WasmContext.h - mozsearch

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/*

 * Copyright 2020 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

 *     http://www.apache.org/licenses/LICENSE-2.0

 * Unless required by applicable law or agreed to in writing, software

 * distributed under the License is distributed on an "AS IS" BASIS,

 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

 * See the License for the specific language governing permissions and

 * limitations under the License.

*/

#ifndef wasm_context_h

#define wasm_context_h

#ifdef ENABLE_WASM_JSPI

#  include "wasm/WasmStacks.h"

#endif  // ENABLE_WASM_JSPI

#include "js/AllocPolicy.h"

#include "js/NativeStackLimits.h"

#ifdef _WIN32

struct _NT_TIB;

#endif

namespace js::wasm {

struct Handlers;

class ContObject;

class ContStack;

class ContStackArena;

// wasm::Context lives in JSContext and contains the wasm-related per-context

// state.

class Context {

 public:

  Context();

  ~Context();

  static constexpr size_t offsetOfStackLimit() {

    return offsetof(Context, stackLimit);

  void initStackLimit(JSContext* cx);

#ifdef ENABLE_WASM_JSPI

  static constexpr size_t offsetOfCurrentStack() {

    return offsetof(Context, currentStack_);

  static constexpr size_t offsetOfBaseHandlers() {

    return offsetof(Context, baseHandlers_);

  static constexpr size_t offsetOfMainStackTarget() {

    return offsetof(Context, mainStackTarget_);

#  ifdef _WIN32

  static constexpr size_t offsetOfTib() { return offsetof(Context, tib_); }

  // Load the current TIB stack fields and refresh our cached fields.

  void updateWin32TibFields();

#  endif

  ContStack* currentStack() { return currentStack_; }

  Handlers* baseHandlers() { return baseHandlers_; }

  bool onContStack() const { return currentStack_ != nullptr; }

  ContStackAllocator& contStacks() { return contStacks_; }

  const ContStackAllocator& contStacks() const { return contStacks_; }

  const StackTarget& mainStackTarget() const { return mainStackTarget_; }

  ContStack* findStackForAddress(JSContext* cx, uintptr_t stackAddress);

#endif  // ENABLE_WASM_JSPI

  // Used by wasm::EnsureThreadSignalHandlers(cx) to install thread signal

  // handlers once per JSContext/thread.

  bool triedToInstallSignalHandlers;

  bool haveSignalHandlers;

  // Like JSContext::jitStackLimit but used for wasm code. Wasm code doesn't

  // use the stack limit for interrupts, but it does update it for stack

  // switching.

  JS::NativeStackLimit stackLimit;

 private:

#ifdef ENABLE_WASM_JSPI

  // A stack target for use when switching to the main stack.

  StackTarget mainStackTarget_;

#  if defined(_WIN32)

  // On WIN64, the Thread Information Block stack limits must be updated on

  // stack switches to avoid failures on SP checks during vectored exeption

  // handling for traps. We cache the TIB here for easy manipulation.

  _NT_TIB* tib_ = nullptr;

#  endif

  // The currently active continuation. Null if we're executing on the

  // main stack, otherwise we're on a continuation stack. This is a non owning

  // pointer.

  ContStack* currentStack_;

  // The handlers pushed on the main stack to enter onto the current stack of

  // continuations. A cached version of currentStack_->findBaseHandlers().

//

  // Non-null iff we are on a continuation's stack. Handlers are always the

  // last thing pushed on a stack before a `resume`, and so this also doubles

  // as the last SP value on the main stack before we switching into

  // continuation stacks. Wasm exits into VM code use this value to switch back

  // to the main stack.

//

  // A continuation can call into VM/JS code on the main stack, which can then

  // call into a new stack of continuations. The switch to the main stack saves

  // and restores these fields, and we only track the top-most values for these

  // fields.

  Handlers* baseHandlers_;

  // Allocator for all ContStack objects owned by this context.

  ContStackAllocator contStacks_;

#endif

};

}  // namespace js::wasm

#endif  // wasm_context_h