rust/src/librustc/mir/interpret/allocation.rs

// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

//! The virtual memory representation of the MIR interpreter

use super::{Pointer, EvalResult, AllocId};

use ty::layout::{Size, Align};
use syntax::ast::Mutability;
use std::iter;
use mir;
use std::ops::{Deref, DerefMut};
use rustc_data_structures::sorted_map::SortedMap;

#[derive(Clone, Debug, Eq, PartialEq, PartialOrd, Ord, Hash, RustcEncodable, RustcDecodable)]
pub struct Allocation<Tag=(),Extra=()> {
    /// The actual bytes of the allocation.
    /// Note that the bytes of a pointer represent the offset of the pointer
    pub bytes: Vec<u8>,
    /// Maps from byte addresses to extra data for each pointer.
    /// Only the first byte of a pointer is inserted into the map; i.e.,
    /// every entry in this map applies to `pointer_size` consecutive bytes starting
    /// at the given offset.
    pub relocations: Relocations<Tag>,
    /// Denotes undefined memory. Reading from undefined memory is forbidden in miri
    pub undef_mask: UndefMask,
    /// The alignment of the allocation to detect unaligned reads.
    pub align: Align,
    /// Whether the allocation is mutable.
    /// Also used by codegen to determine if a static should be put into mutable memory,
    /// which happens for `static mut` and `static` with interior mutability.
    pub mutability: Mutability,
    /// Extra state for the machine.
    pub extra: Extra,
}

pub trait AllocationExtra<Tag>: ::std::fmt::Debug + Default + Clone {
    /// Hook for performing extra checks on a memory read access.
    ///
    /// Takes read-only access to the allocation so we can keep all the memory read
    /// operations take `&self`.  Use a `RefCell` in `AllocExtra` if you
    /// need to mutate.
    #[inline]
    fn memory_read(
        _alloc: &Allocation<Tag, Self>,
        _ptr: Pointer<Tag>,
        _size: Size,
    ) -> EvalResult<'tcx> {
        Ok(())
    }

    /// Hook for performing extra checks on a memory write access.
    #[inline]
    fn memory_written(
        _alloc: &mut Allocation<Tag, Self>,
        _ptr: Pointer<Tag>,
        _size: Size,
    ) -> EvalResult<'tcx> {
        Ok(())
    }

    /// Hook for performing extra checks on a memory deallocation.
    /// `size` will be the size of the allocation.
    #[inline]
    fn memory_deallocated(
        _alloc: &mut Allocation<Tag, Self>,
        _ptr: Pointer<Tag>,
        _size: Size,
    ) -> EvalResult<'tcx> {
        Ok(())
    }
}

impl AllocationExtra<()> for () {}

impl<Tag, Extra: Default> Allocation<Tag, Extra> {
    /// Creates a read-only allocation initialized by the given bytes
    pub fn from_bytes(slice: &[u8], align: Align) -> Self {
        let mut undef_mask = UndefMask::new(Size::ZERO);
        undef_mask.grow(Size::from_bytes(slice.len() as u64), true);
        Self {
            bytes: slice.to_owned(),
            relocations: Relocations::new(),
            undef_mask,
            align,
            mutability: Mutability::Immutable,
            extra: Extra::default(),
        }
    }

    pub fn from_byte_aligned_bytes(slice: &[u8]) -> Self {
        Allocation::from_bytes(slice, Align::from_bytes(1, 1).unwrap())
    }

    pub fn undef(size: Size, align: Align) -> Self {
        assert_eq!(size.bytes() as usize as u64, size.bytes());
        Allocation {
            bytes: vec![0; size.bytes() as usize],
            relocations: Relocations::new(),
            undef_mask: UndefMask::new(size),
            align,
            mutability: Mutability::Mutable,
            extra: Extra::default(),
        }
    }
}

impl<'tcx> ::serialize::UseSpecializedDecodable for &'tcx Allocation {}

#[derive(Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Debug, RustcEncodable, RustcDecodable)]
pub struct Relocations<Tag=(), Id=AllocId>(SortedMap<Size, (Tag, Id)>);

impl<Tag, Id> Relocations<Tag, Id> {
    pub fn new() -> Self {
        Relocations(SortedMap::new())
    }

    // The caller must guarantee that the given relocations are already sorted
    // by address and contain no duplicates.
    pub fn from_presorted(r: Vec<(Size, (Tag, Id))>) -> Self {
        Relocations(SortedMap::from_presorted_elements(r))
    }
}

impl<Tag> Deref for Relocations<Tag> {
    type Target = SortedMap<Size, (Tag, AllocId)>;

    fn deref(&self) -> &Self::Target {
        &self.0
    }
}

impl<Tag> DerefMut for Relocations<Tag> {
    fn deref_mut(&mut self) -> &mut Self::Target {
        &mut self.0
    }
}

////////////////////////////////////////////////////////////////////////////////
// Undefined byte tracking
////////////////////////////////////////////////////////////////////////////////

type Block = u64;
const BLOCK_SIZE: u64 = 64;

#[derive(Clone, Debug, Eq, PartialEq, PartialOrd, Ord, Hash, RustcEncodable, RustcDecodable)]
pub struct UndefMask {
    blocks: Vec<Block>,
    len: Size,
}

impl_stable_hash_for!(struct mir::interpret::UndefMask{blocks, len});

impl UndefMask {
    pub fn new(size: Size) -> Self {
        let mut m = UndefMask {
            blocks: vec![],
            len: Size::ZERO,
        };
        m.grow(size, false);
        m
    }

    /// Check whether the range `start..end` (end-exclusive) is entirely defined.
    ///
    /// Returns `Ok(())` if it's defined. Otherwise returns the index of the byte
    /// at which the first undefined access begins.
    #[inline]
    pub fn is_range_defined(&self, start: Size, end: Size) -> Result<(), Size> {
        if end > self.len {
            return Err(self.len);
        }

        let idx = (start.bytes()..end.bytes())
            .map(|i| Size::from_bytes(i))
            .find(|&i| !self.get(i));

        match idx {
            Some(idx) => Err(idx),
            None => Ok(())
        }
    }

    pub fn set_range(&mut self, start: Size, end: Size, new_state: bool) {
        let len = self.len;
        if end > len {
            self.grow(end - len, new_state);
        }
        self.set_range_inbounds(start, end, new_state);
    }

    pub fn set_range_inbounds(&mut self, start: Size, end: Size, new_state: bool) {
        for i in start.bytes()..end.bytes() {
            self.set(Size::from_bytes(i), new_state);
        }
    }

    #[inline]
    pub fn get(&self, i: Size) -> bool {
        let (block, bit) = bit_index(i);
        (self.blocks[block] & 1 << bit) != 0
    }

    #[inline]
    pub fn set(&mut self, i: Size, new_state: bool) {
        let (block, bit) = bit_index(i);
        if new_state {
            self.blocks[block] |= 1 << bit;
        } else {
            self.blocks[block] &= !(1 << bit);
        }
    }

    pub fn grow(&mut self, amount: Size, new_state: bool) {
        let unused_trailing_bits = self.blocks.len() as u64 * BLOCK_SIZE - self.len.bytes();
        if amount.bytes() > unused_trailing_bits {
            let additional_blocks = amount.bytes() / BLOCK_SIZE + 1;
            assert_eq!(additional_blocks as usize as u64, additional_blocks);
            self.blocks.extend(
                iter::repeat(0).take(additional_blocks as usize),
            );
        }
        let start = self.len;
        self.len += amount;
        self.set_range_inbounds(start, start + amount, new_state);
    }
}

#[inline]
fn bit_index(bits: Size) -> (usize, usize) {
    let bits = bits.bytes();
    let a = bits / BLOCK_SIZE;
    let b = bits % BLOCK_SIZE;
    assert_eq!(a as usize as u64, a);
    assert_eq!(b as usize as u64, b);
    (a as usize, b as usize)
}