146 lines
4.5 KiB
Rust
146 lines
4.5 KiB
Rust
//! Memory management for tables.
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//!
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//! `Table` is to WebAssembly tables what `LinearMemory` is to WebAssembly linear memories.
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use crate::vmcontext::{VMCallerCheckedAnyfunc, VMTableDefinition};
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use crate::Trap;
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use std::cell::RefCell;
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use std::convert::{TryFrom, TryInto};
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use wasmtime_environ::wasm::TableElementType;
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use wasmtime_environ::{ir, TablePlan, TableStyle};
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/// A table instance.
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#[derive(Debug)]
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pub struct Table {
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vec: RefCell<Vec<VMCallerCheckedAnyfunc>>,
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maximum: Option<u32>,
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}
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impl Table {
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/// Create a new table instance with specified minimum and maximum number of elements.
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pub fn new(plan: &TablePlan) -> Self {
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match plan.table.ty {
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TableElementType::Func => (),
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TableElementType::Val(ty) => {
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unimplemented!("tables of types other than anyfunc ({})", ty)
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}
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};
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match plan.style {
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TableStyle::CallerChecksSignature => Self {
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vec: RefCell::new(vec![
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VMCallerCheckedAnyfunc::default();
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usize::try_from(plan.table.minimum).unwrap()
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]),
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maximum: plan.table.maximum,
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},
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}
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}
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/// Returns the number of allocated elements.
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pub fn size(&self) -> u32 {
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self.vec.borrow().len().try_into().unwrap()
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}
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/// Grow table by the specified amount of elements.
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///
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/// Returns `None` if table can't be grown by the specified amount
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/// of elements.
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pub fn grow(&self, delta: u32) -> Option<u32> {
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let new_len = match self.size().checked_add(delta) {
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Some(len) => {
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if let Some(max) = self.maximum {
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if len > max {
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return None;
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}
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}
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len
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}
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None => {
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return None;
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}
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};
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self.vec.borrow_mut().resize(
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usize::try_from(new_len).unwrap(),
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VMCallerCheckedAnyfunc::default(),
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);
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Some(new_len)
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}
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/// Get reference to the specified element.
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///
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/// Returns `None` if the index is out of bounds.
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pub fn get(&self, index: u32) -> Option<VMCallerCheckedAnyfunc> {
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self.vec.borrow().get(index as usize).cloned()
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}
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/// Set reference to the specified element.
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///
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/// # Panics
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///
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/// Panics if `index` is out of bounds.
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pub fn set(&self, index: u32, func: VMCallerCheckedAnyfunc) -> Result<(), ()> {
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match self.vec.borrow_mut().get_mut(index as usize) {
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Some(slot) => {
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*slot = func;
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Ok(())
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}
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None => Err(()),
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}
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}
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/// Copy `len` elements from `src_table[src_index..]` into `dst_table[dst_index..]`.
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///
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/// # Errors
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///
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/// Returns an error if the range is out of bounds of either the source or
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/// destination tables.
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pub fn copy(
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dst_table: &Self,
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src_table: &Self,
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dst_index: u32,
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src_index: u32,
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len: u32,
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source_loc: ir::SourceLoc,
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) -> Result<(), Trap> {
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// https://webassembly.github.io/bulk-memory-operations/core/exec/instructions.html#exec-table-copy
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if src_index
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.checked_add(len)
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.map_or(true, |n| n > src_table.size())
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|| dst_index
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.checked_add(len)
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.map_or(true, |m| m > dst_table.size())
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{
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return Err(Trap::wasm(source_loc, ir::TrapCode::TableOutOfBounds));
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}
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let srcs = src_index..src_index + len;
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let dsts = dst_index..dst_index + len;
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// Note on the unwraps: the bounds check above means that these will
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// never panic.
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//
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// TODO(#983): investigate replacing this get/set loop with a `memcpy`.
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if dst_index <= src_index {
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for (s, d) in (srcs).zip(dsts) {
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dst_table.set(d, src_table.get(s).unwrap()).unwrap();
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}
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} else {
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for (s, d) in srcs.rev().zip(dsts.rev()) {
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dst_table.set(d, src_table.get(s).unwrap()).unwrap();
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}
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}
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Ok(())
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}
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/// Return a `VMTableDefinition` for exposing the table to compiled wasm code.
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pub fn vmtable(&self) -> VMTableDefinition {
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let mut vec = self.vec.borrow_mut();
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VMTableDefinition {
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base: vec.as_mut_ptr() as *mut u8,
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current_elements: vec.len().try_into().unwrap(),
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}
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}
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}
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