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LibWeb: Don't create a copy SharedArrayBuffer for shared Wasm memories

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For whatever reason, the implementation of "create a fixed length memory
buffer" was borked for shared Wasm memories, in that a new
SharedArrayBuffer was created, with the contents of the Wasm memory
copied into it. This is incorrect, since the SharedArrayBuffer should be
a view into the Wasm memory's span, not a copy of it. This helps pass a
WPT subtest in wasm/jsapi/memory/grow.any.html.
This commit is contained in:
CountBleck 2025-08-17 12:19:55 -07:00 • committed by Ali Mohammad Pur
commit 0bda014c96
Notes: github-actions[bot] 2025-08-23 06:28:07 +00:00
1 changed files with 5 additions and 6 deletions
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11
Libraries/LibWeb/WebAssembly/Memory.cpp
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@ -135,13 +135,12 @@ WebIDL::ExceptionOr<GC::Ref<JS::ArrayBuffer>> Memory::create_a_fixed_length_memo
// 3. If share is shared,
if (shared == Shared::Yes) {
// 1. Let block be a Shared Data Block which is identified with the underlying memory of memaddr.
auto bytes = memory->data();
// 2. Let buffer be a new SharedArrayBuffer with the internal slots [[ArrayBufferData]] and [[ArrayBufferByteLength]].
array_buffer = TRY(JS::allocate_shared_array_buffer(vm, realm.intrinsics().shared_array_buffer_constructor(), bytes.size()));
bytes.span().copy_to(array_buffer->buffer().span());
// 3. FIXME: Set buffer.[[ArrayBufferData]] to block.
// 4. FIXME: Set buffer.[[ArrayBufferByteLength]] to the length of block.
// 3. Set buffer.[[ArrayBufferData]] to block.
array_buffer = JS::ArrayBuffer::create(realm, &memory->data(), JS::DataBlock::Shared::Yes);
// 4. Set buffer.[[ArrayBufferByteLength]] to the length of block.
VERIFY(array_buffer->byte_length() == memory->size());
// 5. Perform ! SetIntegrityLevel(buffer, "frozen").
MUST(array_buffer->set_integrity_level(JS::Object::IntegrityLevel::Frozen));