Index: include/sanitizer/hwasan_interface.h
===================================================================
--- include/sanitizer/hwasan_interface.h
+++ include/sanitizer/hwasan_interface.h
@@ -32,6 +32,18 @@
   void __hwasan_enable_allocator_tagging(void);
   void __hwasan_disable_allocator_tagging(void);
 
+  // Mark region of memory with the given tag. Both address and size need to be
+  // 16-byte aligned.
+  void __hwasan_tag_memory(const volatile void *p, unsigned char tag,
+                           size_t size);
+
+  /// Set pointer tag. Previous tag is lost.
+  void *__hwasan_tag_pointer(const volatile void *p, unsigned char tag);
+
+  // Print shadow and origin for the memory range to stderr in a human-readable
+  // format.
+  void __hwasan_print_shadow(const volatile void *x, size_t size);
+
   int __sanitizer_posix_memalign(void **memptr, size_t alignment, size_t size);
   void * __sanitizer_memalign(size_t alignment, size_t size);
   void * __sanitizer_aligned_alloc(size_t alignment, size_t size);
Index: lib/hwasan/hwasan.cc
===================================================================
--- lib/hwasan/hwasan.cc
+++ lib/hwasan/hwasan.cc
@@ -224,9 +224,14 @@
   hwasan_inited = 1;
 }
 
-void __hwasan_print_shadow(const void *x, uptr size) {
-  // FIXME:
-  Printf("FIXME: __hwasan_print_shadow unimplemented\n");
+void __hwasan_print_shadow(const void *p, uptr sz) {
+  uptr ptr_raw = GetAddressFromPointer((uptr)p);
+  uptr shadow_first = MEM_TO_SHADOW(ptr_raw);
+  uptr shadow_last = MEM_TO_SHADOW(ptr_raw + sz - 1);
+  Printf("HWASan shadow map for %zx .. %zx (pointer tag %x)\n", ptr_raw,
+         ptr_raw + sz, GetTagFromPointer((uptr)p));
+  for (uptr s = shadow_first; s <= shadow_last; ++s)
+    Printf("  %zx: %x\n", SHADOW_TO_MEM(s), *(tag_t *)s);
 }
 
 sptr __hwasan_test_shadow(const void *p, uptr sz) {
@@ -400,6 +405,10 @@
   TagMemoryAligned(p, sz, tag);
 }
 
+uptr __hwasan_tag_pointer(uptr p, u8 tag) {
+  return AddTagToPointer(p, tag);
+}
+
 static const u8 kFallbackTag = 0xBB;
 
 u8 __hwasan_generate_tag() {
Index: lib/hwasan/hwasan_interface_internal.h
===================================================================
--- lib/hwasan/hwasan_interface_internal.h
+++ lib/hwasan/hwasan_interface_internal.h
@@ -94,6 +94,9 @@
 void __hwasan_tag_memory(uptr p, u8 tag, uptr sz);
 
 SANITIZER_INTERFACE_ATTRIBUTE
+uptr __hwasan_tag_pointer(uptr p, u8 tag);
+
+SANITIZER_INTERFACE_ATTRIBUTE
 u8 __hwasan_generate_tag();
 
 // Returns the offset of the first tag mismatch or -1 if the whole range is
Index: test/hwasan/TestCases/hwasan-print-shadow.cc
===================================================================
--- test/hwasan/TestCases/hwasan-print-shadow.cc
+++ test/hwasan/TestCases/hwasan-print-shadow.cc
@@ -0,0 +1,29 @@
+// RUN: %clangxx_hwasan -DSIZE=16 -O0 %s -o %t && %run %t 2>&1 | FileCheck %s
+
+// REQUIRES: stable-runtime
+
+#include <assert.h>
+#include <stdlib.h>
+#include <sys/mman.h>
+#include <sanitizer/hwasan_interface.h>
+
+int main() {
+  char *p = (char *)mmap(nullptr, 4096, PROT_READ | PROT_WRITE,
+                         MAP_PRIVATE | MAP_ANONYMOUS, 0, 0);
+  assert(p);
+
+  __hwasan_tag_memory(p, 1, 32);
+  __hwasan_tag_memory(p + 32, 3, 16);
+  __hwasan_tag_memory(p + 48, 0, 32);
+  __hwasan_tag_memory(p + 80, 4, 16);
+
+  char *q = (char *)__hwasan_tag_pointer(p, 7);
+  __hwasan_print_shadow(q + 5, 89 - 5);
+  // CHECK:      HWASan shadow map for {{.*}}5 .. {{.*}}9 (pointer tag 7)
+  // CHECK-NEXT:   {{.*}}0: 1
+  // CHECK-NEXT:   {{.*}}0: 1
+  // CHECK-NEXT:   {{.*}}0: 3
+  // CHECK-NEXT:   {{.*}}0: 0
+  // CHECK-NEXT:   {{.*}}0: 0
+  // CHECK-NEXT:   {{.*}}0: 4
+}