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//! Table elements within a wasm module.
use crate::emit::{Emit, EmitContext};
use crate::parse::IndicesToIds;
use crate::tombstone_arena::{Id, Tombstone, TombstoneArena};
use crate::{ir::Value, ConstExpr, FunctionId, Module, RefType, Result, TableId, ValType};
use anyhow::{bail, Context};
/// A passive element segment identifier
pub type ElementId = Id<Element>;
/// A passive segment which contains a list of functions
#[derive(Debug)]
pub struct Element {
id: Id<Element>,
/// The kind of the element segment.
pub kind: ElementKind,
/// The initial elements of the element segment.
pub items: ElementItems,
/// The name of this element, used for debugging purposes in the `name`
/// custom section.
pub name: Option<String>,
}
/// The kind of element segment.
#[derive(Debug, Clone)]
pub enum ElementKind {
/// The element segment is passive.
Passive,
/// The element segment is declared.
Declared,
/// The element segment is active.
Active {
/// The ID of the table being initialized.
table: TableId,
/// A constant defining an offset into that table.
offset: ConstExpr,
},
}
/// Represents the items of an element segment.
#[derive(Debug, Clone)]
pub enum ElementItems {
/// This element contains function indices.
Functions(Vec<FunctionId>),
/// This element contains constant expressions used to initialize the table.
Expressions(RefType, Vec<ConstExpr>),
}
impl Element {
/// Get this segment's id
pub fn id(&self) -> Id<Element> {
self.id
}
}
impl Tombstone for Element {
fn on_delete(&mut self) {
// Nothing to do here
}
}
/// All element segments of a wasm module, used to initialize `anyfunc` tables,
/// used as function pointers.
#[derive(Debug, Default)]
pub struct ModuleElements {
arena: TombstoneArena<Element>,
}
impl ModuleElements {
/// Get an element associated with an ID
pub fn get(&self, id: ElementId) -> &Element {
&self.arena[id]
}
/// Get an element associated with an ID
pub fn get_mut(&mut self, id: ElementId) -> &mut Element {
&mut self.arena[id]
}
/// Delete an elements entry from this module.
///
/// It is up to you to ensure that all references to this deleted element
/// are removed.
pub fn delete(&mut self, id: ElementId) {
self.arena.delete(id);
}
/// Get a shared reference to this module's elements.
pub fn iter(&self) -> impl Iterator<Item = &Element> {
self.arena.iter().map(|(_, f)| f)
}
/// Get a mutable reference to this module's elements.
pub fn iter_mut(&mut self) -> impl Iterator<Item = &mut Element> {
self.arena.iter_mut().map(|(_, f)| f)
}
/// Add an element segment
pub fn add(&mut self, kind: ElementKind, items: ElementItems) -> ElementId {
let id = self.arena.next_id();
let id2 = self.arena.alloc(Element {
id,
kind,
items,
name: None,
});
debug_assert_eq!(id, id2);
id
}
}
impl Module {
/// Parses a raw was section into a fully-formed `ModuleElements` instance.
pub(crate) fn parse_elements(
&mut self,
section: wasmparser::ElementSectionReader,
ids: &mut IndicesToIds,
) -> Result<()> {
log::debug!("parse element section");
for (i, segment) in section.into_iter().enumerate() {
let element = segment?;
let items = match element.items {
wasmparser::ElementItems::Functions(funcs) => {
let mut function_ids = Vec::with_capacity(funcs.count() as usize);
for func in funcs {
match ids.get_func(func?) {
Ok(func) => function_ids.push(func),
Err(_) => bail!("invalid function index in element segment {}", i),
}
}
ElementItems::Functions(function_ids)
}
wasmparser::ElementItems::Expressions(ref_type, items) => {
let ty = RefType::from_wasmparser(ref_type, ids, 0)?;
let mut const_exprs = Vec::with_capacity(items.count() as usize);
for item in items {
let const_expr = item?;
let expr = ConstExpr::eval(&const_expr, ids).with_context(|| {
format!(
"Failed to evaluate a const expr in element segment {}:\n{:?}",
i, const_expr
)
})?;
const_exprs.push(expr);
}
ElementItems::Expressions(ty, const_exprs)
}
};
let id = self.elements.arena.next_id();
let kind = match element.kind {
wasmparser::ElementKind::Passive => ElementKind::Passive,
wasmparser::ElementKind::Declared => ElementKind::Declared,
wasmparser::ElementKind::Active {
table_index,
offset_expr,
} => {
// TODO: Why table_index is Option?
let table_id = ids.get_table(table_index.unwrap_or_default())?;
let table = self.tables.get_mut(table_id);
table.elem_segments.insert(id);
let offset = ConstExpr::eval(&offset_expr, ids).with_context(|| {
format!("failed to evaluate the offset of element {}", i)
})?;
if table.table64 {
match offset {
ConstExpr::Value(Value::I64(_)) => {}
ConstExpr::Global(global)
if self.globals.get(global).ty == ValType::I64 => {}
// Extended const expressions are already validated
// by wasmparser to produce the correct type.
ConstExpr::Extended(_) => {}
_ => bail!(
"element {} is active for 64-bit table but has non-i64 offset",
i
),
}
} else {
match offset {
ConstExpr::Value(Value::I32(_)) => {}
ConstExpr::Global(global)
if self.globals.get(global).ty == ValType::I32 => {}
// Extended const expressions are already validated
// by wasmparser to produce the correct type.
ConstExpr::Extended(_) => {}
_ => bail!(
"element {} is active for 32-bit table but has non-i32 offset",
i
),
}
}
ElementKind::Active {
table: table_id,
offset,
}
}
};
self.elements.arena.alloc(Element {
id,
kind,
items,
name: None,
});
ids.push_element(id);
}
Ok(())
}
}
impl Emit for ModuleElements {
fn emit(&self, cx: &mut EmitContext) {
if self.arena.len() == 0 {
return;
}
let mut wasm_element_section = wasm_encoder::ElementSection::new();
for (id, element) in self.arena.iter() {
cx.indices.push_element(id);
match &element.items {
ElementItems::Functions(function_ids) => {
let idx = function_ids
.iter()
.map(|&func| cx.indices.get_func_index(func))
.collect::<Vec<_>>();
let els = wasm_encoder::Elements::Functions(std::borrow::Cow::Borrowed(&idx));
emit_elem(cx, &mut wasm_element_section, &element.kind, els);
}
ElementItems::Expressions(ty, const_exprs) => {
let ref_type = ty.to_wasmencoder_ref_type(cx.indices);
let const_exprs = const_exprs
.iter()
.map(|expr| expr.to_wasmencoder_type(cx))
.collect::<Vec<_>>();
let els = wasm_encoder::Elements::Expressions(
ref_type,
std::borrow::Cow::Borrowed(&const_exprs),
);
emit_elem(cx, &mut wasm_element_section, &element.kind, els);
}
}
fn emit_elem(
cx: &mut EmitContext,
wasm_element_section: &mut wasm_encoder::ElementSection,
kind: &ElementKind,
els: wasm_encoder::Elements,
) {
match kind {
ElementKind::Active { table, offset } => {
// When the table index is 0, set this to `None` to tell `wasm-encoder` to use
// the backwards-compatible MVP encoding.
let table_index =
Some(cx.indices.get_table_index(*table)).filter(|&index| index != 0);
wasm_element_section.active(
table_index,
&offset.to_wasmencoder_type(cx),
els,
);
}
ElementKind::Passive => {
wasm_element_section.passive(els);
}
ElementKind::Declared => {
wasm_element_section.declared(els);
}
}
}
}
cx.wasm_module.section(&wasm_element_section);
}
}