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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_debugframe_h
#define wasm_debugframe_h
#include "mozilla/Assertions.h"
#include <stddef.h>
#include <stdint.h>
#include "js/TypeDecls.h"
#include "js/Value.h"
#include "wasm/WasmCodegenConstants.h"
#include "wasm/WasmFrame.h"
#include "wasm/WasmValType.h"
#include "wasm/WasmValue.h"
namespace js {
class GlobalObject;
namespace wasm {
class Instance;
// A DebugFrame is a Frame with additional fields that are added after the
// normal function prologue by the baseline compiler. If a Module is compiled
// with debugging enabled, then all its code creates DebugFrames on the stack
// instead of just Frames. These extra fields are used by the Debugger API.
class DebugFrame {
// The register results field. Initialized only during the baseline
// compiler's return sequence to allow the debugger to inspect and
// modify the return values of a frame being debugged.
union SpilledRegisterResult {
int32_t i32_;
int64_t i64_;
float f32_;
double f64_;
V128 v128_;
AnyRef anyref_;
#ifdef DEBUG
// Should we add a new value representation, this will remind us to update
// SpilledRegisterResult.
static inline void assertAllValueTypesHandled(ValType type) {
switch (type.kind()) {
case ValType::I32:
case ValType::I64:
case ValType::F32:
case ValType::F64:
case ValType::V128:
case ValType::Ref:
SpilledRegisterResult registerResults_[MaxRegisterResults];
// The returnValue() method returns a HandleValue pointing to this field.
JS::Value cachedReturnJSValue_;
// If the function returns multiple results, this field is initialized
// to a pointer to the stack results.
void* stackResultsPointer_;
// The function index of this frame. Technically, this could be derived
// given a PC into this frame (which could lookup the CodeRange which has
// the function index), but this isn't always readily available.
uint32_t funcIndex_;
// Flags whose meaning are described below.
union Flags {
struct {
uint32_t observing : 1;
uint32_t isDebuggee : 1;
uint32_t prevUpToDate : 1;
uint32_t hasCachedSavedFrame : 1;
uint32_t hasCachedReturnJSValue : 1;
uint32_t hasSpilledRefRegisterResult : MaxRegisterResults;
uint32_t allFlags;
} flags_;
// Avoid -Wunused-private-field warnings.
#if defined(JS_CODEGEN_ARM) || defined(JS_CODEGEN_X86) || defined(__wasi__)
// See alignmentStaticAsserts(). For ARM32 and X86 DebugFrame is only
// 4-byte aligned, so we add another word to get up to 8-byte
// alignment.
uint32_t padding_;
#if defined(ENABLE_WASM_SIMD) && defined(JS_CODEGEN_ARM64)
uint64_t padding_;
// The Frame goes at the end since the stack grows down.
Frame frame_;
static DebugFrame* from(Frame* fp);
Frame& frame() { return frame_; }
uint32_t funcIndex() const { return funcIndex_; }
Instance* instance();
const Instance* instance() const;
GlobalObject* global();
bool hasGlobal(const GlobalObject* global) const;
JSObject* environmentChain();
bool getLocal(uint32_t localIndex, JS::MutableHandleValue vp);
// The return value must be written from the unboxed representation in the
// results union into cachedReturnJSValue_ by updateReturnJSValue() before
// returnValue() can return a Handle to it.
bool hasCachedReturnJSValue() const { return flags_.hasCachedReturnJSValue; }
[[nodiscard]] bool updateReturnJSValue(JSContext* cx);
void discardReturnJSValue();
JS::HandleValue returnValue() const;
void clearReturnJSValue();
// Once the debugger observes a frame, it must be notified via
// onLeaveFrame() before the frame is popped. Calling observe() ensures the
// leave frame traps are enabled. Both methods are idempotent so the caller
// doesn't have to worry about calling them more than once.
void observe(JSContext* cx);
void leave(JSContext* cx);
// The 'isDebugge' bit is initialized to false and set by the WebAssembly
// runtime right before a frame is exposed to the debugger, as required by
// the Debugger API. The bit is then used for Debugger-internal purposes
// afterwards.
bool isDebuggee() const { return flags_.isDebuggee; }
void setIsDebuggee() { flags_.isDebuggee = true; }
void unsetIsDebuggee() { flags_.isDebuggee = false; }
// These are opaque boolean flags used by the debugger to implement
// AbstractFramePtr. They are initialized to false and not otherwise read or
// written by wasm code or runtime.
bool prevUpToDate() const { return flags_.prevUpToDate; }
void setPrevUpToDate() { flags_.prevUpToDate = true; }
void unsetPrevUpToDate() { flags_.prevUpToDate = false; }
bool hasCachedSavedFrame() const { return flags_.hasCachedSavedFrame; }
void setHasCachedSavedFrame() { flags_.hasCachedSavedFrame = true; }
void clearHasCachedSavedFrame() { flags_.hasCachedSavedFrame = false; }
bool hasSpilledRegisterRefResult(size_t n) const {
uint32_t mask = hasSpilledRegisterRefResultBitMask(n);
return (flags_.allFlags & mask) != 0;
// DebugFrame is accessed directly by JIT code.
static constexpr size_t offsetOfRegisterResults() {
return offsetof(DebugFrame, registerResults_);
static constexpr size_t offsetOfRegisterResult(size_t n) {
MOZ_ASSERT(n < MaxRegisterResults);
return offsetOfRegisterResults() + n * sizeof(SpilledRegisterResult);
static constexpr size_t offsetOfCachedReturnJSValue() {
return offsetof(DebugFrame, cachedReturnJSValue_);
static constexpr size_t offsetOfStackResultsPointer() {
return offsetof(DebugFrame, stackResultsPointer_);
static constexpr size_t offsetOfFlags() {
return offsetof(DebugFrame, flags_);
static constexpr uint32_t hasSpilledRegisterRefResultBitMask(size_t n) {
MOZ_ASSERT(n < MaxRegisterResults);
union Flags flags = {.allFlags = 0};
flags.hasSpilledRefRegisterResult = 1 << n;
MOZ_ASSERT(flags.allFlags != 0);
return flags.allFlags;
static constexpr size_t offsetOfFuncIndex() {
return offsetof(DebugFrame, funcIndex_);
static constexpr size_t offsetOfFrame() {
return offsetof(DebugFrame, frame_);
// DebugFrames are aligned to 8-byte aligned, allowing them to be placed in
// an AbstractFramePtr.
static const unsigned Alignment = 8;
static void alignmentStaticAsserts();
} // namespace wasm
} // namespace js
#endif // wasm_debugframe_h