Index: libc/utils/UnitTest/Test.cpp
===================================================================
--- libc/utils/UnitTest/Test.cpp
+++ libc/utils/UnitTest/Test.cpp
@@ -235,7 +235,13 @@
 bool Test::testProcessKilled(RunContext &Ctx, testutils::FunctionCaller *Func,
                              int Signal, const char *LHSStr, const char *RHSStr,
                              const char *File, unsigned long Line) {
-  testutils::ProcessStatus Result = testutils::invokeInSubprocess(Func);
+  testutils::ProcessStatus Result = testutils::invokeInSubprocess(Func, 500);
+
+  if (const char *Error = Result.getError()) {
+    Ctx.markFail();
+    llvm::outs() << File << ":" << Line << ": FAILURE\n" << Error << '\n';
+    return false;
+  }
 
   if (Result.exitedNormally()) {
     Ctx.markFail();
@@ -266,7 +272,13 @@
                             int ExitCode, const char *LHSStr,
                             const char *RHSStr, const char *File,
                             unsigned long Line) {
-  testutils::ProcessStatus Result = testutils::invokeInSubprocess(Func);
+  testutils::ProcessStatus Result = testutils::invokeInSubprocess(Func, 500);
+
+  if (const char *Error = Result.getError()) {
+    Ctx.markFail();
+    llvm::outs() << File << ":" << Line << ": FAILURE\n" << Error << '\n';
+    return false;
+  }
 
   if (!Result.exitedNormally()) {
     Ctx.markFail();
Index: libc/utils/testutils/ExecuteFunction.h
===================================================================
--- libc/utils/testutils/ExecuteFunction.h
+++ libc/utils/testutils/ExecuteFunction.h
@@ -20,13 +20,17 @@
 
 struct ProcessStatus {
   int PlatformDefined;
+  const char *Failure = nullptr;
 
-  bool exitedNormally();
-  int getExitCode();
-  int getFatalSignal();
+  static ProcessStatus Error(const char *Error) { return {0, Error}; }
+
+  const char *getError() const { return Failure; }
+  bool exitedNormally() const;
+  int getExitCode() const;
+  int getFatalSignal() const;
 };
 
-ProcessStatus invokeInSubprocess(FunctionCaller *Func);
+ProcessStatus invokeInSubprocess(FunctionCaller *Func, unsigned TimeoutMS = -1);
 
 const char *signalAsString(int Signum);
 
Index: libc/utils/testutils/ExecuteFunctionUnix.cpp
===================================================================
--- libc/utils/testutils/ExecuteFunctionUnix.cpp
+++ libc/utils/testutils/ExecuteFunctionUnix.cpp
@@ -10,6 +10,8 @@
 #include "llvm/Support/raw_ostream.h"
 #include <cassert>
 #include <cstdlib>
+#include <memory>
+#include <poll.h>
 #include <signal.h>
 #include <sys/wait.h>
 #include <unistd.h>
@@ -17,32 +19,55 @@
 namespace __llvm_libc {
 namespace testutils {
 
-bool ProcessStatus::exitedNormally() { return WIFEXITED(PlatformDefined); }
+bool ProcessStatus::exitedNormally() const {
+  return WIFEXITED(PlatformDefined);
+}
 
-int ProcessStatus::getExitCode() {
+int ProcessStatus::getExitCode() const {
   assert(exitedNormally() && "Abnormal termination, no exit code");
   return WEXITSTATUS(PlatformDefined);
 }
 
-int ProcessStatus::getFatalSignal() {
+int ProcessStatus::getFatalSignal() const {
   if (exitedNormally())
     return 0;
   return WTERMSIG(PlatformDefined);
 }
 
-ProcessStatus invokeInSubprocess(FunctionCaller *Func) {
+ProcessStatus invokeInSubprocess(FunctionCaller *Func, unsigned TimeoutMS) {
+  std::unique_ptr<FunctionCaller> X(Func);
+  int PipeFDs[2];
+  if (::pipe(PipeFDs) == -1)
+    return ProcessStatus::Error("pipe(2) failed");
+
   // Don't copy the buffers into the child process and print twice.
   llvm::outs().flush();
   llvm::errs().flush();
   pid_t Pid = ::fork();
+  if (Pid == -1)
+    return ProcessStatus::Error("fork(2) failed");
+
   if (!Pid) {
     (*Func)();
     std::exit(0);
   }
+  ::close(PipeFDs[1]);
+
+  struct pollfd PollFD {
+    PipeFDs[0], 0, 0
+  };
+  if (::poll(&PollFD, 1, TimeoutMS) == -1)
+    return ProcessStatus::Error("poll(2) failed");
+  // If the pipe wasn't closed by the child yet then timeout has expired.
+  if (!(PollFD.revents & POLLHUP)) {
+    ::kill(Pid, SIGKILL);
+    return ProcessStatus::Error("Process timed out");
+  }
 
-  int WStatus;
-  ::waitpid(Pid, &WStatus, 0);
-  delete Func;
+  int WStatus = 0;
+  int Status = ::waitpid(Pid, &WStatus, WNOHANG);
+  assert(Status == Pid && "wait call should not block here");
+  (void)Status;
   return {WStatus};
 }