text: // Copyright 2017 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.
  
  #include "src/base/page-allocator.h"
  
  #include "src/base/platform/platform.h"
  #include "src/base/platform/wrappers.h"
  
  #if V8_OS_DARWIN
  #include <sys/mman.h>  // For MAP_JIT.
  #endif
  
  namespace v8 {
  namespace base {
  
  #define STATIC_ASSERT_ENUM(a, b)                            \
    static_assert(static_cast<int>(a) == static_cast<int>(b), \
                  "mismatching enum: " #a)
  
  STATIC_ASSERT_ENUM(PageAllocator::kNoAccess,
                     base::OS::MemoryPermission::kNoAccess);
  STATIC_ASSERT_ENUM(PageAllocator::kReadWrite,
                     base::OS::MemoryPermission::kReadWrite);
  STATIC_ASSERT_ENUM(PageAllocator::kReadWriteExecute,
                     base::OS::MemoryPermission::kReadWriteExecute);
  STATIC_ASSERT_ENUM(PageAllocator::kReadExecute,
                     base::OS::MemoryPermission::kReadExecute);
  STATIC_ASSERT_ENUM(PageAllocator::kNoAccessWillJitLater,
                     base::OS::MemoryPermission::kNoAccessWillJitLater);
  
  #undef STATIC_ASSERT_ENUM
  
  PageAllocator::PageAllocator()
      : allocate_page_size_(base::OS::AllocatePageSize()),
        commit_page_size_(base::OS::CommitPageSize()) {}
  
  void PageAllocator::SetRandomMmapSeed(int64_t seed) {
    base::OS::SetRandomMmapSeed(seed);
  }
  
  void* PageAllocator::GetRandomMmapAddr() {
    return base::OS::GetRandomMmapAddr();
  }
  
  void* PageAllocator::AllocatePages(void* hint, size_t size, size_t alignment,
                                     PageAllocator::Permission access) {
  #if !V8_HAS_PTHREAD_JIT_WRITE_PROTECT
    // kNoAccessWillJitLater is only used on Apple Silicon. Map it to regular
    // kNoAccess on other platforms, so code doesn't have to handle both enum
    // values.
    if (access == PageAllocator::kNoAccessWillJitLater) {
      access = PageAllocator::kNoAccess;
    }
  #endif
    return base::OS::Allocate(hint, size, alignment,
                              static_cast<base::OS::MemoryPermission>(access));
  }
  
  class SharedMemoryMapping : public ::v8::PageAllocator::SharedMemoryMapping {
   public:
    explicit SharedMemoryMapping(PageAllocator* page_allocator, void* ptr,
                                 size_t size)
        : page_allocator_(page_allocator), ptr_(ptr), size_(size) {}
    ~SharedMemoryMapping() override { page_allocator_->FreePages(ptr_, size_); }
    void* GetMemory() const override { return ptr_; }
  
   private:
    PageAllocator* page_allocator_;
    void* ptr_;
    size_t size_;
  };
  
  class SharedMemory : public ::v8::PageAllocator::SharedMemory {
   public:
    SharedMemory(PageAllocator* allocator, void* memory, size_t size)
        : allocator_(allocator), ptr_(memory), size_(size) {}
    void* GetMemory() const override { return ptr_; }
    size_t GetSize() const override { return size_; }
    std::unique_ptr<::v8::PageAllocator::SharedMemoryMapping> RemapTo(
        void* new_address) const override {
      if (allocator_->RemapShared(ptr_, new_address, size_)) {
        return std::make_unique<SharedMemoryMapping>(allocator_, new_address,
                                                     size_);
      } else {
        return {};
      }
    }
  
    ~SharedMemory() override { allocator_->FreePages(ptr_, size_); }
  
   private:
    PageAllocator* allocator_;
    void* ptr_;
    size_t size_;
  };
  
  bool PageAllocator::CanAllocateSharedPages() {
  #ifdef V8_OS_LINUX
    return true;
  #else
    return false;
  #endif
  }
  
  std::unique_ptr<v8::PageAllocator::SharedMemory>
  PageAllocator::AllocateSharedPages(size_t size, const void* original_address) {
  #ifdef V8_OS_LINUX
    void* ptr =
        base::OS::AllocateShared(size, base::OS::MemoryPermission::kReadWrite);
    CHECK_NOT_NULL(ptr);
    memcpy(ptr, original_address, size);
    bool success = base::OS::SetPermissions(
        ptr, size, base::OS::MemoryPermission::kReadWrite);
    CHECK(success);
  
    auto shared_memory =
        std::make_unique<v8::base::SharedMemory>(this, ptr, size);
    return shared_memory;
  #else
    return {};
  #endif
  }
  
  void* PageAllocator::RemapShared(void* old_address, void* new_address,
                                   size_t size) {
  #ifdef V8_OS_LINUX
    return base::OS::RemapShared(old_address, new_address, size);
  #else
    return nullptr;
  #endif
  }
  
  bool PageAllocator::FreePages(void* address, size_t size) {
    base::OS::Free(address, size);
    return true;
  }
  
  bool PageAllocator::ReleasePages(void* address, size_t size, size_t new_size) {
    DCHECK_LT(new_size, size);
    base::OS::Release(reinterpret_cast<uint8_t*>(address) + new_size,
                      size - new_size);
    return true;
  }
  
  bool PageAllocator::SetPermissions(void* address, size_t size,
                                     PageAllocator::Permission access) {
    return base::OS::SetPermissions(
        address, size, static_cast<base::OS::MemoryPermission>(access));
  }
  
  bool PageAllocator::DiscardSystemPages(void* address, size_t size) {
    return base::OS::DiscardSystemPages(address, size);
  }
  
  bool PageAllocator::DecommitPages(void* address, size_t size) {
    return base::OS::DecommitPages(address, size);
  }
  
  }  // namespace base
  }  // namespace v8
  