wasm-utils/src/ext.rs

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use parity_wasm::{elements, builder};
type Insertion = (usize, u32, u32, String);
pub fn update_call_index(opcodes: &mut elements::Opcodes, original_imports: usize, inserts: &[Insertion]) {
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use parity_wasm::elements::Opcode::*;
for opcode in opcodes.elements_mut().iter_mut() {
match opcode {
&mut Block(_, ref mut block) | &mut If(_, ref mut block) | &mut Loop(_, ref mut block) => {
update_call_index(block, original_imports, inserts)
},
&mut Call(ref mut call_index) => {
if let Some(pos) = inserts.iter().position(|x| x.1 == *call_index) {
*call_index = (original_imports + pos) as u32;
} else if *call_index as usize > original_imports {
*call_index += inserts.len() as u32;
}
},
_ => { }
}
}
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}
pub fn externalize(
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module: elements::Module,
replaced_funcs: Vec<&str>,
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) -> elements::Module {
// Save import functions number for later
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let import_funcs_total = module
.import_section().expect("Import section to exist")
.entries()
.iter()
.filter(|e| if let &elements::External::Function(_) = e.external() { true } else { false })
.count();
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// First, we find functions indices that are to be rewired to externals
// Triple is (function_index (callable), type_index, function_name)
let mut replaces: Vec<Insertion> = replaced_funcs
.into_iter()
.filter_map(|f| {
let export = module
.export_section().expect("Export section to exist")
.entries().iter().enumerate()
.find(|&(_, entry)| entry.field() == f)
.expect("All functions of interest to exist");
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if let &elements::Internal::Function(func_idx) = export.1.internal() {
let type_ref = module
.functions_section().expect("Functions section to exist")
.entries()[func_idx as usize - import_funcs_total]
.type_ref();
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Some((export.0, func_idx, type_ref, export.1.field().to_owned()))
} else {
None
}
})
.collect();
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replaces.sort_by_key(|e| e.0);
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// Second, we duplicate them as import definitions
let mut mbuilder = builder::from_module(module);
for &(_, _, type_ref, ref field) in replaces.iter() {
mbuilder.push_import(
builder::import()
.module("env")
.field(field)
.external().func(type_ref)
.build()
);
}
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// Back to mutable access
let mut module = mbuilder.build();
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// Third, rewire all calls to imported functions and update all other calls indices
for section in module.sections_mut() {
match section {
&mut elements::Section::Code(ref mut code_section) => {
for ref mut func_body in code_section.bodies_mut() {
update_call_index(func_body.code_mut(), import_funcs_total, &replaces);
}
},
&mut elements::Section::Export(ref mut export_section) => {
for ref mut export in export_section.entries_mut() {
match export.internal_mut() {
&mut elements::Internal::Function(ref mut func_index) => {
if *func_index >= import_funcs_total as u32 { *func_index += replaces.len() as u32; }
},
_ => {}
}
}
},
_ => { }
}
}
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module
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}