diff --git a/clang/lib/Driver/ToolChains/Darwin.cpp b/clang/lib/Driver/ToolChains/Darwin.cpp
--- a/clang/lib/Driver/ToolChains/Darwin.cpp
+++ b/clang/lib/Driver/ToolChains/Darwin.cpp
@@ -1173,6 +1173,7 @@
       addExportedSymbol(CmdArgs, "___gcov_flush");
       addExportedSymbol(CmdArgs, "_flush_fn_list");
       addExportedSymbol(CmdArgs, "_writeout_fn_list");
+      addExportedSymbol(CmdArgs, "_reset_fn_list");
     } else {
       addExportedSymbol(CmdArgs, "___llvm_profile_filename");
       addExportedSymbol(CmdArgs, "___llvm_profile_raw_version");
diff --git a/compiler-rt/lib/profile/GCDAProfiling.c b/compiler-rt/lib/profile/GCDAProfiling.c
--- a/compiler-rt/lib/profile/GCDAProfiling.c
+++ b/compiler-rt/lib/profile/GCDAProfiling.c
@@ -32,8 +32,10 @@
 #include <windows.h>
 #include "WindowsMMap.h"
 #else
-#include <sys/mman.h>
 #include <sys/file.h>
+#include <sys/mman.h>
+#include <sys/types.h>
+#include <unistd.h>
 #endif
 
 #if defined(__FreeBSD__) && defined(__i386__)
@@ -119,6 +121,11 @@
  */
 struct fn_list flush_fn_list;
 
+/*
+ *  A list of reset functions, shared between all dynamic objects.
+ */
+struct fn_list reset_fn_list;
+
 static void fn_list_insert(struct fn_list* list, fn_ptr fn) {
   struct fn_node* new_node = malloc(sizeof(struct fn_node));
   new_node->fn = fn;
@@ -643,7 +650,46 @@
 }
 
 COMPILER_RT_VISIBILITY
-void llvm_gcov_init(fn_ptr wfn, fn_ptr ffn) {
+void llvm_register_reset_function(fn_ptr fn) {
+  fn_list_insert(&reset_fn_list, fn);
+}
+
+COMPILER_RT_VISIBILITY
+void llvm_delete_reset_function_list(void) { fn_list_remove(&reset_fn_list); }
+
+COMPILER_RT_VISIBILITY
+void llvm_reset_counters(void) {
+  struct fn_node *curr = reset_fn_list.head;
+
+  while (curr) {
+    if (curr->id == CURRENT_ID) {
+      curr->fn();
+    }
+    curr = curr->next;
+  }
+}
+
+#if !defined(_WIN32)
+COMPILER_RT_VISIBILITY
+pid_t __gcov_fork() {
+  pid_t parent_pid = getpid();
+  pid_t pid = fork();
+
+  if (pid == 0) {
+    pid_t child_pid = getpid();
+    if (child_pid != parent_pid) {
+      // The pid changed so we've a fork (one could have its own fork function)
+      // Just reset the counters for this child process
+      // threads.
+      llvm_reset_counters();
+    }
+  }
+  return pid;
+}
+#endif
+
+COMPILER_RT_VISIBILITY
+void llvm_gcov_init(fn_ptr wfn, fn_ptr ffn, fn_ptr rfn) {
   static int atexit_ran = 0;
 
   if (wfn)
@@ -652,10 +698,14 @@
   if (ffn)
     llvm_register_flush_function(ffn);
 
+  if (rfn)
+    llvm_register_reset_function(rfn);
+
   if (atexit_ran == 0) {
     atexit_ran = 1;
 
     /* Make sure we write out the data and delete the data structures. */
+    atexit(llvm_delete_reset_function_list);
     atexit(llvm_delete_flush_function_list);
     atexit(llvm_delete_writeout_function_list);
     atexit(llvm_writeout_files);
diff --git a/compiler-rt/test/profile/Inputs/instrprof-gcov-multithread_fork.cpp b/compiler-rt/test/profile/Inputs/instrprof-gcov-multithread_fork.cpp
new file mode 100644
--- /dev/null
+++ b/compiler-rt/test/profile/Inputs/instrprof-gcov-multithread_fork.cpp
@@ -0,0 +1,35 @@
+#include <sys/types.h>
+#include <thread>
+#include <unistd.h>
+#include <vector>
+
+template <typename T>
+void launcher(T func) {
+  std::vector<std::thread> pool;
+
+  for (int i = 0; i < 10; i++) {
+    pool.emplace_back(std::thread(func));
+  }
+
+  for (auto &t : pool) {
+    t.join();
+  }
+}
+
+void h() {}
+
+void g() {
+  fork();
+  launcher<>(h);
+}
+
+void f() {
+  fork();
+  launcher<>(g);
+}
+
+int main() {
+  launcher<>(f);
+
+  return 0;
+}
diff --git a/compiler-rt/test/profile/instrprof-gcov-multithread_fork.test b/compiler-rt/test/profile/instrprof-gcov-multithread_fork.test
new file mode 100644
--- /dev/null
+++ b/compiler-rt/test/profile/instrprof-gcov-multithread_fork.test
@@ -0,0 +1,11 @@
+UNSUPPORTED: windows
+
+RUN: mkdir -p %t.d
+RUN: cd %t.d
+
+RUN: %clangxx --coverage -lpthread -o %t %S/Inputs/instrprof-gcov-multithread_fork.cpp
+RUN: test -f instrprof-gcov-multithread_fork.gcno
+
+RUN: rm -f instrprof-gcov-multithread_fork.gcda
+RUN: %run %t
+RUN: llvm-cov gcov instrprof-gcov-multithread_fork.gcda
diff --git a/llvm/lib/Transforms/Instrumentation/GCOVProfiling.cpp b/llvm/lib/Transforms/Instrumentation/GCOVProfiling.cpp
--- a/llvm/lib/Transforms/Instrumentation/GCOVProfiling.cpp
+++ b/llvm/lib/Transforms/Instrumentation/GCOVProfiling.cpp
@@ -115,7 +115,8 @@
   // list.
   Function *
   insertCounterWriteout(ArrayRef<std::pair<GlobalVariable *, MDNode *>>);
-  Function *insertFlush(ArrayRef<std::pair<GlobalVariable *, MDNode *>>);
+  Function *insertReset(ArrayRef<std::pair<GlobalVariable *, MDNode *>>);
+  Function *insertFlush(Function *ResetF);
 
   void AddFlushBeforeForkAndExec();
 
@@ -631,35 +632,76 @@
 }
 
 void GCOVProfiler::AddFlushBeforeForkAndExec() {
-  SmallVector<Instruction *, 2> ForkAndExecs;
+  SmallVector<CallInst *, 2> Forks;
+  SmallVector<CallInst *, 2> Execs;
   for (auto &F : M->functions()) {
     auto *TLI = &GetTLI(F);
     for (auto &I : instructions(F)) {
       if (CallInst *CI = dyn_cast<CallInst>(&I)) {
         if (Function *Callee = CI->getCalledFunction()) {
           LibFunc LF;
-          if (TLI->getLibFunc(*Callee, LF) &&
-              (LF == LibFunc_fork || LF == LibFunc_execl ||
-               LF == LibFunc_execle || LF == LibFunc_execlp ||
-               LF == LibFunc_execv || LF == LibFunc_execvp ||
-               LF == LibFunc_execve || LF == LibFunc_execvpe ||
-               LF == LibFunc_execvP)) {
-            ForkAndExecs.push_back(&I);
+          if (TLI->getLibFunc(*Callee, LF)) {
+            if (LF == LibFunc_fork) {
+#if !defined(_WIN32)
+              Forks.push_back(CI);
+#endif
+            } else if (LF == LibFunc_execl || LF == LibFunc_execle ||
+                       LF == LibFunc_execlp || LF == LibFunc_execv ||
+                       LF == LibFunc_execvp || LF == LibFunc_execve ||
+                       LF == LibFunc_execvpe || LF == LibFunc_execvP) {
+              Execs.push_back(CI);
+            }
           }
         }
       }
     }
   }
 
-  // We need to split the block after the fork/exec call
-  // because else the counters for the lines after will be
-  // the same as before the call.
-  for (auto I : ForkAndExecs) {
-    IRBuilder<> Builder(I);
+  for (auto F : Forks) {
+    IRBuilder<> Builder(F);
+    BasicBlock *Parent = F->getParent();
+    auto NextInst = ++F->getIterator();
+
+    // We've a fork so just reset the counters in the child process
+    FunctionType *FTy = FunctionType::get(Builder.getInt32Ty(), {}, false);
+    FunctionCallee GCOVFork = M->getOrInsertFunction("__gcov_fork", FTy);
+    F->setCalledFunction(GCOVFork);
+
+    // We split just after the fork to have a counter for the lines after
+    // Anyway there's a bug:
+    // void foo() { fork(); }
+    // void bar() { foo(); blah(); }
+    // then "blah();" will be called 2 times but showed as 1
+    // because "blah()" belongs to the same block as "foo();"
+    Parent->splitBasicBlock(NextInst);
+
+    // back() is a br instruction with a debug location
+    // equals to the one from NextAfterFork
+    // So to avoid to have two debug locs on two blocks just change it
+    DebugLoc Loc = F->getDebugLoc();
+    Parent->back().setDebugLoc(Loc);
+  }
+
+  for (auto E : Execs) {
+    IRBuilder<> Builder(E);
+    BasicBlock *Parent = E->getParent();
+    auto NextInst = ++E->getIterator();
+
+    // Since the process is replaced by a new one we need to write out gcdas
+    // No need to reset the counters since they'll be lost after the exec**
     FunctionType *FTy = FunctionType::get(Builder.getVoidTy(), {}, false);
-    FunctionCallee GCOVFlush = M->getOrInsertFunction("__gcov_flush", FTy);
-    Builder.CreateCall(GCOVFlush);
-    I->getParent()->splitBasicBlock(I);
+    FunctionCallee WriteoutF =
+        M->getOrInsertFunction("llvm_writeout_files", FTy);
+    Builder.CreateCall(WriteoutF);
+
+    DebugLoc Loc = E->getDebugLoc();
+    Builder.SetInsertPoint(&*NextInst);
+    // If the exec** fails we must reset the counters since they've been
+    // dumped
+    FunctionCallee ResetF = M->getOrInsertFunction("llvm_reset_counters", FTy);
+    Builder.CreateCall(ResetF)->setDebugLoc(Loc);
+    Parent->splitBasicBlock(NextInst);
+    Parent->back().setDebugLoc(Loc);
   }
 }
 
@@ -851,7 +893,8 @@
     }
 
     Function *WriteoutF = insertCounterWriteout(CountersBySP);
-    Function *FlushF = insertFlush(CountersBySP);
+    Function *ResetF = insertReset(CountersBySP);
+    Function *FlushF = insertFlush(ResetF);
 
     // Create a small bit of code that registers the "__llvm_gcov_writeout" to
     // be executed at exit and the "__llvm_gcov_flush" function to be executed
@@ -869,16 +912,14 @@
     IRBuilder<> Builder(BB);
 
     FTy = FunctionType::get(Type::getVoidTy(*Ctx), false);
-    Type *Params[] = {
-      PointerType::get(FTy, 0),
-      PointerType::get(FTy, 0)
-    };
+    Type *Params[] = {PointerType::get(FTy, 0), PointerType::get(FTy, 0),
+                      PointerType::get(FTy, 0)};
     FTy = FunctionType::get(Builder.getVoidTy(), Params, false);
 
-    // Initialize the environment and register the local writeout and flush
-    // functions.
+    // Initialize the environment and register the local writeout, flush and
+    // reset functions.
     FunctionCallee GCOVInit = M->getOrInsertFunction("llvm_gcov_init", FTy);
-    Builder.CreateCall(GCOVInit, {WriteoutF, FlushF});
+    Builder.CreateCall(GCOVInit, {WriteoutF, FlushF, ResetF});
     Builder.CreateRetVoid();
 
     appendToGlobalCtors(*M, F, 0);
@@ -1191,8 +1232,43 @@
   return WriteoutF;
 }
 
-Function *GCOVProfiler::
-insertFlush(ArrayRef<std::pair<GlobalVariable*, MDNode*> > CountersBySP) {
+Function *GCOVProfiler::insertReset(
+    ArrayRef<std::pair<GlobalVariable *, MDNode *>> CountersBySP) {
+  FunctionType *FTy = FunctionType::get(Type::getVoidTy(*Ctx), false);
+  Function *ResetF = M->getFunction("__llvm_gcov_reset");
+  if (!ResetF)
+    ResetF = Function::Create(FTy, GlobalValue::InternalLinkage,
+                              "__llvm_gcov_reset", M);
+  else
+    ResetF->setLinkage(GlobalValue::InternalLinkage);
+  ResetF->setUnnamedAddr(GlobalValue::UnnamedAddr::Global);
+  ResetF->addFnAttr(Attribute::NoInline);
+  if (Options.NoRedZone)
+    ResetF->addFnAttr(Attribute::NoRedZone);
+
+  BasicBlock *Entry = BasicBlock::Create(*Ctx, "entry", ResetF);
+  IRBuilder<> Builder(Entry);
+
+  // Zero out the counters.
+  for (const auto &I : CountersBySP) {
+    GlobalVariable *GV = I.first;
+    Constant *Null = Constant::getNullValue(GV->getValueType());
+    Builder.CreateStore(Null, GV);
+  }
+
+  Type *RetTy = ResetF->getReturnType();
+  if (RetTy->isVoidTy())
+    Builder.CreateRetVoid();
+  else if (RetTy->isIntegerTy())
+    // Used if __llvm_gcov_reset was implicitly declared.
+    Builder.CreateRet(ConstantInt::get(RetTy, 0));
+  else
+    report_fatal_error("invalid return type for __llvm_gcov_reset");
+
+  return ResetF;
+}
+
+Function *GCOVProfiler::insertFlush(Function *ResetF) {
   FunctionType *FTy = FunctionType::get(Type::getVoidTy(*Ctx), false);
   Function *FlushF = M->getFunction("__llvm_gcov_flush");
   if (!FlushF)
@@ -1213,16 +1289,10 @@
 
   IRBuilder<> Builder(Entry);
   Builder.CreateCall(WriteoutF, {});
-
-  // Zero out the counters.
-  for (const auto &I : CountersBySP) {
-    GlobalVariable *GV = I.first;
-    Constant *Null = Constant::getNullValue(GV->getValueType());
-    Builder.CreateStore(Null, GV);
-  }
+  Builder.CreateCall(ResetF, {});
 
   Type *RetTy = FlushF->getReturnType();
-  if (RetTy == Type::getVoidTy(*Ctx))
+  if (RetTy->isVoidTy())
     Builder.CreateRetVoid();
   else if (RetTy->isIntegerTy())
     // Used if __llvm_gcov_flush was implicitly declared.