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LibWasm: Make traps hold on to externally-managed data

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...instead of specially handling JS::Completion.
This makes it possible for LibWeb/LibJS to have full control over how
these things are made, stored, and visited (whenever).

Fixes an issue where we couldn't roundtrip a JS exception through Wasm.
This commit is contained in:
Ali Mohammad Pur 2025-04-22 09:48:26 +02:00 • committed by Andrew Kaster
commit 51bab5b186
Notes: github-actions[bot] 2025-04-22 14:45:25 +00:00
11 changed files with 176 additions and 111 deletions
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53
Libraries/LibWeb/WebAssembly/WebAssembly.cpp
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@ -59,6 +59,10 @@ void visit_edges(JS::Object& object, JS::Cell::Visitor& visitor)
visitor.visit(cache.imported_objects());
visitor.visit(cache.extern_values());
visitor.visit(cache.global_instances());
cache.abstract_machine().visit_external_resources({ .visit_trap = [&visitor](Wasm::ExternallyManagedTrap const& trap) {
auto& completion = trap.unsafe_external_object_as<JS::Completion>();
visitor.visit(completion.value());
} });
}
}
@ -156,6 +160,32 @@ WebIDL::ExceptionOr<GC::Ref<WebIDL::Promise>> instantiate_streaming(JS::VM& vm,
namespace Detail {
#define TRY_OR_RETURN_TRAP(...) \
({ \
/* Ignore -Wshadow to allow nesting the macro. */ \
AK_IGNORE_DIAGNOSTIC("-Wshadow", \
auto&& _temporary_result = (__VA_ARGS__)); \
static_assert(!::AK::Detail::IsLvalueReference<decltype(_temporary_result.release_value())>, \
"Do not return a reference from a fallible expression"); \
if (_temporary_result.is_error()) [[unlikely]] \
return Wasm::Trap::from_external_object(_temporary_result.release_error()); \
_temporary_result.release_value(); \
})
#define TRY_OR_RETURN_OOM_TRAP(vm, ...) \
({ \
/* Ignore -Wshadow to allow nesting the macro. */ \
AK_IGNORE_DIAGNOSTIC("-Wshadow", \
auto&& _temporary_result = (__VA_ARGS__)); \
if (_temporary_result.is_error()) { \
VERIFY(_temporary_result.error().code() == ENOMEM); \
return Wasm::Trap::from_external_object((vm).throw_completion<JS::InternalError>((vm).error_message(::JS::VM::ErrorMessage::OutOfMemory))); \
} \
static_assert(!::AK::Detail::IsLvalueReference<decltype(_temporary_result.release_value())>, \
"Do not return a reference from a fallible expression"); \
_temporary_result.release_value(); \
})
JS::ThrowCompletionOr<NonnullOwnPtr<Wasm::ModuleInstance>> instantiate_module(JS::VM& vm, Wasm::Module const& module, GC::Ptr<JS::Object> import_object)
{
Wasm::Linker linker { module };
@ -216,28 +246,28 @@ JS::ThrowCompletionOr<NonnullOwnPtr<Wasm::ModuleInstance>> instantiate_module(JS
++index;
}
auto result = TRY(JS::call(vm, function, JS::js_undefined(), argument_values.span()));
auto result = TRY_OR_RETURN_TRAP(JS::call(vm, function, JS::js_undefined(), argument_values.span()));
if (type.results().is_empty())
return Wasm::Result { Vector<Wasm::Value> {} };
if (type.results().size() == 1)
return Wasm::Result { Vector<Wasm::Value> { TRY(to_webassembly_value(vm, result, type.results().first())) } };
return Wasm::Result { Vector<Wasm::Value> { TRY_OR_RETURN_TRAP(to_webassembly_value(vm, result, type.results().first())) } };
auto method = TRY(result.get_method(vm, vm.names.iterator));
auto method = TRY_OR_RETURN_TRAP(result.get_method(vm, vm.names.iterator));
if (method == JS::js_undefined())
return vm.throw_completion<JS::TypeError>(JS::ErrorType::NotIterable, result.to_string_without_side_effects());
return Wasm::Trap::from_external_object(vm.throw_completion<JS::TypeError>(JS::ErrorType::NotIterable, result.to_string_without_side_effects()));
auto values = TRY(JS::iterator_to_list(vm, TRY(JS::get_iterator_from_method(vm, result, *method))));
auto values = TRY_OR_RETURN_TRAP(JS::iterator_to_list(vm, TRY_OR_RETURN_TRAP(JS::get_iterator_from_method(vm, result, *method))));
if (values.size() != type.results().size())
return vm.throw_completion<JS::TypeError>(ByteString::formatted("Invalid number of return values for multi-value wasm return of {} objects", type.results().size()));
return Wasm::Trap::from_external_object(vm.throw_completion<JS::TypeError>(ByteString::formatted("Invalid number of return values for multi-value wasm return of {} objects", type.results().size())));
Vector<Wasm::Value> wasm_values;
TRY_OR_THROW_OOM(vm, wasm_values.try_ensure_capacity(values.size()));
TRY_OR_RETURN_OOM_TRAP(vm, wasm_values.try_ensure_capacity(values.size()));
size_t i = 0;
for (auto& value : values)
wasm_values.append(TRY(to_webassembly_value(vm, value, type.results()[i++])));
wasm_values.append(TRY_OR_RETURN_TRAP(to_webassembly_value(vm, value, type.results()[i++])));
return Wasm::Result { move(wasm_values) };
},
@ -415,8 +445,11 @@ JS::NativeFunction* create_native_function(JS::VM& vm, Wasm::FunctionAddress add
auto& cache = get_cache(realm);
auto result = cache.abstract_machine().invoke(address, move(values));
// FIXME: Use the convoluted mapping of errors defined in the spec.
if (result.is_trap())
return vm.throw_completion<JS::TypeError>(TRY_OR_THROW_OOM(vm, String::formatted("Wasm execution trapped (WIP): {}", result.trap().reason)));
if (result.is_trap()) {
if (auto ptr = result.trap().data.get_pointer<Wasm::ExternallyManagedTrap>())
return ptr->unsafe_external_object_as<JS::Completion>();
return vm.throw_completion<JS::TypeError>(TRY_OR_THROW_OOM(vm, String::formatted("Wasm execution trapped (WIP): {}", result.trap().format())));
}
if (result.values().is_empty())
return JS::js_undefined();