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Implement a FNV1-a style checksum to the binary decoded Wasm data in debug builds #25910

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Implement a FNV1-a style checksum to the binary decoded Wasm data in debug builds #25910

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Implement a FNV1-a style checksum to the binary decoded Wasm data, an…
juj Dec 6, 2025
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juj Dec 6, 2025
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3 changes: 3 additions & 0 deletions src/postamble_minimal.js
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Original file line number Diff line number Diff line change
Expand Up @@ -151,6 +151,9 @@ function initRuntime(wasmExports) {

#if SINGLE_FILE && SINGLE_FILE_BINARY_ENCODE && !WASM2JS
Module['wasm'] = binaryDecode("<<< WASM_BINARY_DATA >>>");
#if ASSERTIONS
assert(Module['wasm'].reduce((x,y) => ((x^y)*65599) >>> 0, 2166136261) == "<<< WASM_BINARY_DATA_CHECKSUM >>>", "The checksum of the binary decoded WebAssembly Module code does not match the original data. Double check that this .html/.js file is interpreted with UTF-8 encoding, e.g. by setting <meta charset='utf-8'> inside <head> of the HTML file, or by passing 'Content-Type: application/javascript; charset=utf-8' HTTP header.");
#endif
#elif SINGLE_FILE && WASM == 1 && !WASM2JS
Module['wasm'] = base64Decode('<<< WASM_BINARY_DATA >>>');
#endif
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4 changes: 4 additions & 0 deletions src/preamble.js
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Expand Up @@ -876,6 +876,10 @@ function getWasmImports() {
return exports;
#else
wasmBinaryFile ??= findWasmBinary();
#if SINGLE_FILE && SINGLE_FILE_BINARY_ENCODE && !WASM2JS && ASSERTIONS
assert(wasmBinaryFile.reduce((x,y) => ((x^y)*65599) >>> 0, 2166136261) == "<<< WASM_BINARY_DATA_CHECKSUM >>>", "The checksum of the binary decoded WebAssembly Module code does not match the original data. Double check that this .html/.js file is interpreted with UTF-8 encoding, e.g. by setting <meta charset='utf-8'> inside <head> of the HTML file, or by passing 'Content-Type: application/javascript; charset=utf-8' HTTP header.");
#endif

#if WASM_ASYNC_COMPILATION
#if RUNTIME_DEBUG
dbg('asynchronously preparing wasm');
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7 changes: 7 additions & 0 deletions tools/link.py
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Expand Up @@ -2490,6 +2490,13 @@ def phase_binaryen(target, options, wasm_target):

if settings.SINGLE_FILE_BINARY_ENCODE:
js = do_replace(js, '"<<< WASM_BINARY_DATA >>>"', binary_encode(wasm_target))
if settings.ASSERTIONS:
def checksum(a):
h = 2166136261
for b in a:
h = (h ^ b) * 65599 & 0xffffffff
return h
js = do_replace(js, '"<<< WASM_BINARY_DATA_CHECKSUM >>>"', str(checksum(utils.read_binary(wasm_target))))
else:
js = do_replace(js, '<<< WASM_BINARY_DATA >>>', base64_encode(wasm_target))
delete_file(wasm_target)
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