tor-browser

regexp-stack.h (7094B)

---

// Copyright 2009 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef V8_REGEXP_REGEXP_STACK_H_
#define V8_REGEXP_REGEXP_STACK_H_

#include "irregexp/RegExpShim.h"

namespace v8 {
namespace internal {

class RegExpStack;

// Maintains a per-v8thread stack area that can be used by irregexp
// implementation for its backtracking stack.
class V8_NODISCARD RegExpStackScope final {
public:
 // Create and delete an instance to control the life-time of a growing stack.

 // Initializes the stack memory area if necessary.
 explicit RegExpStackScope(Isolate* isolate);
 ~RegExpStackScope();  // Releases the stack if it has grown.
 RegExpStackScope(const RegExpStackScope&) = delete;
 RegExpStackScope& operator=(const RegExpStackScope&) = delete;

 RegExpStack* stack() const { return regexp_stack_; }

private:
 RegExpStack* const regexp_stack_;
 const ptrdiff_t old_sp_top_delta_;
};

// TODO(426514762): Currently this entire object is sandbox-accessible as some
// fields of it are being written to. This is unsafe though and we'll need to
// fix this. See the addition TODOs related to https://crbug.com/426514762.
class RegExpStack final {
public:
 RegExpStack(const RegExpStack&) = delete;
 RegExpStack& operator=(const RegExpStack&) = delete;

 static RegExpStack* New();
 static void Delete(RegExpStack* instance);

#if defined(V8_TARGET_ARCH_PPC64) || defined(V8_TARGET_ARCH_S390X)
 static constexpr int kSlotSize = kSystemPointerSize;
#else
 static constexpr int kSlotSize = kInt32Size;
#endif
 // Number of allocated locations on the stack below the limit. No sequence of
 // pushes must be longer than this without doing a stack-limit check.
 static constexpr int kStackLimitSlackSlotCount = 32;
 static constexpr int kStackLimitSlackSize =
     kStackLimitSlackSlotCount * kSlotSize;

 Address begin() const {
   return reinterpret_cast<Address>(thread_local_.memory_);
 }
 Address end() const {
   DCHECK_NE(0, thread_local_.memory_size_);
   DCHECK_EQ(thread_local_.memory_top_,
             thread_local_.memory_ + thread_local_.memory_size_);
   return reinterpret_cast<Address>(thread_local_.memory_top_);
 }
 Address memory_top() const { return end(); }

 Address stack_pointer() const {
   return reinterpret_cast<Address>(thread_local_.stack_pointer_);
 }

 size_t memory_size() const { return thread_local_.memory_size_; }

 // If the stack pointer gets below the limit, we should react and
 // either grow the stack or report an out-of-stack exception.
 // There is only a limited number of locations below the stack limit,
 // so users of the stack should check the stack limit during any
 // sequence of pushes longer that this.
 Address* limit_address_address() { return &thread_local_.limit_; }

 // Ensures that there is a memory area with at least the specified size.
 // If passing zero, the default/minimum size buffer is allocated.
 Address EnsureCapacity(size_t size);

 // Thread local archiving.
 static constexpr int ArchiveSpacePerThread() {
   return static_cast<int>(kThreadLocalSize);
 }
 char* ArchiveStack(char* to);
 char* RestoreStack(char* from);
 void FreeThreadResources() { thread_local_.ResetToStaticStack(this); }

 // Maximal size of allocated stack area.
 static constexpr size_t kMaximumStackSize = 64 * MB;

 RegExpStack();
 ~RegExpStack();

private:
 // Artificial limit used when the thread-local state has been destroyed.
 static const Address kMemoryTop =
     static_cast<Address>(static_cast<uintptr_t>(-1));

 // In addition to dynamically-allocated, variable-sized stacks, we also have
 // a statically allocated and sized area that is used whenever no dynamic
 // stack is allocated. This guarantees that a stack is always available and
 // we can skip availability-checks later on.
 static constexpr size_t kStaticStackSize = 1 * KB;
 // It's at least double the slack size to ensure that we have a bit of
 // breathing room before NativeRegExpMacroAssembler::GrowStack must be
 // called.
 static_assert(kStaticStackSize >= 2 * kStackLimitSlackSize);
 static_assert(kStaticStackSize <= kMaximumStackSize);
 // TODO(426514762): this buffer is being written to from generated code.
 // We could probably just allocate dedicated OS pages for it like we do for
 // dynamically-sized stack buffers though (see EnsureCapacity).
 uint8_t static_stack_[kStaticStackSize] = {0};

 // Minimal size of dynamically-allocated stack area.
 static constexpr size_t kMinimumDynamicStackSize = 2 * KB;
 static_assert(kMinimumDynamicStackSize == 2 * kStaticStackSize);

 // Structure holding the allocated memory, size and limit. Thread switching
 // archives and restores this struct.
 struct ThreadLocal {
   explicit ThreadLocal(RegExpStack* regexp_stack) {
     ResetToStaticStack(regexp_stack);
   }

   // If memory_size_ > 0 then
   //  - memory_, memory_top_, stack_pointer_ must be non-nullptr
   //  - memory_top_ = memory_ + memory_size_
   //  - memory_ <= stack_pointer_ <= memory_top_
   uint8_t* memory_ = nullptr;
   uint8_t* memory_top_ = nullptr;
   size_t memory_size_ = 0;
   // TODO(426514762): this field is currently written to from generated code.
   // Either we find a way to avoid that, or we have to move this field to
   // it's own sandbox-accessible memory page.
   uint8_t* stack_pointer_ = nullptr;
   Address limit_ = kNullAddress;
   bool owns_memory_ = false;  // Whether memory_ is owned and must be freed.

   void ResetToStaticStack(RegExpStack* regexp_stack);
   void ResetToStaticStackIfEmpty(RegExpStack* regexp_stack) {
     if (stack_pointer_ == memory_top_) ResetToStaticStack(regexp_stack);
   }
   void FreeAndInvalidate();

   // Allocates and returns new memory for a dynamic stack.
   static uint8_t* NewDynamicStack(size_t size);
   // If a dynamic stack is used, delete its memory.
   void DeleteDynamicStack();
 };
 static constexpr size_t kThreadLocalSize = sizeof(ThreadLocal);

 Address memory_top_address_address() {
   return reinterpret_cast<Address>(&thread_local_.memory_top_);
 }

 Address stack_pointer_address() {
   return reinterpret_cast<Address>(&thread_local_.stack_pointer_);
 }

 // A position-independent representation of the stack pointer.
 ptrdiff_t sp_top_delta() const {
   ptrdiff_t result =
       reinterpret_cast<intptr_t>(thread_local_.stack_pointer_) -
       reinterpret_cast<intptr_t>(thread_local_.memory_top_);
   DCHECK_LE(result, 0);
   return result;
 }

 // Resets the buffer if it has grown beyond the default/minimum size and is
 // empty.
 void ResetIfEmpty() { thread_local_.ResetToStaticStackIfEmpty(this); }

 // Whether the ThreadLocal storage has been invalidated.
 bool IsValid() const { return thread_local_.memory_ != nullptr; }

 ThreadLocal thread_local_;

 friend class ExternalReference;
 friend class RegExpStackScope;
};

}  // namespace internal
}  // namespace v8

#endif  // V8_REGEXP_REGEXP_STACK_H_