Roll forward poisoned pointer API and fix portability issues.

Also, return the middle of the poisoned block.

PiperOrigin-RevId: 651119057
Change-Id: Iae0fc3dcb40e32cd449f469d9b8d62c37f3773f4

1 files changed, 59 insertions, 0 deletions

diff --git a/absl/base/internal/poison.h b/absl/base/internal/poison.h
new file mode 100644
index 00000000..28113bdd
--- /dev/null
+++ b/absl/base/internal/poison.h
@@ -0,0 +1,59 @@
+// 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 ABSL_BASE_INTERNAL_POISON_H_
+#define ABSL_BASE_INTERNAL_POISON_H_
+
+#include <cstdint>
+
+#include "absl/base/config.h"
+
+namespace absl {
+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(ABSL_HAVE_ADDRESS_SANITIZER) && \
+    !defined(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
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_BASE_INTERNAL_POISON_H_