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diff --git a/compiler-rt/lib/gwp_asan/common.h b/compiler-rt/lib/gwp_asan/common.h
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+++ b/compiler-rt/lib/gwp_asan/common.h
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+//===-- common.h ------------------------------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// This file contains code that is common between the crash handler and the
+// GuardedPoolAllocator.
+
+#ifndef GWP_ASAN_COMMON_H_
+#define GWP_ASAN_COMMON_H_
+
+#include "gwp_asan/definitions.h"
+#include "gwp_asan/options.h"
+
+#include <stddef.h>
+#include <stdint.h>
+
+namespace gwp_asan {
+enum class Error {
+  UNKNOWN,
+  USE_AFTER_FREE,
+  DOUBLE_FREE,
+  INVALID_FREE,
+  BUFFER_OVERFLOW,
+  BUFFER_UNDERFLOW
+};
+
+const char *ErrorToString(const Error &E);
+
+static constexpr uint64_t kInvalidThreadID = UINT64_MAX;
+// Get the current thread ID, or kInvalidThreadID if failure. Note: This
+// implementation is platform-specific.
+uint64_t getThreadID();
+
+// This struct contains all the metadata recorded about a single allocation made
+// by GWP-ASan. If `AllocationMetadata.Addr` is zero, the metadata is non-valid.
+struct AllocationMetadata {
+  // The number of bytes used to store a compressed stack frame. On 64-bit
+  // platforms, assuming a compression ratio of 50%, this should allow us to
+  // store ~64 frames per trace.
+  static constexpr size_t kStackFrameStorageBytes = 256;
+
+  // Maximum number of stack frames to collect on allocation/deallocation. The
+  // actual number of collected frames may be less than this as the stack
+  // frames are compressed into a fixed memory range.
+  static constexpr size_t kMaxTraceLengthToCollect = 128;
+
+  // Records the given allocation metadata into this struct.
+  void RecordAllocation(uintptr_t Addr, size_t Size);
+  // Record that this allocation is now deallocated.
+  void RecordDeallocation();
+
+  struct CallSiteInfo {
+    // Record the current backtrace to this callsite.
+    void RecordBacktrace(options::Backtrace_t Backtrace);
+
+    // The compressed backtrace to the allocation/deallocation.
+    uint8_t CompressedTrace[kStackFrameStorageBytes];
+    // The thread ID for this trace, or kInvalidThreadID if not available.
+    uint64_t ThreadID = kInvalidThreadID;
+    // The size of the compressed trace (in bytes). Zero indicates that no
+    // trace was collected.
+    size_t TraceSize = 0;
+  };
+
+  // The address of this allocation. If zero, the rest of this struct isn't
+  // valid, as the allocation has never occurred.
+  uintptr_t Addr = 0;
+  // Represents the actual size of the allocation.
+  size_t Size = 0;
+
+  CallSiteInfo AllocationTrace;
+  CallSiteInfo DeallocationTrace;
+
+  // Whether this allocation has been deallocated yet.
+  bool IsDeallocated = false;
+};
+
+// This holds the state that's shared between the GWP-ASan allocator and the
+// crash handler. This, in conjunction with the Metadata array, forms the entire
+// set of information required for understanding a GWP-ASan crash.
+struct AllocatorState {
+  // Returns whether the provided pointer is a current sampled allocation that
+  // is owned by this pool.
+  GWP_ASAN_ALWAYS_INLINE bool pointerIsMine(const void *Ptr) const {
+    uintptr_t P = reinterpret_cast<uintptr_t>(Ptr);
+    return P < GuardedPagePoolEnd && GuardedPagePool <= P;
+  }
+
+  // Returns the address of the N-th guarded slot.
+  uintptr_t slotToAddr(size_t N) const;
+
+  // Returns the largest allocation that is supported by this pool.
+  size_t maximumAllocationSize() const;
+
+  // Gets the nearest slot to the provided address.
+  size_t getNearestSlot(uintptr_t Ptr) const;
+
+  // Returns whether the provided pointer is a guard page or not. The pointer
+  // must be within memory owned by this pool, else the result is undefined.
+  bool isGuardPage(uintptr_t Ptr) const;
+
+  // The number of guarded slots that this pool holds.
+  size_t MaxSimultaneousAllocations = 0;
+
+  // Pointer to the pool of guarded slots. Note that this points to the start of
+  // the pool (which is a guard page), not a pointer to the first guarded page.
+  uintptr_t GuardedPagePool = 0;
+  uintptr_t GuardedPagePoolEnd = 0;
+
+  // Cached page size for this system in bytes.
+  size_t PageSize = 0;
+
+  // The type and address of an internally-detected failure. For INVALID_FREE
+  // and DOUBLE_FREE, these errors are detected in GWP-ASan, which will set
+  // these values and terminate the process.
+  Error FailureType = Error::UNKNOWN;
+  uintptr_t FailureAddress = 0;
+};
+
+} // namespace gwp_asan
+#endif // GWP_ASAN_COMMON_H_