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// This file contains code from external sources.
// Attributions: https://github.com/wasmerio/wasmer/blob/main/docs/ATTRIBUTIONS.md
//! Memory management for tables.
//!
//! `Table` is to WebAssembly tables what `Memory` is to WebAssembly linear memories.
use crate::store::MaybeInstanceOwned;
use crate::vmcontext::VMTableDefinition;
use crate::Trap;
use crate::VMExternRef;
use crate::VMFuncRef;
use std::cell::UnsafeCell;
use std::convert::TryFrom;
use std::fmt;
use std::ptr::NonNull;
use wasmer_types::TableStyle;
use wasmer_types::{TableType, TrapCode, Type as ValType};
/// A reference stored in a table. Can be either an externref or a funcref.
#[derive(Debug, Clone)]
pub enum TableElement {
/// Opaque pointer to arbitrary hostdata.
ExternRef(Option<VMExternRef>),
/// Pointer to function: contains enough information to call it.
FuncRef(Option<VMFuncRef>),
}
impl From<TableElement> for RawTableElement {
fn from(other: TableElement) -> Self {
match other {
TableElement::ExternRef(extern_ref) => Self { extern_ref },
TableElement::FuncRef(func_ref) => Self { func_ref },
}
}
}
#[repr(C)]
#[derive(Clone, Copy)]
pub union RawTableElement {
pub(crate) extern_ref: Option<VMExternRef>,
pub(crate) func_ref: Option<VMFuncRef>,
}
#[cfg(test)]
#[test]
fn table_element_size_test() {
use std::mem::size_of;
assert_eq!(size_of::<RawTableElement>(), size_of::<VMExternRef>());
assert_eq!(size_of::<RawTableElement>(), size_of::<VMFuncRef>());
}
impl fmt::Debug for RawTableElement {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
f.debug_struct("RawTableElement").finish()
}
}
impl Default for RawTableElement {
fn default() -> Self {
Self { func_ref: None }
}
}
impl Default for TableElement {
fn default() -> Self {
Self::FuncRef(None)
}
}
/// A table instance.
#[derive(Debug)]
pub struct VMTable {
vec: Vec<RawTableElement>,
maximum: Option<u32>,
/// The WebAssembly table description.
table: TableType,
/// Our chosen implementation style.
style: TableStyle,
vm_table_definition: MaybeInstanceOwned<VMTableDefinition>,
}
impl VMTable {
/// Create a new linear table instance with specified minimum and maximum number of elements.
///
/// This creates a `Table` with metadata owned by a VM, pointed to by
/// `vm_table_location`: this can be used to create a local table.
pub fn new(table: &TableType, style: &TableStyle) -> Result<Self, String> {
unsafe { Self::new_inner(table, style, None) }
}
/// Returns the size of the table
pub fn get_runtime_size(&self) -> u32 {
self.vec.len() as u32
}
/// Create a new linear table instance with specified minimum and maximum number of elements.
///
/// This creates a `Table` with metadata owned by a VM, pointed to by
/// `vm_table_location`: this can be used to create a local table.
///
/// # Safety
/// - `vm_table_location` must point to a valid location in VM memory.
pub unsafe fn from_definition(
table: &TableType,
style: &TableStyle,
vm_table_location: NonNull<VMTableDefinition>,
) -> Result<Self, String> {
Self::new_inner(table, style, Some(vm_table_location))
}
/// Create a new `Table` with either self-owned or VM owned metadata.
unsafe fn new_inner(
table: &TableType,
style: &TableStyle,
vm_table_location: Option<NonNull<VMTableDefinition>>,
) -> Result<Self, String> {
match table.ty {
ValType::FuncRef | ValType::ExternRef => (),
ty => {
return Err(format!(
"tables of types other than funcref or externref ({})",
ty
))
}
};
if let Some(max) = table.maximum {
if max < table.minimum {
return Err(format!(
"Table minimum ({}) is larger than maximum ({})!",
table.minimum, max
));
}
}
let table_minimum = usize::try_from(table.minimum)
.map_err(|_| "Table minimum is bigger than usize".to_string())?;
let mut vec = vec![RawTableElement::default(); table_minimum];
let base = vec.as_mut_ptr();
match style {
TableStyle::CallerChecksSignature => Ok(Self {
vec,
maximum: table.maximum,
table: *table,
style: style.clone(),
vm_table_definition: if let Some(table_loc) = vm_table_location {
{
let mut ptr = table_loc;
let td = ptr.as_mut();
td.base = base as _;
td.current_elements = table_minimum as _;
}
MaybeInstanceOwned::Instance(table_loc)
} else {
MaybeInstanceOwned::Host(Box::new(UnsafeCell::new(VMTableDefinition {
base: base as _,
current_elements: table_minimum as _,
})))
},
}),
}
}
/// Get the `VMTableDefinition`.
fn get_vm_table_definition(&self) -> NonNull<VMTableDefinition> {
self.vm_table_definition.as_ptr()
}
/// Returns the type for this Table.
pub fn ty(&self) -> &TableType {
&self.table
}
/// Returns the style for this Table.
pub fn style(&self) -> &TableStyle {
&self.style
}
/// Returns the number of allocated elements.
pub fn size(&self) -> u32 {
// TODO: investigate this function for race conditions
unsafe {
let td_ptr = self.get_vm_table_definition();
let td = td_ptr.as_ref();
td.current_elements
}
}
/// Grow table by the specified amount of elements.
///
/// Returns `None` if table can't be grown by the specified amount
/// of elements, otherwise returns the previous size of the table.
pub fn grow(&mut self, delta: u32, init_value: TableElement) -> Option<u32> {
let size = self.size();
let new_len = size.checked_add(delta)?;
if self.maximum.map_or(false, |max| new_len > max) {
return None;
}
if new_len == size {
debug_assert_eq!(delta, 0);
return Some(size);
}
self.vec
.resize(usize::try_from(new_len).unwrap(), init_value.into());
// update table definition
unsafe {
let mut td_ptr = self.get_vm_table_definition();
let td = td_ptr.as_mut();
td.current_elements = new_len;
td.base = self.vec.as_mut_ptr() as _;
}
Some(size)
}
/// Get reference to the specified element.
///
/// Returns `None` if the index is out of bounds.
pub fn get(&self, index: u32) -> Option<TableElement> {
let raw_data = self.vec.get(index as usize).cloned()?;
Some(match self.table.ty {
ValType::ExternRef => TableElement::ExternRef(unsafe { raw_data.extern_ref }),
ValType::FuncRef => TableElement::FuncRef(unsafe { raw_data.func_ref }),
_ => todo!("getting invalid type from table, handle this error"),
})
}
/// Set reference to the specified element.
///
/// # Errors
///
/// Returns an error if the index is out of bounds.
pub fn set(&mut self, index: u32, reference: TableElement) -> Result<(), Trap> {
match self.vec.get_mut(index as usize) {
Some(slot) => {
match (self.table.ty, reference) {
(ValType::ExternRef, r @ TableElement::ExternRef(_)) => {
*slot = r.into();
}
(ValType::FuncRef, r @ TableElement::FuncRef(_)) => {
*slot = r.into();
}
// This path should never be hit by the generated code due to Wasm
// validation.
(ty, v) => {
panic!(
"Attempted to set a table of type {} with the value {:?}",
ty, v
)
}
};
Ok(())
}
None => Err(Trap::lib(TrapCode::TableAccessOutOfBounds)),
}
}
/// Return a `VMTableDefinition` for exposing the table to compiled wasm code.
pub fn vmtable(&self) -> NonNull<VMTableDefinition> {
self.get_vm_table_definition()
}
/// Copy `len` elements from `src_table[src_index..]` into `dst_table[dst_index..]`.
///
/// # Errors
///
/// Returns an error if the range is out of bounds of either the source or
/// destination tables.
pub fn copy(
&mut self,
src_table: &Self,
dst_index: u32,
src_index: u32,
len: u32,
) -> Result<(), Trap> {
// https://webassembly.github.io/bulk-memory-operations/core/exec/instructions.html#exec-table-copy
if src_index
.checked_add(len)
.map_or(true, |n| n > src_table.size())
{
return Err(Trap::lib(TrapCode::TableAccessOutOfBounds));
}
if dst_index.checked_add(len).map_or(true, |m| m > self.size()) {
return Err(Trap::lib(TrapCode::TableAccessOutOfBounds));
}
let srcs = src_index..src_index + len;
let dsts = dst_index..dst_index + len;
// Note on the unwraps: the bounds check above means that these will
// never panic.
//
// TODO: investigate replacing this get/set loop with a `memcpy`.
if dst_index <= src_index {
for (s, d) in (srcs).zip(dsts) {
self.set(d, src_table.get(s).unwrap())?;
}
} else {
for (s, d) in srcs.rev().zip(dsts.rev()) {
self.set(d, src_table.get(s).unwrap())?;
}
}
Ok(())
}
/// Copies the table into a new table
pub fn copy_on_write(&self) -> Result<Self, String> {
let mut ret = Self::new(&self.table, &self.style)?;
ret.copy(self, 0, 0, self.size())
.map_err(|trap| format!("failed to copy the table - {:?}", trap))?;
Ok(ret)
}
/// Copy `len` elements from `table[src_index..]` to `table[dst_index..]`.
///
/// # Errors
///
/// Returns an error if the range is out of bounds of either the source or
/// destination tables.
pub fn copy_within(&mut self, dst_index: u32, src_index: u32, len: u32) -> Result<(), Trap> {
// https://webassembly.github.io/bulk-memory-operations/core/exec/instructions.html#exec-table-copy
if src_index.checked_add(len).map_or(true, |n| n > self.size()) {
return Err(Trap::lib(TrapCode::TableAccessOutOfBounds));
}
if dst_index.checked_add(len).map_or(true, |m| m > self.size()) {
return Err(Trap::lib(TrapCode::TableAccessOutOfBounds));
}
let srcs = src_index..src_index + len;
let dsts = dst_index..dst_index + len;
// Note on the unwraps: the bounds check above means that these will
// never panic.
//
// TODO: investigate replacing this get/set loop with a `memcpy`.
if dst_index <= src_index {
for (s, d) in (srcs).zip(dsts) {
self.set(d, self.get(s).unwrap())?;
}
} else {
for (s, d) in srcs.rev().zip(dsts.rev()) {
self.set(d, self.get(s).unwrap())?;
}
}
Ok(())
}
}