y + 8 };
        let buffer = vec![0u8; get_buff_len(data_offset, data_end_offset)];
        let mbuff = MetaBuff {
            data_offset,
            data_end_offset,
            buffer,
        };
        Ok(EbpfVmFixedMbuff { parent, mbuff })
    }

    /// Load a new eBPF program into the virtual machine instance.
    ///
    /// At the same time, load new offsets for storing pointers to start and end of packet data in
    /// the internal metadata buffer.
    ///
    /// # Examples
    ///
    /// ```
    /// let prog1 = &[
    ///     0xb7, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // mov r0, 0
    ///     0x95, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00  // exit
    /// ];
    /// let prog2 = &[
    ///     0xb7, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // mov r0, 0
    ///     0x79, 0x12, 0x40, 0x00, 0x00, 0x00, 0x00, 0x00, // load mem from r1[0x40] to r2
    ///     0x07, 0x02, 0x00, 0x00, 0x05, 0x00, 0x00, 0x00, // add r2, 5
    ///     0x79, 0x11, 0x50, 0x00, 0x00, 0x00, 0x00, 0x00, // load mem_end from r1[0x50] to r1
    ///     0x2d, 0x12, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, // if r2 > r1 skip 3 instructions
    ///     0x71, 0x20, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // load r2 (= *(mem + 5)) into r0
    ///     0x95, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00  // exit
    /// ];
    ///
    /// let mem = &mut [
    ///     0xaa, 0xbb, 0x11, 0x22, 0xcc, 0x27,
    /// ];
    ///
    /// let mut vm = rbpf::EbpfVmFixedMbuff::new(Some(prog1), 0, 0).unwrap();
    /// vm.set_program(prog2, 0x40, 0x50);
    ///
    /// let res = vm.execute_program(mem).unwrap();
    /// assert_eq!(res, 0x27);
    /// ```
    pub fn set_program(
        &mut self,
        prog: &'a [u8],
        data_offset: usize,
        data_end_offset: usize,
    ) -> Result<(), Error> {
        let get_buff_len = |x: usize, y: usize| if x >= y { x + 8 } else { y + 8 };
        let buffer = vec![0u8; get_buff_len(data_offset, data_end_offset)];
        self.mbuff.buffer = buffer;
        self.mbuff.data_offset = data_offset;
        self.mbuff.data_end_offset = data_end_offset;
        self.parent.set_program(prog)?;
        Ok(())
    }

    /// Set a new verifier function. The function should return an `Error` if the program should be
    /// rejected by the virtual machine. If a program has been loaded to the VM already, the
    /// verifier is immediately run.
    ///
    /// # Examples
    ///
    /// ```
    /// use rbpf::lib::{Error, ErrorKind};
    /// use rbpf::ebpf;
    ///
    /// // Define a simple verifier function.
    /// fn verifier(prog: &[u8]) -> Result<(), Error> {
    ///     let last_insn = ebpf::get_insn(prog, (prog.len() / ebpf::INSN_SIZE) - 1);
    ///     if last_insn.opc != ebpf::EXIT {
    ///         return Err(Error::new(ErrorKind::Other,
    ///                    "[Verifier] Error: program does not end with “EXIT” instruction"));
    ///     }
    ///     Ok(())
    /// }
    ///
    /// let prog1 = &[
    ///     0xb7, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // mov r0, 0
    ///     0x95, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00  // exit
    /// ];
    ///
    /// // Instantiate a VM.
    /// let mut vm = rbpf::EbpfVmMbuff::new(Some(prog1)).unwrap();
    /// // Change the verifier.
    /// vm.set_verifier(verifier).unwrap();
    /// ```
    pub fn set_verifier(&mut self, verifier: Verifier) -> Result<(), Error> {
        self.parent.set_verifier(verifier)
    }

    /// Register a built-in or user-defined helper function in order to use it later from within
    /// the eBPF program. The helper is registered into a hashmap, so the `key` can be any `u32`.
    ///
    /// If using JIT-compiled eBPF programs, be sure to register all helpers before compiling the
    /// program. You should be able to change registered helpers after compiling, but not to add
    /// new ones (i.e. with new keys).
    ///
    /// # Examples
    ///
    /// ```
    /// #[cfg(feature = "std")] {
    ///     use rbpf::helpers;
    ///
    ///     // This program was compiled with clang, from a C program containing the following single
    ///     // instruction: `return bpf_trace_printk("foo %c %c %c\n", 10, 1, 2, 3);`
    ///     let prog = &[
    ///         0xb7, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // mov r0, 0
    ///         0x79, 0x12, 0x40, 0x00, 0x00, 0x00, 0x00, 0x00, // load mem from r1[0x40] to r2
    ///         0x07, 0x02, 0x00, 0x00, 0x05, 0x00, 0x00, 0x00, // add r2, 5
    ///         0x79, 0x11, 0x50, 0x00, 0x00, 0x00, 0x00, 0x00, // load mem_end from r1[0x50] to r1
    ///         0x2d, 0x12, 0x06, 0x00, 0x00, 0x00, 0x00, 0x00, // if r2 > r1 skip 6 instructions
    ///         0x71, 0x21, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // load r2 (= *(mem + 5)) into r1
    ///         0xb7, 0x02, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // mov r2, 0
    ///         0xb7, 0x03, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // mov r3, 0
    ///         0xb7, 0x04, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // mov r4, 0
    ///         0xb7, 0x05, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // mov r5, 0
    ///         0x85, 0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, // call helper with key 1
    ///         0x95, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00  // exit
    ///     ];
    ///
    ///     let mem = &mut [
    ///         0xaa, 0xbb, 0x11, 0x22, 0xcc, 0x09,
    ///     ];
    ///
    ///     // Instantiate a VM.
    ///     let mut vm = rbpf::EbpfVmFixedMbuff::new(Some(prog), 0x40, 0x50).unwrap();
    ///
    ///     // Register a helper. This helper will store the result of the square root of r1 into r0.
    ///     vm.register_helper(1, helpers::sqrti);
    ///
    ///     let res = vm.execute_program(mem).unwrap();
    ///     assert_eq!(res, 3);
    /// }
    /// ```
    pub fn register_helper(
        &mut self,
        key: u32,
        function: fn(u64, u64, u64, u64, u64) -> u64,
    ) -> Result<(), Error> {
        self.parent.register_helper(key, function)
    }

    /// Register an object that the eBPF program is allowed to load and store.
    ///
    /// When using certain helpers, typically map lookups, the Linux kernel will return pointers
    /// to structs that the eBPF program needs to interact with. By default rbpf only allows the
    /// program to interact with its stack, the memory buffer and the program itself, making it
    /// impossible to supply functional implementations of these helpers.
    /// This option allows you to pass in a list of addresses that rbpf will allow the program
    /// to load and store to. Given Rust's memory model you will always know these addresses up
    /// front when implementing the helpers.
    ///
    /// Each invocation of this method will append to the set of allowed addresses.
    ///
    /// # Examples
    ///
    /// ```
    /// use std::iter::FromIterator;
    /// use std::ptr::addr_of;
    ///
    /// struct MapValue {
    ///     data: u8
    /// }
    /// static VALUE: MapValue = MapValue { data: 1 };
    ///
    /// let prog = &[
    ///     0xb7, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // mov r0, 0
    ///     0x95, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00  // exit
    /// ];
    ///
    /// // Instantiate a VM.
    /// let mut vm = rbpf::EbpfVmFixedMbuff::new(Some(prog), 0x40, 0x50).unwrap();
    /// let start = addr_of!(VALUE) as u64;
    /// let addrs = Vec::from_iter(start..start+size_of::<MapValue>() as u64);
    /// vm.register_allowed_memory(&addrs);
    /// ```
    pub fn register_allowed_memory(&mut self, allowed: &[u64]) {
        self.parent.register_allowed_memory(allowed)
    }

    /// Execute the program loaded, with the given packet data.
    ///
    /// If the program is made to be compatible with Linux kernel, it is expected to load the
    /// address of the beginning and of the end of the memory area used for packet data from some
    /// metadata buffer, which in the case of this VM is handled internally. The offsets at which
    /// the addresses should be placed should have be set at the creation of the VM.
    ///
    /// # Examples
    ///
    /// ```
    /// let prog = &[
    ///     0xb7, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // mov r0, 0
    ///     0x79, 0x12, 0x40, 0x00, 0x00, 0x00, 0x00, 0x00, // load mem from r1[0x40] to r2
    ///     0x07, 0x02, 0x00, 0x00, 0x05, 0x00, 0x00, 0x00, // add r2, 5
    ///     0x79, 0x11, 0x50, 0x00, 0x00, 0x00, 0x00, 0x00, // load mem_end from r1[0x50] to r1
    ///     0x2d, 0x12, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, // if r2 > r1 skip 3 instructions
    ///     0x71, 0x20, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // load r2 (= *(mem + 5)) into r0
    ///     0x95, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00  // exit
    /// ];
    /// let mem = &mut [
    ///     0xaa, 0xbb, 0x11, 0x22, 0xcc, 0xdd
    /// ];
    ///
    /// // Instantiate a VM. Note that we provide the start and end offsets for mem pointers.
    /// let mut vm = rbpf::EbpfVmFixedMbuff::new(Some(prog), 0x40, 0x50).unwrap();
    ///
    /// // Provide only a reference to the packet data. We do not manage the metadata buffer.
    /// let res = vm.execute_program(mem).unwrap();
    /// assert_eq!(res, 0xdd);
    /// ```
    pub fn execute_program(&mut self, mem: &'a mut [u8]) -> Result<u64, Error> {
        let l = self.mbuff.buffer.len();
        // Can this ever happen? Probably not, should be ensured at mbuff creation.
        if self.mbuff.data_offset + 8 > l || self.mbuff.data_end_offset + 8 > l {
            Err(Error::new(ErrorKind::Other, format!("Error: buffer too small ({:?}), cannot use data_offset {:?} and data_end_offset {:?}",
            l, self.mbuff.data_offset, self.mbuff.data_end_offset)))?;
        }
        LittleEndian::write_u64(
            &mut self.mbuff.buffer[(self.mbuff.data_offset)..],
            mem.as_ptr() as u64,
        );
        LittleEndian::write_u64(
            &mut self.mbuff.buffer[(self.mbuff.data_end_offset)..],
            mem.as_ptr() as u64 + mem.len() as u64,
        );
        self.parent.execute_program(mem, &self.mbuff.buffer)
    }

    /// JIT-compile the loaded program. No argument required for this.
    ///
    /// If using helper functions, be sure to register them into the VM before calling this
    /// function.
    ///
    /// # Examples
    ///
    /// ```
    /// let prog = &[
    ///     0xb7, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // mov r0, 0
    ///     0x79, 0x12, 0x40, 0x00, 0x00, 0x00, 0x00, 0x00, // load mem from r1[0x40] to r2
    ///     0x07, 0x02, 0x00, 0x00, 0x05, 0x00, 0x00, 0x00, // add r2, 5
    ///     0x79, 0x11, 0x50, 0x00, 0x00, 0x00, 0x00, 0x00, // load mem_end from r1[0x50] to r1
    ///     0x2d, 0x12, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, // if r2 > r1 skip 3 instructions
    ///     0x71, 0x20, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // load r2 (= *(mem + 5)) into r0
    ///     0x95, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00  // exit
    /// ];
    ///
    /// // Instantiate a VM. Note that we provide the start and end offsets for mem pointers.
    /// let mut vm = rbpf::EbpfVmFixedMbuff::new(Some(prog), 0x40, 0x50).unwrap();
    ///
    /// vm.jit_compile();
    /// ```
    #[cfg(all(not(windows), feature = "std"))]
    pub fn jit_compile(&mut self) -> Result<(), Error> {
        let prog = match self.parent.prog {
            Some(prog) => prog,
            None => Err(Error::new(
                ErrorKind::Other,
                "Error: No program set, call prog_set() to load one",
            ))?,
        };
        self.parent.jit = Some(jit::JitMemory::new(prog, &self.parent.helpers, true, true)?);
        Ok(())
    }

    /// Execute the previously JIT-compiled program, with the given packet data, in a manner very
    /// similar to `execute_program()`.
    ///
    /// If the program is made to be compatible with Linux kernel, it is expected to load the
    /// address of the beginning and of the end of the memory area used for packet data from some
    /// metadata buffer, which in the case of this VM is handled internally. The offsets at which
    /// the addresses should be placed should have be set at the creation of the VM.
    ///
    /// # Safety
    ///
    /// **WARNING:** JIT-compiled assembly code is not safe, in particular there is no runtime
    /// check for memory access; so if the eBPF program attempts erroneous accesses, this may end
    /// very bad (program may segfault). It may be wise to check that the program works with the
    /// interpreter before running the JIT-compiled version of it.
    ///
    /// For this reason the function should be called from within an `unsafe` bloc.
    ///
    /// # Examples
    ///
    /// ```
    /// let prog = &[
    ///     0xb7, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // mov r0, 0
    ///     0x79, 0x12, 0x40, 0x00, 0x00, 0x00, 0x00, 0x00, // load mem from r1[0x40] to r2
    ///     0x07, 0x02, 0x00, 0x00, 0x05, 0x00, 0x00, 0x00, // add r2, 5
    ///     0x79, 0x11, 0x50, 0x00, 0x00, 0x00, 0x00, 0x00, // load mem_end from r1[0x50] to r1
    ///     0x2d, 0x12, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, // if r2 > r1 skip 3 instructions
    ///     0x71, 0x20, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // load r2 (= *(mem + 5)) into r0
    ///     0x95, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00  // exit
    /// ];
    /// let mem = &mut [
    ///     0xaa, 0xbb, 0x11, 0x22, 0xcc, 0xdd
    /// ];
    ///
    /// // Instantiate a VM. Note that we provide the start and end offsets for mem pointers.
    /// let mut vm = rbpf::EbpfVmFixedMbuff::new(Some(prog), 0x40, 0x50).unwrap();
    ///
    /// # #[cfg(all(not(windows), feature = "std"))]
    /// vm.jit_compile();
    ///
    /// // Provide only a reference to the packet data. We do not manage the metadata buffer.
    /// # #[cfg(all(not(windows), feature = "std"))]
    /// unsafe {
    ///     let res = vm.execute_program_jit(mem).unwrap();
    ///     assert_eq!(res, 0xdd);
    /// }
    /// ```
    // This struct redefines the `execute_program_jit()` function, in order to pass the offsets
    // associated with the fixed mbuff.
    #[cfg(all(not(windows), feature = "std"))]
    pub unsafe fn execute_program_jit(&mut self, mem: &'a mut [u8]) -> Result<u64, Error> {
        // If packet data is empty, do not send the address of an empty slice; send a null pointer
        //  as first argument instead, as this is uBPF's behavior (empty packet should not happen
        //  in the kernel; anyway the verifier would prevent the use of uninitialized registers).
        //  See `mul_loop` test.
        let mem_ptr = match mem.len() {
            0 => ptr::null_mut(),
            _ => mem.as_ptr() as *mut u8,
        };

        match &self.parent.jit {
            Some(jit) => Ok(jit.get_prog()(
                self.mbuff.buffer.as_ptr() as *mut u8,
                self.mbuff.buffer.len(),
                mem_ptr,
                mem.len(),
                self.mbuff.data_offset,
                self.mbuff.data_end_offset,
            )),
            None => Err(Error::new(
                ErrorKind::Other,
                "Error: program has not been JIT-compiled",
            )),
        }
    }

    /// Compile the loaded program using the Cranelift JIT.
    ///
    /// If using helper functions, be sure to register them into the VM before calling this
    /// function.
    ///
    /// # Examples
    ///
    /// ```
    /// let prog = &[
    ///     0xb7, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // mov r0, 0
    ///     0x79, 0x12, 0x40, 0x00, 0x00, 0x00, 0x00, 0x00, // load mem from r1[0x40] to r2
    ///     0x07, 0x02, 0x00, 0x00, 0x05, 0x00, 0x00, 0x00, // add r2, 5
    ///     0x79, 0x11, 0x50, 0x00, 0x00, 0x00, 0x00, 0x00, // load mem_end from r1[0x50] to r1
    ///     0x2d, 0x12, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, // if r2 > r1 skip 3 instructions
    ///     0x71, 0x20, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // load r2 (= *(mem + 5)) into r0
    ///     0x95, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00  // exit
    /// ];
    ///
    /// // Instantiate a VM. Note that we provide the start and end offsets for mem pointers.
    /// let mut vm = rbpf::EbpfVmFixedMbuff::new(Some(prog), 0x40, 0x50).unwrap();
    ///
    /// vm.cranelift_compile();
    /// ```
    #[cfg(feature = "cranelift")]
    pub fn cranelift_compile(&mut self) -> Result<(), Error> {
        use crate::cranelift::CraneliftCompiler;

        let prog = match self.parent.prog {
            Some(prog) => prog,
            None => Err(Error::new(
                ErrorKind::Other,
                "Error: No program set, call prog_set() to load one",
            ))?,
        };

        let compiler = CraneliftCompiler::new(self.parent.helpers.clone());
        let program = compiler.compile_function(prog)?;

        self.parent.cranelift_prog = Some(program);
        Ok(())
    }

    /// Execute the previously compiled program, with the given packet data and metadata
    /// buffer, in a manner very similar to `execute_program()`.
    ///
    /// If the program is made to be compatible with Linux kernel, it is expected to load the
    /// address of the beginning and of the end of the memory area used for packet data from some
    /// metadata buffer, which in the case of this VM is handled internally. The offsets at which
    /// the addresses should be placed should have be set at the creation of the VM.
    ///
    /// # Examples
    ///
    /// ```
    /// let prog = &[
    ///     0xb7, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // mov r0, 0
    ///     0x79, 0x12, 0x40, 0x00, 0x00, 0x00, 0x00, 0x00, // load mem from r1[0x40] to r2
    ///     0x07, 0x02, 0x00, 0x00, 0x05, 0x00, 0x00, 0x00, // add r2, 5
    ///     0x79, 0x11, 0x50, 0x00, 0x00, 0x00, 0x00, 0x00, // load mem_end from r1[0x50] to r1
    ///     0x2d, 0x12, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, // if r2 > r1 skip 3 instructions
    ///     0x71, 0x20, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // load r2 (= *(mem + 5)) into r0
    ///     0x95, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00  // exit
    /// ];
    /// let mem = &mut [
    ///     0xaa, 0xbb, 0x11, 0x22, 0xcc, 0xdd
    /// ];
    ///
    /// // Instantiate a VM. Note that we provide the start and end offsets for mem pointers.
    /// let mut vm = rbpf::EbpfVmFixedMbuff::new(Some(prog), 0x40, 0x50).unwrap();
    ///
    /// vm.cranelift_compile();
    ///
    /// // Provide only a reference to the packet data. We do not manage the metadata buffer.
    /// let res = vm.execute_program_cranelift(mem).unwrap();
    /// assert_eq!(res, 0xdd);
    /// ```
    #[cfg(feature = "cranelift")]
    pub fn execute_program_cranelift(&mut self, mem: &'a mut [u8]) -> Result<u64, Error> {
        // If packet data is empty, do not send the address of an empty slice; send a null pointer
        //  as first argument instead, as this is uBPF's behavior (empty packet should not happen
        //  in the kernel; anyway the verifier would prevent the use of uninitialized registers).
        //  See `mul_loop` test.
        let mem_ptr = match mem.len() {
            0 => ptr::null_mut(),
            _ => mem.as_ptr() as *mut u8,
        };

        let l = self.mbuff.buffer.len();
        // Can this ever happen? Probably not, should be ensured at mbuff creation.
        if self.mbuff.data_offset + 8 > l || self.mbuff.data_end_offset + 8 > l {
            Err(Error::new(ErrorKind::Other, format!("Error: buffer too small ({:?}), cannot use data_offset {:?} and data_end_offset {:?}",
            l, self.mbuff.data_offset, self.mbuff.data_end_offset)))?;
        }
        LittleEndian::write_u64(
            &mut self.mbuff.buffer[(self.mbuff.data_offset)..],
            mem.as_ptr() as u64,
        );
        LittleEndian::write_u64(
            &mut self.mbuff.buffer[(self.mbuff.data_end_offset)..],
            mem.as_ptr() as u64 + mem.len() as u64,
        );

        match &self.parent.cranelift_prog {
            Some(prog) => Ok(prog.execute(
                mem_ptr,
                mem.len(),
                self.mbuff.buffer.as_ptr() as *mut u8,
                self.mbuff.buffer.len(),
            )),
            None => Err(Error::new(
                ErrorKind::Other,
                "Error: program has not been compiled with cranelift",
            )),
        }
    }
}

/// A virtual machine to run eBPF program. This kind of VM is used for programs expecting to work
/// directly on the memory area representing packet data.
///
/// # Examples
///
/// ```
/// let prog = &[
///     0x71, 0x11, 0x04, 0x00, 0x00, 0x00, 0x00, 0x00, // ldxb r1[0x04], r1
///     0x07, 0x01, 0x00, 0x00, 0x00, 0x22, 0x00, 0x00, // add r1, 0x22
///     0xbf, 0x10, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // mov r0, r1
///     0x95, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00  // exit
/// ];
/// let mem = &mut [
///     0xaa, 0xbb, 0x11, 0x22, 0xcc, 0xdd
/// ];
///
/// // Instantiate a VM.
/// let vm = rbpf::EbpfVmRaw::new(Some(prog)).unwrap();
///
/// // Provide only a reference to the packet data.
/// let res = vm.execute_program(mem).unwrap();
/// assert_eq!(res, 0x22cc);
/// ```
pub struct EbpfVmRaw<'a> {
    parent: EbpfVmMbuff<'a>,
}

impl<'a> EbpfVmRaw<'a> {
    /// Create a new virtual machine instance, and load an eBPF program into that instance.
    /// When attempting to load the program, it passes through a simple verifier.
    ///
    /// # Examples
    ///
    /// ```
    /// let prog = &[
    ///     0x71, 0x11, 0x04, 0x00, 0x00, 0x00, 0x00, 0x00, // ldxb r1[0x04], r1
    ///     0x07, 0x01, 0x00, 0x00, 0x00, 0x22, 0x00, 0x00, // add r1, 0x22
    ///     0xbf, 0x10, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // mov r0, r1
    ///     0x95, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00  // exit
    /// ];
    ///
    /// // Instantiate a VM.
    /// let vm = rbpf::EbpfVmRaw::new(Some(prog)).unwrap();
    /// ```
    pub fn new(prog: Option<&'a [u8]>) -> Result<EbpfVmRaw<'a>, Error> {
        let parent = EbpfVmMbuff::new(prog)?;
        Ok(EbpfVmRaw { parent })
    }

    /// Load a new eBPF program into the virtual machine instance.
    ///
    /// # Examples
    ///
    /// ```
    /// let prog1 = &[
    ///     0xb7, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // mov r0, 0
    ///     0x95, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00  // exit
    /// ];
    /// let prog2 = &[
    ///     0x71, 0x11, 0x04, 0x00, 0x00, 0x00, 0x00, 0x00, // ldxb r1[0x04], r1
    ///     0x07, 0x01, 0x00, 0x00, 0x00, 0x22, 0x00, 0x00, // add r1, 0x22
    ///     0xbf, 0x10, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // mov r0, r1
    ///     0x95, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00  // exit
    /// ];
    ///
    /// let mem = &mut [
    ///     0xaa, 0xbb, 0x11, 0x22, 0xcc, 0x27,
    /// ];
    ///
    /// let mut vm = rbpf::EbpfVmRaw::new(Some(prog1)).unwrap();
    /// vm.set_program(prog2);
    ///
    /// let res = vm.execute_program(mem).unwrap();
    /// assert_eq!(res, 0x22cc);
    /// ```
    pub fn set_program(&mut self, prog: &'a [u8]) -> Result<(), Error> {
        self.parent.set_program(prog)?;
        Ok(())
    }

    /// Set a new verifier function. The function should return an `Error` if the program should be
    /// rejected by the virtual machine. If a program has been loaded to the VM already, the
    /// verifier is immediately run.
    ///
    /// # Examples
    ///
    /// ```
    /// use rbpf::lib::{Error, ErrorKind};
    /// use rbpf::ebpf;
    ///
    /// // Define a simple verifier function.
    /// fn verifier(prog: &[u8]) -> Result<(), Error> {
    ///     let last_insn = ebpf::get_insn(prog, (prog.len() / ebpf::INSN_SIZE) - 1);
    ///     if last_insn.opc != ebpf::EXIT {
    ///         return Err(Error::new(ErrorKind::Other,
    ///                    "[Verifier] Error: program does not end with “EXIT” instruction"));
    ///     }
    ///     Ok(())
    /// }
    ///
    /// let prog1 = &[
    ///     0xb7, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // mov r0, 0
    ///     0x95, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00  // exit
    /// ];
    ///
    /// // Instantiate a VM.
    /// let mut vm = rbpf::EbpfVmMbuff::new(Some(prog1)).unwrap();
    /// // Change the verifier.
    /// vm.set_verifier(verifier).unwrap();
    /// ```
    pub fn set_verifier(&mut self, verifier: Verifier) -> Result<(), Error> {
        self.parent.set_verifier(verifier)
    }

    /// Register a built-in or user-defined helper function in order to use it later from within
    /// the eBPF program. The helper is registered into a hashmap, so the `key` can be any `u32`.
    ///
    /// If using JIT-compiled eBPF programs, be sure to register all helpers before compiling the
    /// program. You should be able to change registered helpers after compiling, but not to add
    /// new ones (i.e. with new keys).
    ///
    /// # Examples
    ///
    /// ```
    /// #[cfg(feature = "std")] {
    ///     use rbpf::helpers;
    ///
    ///     let prog = &[
    ///         0x79, 0x11, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // ldxdw r1, r1[0x00]
    ///         0xb7, 0x02, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // mov r2, 0
    ///         0xb7, 0x03, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // mov r3, 0
    ///         0xb7, 0x04, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // mov r4, 0
    ///         0xb7, 0x05, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // mov r5, 0
    ///         0x85, 0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, // call helper with key 1
    ///         0x95, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00  // exit
    ///     ];
    ///
    ///     let mem = &mut [
    ///         0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01
    ///     ];
    ///
    ///     // Instantiate a VM.
    ///     let mut vm = rbpf::EbpfVmRaw::new(Some(prog)).unwrap();
    ///
    ///     // Register a helper. This helper will store the result of the square root of r1 into r0.
    ///     vm.register_helper(1, helpers::sqrti);
    ///
    ///     let res = vm.execute_program(mem).unwrap();
    ///     assert_eq!(res, 0x10000000);
    /// }
    /// ```
    pub fn register_helper(
        &mut self,
        key: u32,
        function: fn(u64, u64, u64, u64, u64) -> u64,
    ) -> Result<(), Error> {
        self.parent.register_helper(key, function)
    }

    /// Register an object that the eBPF program is allowed to load and store.
    ///
    /// When using certain helpers, typically map lookups, the Linux kernel will return pointers
    /// to structs that the eBPF program needs to interact with. By default rbpf only allows the
    /// program to interact with its stack, the memory buffer and the program itself, making it
    /// impossible to supply functional implementations of these helpers.
    /// This option allows you to pass in a list of addresses that rbpf will allow the program
    /// to load and store to. Given Rust's memory model you will always know these addresses up
    /// front when implementing the helpers.
    ///
    /// Each invocation of this method will append to the set of allowed addresses.
    ///
    /// # Examples
    ///
    /// ```
    /// use std::iter::FromIterator;
    /// use std::ptr::addr_of;
    ///
    /// struct MapValue {
    ///     data: u8
    /// }
    /// static VALUE: MapValue = MapValue { data: 1 };
    ///
    /// let prog = &[
    ///     0xb7, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // mov r0, 0
    ///     0x95, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00  // exit
    /// ];
    ///
    /// // Instantiate a VM.
    /// let mut vm = rbpf::EbpfVmRaw::new(Some(prog)).unwrap();
    /// let start = addr_of!(VALUE) as u64;
    /// let addrs = Vec::from_iter(start..start+size_of::<MapValue>() as u64);
    /// vm.register_allowed_memory(&addrs);
    /// ```
    pub fn register_allowed_memory(&mut self, allowed: &[u64]) {
        self.parent.register_allowed_memory(allowed)
    }

    /// Execute the program loaded, with the given packet data.
    ///
    /// # Examples
    ///
    /// ```
    /// let prog = &[
    ///     0x71, 0x11, 0x04, 0x00, 0x00, 0x00, 0x00, 0x00, // ldxb r1[0x04], r1
    ///     0x07, 0x01, 0x00, 0x00, 0x00, 0x22, 0x00, 0x00, // add r1, 0x22
    ///     0xbf, 0x10, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // mov r0, r1
    ///     0x95, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00  // exit
    /// ];
    ///
    /// let mem = &mut [
    ///     0xaa, 0xbb, 0x11, 0x22, 0xcc, 0x27
    /// ];
    ///
    /// let mut vm = rbpf::EbpfVmRaw::new(Some(prog)).unwrap();
    ///
    /// let res = vm.execute_program(mem).unwrap();
    /// assert_eq!(res, 0x22cc);
    /// ```
    pub fn execute_program(&self, mem: &'a mut [u8]) -> Result<u64, Error> {
        self.parent.execute_program(mem, &[])
    }

    /// JIT-compile the loaded program. No argument required for this.
    ///
    /// If using helper functions, be sure to register them into the VM before calling this
    /// function.
    ///
    /// # Examples
    ///
    /// ```
    /// let prog = &[
    ///     0x71, 0x11, 0x04, 0x00, 0x00, 0x00, 0x00, 0x00, // ldxb r1[0x04], r1
    ///     0x07, 0x01, 0x00, 0x00, 0x00, 0x22, 0x00, 0x00, // add r1, 0x22
    ///     0xbf, 0x10, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // mov r0, r1
    ///     0x95, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00  // exit
    /// ];
    ///
    /// let mut vm = rbpf::EbpfVmRaw::new(Some(prog)).unwrap();
    ///
    /// vm.jit_compile();
    /// ```
    #[cfg(all(not(windows), feature = "std"))]
    pub fn jit_compile(&mut self) -> Result<(), Error> {
        let prog = match self.parent.prog {
            Some(prog) => prog,
            None => Err(Error::new(
                ErrorKind::Other,
                "Error: No program set, call prog_set() to load one",
            ))?,
        };
        self.parent.jit = Some(jit::JitMemory::new(
            prog,
            &self.parent.helpers,
            false,
            false,
        )?);
        Ok(())
    }

    /// Execute the previously JIT-compiled program, with the given packet data, in a manner very
    /// similar to `execute_program()`.
    ///
    /// # Safety
    ///
    /// **WARNING:** JIT-compiled assembly code is not safe, in particular there is no runtime
    /// check for memory access; so if the eBPF program attempts erroneous accesses, this may end
    /// very bad (program may segfault). It may be wise to check that the program works with the
    /// interpreter before running the JIT-compiled version of it.
    ///
    /// For this reason the function should be called from within an `unsafe` bloc.
    ///
    /// # Examples
    ///
    /// ```
    /// let prog = &[
    ///     0x71, 0x11, 0x04, 0x00, 0x00, 0x00, 0x00, 0x00, // ldxb r1[0x04], r1
    ///     0x07, 0x01, 0x00, 0x00, 0x00, 0x22, 0x00, 0x00, // add r1, 0x22
    ///     0xbf, 0x10, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // mov r0, r1
    ///     0x95, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00  // exit
    /// ];
    ///
    /// let mem = &mut [
    ///     0xaa, 0xbb, 0x11, 0x22, 0xcc, 0x27
    /// ];
    ///
    /// let mut vm = rbpf::EbpfVmRaw::new(Some(prog)).unwrap();
    ///
    /// # #[cfg(all(not(windows), feature = "std"))]
    /// vm.jit_compile();
    ///
    /// # #[cfg(all(not(windows), feature = "std"))]
    /// unsafe {
    ///     let res = vm.execute_program_jit(mem).unwrap();
    ///     assert_eq!(res, 0x22cc);
    /// }
    /// ```
    #[cfg(all(not(windows), feature = "std"))]
    pub unsafe fn execute_program_jit(&self, mem: &'a mut [u8]) -> Result<u64, Error> {
        let mut mbuff = vec![];
        self.parent.execute_program_jit(mem, &mut mbuff)
    }

    /// Compile the loaded program using the Cranelift JIT.
    ///
    /// If using helper functions, be sure to register them into the VM before calling this
    /// function.
    ///
    /// # Examples
    ///
    /// ```
    /// let prog = &[
    ///     0x71, 0x11, 0x04, 0x00, 0x00, 0x00, 0x00, 0x00, // ldxb r1[0x04], r1
    ///     0x07, 0x01, 0x00, 0x00, 0x00, 0x22, 0x00, 0x00, // add r1, 0x22
    ///     0xbf, 0x10, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // mov r0, r1
    ///     0x95, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00  // exit
    /// ];
    ///
    /// let mut vm = rbpf::EbpfVmRaw::new(Some(prog)).unwrap();
    ///
    /// vm.cranelift_compile();
    /// ```
    #[cfg(feature = "cranelift")]
    pub fn cranelift_compile(&mut self) -> Result<(), Error> {
        use crate::cranelift::CraneliftCompiler;

        let prog = match self.parent.prog {
            Some(prog) => prog,
            None => Err(Error::new(
                ErrorKind::Other,
                "Error: No program set, call prog_set() to load one",
            ))?,
        };

        let compiler = CraneliftCompiler::new(self.parent.helpers.clone());
        let program = compiler.compile_function(prog)?;

        self.parent.cranelift_prog = Some(program);
        Ok(())
    }

    /// Execute the previously compiled program, with the given packet data, in a manner very
    /// similar to `execute_program()`.
    ///
    /// # Examples
    ///
    /// ```
    /// let prog = &[
    ///     0x71, 0x11, 0x04, 0x00, 0x00, 0x00, 0x00, 0x00, // ldxb r1[0x04], r1
    ///     0x07, 0x01, 0x00, 0x00, 0x00, 0x22, 0x00, 0x00, // add r1, 0x22
    ///     0xbf, 0x10, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // mov r0, r1
    ///     0x95, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00  // exit
    /// ];
    ///
    /// let mem = &mut [
    ///     0xaa, 0xbb, 0x11, 0x22, 0xcc, 0x27
    /// ];
    ///
    /// let mut vm = rbpf::EbpfVmRaw::new(Some(prog)).unwrap();
    ///
    /// vm.cranelift_compile();
    ///
    /// let res = vm.execute_program_cranelift(mem).unwrap();
    /// assert_eq!(res, 0x22cc);
    /// ```
    #[cfg(feature = "cranelift")]
    pub fn execute_program_cranelift(&self, mem: &'a mut [u8]) -> Result<u64, Error> {
        let mut mbuff = vec![];
        self.parent.execute_program_cranelift(mem, &mut mbuff)
    }
}

/// A virtual machine to run eBPF program. This kind of VM is used for programs that do not work
/// with any memory area—no metadata buffer, no packet data either.
///
/// # Examples
///
/// ```
/// let prog = &[
///     0xb7, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // mov r0, 0
///     0xb7, 0x01, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, // mov r1, 1
///     0xb7, 0x02, 0x00, 0x00, 0x02, 0x00, 0x00, 0x00, // mov r2, 2
///     0xb7, 0x03, 0x00, 0x00, 0x03, 0x00, 0x00, 0x00, // mov r3, 3
///     0xb7, 0x04, 0x00, 0x00, 0x04, 0x00, 0x00, 0x00, // mov r4, 4
///     0xb7, 0x05, 0x00, 0x00, 0x05, 0x00, 0x00, 0x00, // mov r5, 5
///     0xb7, 0x06, 0x00, 0x00, 0x06, 0x00, 0x00, 0x00, // mov r6, 6
///     0xb7, 0x07, 0x00, 0x00, 0x07, 0x00, 0x00, 0x00, // mov r7, 7
///     0xb7, 0x08, 0x00, 0x00, 0x08, 0x00, 0x00, 0x00, // mov r8, 8
///     0x4f, 0x50, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // or r0, r5
///     0x47, 0x00, 0x00, 0x00, 0xa0, 0x00, 0x00, 0x00, // or r0, 0xa0
///     0x57, 0x00, 0x00, 0x00, 0xa3, 0x00, 0x00, 0x00, // and r0, 0xa3
///     0xb7, 0x09, 0x00, 0x00, 0x91, 0x00, 0x00, 0x00, // mov r9, 0x91
///     0x5f, 0x90, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // and r0, r9
///     0x67, 0x00, 0x00, 0x00, 0x20, 0x00, 0x00, 0x00, // lsh r0, 32
///     0x67, 0x00, 0x00, 0x00, 0x16, 0x00, 0x00, 0x00, // lsh r0, 22
///     0x6f, 0x80, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // lsh r0, r8
///     0x77, 0x00, 0x00, 0x00, 0x20, 0x00, 0x00, 0x00, // rsh r0, 32
///     0x77, 0x00, 0x00, 0x00, 0x13, 0x00, 0x00, 0x00, // rsh r0, 19
///     0x7f, 0x70, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // rsh r0, r7
///     0xa7, 0x00, 0x00, 0x00, 0x03, 0x00, 0x00, 0x00, // xor r0, 0x03
///     0xaf, 0x20, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // xor r0, r2
///     0x95, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00  // exit
/// ];
///
/// // Instantiate a VM.
/// let vm = rbpf::EbpfVmNoData::new(Some(prog)).unwrap();
///
/// // Provide only a reference to the packet data.
/// let res = vm.execute_program().unwrap();
/// assert_eq!(res, 0x11);
/// ```
pub struct EbpfVmNoData<'a> {
    parent: EbpfVmRaw<'a>,
}

impl<'a> EbpfVmNoData<'a> {
    /// Create a new virtual machine instance, and load an eBPF program into that instance.
    /// When attempting to load the program, it passes through a simple verifier.
    ///
    /// # Examples
    ///
    /// ```
    /// let prog = &[
    ///     0xb7, 0x00, 0x00, 0x00, 0x11, 0x22, 0x00, 0x00, // mov r0, 0x2211
    ///     0xdc, 0x00, 0x00, 0x00, 0x10, 0x00, 0x00, 0x00, // be16 r0
    ///     0x95, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00  // exit
    /// ];
    ///
    /// // Instantiate a VM.
    /// let vm = rbpf::EbpfVmNoData::new(Some(prog));
    /// ```
    pub fn new(prog: Option<&'a [u8]>) -> Result<EbpfVmNoData<'a>, Error> {
        let parent = EbpfVmRaw::new(prog)?;
        Ok(EbpfVmNoData { parent })
    }

    /// Load a new eBPF program into the virtual machine instance.
    ///
    /// # Examples
    ///
    /// ```
    /// let prog1 = &[
    ///     0xb7, 0x00, 0x00, 0x00, 0x11, 0x22, 0x00, 0x00, // mov r0, 0x2211
    ///     0x95, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00  // exit
    /// ];
    /// let prog2 = &[
    ///     0xb7, 0x00, 0x00, 0x00, 0x11, 0x22, 0x00, 0x00, // mov r0, 0x2211
    ///     0xdc, 0x00, 0x00, 0x00, 0x10, 0x00, 0x00, 0x00, // be16 r0
    ///     0x95, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00  // exit
    /// ];
    ///
    /// let mut vm = rbpf::EbpfVmNoData::new(Some(prog1)).unwrap();
    ///
    /// let res = vm.execute_program().unwrap();
    /// assert_eq!(res, 0x2211);
    ///
    /// vm.set_program(prog2);
    ///
    /// let res = vm.execute_program().unwrap();
    /// assert_eq!(res, 0x1122);
    /// ```
    pub fn set_program(&mut self, prog: &'a [u8]) -> Result<(), Error> {
        self.parent.set_program(prog)?;
        Ok(())
    }

    /// Set a new verifier function. The function should return an `Error` if the program should be
    /// rejected by the virtual machine. If a program has been loaded to the VM already, the
    /// verifier is immediately run.
    ///
    /// # Examples
    ///
    /// ```
    /// use rbpf::lib::{Error, ErrorKind};
    /// use rbpf::ebpf;
    ///
    /// // Define a simple verifier function.
    /// fn verifier(prog: &[u8]) -> Result<(), Error> {
    ///     let last_insn = ebpf::get_insn(prog, (prog.len() / ebpf::INSN_SIZE) - 1);
    ///     if last_insn.opc != ebpf::EXIT {
    ///         return Err(Error::new(ErrorKind::Other,
    ///                    "[Verifier] Error: program does not end with “EXIT” instruction"));
    ///     }
    ///     Ok(())
    /// }
    ///
    /// let prog1 = &[
    ///     0xb7, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // mov r0, 0
    ///     0x95, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00  // exit
    /// ];
    ///
    /// // Instantiate a VM.
    /// let mut vm = rbpf::EbpfVmMbuff::new(Some(prog1)).unwrap();
    /// // Change the verifier.
    /// vm.set_verifier(verifier).unwrap();
    /// ```
    pub fn set_verifier(&mut self, verifier: Verifier) -> Result<(), Error> {
        self.parent.set_verifier(verifier)
    }

    /// Register a built-in or user-defined helper function in order to use it later from within
    /// the eBPF program. The helper is registered into a hashmap, so the `key` can be any `u32`.
    ///
    /// If using JIT-compiled eBPF programs, be sure to register all helpers before compiling the
    /// program. You should be able to change registered helpers after compiling, but not to add
    /// new ones (i.e. with new keys).
    ///
    /// # Examples
    ///
    /// ```
    /// #[cfg(feature = "std")] {
    ///     use rbpf::helpers;
    ///
    ///     let prog = &[
    ///         0xb7, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01, // mov r1, 0x010000000
    ///         0xb7, 0x02, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // mov r2, 0
    ///         0xb7, 0x03, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // mov r3, 0
    ///         0xb7, 0x04, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // mov r4, 0
    ///         0xb7, 0x05, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // mov r5, 0
    ///         0x85, 0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, // call helper with key 1
    ///         0x95, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00  // exit
    ///     ];
    ///
    ///     let mut vm = rbpf::EbpfVmNoData::new(Some(prog)).unwrap();
    ///
    ///     // Register a helper. This helper will store the result of the square root of r1 into r0.
    ///     vm.register_helper(1, helpers::sqrti).unwrap();
    ///
    ///     let res = vm.execute_program().unwrap();
    ///     assert_eq!(res, 0x1000);
    /// }
    /// ```
    pub fn register_helper(
        &mut self,
        key: u32,
        function: fn(u64, u64, u64, u64, u64) -> u64,
    ) -> Result<(), Error> {
        self.parent.register_helper(key, function)
    }

    /// Register an object that the eBPF program is allowed to load and store.
    ///
    /// When using certain helpers, typically map lookups, the Linux kernel will return pointers
    /// to structs that the eBPF program needs to interact with. By default rbpf only allows the
    /// program to interact with its stack, the memory buffer and the program itself, making it
    /// impossible to supply functional implementations of these helpers.
    /// This option allows you to pass in a list of addresses that rbpf will allow the program
    /// to load and store to. Given Rust's memory model you will always know these addresses up
    /// front when implementing the helpers.
    ///
    /// Each invocation of this method will append to the set of allowed addresses.
    ///
    /// # Examples
    ///
    /// ```
    /// use std::iter::FromIterator;
    /// use std::ptr::addr_of;
    ///
    /// struct MapValue {
    ///     data: u8
    /// }
    /// static VALUE: MapValue = MapValue { data: 1 };
    ///
    /// let prog = &[
    ///     0xb7, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // mov r0, 0
    ///     0x95, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00  // exit
    /// ];
    ///
    /// // Instantiate a VM.
    /// let mut vm = rbpf::EbpfVmNoData::new(Some(prog)).unwrap();
    /// let start = addr_of!(VALUE) as u64;
    /// let addrs = Vec::from_iter(start..start+size_of::<MapValue>() as u64);
    /// vm.register_allowed_memory(&addrs);
    /// ```
    pub fn register_allowed_memory(&mut self, allowed: &[u64]) {
        self.parent.register_allowed_memory(allowed)
    }

    /// JIT-compile the loaded program. No argument required for this.
    ///
    /// If using helper functions, be sure to register them into the VM before calling this
    /// function.
    ///
    /// # Examples
    ///
    /// ```
    /// let prog = &[
    ///     0xb7, 0x00, 0x00, 0x00, 0x11, 0x22, 0x00, 0x00, // mov r0, 0x2211
    ///     0xdc, 0x00, 0x00, 0x00, 0x10, 0x00, 0x00, 0x00, // be16 r0
    ///     0x95, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00  // exit
    /// ];
    ///
    /// let mut vm = rbpf::EbpfVmNoData::new(Some(prog)).unwrap();
    ///
    ///
    /// vm.jit_compile();
    /// ```
    #[cfg(all(not(windows), feature = "std"))]
    pub fn jit_compile(&mut self) -> Result<(), Error> {
        self.parent.jit_compile()
    }

    /// Execute the program loaded, without providing pointers to any memory area whatsoever.
    ///
    /// # Examples
    ///
    /// ```
    /// let prog = &[
    ///     0xb7, 0x00, 0x00, 0x00, 0x11, 0x22, 0x00, 0x00, // mov r0, 0x2211
    ///     0xdc, 0x00, 0x00, 0x00, 0x10, 0x00, 0x00, 0x00, // be16 r0
    ///     0x95, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00  // exit
    /// ];
    ///
    /// let vm = rbpf::EbpfVmNoData::new(Some(prog)).unwrap();
    ///
    /// // For this kind of VM, the `execute_program()` function needs no argument.
    /// let res = vm.execute_program().unwrap();
    /// assert_eq!(res, 0x1122);
    /// ```
    pub fn execute_program(&self) -> Result<u64, Error> {
        self.parent.execute_program(&mut [])
    }

    /// Execute the previously JIT-compiled program, without providing pointers to any memory area
    /// whatsoever, in a manner very similar to `execute_program()`.
    ///
    /// # Safety
    ///
    /// **WARNING:** JIT-compiled assembly code is not safe, in particular there is no runtime
    /// check for memory access; so if the eBPF program attempts erroneous accesses, this may end
    /// very bad (program may segfault). It may be wise to check that the program works with the
    /// interpreter before running the JIT-compiled version of it.
    ///
    /// For this reason the function should be called from within an `unsafe` bloc.
    ///
    /// # Examples
    ///
    /// ```
    /// let prog = &[
    ///     0xb7, 0x00, 0x00, 0x00, 0x11, 0x22, 0x00, 0x00, // mov r0, 0x2211
    ///     0xdc, 0x00, 0x00, 0x00, 0x10, 0x00, 0x00, 0x00, // be16 r0
    ///     0x95, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00  // exit
    /// ];
    ///
    /// let mut vm = rbpf::EbpfVmNoData::new(Some(prog)).unwrap();
    ///
    /// # #[cfg(all(not(windows), feature = "std"))]
    /// vm.jit_compile();
    ///
    /// # #[cfg(all(not(windows), feature = "std"))]
    /// unsafe {
    ///     let res = vm.execute_program_jit().unwrap();
    ///     assert_eq!(res, 0x1122);
    /// }
    /// ```
    #[cfg(all(not(windows), feature = "std"))]
    pub unsafe fn execute_program_jit(&self) -> Result<u64, Error> {
        self.parent.execute_program_jit(&mut [])
    }

    /// Compile the loaded program using the Cranelift JIT.
    ///
    /// If using helper functions, be sure to register them into the VM before calling this
    /// function.
    ///
    /// # Examples
    ///
    /// ```
    /// let prog = &[
    ///     0xb7, 0x00, 0x00, 0x00, 0x11, 0x22, 0x00, 0x00, // mov r0, 0x2211
    ///     0xdc, 0x00, 0x00, 0x00, 0x10, 0x00, 0x00, 0x00, // be16 r0
    ///     0x95, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00  // exit
    /// ];
    ///
    /// let mut vm = rbpf::EbpfVmNoData::new(Some(prog)).unwrap();
    ///
    ///
    /// vm.cranelift_compile();
    /// ```
    #[cfg(feature = "cranelift")]
    pub fn cranelift_compile(&mut self) -> Result<(), Error> {
        self.parent.cranelift_compile()
    }

    /// Execute the previously JIT-compiled program, without providing pointers to any memory area
    /// whatsoever, in a manner very similar to `execute_program()`.
    ///
    /// # Examples
    ///
    /// ```
    /// let prog = &[
    ///     0xb7, 0x00, 0x00, 0x00, 0x11, 0x22, 0x00, 0x00, // mov r0, 0x2211
    ///     0xdc, 0x00, 0x00, 0x00, 0x10, 0x00, 0x00, 0x00, // be16 r0
    ///     0x95, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00  // exit
    /// ];
    ///
    /// let mut vm = rbpf::EbpfVmNoData::new(Some(prog)).unwrap();
    ///
    /// vm.cranelift_compile();
    ///
    /// let res = vm.execute_program_cranelift().unwrap();
    /// assert_eq!(res, 0x1122);
    /// ```
    #[cfg(feature = "cranelift")]
    pub fn execute_program_cranelift(&self) -> Result<u64, Error> {
        self.parent.execute_program_cranelift(&mut [])
    }
}