sdk/lib/ld/allocator.h

// Copyright 2023 The Fuchsia 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 LIB_LD_ALLOCATOR_H_
#define LIB_LD_ALLOCATOR_H_

#include <lib/trivial-allocator/basic-leaky-allocator.h>
#include <lib/trivial-allocator/basic-owning-allocator.h>
#include <lib/trivial-allocator/new.h>
#include <lib/trivial-allocator/page-allocator.h>
#include <lib/trivial-allocator/sealed-page-allocator.h>

#include <utility>

#include "startup-diagnostics.h"

namespace ld {

// The scratch allocator gets fresh pages from the system and then unmaps them
// all at the end of the allocator object's lifetime.
template <class Memory>
inline auto MakeScratchAllocator(Memory memory) {
  return trivial_allocator::BasicOwningAllocator(
      trivial_allocator::PageAllocator(std::move(memory)));
}

// The initial-exec allocator gets fresh pages from the system.  When they've
// been written, they'll be made read-only.  They're never freed.  Both the
// current whole-page chunk and the previous one allocated are kept writable.
// This always permits doing two consecutive allocations of data structures and
// then updating the first data structure to point to the second.
template <class Memory>
inline auto MakeInitialExecAllocator(Memory memory) {
  using InitialExecAllocatorBase =
      trivial_allocator::BasicLeakyAllocator<trivial_allocator::SealedPageAllocator<Memory, 1>>;

  class InitialExecAllocator : public InitialExecAllocatorBase {
   public:
    using InitialExecAllocatorBase::InitialExecAllocatorBase;

    // On destruction, seal the outstanding pages.
    ~InitialExecAllocator() { std::move(this->allocate_function()).Seal(); }
  };

  return InitialExecAllocator{std::move(memory)};
}

inline void CheckAlloc(Diagnostics& diag, fbl::AllocChecker& ac, std::string_view what) {
  if (ac.check()) [[likely]] {
    return;
  }
  diag.SystemError("out of memory allocating ", what);
  __builtin_trap();
}

}  // namespace ld

#endif  // LIB_LD_ALLOCATOR_H_