absl/base/internal/unaligned_access.h

//
// Copyright 2017 The Abseil Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//

#ifndef ABSL_BASE_INTERNAL_UNALIGNED_ACCESS_H_
#define ABSL_BASE_INTERNAL_UNALIGNED_ACCESS_H_

#include <string.h>
#include <cstdint>

#include "absl/base/attributes.h"

// unaligned APIs

// Portable handling of unaligned loads, stores, and copies.

// The unaligned API is C++ only.  The declarations use C++ features
// (namespaces, inline) which are absent or incompatible in C.
#if defined(__cplusplus)

#if defined(ADDRESS_SANITIZER) || defined(THREAD_SANITIZER) ||\
    defined(MEMORY_SANITIZER)
// Consider we have an unaligned load/store of 4 bytes from address 0x...05.
// AddressSanitizer will treat it as a 3-byte access to the range 05:07 and
// will miss a bug if 08 is the first unaddressable byte.
// ThreadSanitizer will also treat this as a 3-byte access to 05:07 and will
// miss a race between this access and some other accesses to 08.
// MemorySanitizer will correctly propagate the shadow on unaligned stores
// and correctly report bugs on unaligned loads, but it may not properly
// update and report the origin of the uninitialized memory.
// For all three tools, replacing an unaligned access with a tool-specific
// callback solves the problem.

// Make sure uint16_t/uint32_t/uint64_t are defined.
#include <stdint.h>

extern "C" {
uint16_t __sanitizer_unaligned_load16(const void *p);
uint32_t __sanitizer_unaligned_load32(const void *p);
uint64_t __sanitizer_unaligned_load64(const void *p);
void __sanitizer_unaligned_store16(void *p, uint16_t v);
void __sanitizer_unaligned_store32(void *p, uint32_t v);
void __sanitizer_unaligned_store64(void *p, uint64_t v);
}  // extern "C"

namespace absl {
inline namespace lts_2019_08_08 {
namespace base_internal {

inline uint16_t UnalignedLoad16(const void *p) {
  return __sanitizer_unaligned_load16(p);
}

inline uint32_t UnalignedLoad32(const void *p) {
  return __sanitizer_unaligned_load32(p);
}

inline uint64_t UnalignedLoad64(const void *p) {
  return __sanitizer_unaligned_load64(p);
}

inline void UnalignedStore16(void *p, uint16_t v) {
  __sanitizer_unaligned_store16(p, v);
}

inline void UnalignedStore32(void *p, uint32_t v) {
  __sanitizer_unaligned_store32(p, v);
}

inline void UnalignedStore64(void *p, uint64_t v) {
  __sanitizer_unaligned_store64(p, v);
}

}  // namespace base_internal
}  // inline namespace lts_2019_08_08
}  // namespace absl

#define ABSL_INTERNAL_UNALIGNED_LOAD16(_p) \
  (absl::base_internal::UnalignedLoad16(_p))
#define ABSL_INTERNAL_UNALIGNED_LOAD32(_p) \
  (absl::base_internal::UnalignedLoad32(_p))
#define ABSL_INTERNAL_UNALIGNED_LOAD64(_p) \
  (absl::base_internal::UnalignedLoad64(_p))

#define ABSL_INTERNAL_UNALIGNED_STORE16(_p, _val) \
  (absl::base_internal::UnalignedStore16(_p, _val))
#define ABSL_INTERNAL_UNALIGNED_STORE32(_p, _val) \
  (absl::base_internal::UnalignedStore32(_p, _val))
#define ABSL_INTERNAL_UNALIGNED_STORE64(_p, _val) \
  (absl::base_internal::UnalignedStore64(_p, _val))

#else

namespace absl {
inline namespace lts_2019_08_08 {
namespace base_internal {

inline uint16_t UnalignedLoad16(const void *p) {
  uint16_t t;
  memcpy(&t, p, sizeof t);
  return t;
}

inline uint32_t UnalignedLoad32(const void *p) {
  uint32_t t;
  memcpy(&t, p, sizeof t);
  return t;
}

inline uint64_t UnalignedLoad64(const void *p) {
  uint64_t t;
  memcpy(&t, p, sizeof t);
  return t;
}

inline void UnalignedStore16(void *p, uint16_t v) { memcpy(p, &v, sizeof v); }

inline void UnalignedStore32(void *p, uint32_t v) { memcpy(p, &v, sizeof v); }

inline void UnalignedStore64(void *p, uint64_t v) { memcpy(p, &v, sizeof v); }

}  // namespace base_internal
}  // inline namespace lts_2019_08_08
}  // namespace absl

#define ABSL_INTERNAL_UNALIGNED_LOAD16(_p) \
  (absl::base_internal::UnalignedLoad16(_p))
#define ABSL_INTERNAL_UNALIGNED_LOAD32(_p) \
  (absl::base_internal::UnalignedLoad32(_p))
#define ABSL_INTERNAL_UNALIGNED_LOAD64(_p) \
  (absl::base_internal::UnalignedLoad64(_p))

#define ABSL_INTERNAL_UNALIGNED_STORE16(_p, _val) \
  (absl::base_internal::UnalignedStore16(_p, _val))
#define ABSL_INTERNAL_UNALIGNED_STORE32(_p, _val) \
  (absl::base_internal::UnalignedStore32(_p, _val))
#define ABSL_INTERNAL_UNALIGNED_STORE64(_p, _val) \
  (absl::base_internal::UnalignedStore64(_p, _val))

#endif

#endif  // defined(__cplusplus), end of unaligned API

#endif  // ABSL_BASE_INTERNAL_UNALIGNED_ACCESS_H_