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use std::fs;
use std::path::Path;
use std::str;
use rustc_data_structures::fx::FxHashMap;
use serialize::leb128;
const WASM_IMPORT_SECTION_ID: u8 = 2;
const WASM_EXTERNAL_KIND_FUNCTION: u8 = 0;
const WASM_EXTERNAL_KIND_TABLE: u8 = 1;
const WASM_EXTERNAL_KIND_MEMORY: u8 = 2;
const WASM_EXTERNAL_KIND_GLOBAL: u8 = 3;
pub fn rewrite_imports(path: &Path, import_map: &FxHashMap<String, String>) {
if import_map.len() == 0 {
return
}
let wasm = fs::read(path).expect("failed to read wasm output");
let mut ret = WasmEncoder::new();
ret.data.extend(&wasm[..8]);
for (id, raw) in WasmSections(WasmDecoder::new(&wasm[8..])) {
ret.byte(id);
if id == WASM_IMPORT_SECTION_ID {
info!("rewriting import section");
let data = rewrite_import_section(
&mut WasmDecoder::new(raw),
import_map,
);
ret.bytes(&data);
} else {
info!("carry forward section {}, {} bytes long", id, raw.len());
ret.bytes(raw);
}
}
fs::write(path, &ret.data).expect("failed to write wasm output");
fn rewrite_import_section(
wasm: &mut WasmDecoder,
import_map: &FxHashMap<String, String>,
)
-> Vec<u8>
{
let mut dst = WasmEncoder::new();
let n = wasm.u32();
dst.u32(n);
info!("rewriting {} imports", n);
for _ in 0..n {
rewrite_import_entry(wasm, &mut dst, import_map);
}
return dst.data
}
fn rewrite_import_entry(wasm: &mut WasmDecoder,
dst: &mut WasmEncoder,
import_map: &FxHashMap<String, String>) {
let module = wasm.str();
let field = wasm.str();
let new_module = if module == "env" {
import_map.get(field).map(|s| &**s).unwrap_or(module)
} else {
module
};
info!("import rewrite ({} => {}) / {}", module, new_module, field);
dst.str(new_module);
dst.str(field);
let kind = wasm.byte();
dst.byte(kind);
match kind {
WASM_EXTERNAL_KIND_FUNCTION => dst.u32(wasm.u32()),
WASM_EXTERNAL_KIND_TABLE => {
dst.byte(wasm.byte());
dst.limits(wasm.limits());
}
WASM_EXTERNAL_KIND_MEMORY => dst.limits(wasm.limits()),
WASM_EXTERNAL_KIND_GLOBAL => {
dst.byte(wasm.byte());
dst.bool(wasm.bool());
}
b => panic!("unknown kind: {}", b),
}
}
}
struct WasmSections<'a>(WasmDecoder<'a>);
impl<'a> Iterator for WasmSections<'a> {
type Item = (u8, &'a [u8]);
fn next(&mut self) -> Option<(u8, &'a [u8])> {
if self.0.data.len() == 0 {
return None
}
let id = self.0.byte();
let section_len = self.0.u32();
info!("new section {} / {} bytes", id, section_len);
let section = self.0.skip(section_len as usize);
Some((id, section))
}
}
struct WasmDecoder<'a> {
data: &'a [u8],
}
impl<'a> WasmDecoder<'a> {
fn new(data: &'a [u8]) -> WasmDecoder<'a> {
WasmDecoder { data }
}
fn byte(&mut self) -> u8 {
self.skip(1)[0]
}
fn u32(&mut self) -> u32 {
let (n, l1) = leb128::read_u32_leb128(self.data);
self.data = &self.data[l1..];
return n
}
fn skip(&mut self, amt: usize) -> &'a [u8] {
let (data, rest) = self.data.split_at(amt);
self.data = rest;
data
}
fn str(&mut self) -> &'a str {
let len = self.u32();
str::from_utf8(self.skip(len as usize)).unwrap()
}
fn bool(&mut self) -> bool {
self.byte() == 1
}
fn limits(&mut self) -> (u32, Option<u32>) {
let has_max = self.bool();
(self.u32(), if has_max { Some(self.u32()) } else { None })
}
}
struct WasmEncoder {
data: Vec<u8>,
}
impl WasmEncoder {
fn new() -> WasmEncoder {
WasmEncoder { data: Vec::new() }
}
fn u32(&mut self, val: u32) {
leb128::write_u32_leb128(&mut self.data, val);
}
fn byte(&mut self, val: u8) {
self.data.push(val);
}
fn bytes(&mut self, val: &[u8]) {
self.u32(val.len() as u32);
self.data.extend_from_slice(val);
}
fn str(&mut self, val: &str) {
self.bytes(val.as_bytes())
}
fn bool(&mut self, b: bool) {
self.byte(b as u8);
}
fn limits(&mut self, limits: (u32, Option<u32>)) {
self.bool(limits.1.is_some());
self.u32(limits.0);
if let Some(c) = limits.1 {
self.u32(c);
}
}
}