wasmi/src/memory.rs

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use std::u32;
use std::ops::Range;
use std::cmp;
use std::fmt;
use std::rc::Rc;
use std::cell::RefCell;
use parity_wasm::elements::ResizableLimits;
use Error;
use memory_units::{RoundUpTo, Pages, Bytes};
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/// Size of a page of [linear memory][`MemoryInstance`] - 64KiB.
///
/// The size of a memory is always a integer multiple of a page size.
///
/// [`MemoryInstance`]: struct.MemoryInstance.html
pub const LINEAR_MEMORY_PAGE_SIZE: Bytes = Bytes(65536);
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/// Maximal number of pages.
const LINEAR_MEMORY_MAX_PAGES: Pages = Pages(65536);
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/// Reference to a memory (See [`MemoryInstance`] for details).
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///
/// This reference has a reference-counting semantics.
///
/// [`MemoryInstance`]: struct.MemoryInstance.html
///
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#[derive(Clone, Debug)]
pub struct MemoryRef(Rc<MemoryInstance>);
impl ::std::ops::Deref for MemoryRef {
type Target = MemoryInstance;
fn deref(&self) -> &MemoryInstance {
&self.0
}
}
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/// Runtime representation of a linear memory (or `memory` for short).
///
/// A memory is a contiguous, mutable array of raw bytes. Wasm code can load and store values
/// from/to a linear memory at any byte address.
/// A trap occurs if an access is not within the bounds of the current memory size.
///
/// A memory is created with an initial size but can be grown dynamically.
/// The growth can be limited by specifying maximum size.
/// The size of a memory is always a integer multiple of a [page size][`LINEAR_MEMORY_PAGE_SIZE`] - 64KiB.
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///
/// At the moment, wasm doesn't provide any way to shrink the memory.
///
/// [`LINEAR_MEMORY_PAGE_SIZE`]: constant.LINEAR_MEMORY_PAGE_SIZE.html
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pub struct MemoryInstance {
/// Memory limits.
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limits: ResizableLimits,
/// Linear memory buffer.
buffer: RefCell<Vec<u8>>,
initial: Pages,
maximum: Option<Pages>,
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}
impl fmt::Debug for MemoryInstance {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
f.debug_struct("MemoryInstance")
.field("limits", &self.limits)
.field("buffer.len", &self.buffer.borrow().len())
.field("maximum", &self.maximum)
.field("initial", &self.initial)
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.finish()
}
}
struct CheckedRegion<'a, B: 'a> where B: ::std::ops::Deref<Target=Vec<u8>> {
buffer: &'a B,
offset: usize,
size: usize,
}
impl<'a, B: 'a> CheckedRegion<'a, B> where B: ::std::ops::Deref<Target=Vec<u8>> {
fn range(&self) -> Range<usize> {
self.offset..self.offset+self.size
}
fn slice(&self) -> &[u8] {
&self.buffer[self.range()]
}
fn intersects(&self, other: &Self) -> bool {
let low = cmp::max(self.offset, other.offset);
let high = cmp::min(self.offset + self.size, other.offset + other.size);
low < high
}
}
impl MemoryInstance {
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/// Allocate a memory instance.
///
/// The memory allocated with initial number of pages specified by `initial`.
/// Minimal possible value for `initial` is 0 and maximum possible is `65536`.
/// (Since maximum addressible memory is 2<sup>32</sup> = 4GiB = 65536 * [64KiB][`LINEAR_MEMORY_PAGE_SIZE`]).
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///
/// It is possible to limit maximum number of pages this memory instance can have by specifying
/// `maximum`. If not specified, this memory instance would be able to allocate up to 4GiB.
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///
/// Allocated memory is always zeroed.
///
/// # Errors
///
/// Returns `Err` if:
///
/// - `initial` is greater than `maximum`
/// - either `initial` or `maximum` is greater than `65536`.
///
/// [`LINEAR_MEMORY_PAGE_SIZE`]: constant.LINEAR_MEMORY_PAGE_SIZE.html
pub fn alloc(initial: Pages, maximum: Option<Pages>) -> Result<MemoryRef, Error> {
validate_memory(initial, maximum).map_err(Error::Memory)?;
let memory = MemoryInstance::new(initial, maximum);
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Ok(MemoryRef(Rc::new(memory)))
}
/// Create new linear memory instance.
fn new(initial: Pages, maximum: Option<Pages>) -> Self {
let limits = ResizableLimits::new(initial.0 as u32, maximum.map(|p| p.0 as u32));
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let initial_size: Bytes = initial.into();
MemoryInstance {
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limits: limits,
buffer: RefCell::new(vec![0; initial_size.0]),
initial: initial,
maximum: maximum,
}
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}
/// Return linear memory limits.
pub(crate) fn limits(&self) -> &ResizableLimits {
&self.limits
}
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/// Returns number of pages this `MemoryInstance` was created with.
pub fn initial(&self) -> Pages {
self.initial
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}
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/// Returns maximum amount of pages this `MemoryInstance` can grow to.
///
/// Returns `None` if there is no limit set.
/// Maximum memory size cannot exceed `65536` pages or 4GiB.
pub fn maximum(&self) -> Option<Pages> {
self.maximum
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}
/// Returns current linear memory size.
///
/// Maximum memory size cannot exceed `65536` pages or 4GiB.
///
/// # Example
///
/// To convert number of pages to number of bytes you can use the following code:
///
/// ```rust
/// use wasmi::MemoryInstance;
/// use wasmi::memory_units::*;
///
/// let memory = MemoryInstance::alloc(Pages(1), None).unwrap();
/// let byte_size: Bytes = memory.current_size().into();
/// assert_eq!(
/// byte_size,
/// Bytes(65536),
/// );
/// ```
pub fn current_size(&self) -> Pages {
Bytes(self.buffer.borrow().len()).round_up_to()
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}
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/// Copy data from memory at given offset.
///
/// This will allocate vector for you.
/// If you can provide a mutable slice you can use [`get_into`].
///
/// [`get_into`]: #method.get_into
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pub fn get(&self, offset: u32, size: usize) -> Result<Vec<u8>, Error> {
let buffer = self.buffer.borrow();
let region = self.checked_region(&buffer, offset as usize, size)?;
Ok(region.slice().to_vec())
}
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/// Copy data from given offset in the memory into `target` slice.
///
/// # Errors
///
/// Returns `Err` if the specified region is out of bounds.
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pub fn get_into(&self, offset: u32, target: &mut [u8]) -> Result<(), Error> {
let buffer = self.buffer.borrow();
let region = self.checked_region(&buffer, offset as usize, target.len())?;
target.copy_from_slice(region.slice());
Ok(())
}
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/// Copy data in the memory at given offset.
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pub fn set(&self, offset: u32, value: &[u8]) -> Result<(), Error> {
let mut buffer = self.buffer.borrow_mut();
let range = self.checked_region(&buffer, offset as usize, value.len())?.range();
buffer[range].copy_from_slice(value);
Ok(())
}
/// Increases the size of the linear memory by given number of pages.
/// Returns previous memory size if succeeds.
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///
/// # Errors
///
/// Returns `Err` if attempted to allocate more memory than permited by the limit.
pub fn grow(&self, additional: Pages) -> Result<Pages, Error> {
let size_before_grow: Pages = self.current_size();
if additional == Pages(0) {
return Ok(size_before_grow);
}
if additional > Pages(65536) {
return Err(Error::Memory(format!(
"Trying to grow memory by more than 65536 pages"
)));
}
let new_size: Pages = size_before_grow + additional;
let maximum = self.maximum.unwrap_or(LINEAR_MEMORY_MAX_PAGES);
if new_size > maximum {
return Err(Error::Memory(format!(
"Trying to grow memory by {} pages when already have {}",
additional.0, size_before_grow.0,
)));
}
// Resize underlying buffer up to a new size filling newly allocated space with zeroes.
// This size is guaranteed to be larger than current size.
let new_buffer_length: Bytes = new_size.into();
{
let mut buffer = self.buffer.borrow_mut();
debug_assert!(new_buffer_length.0 > buffer.len());
buffer.resize(new_buffer_length.0, 0);
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}
Ok(size_before_grow)
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}
fn checked_region<'a, B>(&self, buffer: &'a B, offset: usize, size: usize) -> Result<CheckedRegion<'a, B>, Error>
where B: ::std::ops::Deref<Target=Vec<u8>>
{
let end = offset.checked_add(size)
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.ok_or_else(|| Error::Memory(format!("trying to access memory block of size {} from offset {}", size, offset)))?;
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if end > buffer.len() {
return Err(Error::Memory(format!("trying to access region [{}..{}] in memory [0..{}]", offset, end, buffer.len())));
}
Ok(CheckedRegion {
buffer: buffer,
offset: offset,
size: size,
})
}
/// Copy contents of one memory region to another.
///
/// Semantically equivalent to `memmove`.
///
/// # Errors
///
/// Returns `Err` if either of specified regions is out of bounds.
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pub fn copy(&self, src_offset: usize, dst_offset: usize, len: usize) -> Result<(), Error> {
let buffer = self.buffer.borrow_mut();
let read_region = self.checked_region(&buffer, src_offset, len)?;
let write_region = self.checked_region(&buffer, dst_offset, len)?;
unsafe { ::std::ptr::copy(
buffer[read_region.range()].as_ptr(),
buffer[write_region.range()].as_ptr() as *mut _,
len,
)}
Ok(())
}
/// Copy contents of one memory region to another (non-overlapping version).
///
/// Semantically equivalent to `memcpy`.
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/// but returns Error if source overlaping with destination.
///
/// # Errors
///
/// Returns `Err` if:
///
/// - either of specified regions is out of bounds,
/// - these regions overlaps.
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pub fn copy_nonoverlapping(&self, src_offset: usize, dst_offset: usize, len: usize) -> Result<(), Error> {
let buffer = self.buffer.borrow_mut();
let read_region = self.checked_region(&buffer, src_offset, len)?;
let write_region = self.checked_region(&buffer, dst_offset, len)?;
if read_region.intersects(&write_region) {
return Err(Error::Memory(format!("non-overlapping copy is used for overlapping regions")))
}
unsafe { ::std::ptr::copy_nonoverlapping(
buffer[read_region.range()].as_ptr(),
buffer[write_region.range()].as_ptr() as *mut _,
len,
)}
Ok(())
}
/// Fill the memory region with the specified value.
///
/// Semantically equivalent to `memset`.
///
/// # Errors
///
/// Returns `Err` if the specified region is out of bounds.
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pub fn clear(&self, offset: usize, new_val: u8, len: usize) -> Result<(), Error> {
let mut buffer = self.buffer.borrow_mut();
let range = self.checked_region(&buffer, offset, len)?.range();
for val in &mut buffer[range] { *val = new_val }
Ok(())
}
/// Fill the specified memory region with zeroes.
///
/// # Errors
///
/// Returns `Err` if the specified region is out of bounds.
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pub fn zero(&self, offset: usize, len: usize) -> Result<(), Error> {
self.clear(offset, 0, len)
}
/// Provides direct access to the underlying memory buffer.
///
/// # Panics
///
/// Any call that requires write access to memory (such as [`set`], [`clear`], etc) made within
/// the closure will panic. Proceed with caution.
///
/// [`set`]: #method.get
/// [`clear`]: #method.set
pub fn with_direct_access<R, F: FnOnce(&[u8]) -> R>(&self, f: F) -> R {
let buf = self.buffer.borrow();
f(&*buf)
}
/// Provides direct mutable access to the underlying memory buffer.
///
/// # Panics
///
/// Any calls that requires either read or write access to memory (such as [`get`], [`set`], [`copy`], etc) made
/// within the closure will panic. Proceed with caution.
///
/// [`get`]: #method.get
/// [`set`]: #method.set
/// [`copy`]: #method.copy
pub fn with_direct_access_mut<R, F: FnOnce(&mut [u8]) -> R>(&self, f: F) -> R {
let mut buf = self.buffer.borrow_mut();
f(&mut *buf)
}
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}
pub fn validate_memory(initial: Pages, maximum: Option<Pages>) -> Result<(), String> {
if initial > LINEAR_MEMORY_MAX_PAGES {
return Err(format!("initial memory size must be at most {} pages", LINEAR_MEMORY_MAX_PAGES.0));
}
if let Some(maximum) = maximum {
if initial > maximum {
return Err(format!(
"maximum limit {} is less than minimum {}",
maximum.0,
initial.0,
));
}
if maximum > LINEAR_MEMORY_MAX_PAGES {
return Err(format!("maximum memory size must be at most {} pages", LINEAR_MEMORY_MAX_PAGES.0));
}
}
Ok(())
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}
#[cfg(test)]
mod tests {
use super::{MemoryInstance, LINEAR_MEMORY_PAGE_SIZE};
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use Error;
use memory_units::Pages;
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#[test]
fn alloc() {
#[cfg(target_pointer_width = "64")]
let fixtures = &[
(0, None, true),
(0, Some(0), true),
(1, None, true),
(1, Some(1), true),
(0, Some(1), true),
(1, Some(0), false),
(0, Some(65536), true),
(65536, Some(65536), true),
(65536, Some(0), false),
(65536, None, true),
];
#[cfg(target_pointer_width = "32")]
let fixtures = &[
(0, None, true),
(0, Some(0), true),
(1, None, true),
(1, Some(1), true),
(0, Some(1), true),
(1, Some(0), false),
];
for (index, &(initial, maybe_max, expected_ok)) in fixtures.iter().enumerate() {
let initial: Pages = Pages(initial);
let maximum: Option<Pages> = maybe_max.map(|m| Pages(m));
let result = MemoryInstance::alloc(initial, maximum);
if result.is_ok() != expected_ok {
panic!(
"unexpected error at {}, initial={:?}, max={:?}, expected={}, result={:?}",
index,
initial,
maybe_max,
expected_ok,
result,
);
}
}
}
#[test]
fn ensure_page_size() {
use memory_units::ByteSize;
assert_eq!(LINEAR_MEMORY_PAGE_SIZE, Pages::byte_size());
}
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fn create_memory(initial_content: &[u8]) -> MemoryInstance {
let mem = MemoryInstance::new(Pages(1), Some(Pages(1)));
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mem.set(0, initial_content).expect("Successful initialize the memory");
mem
}
#[test]
fn copy_overlaps_1() {
let mem = create_memory(&[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]);
mem.copy(0, 4, 6).expect("Successfully copy the elements");
let result = mem.get(0, 10).expect("Successfully retrieve the result");
assert_eq!(result, &[0, 1, 2, 3, 0, 1, 2, 3, 4, 5]);
}
#[test]
fn copy_overlaps_2() {
let mem = create_memory(&[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]);
mem.copy(4, 0, 6).expect("Successfully copy the elements");
let result = mem.get(0, 10).expect("Successfully retrieve the result");
assert_eq!(result, &[4, 5, 6, 7, 8, 9, 6, 7, 8, 9]);
}
#[test]
fn copy_nonoverlapping() {
let mem = create_memory(&[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]);
mem.copy_nonoverlapping(0, 10, 10).expect("Successfully copy the elements");
let result = mem.get(10, 10).expect("Successfully retrieve the result");
assert_eq!(result, &[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]);
}
#[test]
fn copy_nonoverlapping_overlaps_1() {
let mem = create_memory(&[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]);
let result = mem.copy_nonoverlapping(0, 4, 6);
match result {
Err(Error::Memory(_)) => {},
_ => panic!("Expected Error::Memory(_) result, but got {:?}", result),
}
}
#[test]
fn copy_nonoverlapping_overlaps_2() {
let mem = create_memory(&[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]);
let result = mem.copy_nonoverlapping(4, 0, 6);
match result {
Err(Error::Memory(_)) => {},
_ => panic!("Expected Error::Memory(_), but got {:?}", result),
}
}
#[test]
fn clear() {
let mem = create_memory(&[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]);
mem.clear(0, 0x4A, 10).expect("To successfully clear the memory");
let result = mem.get(0, 10).expect("To successfully retrieve the result");
assert_eq!(result, &[0x4A; 10]);
}
#[test]
fn get_into() {
let mem = MemoryInstance::new(Pages(1), None);
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mem.set(6, &[13, 17, 129]).expect("memory set should not fail");
let mut data = [0u8; 2];
mem.get_into(7, &mut data[..]).expect("get_into should not fail");
assert_eq!(data, [17, 129]);
}
#[test]
fn zero_copy() {
let mem = MemoryInstance::alloc(Pages(1), None).unwrap();
mem.with_direct_access_mut(|buf| {
assert_eq!(buf.len(), 65536);
buf[..10].copy_from_slice(&[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]);
});
mem.with_direct_access(|buf| {
assert_eq!(buf.len(), 65536);
assert_eq!(&buf[..10], &[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]);
});
}
#[should_panic]
#[test]
fn zero_copy_panics_on_nested_access() {
let mem = MemoryInstance::alloc(Pages(1), None).unwrap();
let mem_inner = mem.clone();
mem.with_direct_access(move |_| {
let _ = mem_inner.set(0, &[11, 12, 13]);
});
}
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}