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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
* vim: set ts=8 sts=2 et sw=2 tw=80:
* Copyright 2021 Mozilla Foundation
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* See the License for the specific language governing permissions and
* limitations under the License.
#ifndef wasm_initexpr_h
#define wasm_initexpr_h
#include "wasm/WasmConstants.h"
#include "wasm/WasmSerialize.h"
#include "wasm/WasmTypeDecls.h"
#include "wasm/WasmValType.h"
#include "wasm/WasmValue.h"
namespace js {
namespace wasm {
class Decoder;
struct ModuleEnvironment;
// Validates a constant expression. Returns an optional literal value if the
// final value was from a simple instruction such as i32.const.
[[nodiscard]] bool DecodeConstantExpression(Decoder& d, ModuleEnvironment* env,
ValType expected,
Maybe<LitVal>* literal);
enum class InitExprKind {
// A InitExpr describes a WebAssembly constant expression, such as those used to
// initialize a global, specify memory offsets in data segments, or populate
// element segments. Such expressions are created during decoding and actually
// executed on module instantiation.
// An InitExpr can only contain constant instructions, which are defined here in
// the spec:
class InitExpr {
InitExprKind kind_;
// The bytecode for this constant expression if this is not a literal.
Bytes bytecode_;
// The value if this is a literal.
LitVal literal_;
// The value type of this constant expression in either case.
ValType type_;
InitExpr() : kind_(InitExprKind::None) {}
explicit InitExpr(LitVal literal)
: kind_(InitExprKind::Literal),
type_(literal.type()) {}
// Decode and validate a constant expression given at the current
// position of the decoder. Upon failure, the decoder contains the failure
// message or else the failure was an OOM.
static bool decodeAndValidate(Decoder& d, ModuleEnvironment* env,
ValType expected, InitExpr* expr);
// Decode and evaluate a constant expression at the current position of the
// decoder. Does not validate the expression first, since all InitExprs are
// required to have been validated. Failure conditions are the same as
// InitExpr::evaluate, i.e. failing only on OOM.
[[nodiscard]] static bool decodeAndEvaluate(
JSContext* cx, Handle<WasmInstanceObject*> instanceObj, Decoder& d,
ValType expectedType, MutableHandleVal result);
// Evaluate the constant expresssion with the given context. This may only
// fail due to an OOM, as all InitExpr's are required to have been validated.
bool evaluate(JSContext* cx, Handle<WasmInstanceObject*> instanceObj,
MutableHandleVal result) const;
bool isLiteral() const { return kind_ == InitExprKind::Literal; }
// Gets the result of this expression if it was determined to be a literal.
LitVal literal() const {
return literal_;
// Get the type of the resulting value of this expression.
ValType type() const { return type_; }
// Allow moving, but not implicit copying
InitExpr(const InitExpr&) = delete;
InitExpr& operator=(const InitExpr&) = delete;
InitExpr(InitExpr&&) = default;
InitExpr& operator=(InitExpr&&) = default;
// Allow explicit cloning
[[nodiscard]] bool clone(const InitExpr& src);
size_t sizeOfExcludingThis(mozilla::MallocSizeOf mallocSizeOf) const;
} // namespace wasm
} // namespace js
#endif // wasm_initexpr_h