/*

* Copyright (c) Facebook, Inc. and its affiliates.

*

* This source code is licensed under the MIT license found in the

* LICENSE file in the root directory of this source tree.

*/

#include "hermes/VM/BuildMetadata.h"

#include "hermes/VM/CellKind.h"

#include "llvh/Support/Debug.h"

#include <cstdint>

#define DEBUG_TYPE "metadata"

namespace hermes {

namespace vm {

static size_t getNumCellKinds() {

// This embeds the same value as the CellKind enum, but adds one more at the

// end to know how many values it contains.

enum CellKinds {

#define CELL_KIND(name) name,

#include "hermes/VM/CellKinds.def"

#undef CELL_KIND

numKinds,

};

return numKinds;

}

/// Creates and populates the storage for the metadata of the classes.

/// The caller takes ownership of the memory.

static const Metadata *buildStorage() {

// For each class of object, initialize its metadata

// Only run this once per class, not once per Runtime instantiation.

Metadata *storage = new Metadata[getNumCellKinds()];

size_t i = 0;

#define CELL_KIND(name) \

storage[i++] = buildMetadata(CellKind::name##Kind, name##BuildMeta);

#include "hermes/VM/CellKinds.def"

#undef CELL_KIND

assert(i == getNumCellKinds() && "Incorrect number of metadata populated");

return storage;

}

Metadata buildMetadata(CellKind kind, BuildMetadataCallback *builder) {

const GCCell *base;

#ifdef HERMES_UBSAN

// Using members on a nullptr is UB, but using a pointer to static memory is

// not.

static const int64_t buf[128]{};

base = reinterpret_cast<const GCCell *>(&buf);

#else

// Use nullptr when not building with UBSAN to ensure fast failures.

base = nullptr;

#endif

// This memory should not be read or written to

Metadata::Builder mb(base);

builder(base, mb);

Metadata meta = mb.build();

LLVM_DEBUG(

llvh::dbgs() << "Initialized metadata for cell kind " << cellKindStr(kind)

<< ": " << meta << "\n");

return meta;

}

MetadataTable getMetadataTable() {

// We intentionally leak memory here in order to avoid any static destructors

// running at exit time.

static const Metadata *storage = buildStorage();

return MetadataTable(storage, getNumCellKinds());

}

} // namespace vm

} // namespace hermes