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diff --git a/compiler-rt/lib/asan/asan_poisoning.h b/compiler-rt/lib/asan/asan_poisoning.h
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index 000000000000..62dd9bd0edd3
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+++ b/compiler-rt/lib/asan/asan_poisoning.h
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+//===-- asan_poisoning.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 is a part of AddressSanitizer, an address sanity checker.
+//
+// Shadow memory poisoning by ASan RTL and by user application.
+//===----------------------------------------------------------------------===//
+
+#include "asan_interceptors.h"
+#include "asan_internal.h"
+#include "asan_mapping.h"
+#include "sanitizer_common/sanitizer_flags.h"
+#include "sanitizer_common/sanitizer_platform.h"
+
+namespace __asan {
+
+// Enable/disable memory poisoning.
+void SetCanPoisonMemory(bool value);
+bool CanPoisonMemory();
+
+// Poisons the shadow memory for "size" bytes starting from "addr".
+void PoisonShadow(uptr addr, uptr size, u8 value);
+
+// Poisons the shadow memory for "redzone_size" bytes starting from
+// "addr + size".
+void PoisonShadowPartialRightRedzone(uptr addr,
+                                     uptr size,
+                                     uptr redzone_size,
+                                     u8 value);
+
+// Fast versions of PoisonShadow and PoisonShadowPartialRightRedzone that
+// assume that memory addresses are properly aligned. Use in
+// performance-critical code with care.
+ALWAYS_INLINE void FastPoisonShadow(uptr aligned_beg, uptr aligned_size,
+                                    u8 value) {
+  DCHECK(!value || CanPoisonMemory());
+#if SANITIZER_FUCHSIA
+  __sanitizer_fill_shadow(aligned_beg, aligned_size, value,
+                          common_flags()->clear_shadow_mmap_threshold);
+#else
+  uptr shadow_beg = MEM_TO_SHADOW(aligned_beg);
+  uptr shadow_end = MEM_TO_SHADOW(
+      aligned_beg + aligned_size - SHADOW_GRANULARITY) + 1;
+  // FIXME: Page states are different on Windows, so using the same interface
+  // for mapping shadow and zeroing out pages doesn't "just work", so we should
+  // probably provide higher-level interface for these operations.
+  // For now, just memset on Windows.
+  if (value || SANITIZER_WINDOWS == 1 ||
+      // RTEMS doesn't have have pages, let alone a fast way to zero
+      // them, so default to memset.
+      SANITIZER_RTEMS == 1 ||
+      shadow_end - shadow_beg < common_flags()->clear_shadow_mmap_threshold) {
+    REAL(memset)((void*)shadow_beg, value, shadow_end - shadow_beg);
+  } else {
+    uptr page_size = GetPageSizeCached();
+    uptr page_beg = RoundUpTo(shadow_beg, page_size);
+    uptr page_end = RoundDownTo(shadow_end, page_size);
+
+    if (page_beg >= page_end) {
+      REAL(memset)((void *)shadow_beg, 0, shadow_end - shadow_beg);
+    } else {
+      if (page_beg != shadow_beg) {
+        REAL(memset)((void *)shadow_beg, 0, page_beg - shadow_beg);
+      }
+      if (page_end != shadow_end) {
+        REAL(memset)((void *)page_end, 0, shadow_end - page_end);
+      }
+      ReserveShadowMemoryRange(page_beg, page_end - 1, nullptr);
+    }
+  }
+#endif // SANITIZER_FUCHSIA
+}
+
+ALWAYS_INLINE void FastPoisonShadowPartialRightRedzone(
+    uptr aligned_addr, uptr size, uptr redzone_size, u8 value) {
+  DCHECK(CanPoisonMemory());
+  bool poison_partial = flags()->poison_partial;
+  u8 *shadow = (u8*)MEM_TO_SHADOW(aligned_addr);
+  for (uptr i = 0; i < redzone_size; i += SHADOW_GRANULARITY, shadow++) {
+    if (i + SHADOW_GRANULARITY <= size) {
+      *shadow = 0;  // fully addressable
+    } else if (i >= size) {
+      *shadow = (SHADOW_GRANULARITY == 128) ? 0xff : value;  // unaddressable
+    } else {
+      // first size-i bytes are addressable
+      *shadow = poison_partial ? static_cast<u8>(size - i) : 0;
+    }
+  }
+}
+
+// Calls __sanitizer::ReleaseMemoryPagesToOS() on
+// [MemToShadow(p), MemToShadow(p+size)].
+void FlushUnneededASanShadowMemory(uptr p, uptr size);
+
+}  // namespace __asan