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//! Table elements within a wasm module.
use crate::emit::{Emit, EmitContext, Section};
use crate::ir::Value;
use crate::parse::IndicesToIds;
use crate::tombstone_arena::{Id, Tombstone, TombstoneArena};
use crate::{FunctionId, InitExpr, Module, Result, TableKind, ValType};
use failure::{bail, ResultExt};
/// 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>,
members: Vec<FunctionId>,
}
impl Element {
/// Get this segment's id
pub fn id(&self) -> Id<Element> {
self.id
}
}
impl Tombstone for Element {
fn on_delete(&mut self) {
self.members = Vec::new();
}
}
/// 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 passive elements.
pub fn iter(&self) -> impl Iterator<Item = &Element> {
self.arena.iter().map(|(_, f)| f)
}
}
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 segment = segment?;
match segment.kind {
wasmparser::ElementKind::Passive(ty) => {
drop(ty);
bail!("passive element segments not supported yet");
}
wasmparser::ElementKind::Active {
table_index,
init_expr,
} => {
let table = ids.get_table(table_index)?;
let table = match &mut self.tables.get_mut(table).kind {
TableKind::Function(t) => t,
TableKind::Anyref(_) => {
bail!("active anyref segments not supported yet");
}
};
let offset = InitExpr::eval(&init_expr, ids)
.with_context(|_e| format!("in segment {}", i))?;
let functions = segment.items.get_items_reader()?.into_iter().map(|func| {
let func = func?;
ids.get_func(func)
});
match offset {
InitExpr::Value(Value::I32(n)) => {
let offset = n as usize;
for (i, id) in functions.enumerate() {
while i + offset + 1 > table.elements.len() {
table.elements.push(None);
}
table.elements[i + offset] = Some(id?);
}
}
InitExpr::Global(global) if self.globals.get(global).ty == ValType::I32 => {
let list = functions.collect::<Result<_>>()?;
table.relative_elements.push((global, list));
}
_ => bail!("non-i32 constant in segment {}", i),
}
}
}
}
Ok(())
}
}
impl Emit for ModuleElements {
fn emit(&self, cx: &mut EmitContext) {
log::debug!("emit element section");
// Sort table ids for a deterministic emission for now, eventually we
// may want some sort of sorting heuristic here.
let mut active = cx
.module
.tables
.iter()
.filter_map(|t| match &t.kind {
TableKind::Function(list) => Some((t.id(), list)),
TableKind::Anyref(_) => None,
})
.collect::<Vec<_>>();
active.sort_by_key(|pair| pair.0);
// Append segments as we find them for all table initializers. We can
// skip initializers for unused tables, and otherwise we just want to
// create an initializer for each contiguous chunk of function indices.
let mut chunks = Vec::new();
for (table_id, table) in active.iter() {
let mut offset = 0;
let mut len = 0;
for (i, item) in table.elements.iter().enumerate() {
if item.is_some() {
if len == 0 {
offset = i;
}
len += 1;
} else {
if len > 0 {
chunks.push((table_id, table, offset, len));
}
len = 0;
}
}
if len > 0 {
chunks.push((table_id, table, offset, len));
}
}
let passive = self.iter().count();
let relative = active
.iter()
.map(|(_, table)| table.relative_elements.len())
.sum::<usize>();
let total = passive + relative + chunks.len();
if total == 0 {
return;
}
let mut cx = cx.start_section(Section::Element);
cx.encoder.usize(total);
// Emits the leading data for describing a table's index
//
// Note that much of this is in accordance with the
// currently-in-progress bulk-memory proposal for WebAssembly.
let active_table_header = |cx: &mut EmitContext, index: u32| {
if index == 0 {
cx.encoder.byte(0x00);
} else {
cx.encoder.byte(0x02);
cx.encoder.u32(index);
}
};
// Emit all contiguous chunks of functions pointers that are located at
// constant offsets
for (&id, table, offset, len) in chunks {
let table_index = cx.indices.get_table_index(id);
active_table_header(&mut cx, table_index);
InitExpr::Value(Value::I32(offset as i32)).emit(&mut cx);
cx.encoder.usize(len);
for item in table.elements[offset..][..len].iter() {
let index = cx.indices.get_func_index(item.unwrap());
cx.encoder.u32(index);
}
}
// Emit all chunks of function pointers that are located at relative
// global offsets.
for (id, table) in active.iter() {
let table_index = cx.indices.get_table_index(*id);
for (global, list) in table.relative_elements.iter() {
active_table_header(&mut cx, table_index);
InitExpr::Global(*global).emit(&mut cx);
cx.encoder.usize(list.len());
for func in list {
let index = cx.indices.get_func_index(*func);
cx.encoder.u32(index);
}
}
}
// After all the active segments are added add passive segments next. We
// may want to sort this more intelligently in the future. Otherwise
// emitting a segment here is in general much simpler than above as we
// know there are no holes.
for (id, segment) in self.arena.iter() {
cx.indices.push_element(id);
drop((id, segment));
// TODO: sync this with the upstream spec
panic!(
"encoding a passive element segment requires either \
`ref.null` or `ref.func` encodings, which aren't \
currently implemented"
);
}
}
}