Index: lib/fuzzer/FuzzerInterface.h
===================================================================
--- lib/fuzzer/FuzzerInterface.h
+++ lib/fuzzer/FuzzerInterface.h
@@ -70,6 +70,11 @@
 FUZZER_INTERFACE_VISIBILITY size_t
 LLVMFuzzerMutate(uint8_t *Data, size_t Size, size_t MaxSize);
 
+// Call a user-provided callback for each bitmap region containing coverage
+// info. This can be useful for fuzzers that reset state by forking, or using 
+// memory snapshots, since they shouldn't interfere with the coverage data
+FUZZER_INTERFACE_VISIBILITY void
+LLVMFuzzerIterateFeatureRegions(void (*CB)(void *, size_t));
 #undef FUZZER_INTERFACE_VISIBILITY
 
 #ifdef __cplusplus
Index: lib/fuzzer/FuzzerLoop.cpp
===================================================================
--- lib/fuzzer/FuzzerLoop.cpp
+++ lib/fuzzer/FuzzerLoop.cpp
@@ -863,5 +863,8 @@
   assert(fuzzer::F);
   return fuzzer::F->GetMD().DefaultMutate(Data, Size, MaxSize);
 }
-
+ATTRIBUTE_INTERFACE void LLVMFuzzerIterateFeatureRegions(void (*CB)(void *,
+                                                                    size_t)) {
+  fuzzer::TPC.IterateFeatureRegions(CB);
+}
 } // extern "C"
Index: lib/fuzzer/FuzzerTracePC.h
===================================================================
--- lib/fuzzer/FuzzerTracePC.h
+++ lib/fuzzer/FuzzerTracePC.h
@@ -130,6 +130,7 @@
   const PCTableEntry *PCTableEntryByIdx(uintptr_t Idx);
   static uintptr_t GetNextInstructionPc(uintptr_t PC);
   bool PcIsFuncEntry(const PCTableEntry *TE) { return TE->PCFlags & 1; }
+  void IterateFeatureRegions(void (*CB)(void *, size_t));
 
 private:
   bool UseCounters = false;
Index: lib/fuzzer/FuzzerTracePC.cpp
===================================================================
--- lib/fuzzer/FuzzerTracePC.cpp
+++ lib/fuzzer/FuzzerTracePC.cpp
@@ -440,6 +440,12 @@
   exit(1);
 }
 
+void TracePC::IterateFeatureRegions(void (*CB)(void *, size_t)) {
+  CB(&fuzzer::TPC, sizeof(fuzzer::TPC));
+  IterateCounterRegions(
+      [&](Module::Region &R) { CB(R.Start, R.Stop - R.Start); });
+  CB(ExtraCountersBegin(), ExtraCountersEnd() - ExtraCountersBegin());
+}
 } // namespace fuzzer
 
 extern "C" {
Index: test/fuzzer/DeferredForkTest.cpp
===================================================================
--- /dev/null
+++ test/fuzzer/DeferredForkTest.cpp
@@ -0,0 +1,68 @@
+#include <cstring>
+#include <stdint.h>
+#include <stdio.h>
+#include <sys/mman.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+extern "C" void LLVMFuzzerIterateFeatureRegions(void (*CB)(void *, size_t));
+
+size_t feature_shm_len = 0;
+uintptr_t feature_shm;
+size_t offset = 0;
+
+void count_shm_size(void *start, size_t len) {
+  feature_shm_len += len;
+}
+
+void feature_load(void *start, size_t len) {
+  std::memcpy(start, (void *)(feature_shm + offset), len);
+  offset += len;
+}
+
+void feature_store(void *start, size_t len) {
+  std::memcpy((void *)(feature_shm + offset), start, len);
+  offset += len;
+}
+
+int isPrime(long n, int i) {
+  if (n <= 2)
+    return (n == 2) ? 1 : 0;
+  if (n % i == 0)
+    return 0;
+  if (i * i > n)
+    return 1;
+  return isPrime(n, i + 1);
+}
+
+int fuzz(const uint8_t *Data, size_t Size) {
+  long *nums = (long *)Data;
+  while (Size > sizeof(long)) {
+    Size -= sizeof(long);
+    isPrime(*nums, 2);
+    nums++;
+  }
+  return 0;
+}
+
+extern "C" int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size) {
+  if (fork() == 0) {
+    fuzz(Data, Size);
+    offset = 0;
+    LLVMFuzzerIterateFeatureRegions(&feature_store);
+    _exit(0); // Prevent libfuzzer from catching the exit
+  } else {
+    wait(NULL);
+    offset = 0;
+    LLVMFuzzerIterateFeatureRegions(&feature_load);
+  }
+  return 0;
+}
+
+extern "C" int LLVMFuzzerInitialize(int *argc, char ***argv) {
+  LLVMFuzzerIterateFeatureRegions(&count_shm_size);
+
+  feature_shm = (uintptr_t)mmap(NULL, feature_shm_len,
+                                PROT_READ | PROT_WRITE, MAP_SHARED | MAP_ANONYMOUS, -1, 0);
+  return 0;
+}
Index: test/fuzzer/deferred-fork-test.test
===================================================================
--- /dev/null
+++ test/fuzzer/deferred-fork-test.test
@@ -0,0 +1,3 @@
+RUN: %cpp_compiler %S/DeferredForkTest.cpp -o %t-DeferredForkTest
+
+RUN: not %run %t-DeferredForkTest 2>&1 | FileCheck %s --check-prefix=DEFERRED_FORK