wasmi/src/memory.rs

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#[allow(unused_imports)]
use alloc::prelude::*;
use alloc::rc::Rc;
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use core::cell::{Cell, RefCell};
use core::cmp;
use core::fmt;
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use core::ops::Range;
use core::u32;
use memory_units::{Bytes, Pages, RoundUpTo};
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use parity_wasm::elements::ResizableLimits;
use value::LittleEndianConvert;
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use Error;
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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 ::core::ops::Deref for MemoryRef {
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type Target = MemoryInstance;
fn deref(&self) -> &MemoryInstance {
&self.0
}
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}
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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 {
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/// Memory limits.
limits: ResizableLimits,
/// Linear memory buffer with lazy allocation.
buffer: RefCell<Vec<u8>>,
initial: Pages,
current_size: Cell<usize>,
maximum: Option<Pages>,
lowest_used: Cell<u32>,
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}
impl fmt::Debug for MemoryInstance {
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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)
.finish()
}
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}
struct CheckedRegion {
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offset: usize,
size: usize,
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}
impl CheckedRegion {
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fn range(&self) -> Range<usize> {
self.offset..self.offset + self.size
}
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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);
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low < high
}
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}
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`]).
///
/// 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.
///
/// 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);
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));
let initial_size: Bytes = initial.into();
MemoryInstance {
limits: limits,
buffer: RefCell::new(Vec::with_capacity(4096)),
initial: initial,
current_size: Cell::new(initial_size.0),
maximum: maximum,
lowest_used: Cell::new(u32::max_value()),
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}
}
/// Return linear memory limits.
pub(crate) fn limits(&self) -> &ResizableLimits {
&self.limits
}
/// Returns number of pages this `MemoryInstance` was created with.
pub fn initial(&self) -> Pages {
self.initial
}
/// 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
}
/// Returns lowest offset ever written or `u32::max_value()` if none.
pub fn lowest_used(&self) -> u32 {
self.lowest_used.get()
}
/// Resets tracked lowest offset.
pub fn reset_lowest_used(&self, addr: u32) {
self.lowest_used.set(addr)
}
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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.current_size.get()).round_up_to()
}
/// Returns current used memory size in bytes.
/// This is one more than the highest memory address that had been written to.
pub fn used_size(&self) -> Bytes {
Bytes(self.buffer.borrow().len())
}
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/// Get value from memory at given offset.
pub fn get_value<T: LittleEndianConvert>(&self, offset: u32) -> Result<T, Error> {
let mut buffer = self.buffer.borrow_mut();
let region =
self.checked_region(&mut buffer, offset as usize, ::core::mem::size_of::<T>())?;
Ok(T::from_little_endian(&buffer[region.range()]).expect("Slice size is checked"))
}
/// 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
pub fn get(&self, offset: u32, size: usize) -> Result<Vec<u8>, Error> {
let mut buffer = self.buffer.borrow_mut();
let region = self.checked_region(&mut buffer, offset as usize, size)?;
Ok(buffer[region.range()].to_vec())
}
/// Copy data from given offset in the memory into `target` slice.
///
/// # Errors
///
/// Returns `Err` if the specified region is out of bounds.
pub fn get_into(&self, offset: u32, target: &mut [u8]) -> Result<(), Error> {
let mut buffer = self.buffer.borrow_mut();
let region = self.checked_region(&mut buffer, offset as usize, target.len())?;
target.copy_from_slice(&buffer[region.range()]);
Ok(())
}
/// Copy data in the memory at given offset.
pub fn set(&self, offset: u32, value: &[u8]) -> Result<(), Error> {
let mut buffer = self.buffer.borrow_mut();
let range = self
.checked_region(&mut buffer, offset as usize, value.len())?
.range();
if offset < self.lowest_used.get() {
self.lowest_used.set(offset);
}
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buffer[range].copy_from_slice(value);
Ok(())
}
/// Copy value in the memory at given offset.
pub fn set_value<T: LittleEndianConvert>(&self, offset: u32, value: T) -> Result<(), Error> {
let mut buffer = self.buffer.borrow_mut();
let range = self
.checked_region(&mut buffer, offset as usize, ::core::mem::size_of::<T>())?
.range();
if offset < self.lowest_used.get() {
self.lowest_used.set(offset);
}
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value.into_little_endian(&mut buffer[range]);
Ok(())
}
/// Increases the size of the linear memory by given number of pages.
/// Returns previous memory size if succeeds.
///
/// # 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,
)));
}
let new_buffer_length: Bytes = new_size.into();
self.current_size.set(new_buffer_length.0);
Ok(size_before_grow)
}
fn checked_region<B>(
&self,
buffer: &mut B,
offset: usize,
size: usize,
) -> Result<CheckedRegion, Error>
where
B: ::core::ops::DerefMut<Target = Vec<u8>>,
{
let end = offset.checked_add(size).ok_or_else(|| {
Error::Memory(format!(
"trying to access memory block of size {} from offset {}",
size, offset
))
})?;
if end <= self.current_size.get() && buffer.len() < end {
buffer.resize(end, 0);
}
if end > buffer.len() {
return Err(Error::Memory(format!(
"trying to access region [{}..{}] in memory [0..{}]",
offset,
end,
buffer.len()
)));
}
Ok(CheckedRegion {
offset: offset,
size: size,
})
}
fn checked_region_pair<B>(
&self,
buffer: &mut B,
offset1: usize,
size1: usize,
offset2: usize,
size2: usize,
) -> Result<(CheckedRegion, CheckedRegion), Error>
where
B: ::core::ops::DerefMut<Target = Vec<u8>>,
{
let end1 = offset1.checked_add(size1).ok_or_else(|| {
Error::Memory(format!(
"trying to access memory block of size {} from offset {}",
size1, offset1
))
})?;
let end2 = offset2.checked_add(size2).ok_or_else(|| {
Error::Memory(format!(
"trying to access memory block of size {} from offset {}",
size2, offset2
))
})?;
let max = cmp::max(end1, end2);
if max <= self.current_size.get() && buffer.len() < max {
buffer.resize(max, 0);
}
if end1 > buffer.len() {
return Err(Error::Memory(format!(
"trying to access region [{}..{}] in memory [0..{}]",
offset1,
end1,
buffer.len()
)));
}
if end2 > buffer.len() {
return Err(Error::Memory(format!(
"trying to access region [{}..{}] in memory [0..{}]",
offset2,
end2,
buffer.len()
)));
}
Ok((
CheckedRegion {
offset: offset1,
size: size1,
},
CheckedRegion {
offset: offset2,
size: size2,
},
))
}
/// Copy contents of one memory region to another.
///
/// Semantically equivalent to `memmove`.
///
/// # Errors
///
/// Returns `Err` if either of specified regions is out of bounds.
pub fn copy(&self, src_offset: usize, dst_offset: usize, len: usize) -> Result<(), Error> {
let mut buffer = self.buffer.borrow_mut();
let (read_region, write_region) =
self.checked_region_pair(&mut buffer, src_offset, len, dst_offset, len)?;
if dst_offset < self.lowest_used.get() as usize {
self.lowest_used.set(dst_offset as u32);
}
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unsafe {
::core::ptr::copy(
buffer[read_region.range()].as_ptr(),
buffer[write_region.range()].as_mut_ptr(),
len,
)
}
Ok(())
}
/// Copy contents of one memory region to another (non-overlapping version).
///
/// Semantically equivalent to `memcpy`.
/// but returns Error if source overlaping with destination.
///
/// # Errors
///
/// Returns `Err` if:
///
/// - either of specified regions is out of bounds,
/// - these regions overlaps.
pub fn copy_nonoverlapping(
&self,
src_offset: usize,
dst_offset: usize,
len: usize,
) -> Result<(), Error> {
let mut buffer = self.buffer.borrow_mut();
let (read_region, write_region) =
self.checked_region_pair(&mut buffer, src_offset, len, dst_offset, len)?;
if read_region.intersects(&write_region) {
return Err(Error::Memory(format!(
"non-overlapping copy is used for overlapping regions"
)));
}
if dst_offset < self.lowest_used.get() as usize {
self.lowest_used.set(dst_offset as u32);
}
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unsafe {
::core::ptr::copy_nonoverlapping(
buffer[read_region.range()].as_ptr(),
buffer[write_region.range()].as_mut_ptr(),
len,
)
}
Ok(())
}
/// Copy memory between two (possibly distinct) memory instances.
///
/// If the same memory instance passed as `src` and `dst` then usual `copy` will be used.
pub fn transfer(
src: &MemoryRef,
src_offset: usize,
dst: &MemoryRef,
dst_offset: usize,
len: usize,
) -> Result<(), Error> {
if Rc::ptr_eq(&src.0, &dst.0) {
// `transfer` is invoked with with same source and destination. Let's assume that regions may
// overlap and use `copy`.
return src.copy(src_offset, dst_offset, len);
}
// Because memory references point to different memory instances, it is safe to `borrow_mut`
// both buffers at once (modulo `with_direct_access_mut`).
let mut src_buffer = src.buffer.borrow_mut();
let mut dst_buffer = dst.buffer.borrow_mut();
let src_range = src
.checked_region(&mut src_buffer, src_offset, len)?
.range();
let dst_range = dst
.checked_region(&mut dst_buffer, dst_offset, len)?
.range();
if dst_offset < dst.lowest_used.get() as usize {
dst.lowest_used.set(dst_offset as u32);
}
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dst_buffer[dst_range].copy_from_slice(&src_buffer[src_range]);
Ok(())
}
/// Fill the memory region with the specified value.
///
/// Semantically equivalent to `memset`.
///
/// # Errors
///
/// Returns `Err` if the specified region is out of bounds.
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(&mut buffer, offset, len)?.range();
if offset < self.lowest_used.get() as usize {
self.lowest_used.set(offset as u32);
}
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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.
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. Note that the buffer size may be arbitraty. 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. Note that the buffer size may be arbitraty.
/// The closure may however resize it. Proceed with caution.
///
/// [`get`]: #method.get
/// [`set`]: #method.set
/// [`copy`]: #method.copy
pub fn with_direct_access_mut<R, F: FnOnce(&mut Vec<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> {
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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 {
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use super::{MemoryInstance, MemoryRef, LINEAR_MEMORY_PAGE_SIZE};
use memory_units::Pages;
use std::rc::Rc;
use Error;
#[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());
}
fn create_memory(initial_content: &[u8]) -> MemoryInstance {
let mem = MemoryInstance::new(Pages(1), Some(Pages(1)));
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 transfer_works() {
let src = MemoryRef(Rc::new(create_memory(&[0, 1, 2, 3, 4, 5, 6, 7, 8, 9])));
let dst = MemoryRef(Rc::new(create_memory(&[
10, 11, 12, 13, 14, 15, 16, 17, 18, 19,
])));
MemoryInstance::transfer(&src, 4, &dst, 0, 3).unwrap();
assert_eq!(src.get(0, 10).unwrap(), &[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]);
assert_eq!(
dst.get(0, 10).unwrap(),
&[4, 5, 6, 13, 14, 15, 16, 17, 18, 19]
);
}
#[test]
fn transfer_still_works_with_same_memory() {
let src = MemoryRef(Rc::new(create_memory(&[0, 1, 2, 3, 4, 5, 6, 7, 8, 9])));
MemoryInstance::transfer(&src, 4, &src, 0, 3).unwrap();
assert_eq!(src.get(0, 10).unwrap(), &[4, 5, 6, 3, 4, 5, 6, 7, 8, 9]);
}
#[test]
fn transfer_oob_with_same_memory_errors() {
let src = MemoryRef(Rc::new(create_memory(&[0, 1, 2, 3, 4, 5, 6, 7, 8, 9])));
assert!(MemoryInstance::transfer(&src, 65535, &src, 0, 3).is_err());
// Check that memories content left untouched
assert_eq!(src.get(0, 10).unwrap(), &[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]);
}
#[test]
fn transfer_oob_errors() {
let src = MemoryRef(Rc::new(create_memory(&[0, 1, 2, 3, 4, 5, 6, 7, 8, 9])));
let dst = MemoryRef(Rc::new(create_memory(&[
10, 11, 12, 13, 14, 15, 16, 17, 18, 19,
])));
assert!(MemoryInstance::transfer(&src, 65535, &dst, 0, 3).is_err());
// Check that memories content left untouched
assert_eq!(src.get(0, 10).unwrap(), &[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]);
assert_eq!(
dst.get(0, 10).unwrap(),
&[10, 11, 12, 13, 14, 15, 16, 17, 18, 19]
);
}
#[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);
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.set(100, &[0]).expect("memory set should not fail");
mem.with_direct_access_mut(|buf| {
assert_eq!(buf.len(), 101);
buf[..10].copy_from_slice(&[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]);
});
mem.with_direct_access(|buf| {
assert_eq!(buf.len(), 101);
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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}