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// Copyright 2024 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 Y_ABSL_BASE_INTERNAL_POISON_H_
#define Y_ABSL_BASE_INTERNAL_POISON_H_
#include <cstdint>
#include "y_absl/base/config.h"
namespace y_absl {
Y_ABSL_NAMESPACE_BEGIN
namespace base_internal {
inline void* GetBadPointerInternal() {
// A likely bad pointer. Pointers are required to have high bits that are all
// zero or all one for certain 64-bit CPUs. This pointer value will hopefully
// cause a crash on dereference and also be clearly recognizable as invalid.
constexpr uint64_t kBadPtr = 0xBAD0BAD0BAD0BAD0;
auto ret = reinterpret_cast<void*>(static_cast<uintptr_t>(kBadPtr));
#ifndef _MSC_VER // MSVC doesn't support inline asm with `volatile`.
// Try to prevent the compiler from optimizing out the undefined behavior.
asm volatile("" : : "r"(ret) :); // NOLINT
#endif
return ret;
}
void* InitializePoisonedPointerInternal();
inline void* get_poisoned_pointer() {
#if defined(NDEBUG) && !defined(Y_ABSL_HAVE_ADDRESS_SANITIZER) && \
!defined(Y_ABSL_HAVE_MEMORY_SANITIZER)
// In optimized non-sanitized builds, avoid the function-local static because
// of the codegen and runtime cost.
return GetBadPointerInternal();
#else
// Non-optimized builds may use more robust implementation. Note that we can't
// use a static global because Chromium doesn't allow non-constinit globals.
static void* ptr = InitializePoisonedPointerInternal();
return ptr;
#endif
}
} // namespace base_internal
Y_ABSL_NAMESPACE_END
} // namespace y_absl
#endif // Y_ABSL_BASE_INTERNAL_POISON_H_
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