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Delete DataCountSection. Not well-supported and only needed for instructions we don't use

Browse source 
https://webassembly.github.io/spec/core/binary/modules.html#binary-datacountsec

Tools like wasm2wat and wasm-validate reject the module when this section is included!
Its purpose is to enable single-pass validation for two specific instructions that were
not in the original Wasm MVP: memory.init and data.drop.
We don't use them in our Roc backend. It seems to make sense just to drop the section.
This commit is contained in:
Brian Carroll 2021-11-15 11:58:30 +00:00
parent 46636ef331
commit a5c3809290
1 changed files with 2 additions and 41 deletions
Download patch file Download diff file Expand all files Collapse all files

43
compiler/gen_wasm/src/wasm_module/sections.rs
View file

@ -29,6 +29,8 @@ pub enum SectionId {
Element = 9,
Code = 10,
Data = 11,
/// DataCount section is unused. Only needed for single-pass validation of
/// memory.init and data.drop, which we don't use
DataCount = 12,
}
@ -525,42 +527,6 @@ impl Serialize for DataSection<'_> {
}
}
/*******************************************************************
*
* Data Count section
*
* Pre-declares the number of segments in the Data section.
* This helps the runtime to validate the module in a single pass.
* The order of sections is DataCount -> Code -> Data
*
*******************************************************************/
#[derive(Debug)]
struct DataCountSection {
count: u32,
}
impl DataCountSection {
fn new(data_section: &DataSection<'_>) -> Self {
let count = data_section
.segments
.iter()
.filter(|seg| !seg.init.is_empty())
.count() as u32;
DataCountSection { count }
}
}
impl Serialize for DataCountSection {
fn serialize<T: SerialBuffer>(&self, buffer: &mut T) {
if self.count > 0 {
let header_indices = write_section_header(buffer, SectionId::DataCount);
buffer.encode_u32(self.count);
update_section_size(buffer, header_indices);
}
}
}
/*******************************************************************
*
* Module
@ -658,11 +624,6 @@ impl<'a> WasmModule<'a> {
counter.serialize_and_count(buffer, &self.start);
counter.serialize_and_count(buffer, &self.element);
// Data Count section forward-declares the size of the Data section
// so that Code section can be validated in one pass
let data_count_section = DataCountSection::new(&self.data);
counter.serialize_and_count(buffer, &data_count_section);
// Code section is the only one with relocations so we can stop counting
let code_section_index = counter.section_index;
let code_section_body_index = self