runtime/vm/virtual_memory.cc

// Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

#include "vm/virtual_memory.h"

#include "platform/assert.h"
#include "platform/utils.h"

#if defined(DART_HOST_OS_MACOS)
#include <mach/mach.h>
#endif

namespace dart {

bool VirtualMemory::InSamePage(uword address0, uword address1) {
  return (Utils::RoundDown(address0, PageSize()) ==
          Utils::RoundDown(address1, PageSize()));
}

void VirtualMemory::Truncate(intptr_t new_size) {
  ASSERT(Utils::IsAligned(new_size, PageSize()));
  ASSERT(new_size <= size());
  if (reserved_.size() ==
      region_.size()) {  // Don't create holes in reservation.
    if (FreeSubSegment(reinterpret_cast<void*>(start() + new_size),
                       size() - new_size)) {
      reserved_.set_size(new_size);
    }
  }
  region_.Subregion(region_, 0, new_size);
}

VirtualMemory* VirtualMemory::ForImagePage(void* pointer, uword size) {
  // Memory for precompilated instructions was allocated by the embedder, so
  // create a VirtualMemory without allocating.
  MemoryRegion region(pointer, size);
  MemoryRegion reserved(nullptr, 0);  // null reservation indicates VM should
                                      // not attempt to free this memory.
  VirtualMemory* memory = new VirtualMemory(region, reserved);
  ASSERT(!memory->vm_owns_region());
  return memory;
}

#if !defined(DART_TARGET_OS_FUCHSIA)
// TODO(52579): Reenable on Fuchsia.

bool VirtualMemory::DuplicateRX(VirtualMemory* target) {
  const intptr_t aligned_size = Utils::RoundUp(size(), PageSize());
  ASSERT_LESS_OR_EQUAL(aligned_size, target->size());

#if defined(DART_HOST_OS_MACOS) && defined(DART_PRECOMPILED_RUNTIME)
  // Mac is special cased because iOS doesn't allow allocating new executable
  // memory, so the default approach would fail. We are allowed to make new
  // mappings of existing executable memory using vm_remap though, which is
  // effectively the same for non-writable memory.
  const mach_port_t task = mach_task_self();
  const vm_address_t source_address = reinterpret_cast<vm_address_t>(address());
  const vm_size_t mem_size = aligned_size;
  const vm_prot_t read_execute = VM_PROT_READ | VM_PROT_EXECUTE;
  vm_prot_t current_protection = read_execute;
  vm_prot_t max_protection = read_execute;
  vm_address_t target_address =
      reinterpret_cast<vm_address_t>(target->address());
  kern_return_t status = vm_remap(
      task, &target_address, mem_size,
      /*mask=*/0,
      /*flags=*/VM_FLAGS_FIXED | VM_FLAGS_OVERWRITE, task, source_address,
      /*copy=*/true, &current_protection, &max_protection,
      /*inheritance=*/VM_INHERIT_NONE);
  if (status != KERN_SUCCESS) {
    return false;
  }
  ASSERT(reinterpret_cast<void*>(target_address) == target->address());
  ASSERT_EQUAL(current_protection & read_execute, read_execute);
  ASSERT_EQUAL(max_protection & read_execute, read_execute);
  return true;

#else   // defined(DART_HOST_OS_MACOS)
  // TODO(52497): Use dual mapping on platforms where it's supported.
  // Check that target doesn't overlap with this.
  ASSERT(target->start() >= end() || target->end() <= start());
  memcpy(target->address(), address(), size());  // NOLINT
  Protect(target->address(), aligned_size, kReadExecute);
  return true;
#endif  // defined(DART_HOST_OS_MACOS)
}

#endif  // !defined(DART_TARGET_OS_FUCHSIA)

}  // namespace dart