diff --git a/tests/Android.mk b/tests/Android.mk
index 956b76f..0d57f29 100644
--- a/tests/Android.mk
+++ b/tests/Android.mk
@@ -98,6 +98,7 @@
     sys_personality_test.cpp \
     sys_prctl_test.cpp \
     sys_procfs_test.cpp \
+    sys_ptrace_test.cpp \
     sys_resource_test.cpp \
     sys_select_test.cpp \
     sys_sendfile_test.cpp \
diff --git a/tests/sys_ptrace_test.cpp b/tests/sys_ptrace_test.cpp
new file mode 100644
index 0000000..bd84d30
--- /dev/null
+++ b/tests/sys_ptrace_test.cpp
@@ -0,0 +1,202 @@
+/*
+ * Copyright (C) 2016 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <sys/ptrace.h>
+
+#include <elf.h>
+#include <sched.h>
+#include <sys/prctl.h>
+#include <sys/uio.h>
+#include <sys/user.h>
+#include <unistd.h>
+
+#include <gtest/gtest.h>
+
+// Host libc does not define this.
+#ifndef TRAP_HWBKPT
+#define TRAP_HWBKPT 4
+#endif
+
+template<typename T>
+static void __attribute__((noreturn)) fork_child(unsigned cpu, T &data) {
+  // Extra precaution: make sure we go away if anything happens to our parent.
+  if (prctl(PR_SET_PDEATHSIG, SIGKILL, 0, 0, 0) == -1) {
+    perror("prctl(PR_SET_PDEATHSIG)");
+    _exit(1);
+  }
+
+  cpu_set_t cpus;
+  CPU_ZERO(&cpus);
+  CPU_SET(cpu, &cpus);
+  if (sched_setaffinity(0, sizeof cpus, &cpus) == -1) {
+    perror("sched_setaffinity");
+    _exit(2);
+  }
+  if (ptrace(PTRACE_TRACEME, 0, nullptr, nullptr) == -1) {
+    perror("ptrace(PTRACE_TRACEME)");
+    _exit(3);
+  }
+
+  raise(SIGSTOP); // Synchronize with the tracer, let it set the watchpoint.
+
+  data = 1; // Now trigger the watchpoint.
+
+  _exit(0);
+}
+
+class ChildGuard {
+ public:
+  ChildGuard(pid_t pid) : pid(pid) {}
+
+  ~ChildGuard() {
+    kill(pid, SIGKILL);
+    int status;
+    waitpid(pid, &status, 0);
+  }
+
+ private:
+  pid_t pid;
+};
+
+static bool are_watchpoints_supported(pid_t child) {
+#if defined(__arm__)
+  long capabilities;
+  long result = ptrace(PTRACE_GETHBPREGS, child, 0, &capabilities);
+  if (result == -1) {
+    EXPECT_EQ(EIO, errno);
+    return false;
+  }
+  return ((capabilities >> 8) & 0xff) > 0;
+#elif defined(__aarch64__)
+  user_hwdebug_state dreg_state;
+  iovec iov;
+  iov.iov_base = &dreg_state;
+  iov.iov_len = sizeof(dreg_state);
+
+  long result = ptrace(PTRACE_GETREGSET, child, NT_ARM_HW_WATCH, &iov);
+  if (result == -1) {
+    EXPECT_EQ(EINVAL, errno);
+    return false;
+  }
+  return (dreg_state.dbg_info & 0xff) > 0;
+#elif defined(__i386__) || defined(__x86_64__)
+  // We assume watchpoints are always supported on x86.
+  (void) child;
+  return true;
+#else
+  // TODO: mips support.
+  (void) child;
+  return false;
+#endif
+}
+
+static void set_watchpoint(pid_t child, const void *address, size_t size) {
+#if defined(__arm__) || defined(__aarch64__)
+  const unsigned byte_mask = (1 << size) - 1;
+  const unsigned type = 2; // Write.
+  const unsigned enable = 1;
+  const unsigned control = byte_mask << 5 | type << 3 | enable;
+
+#ifdef __arm__
+  ASSERT_EQ(0, ptrace(PTRACE_SETHBPREGS, child, -1, &address)) << strerror(errno);
+  ASSERT_EQ(0, ptrace(PTRACE_SETHBPREGS, child, -2, &control)) << strerror(errno);
+#else // aarch64
+  user_hwdebug_state dreg_state;
+  memset(&dreg_state, 0, sizeof dreg_state);
+  dreg_state.dbg_regs[0].addr = reinterpret_cast<uintptr_t>(address);
+  dreg_state.dbg_regs[0].ctrl = control;
+
+  iovec iov;
+  iov.iov_base = &dreg_state;
+  iov.iov_len = offsetof(user_hwdebug_state, dbg_regs) + sizeof(dreg_state.dbg_regs[0]);
+
+  ASSERT_EQ(0, ptrace(PTRACE_SETREGSET, child, NT_ARM_HW_WATCH, &iov)) << strerror(errno);
+#endif
+#elif defined(__i386__) || defined(__x86_64__)
+  ASSERT_EQ(0, ptrace(PTRACE_POKEUSER, child, offsetof(user, u_debugreg[0]), address)) << strerror(errno);
+  errno = 0;
+  unsigned data = ptrace(PTRACE_PEEKUSER, child, offsetof(user, u_debugreg[7]), nullptr);
+  ASSERT_EQ(0, errno);
+
+  const unsigned size_flag = (size == 8) ? 2 : size - 1;
+  const unsigned enable = 1;
+  const unsigned type = 1; // Write.
+
+  const unsigned mask = 3 << 18 | 3 << 16 | 1;
+  const unsigned value = size_flag << 18 | type << 16 | enable;
+  data &= mask;
+  data |= value;
+  ASSERT_EQ(0, ptrace(PTRACE_POKEUSER, child, offsetof(user, u_debugreg[7]), data)) << strerror(errno);
+#else
+  (void) child;
+  (void) address;
+  (void) size;
+#endif
+}
+
+template<typename T>
+static void run_watchpoint_test_impl(unsigned cpu) {
+  alignas(8) T data = 0;
+
+  pid_t child = fork();
+  ASSERT_NE(-1, child) << strerror(errno);
+  if (child == 0) fork_child(cpu, data);
+
+  ChildGuard guard(child);
+
+  int status;
+  ASSERT_EQ(child, waitpid(child, &status, __WALL)) << strerror(errno);
+  ASSERT_TRUE(WIFSTOPPED(status)) << "Status was: " << status;
+  ASSERT_EQ(SIGSTOP, WSTOPSIG(status)) << "Status was: " << status;
+
+  if (!are_watchpoints_supported(child)) return;
+
+  set_watchpoint(child, &data, sizeof data);
+
+  ASSERT_EQ(0, ptrace(PTRACE_CONT, child, nullptr, nullptr)) << strerror(errno);
+  ASSERT_EQ(child, waitpid(child, &status, __WALL)) << strerror(errno);
+  ASSERT_TRUE(WIFSTOPPED(status)) << "Status was: " << status;
+  ASSERT_EQ(SIGTRAP, WSTOPSIG(status)) << "Status was: " << status;
+
+  siginfo_t siginfo;
+  ASSERT_EQ(0, ptrace(PTRACE_GETSIGINFO, child, nullptr, &siginfo)) << strerror(errno);
+  ASSERT_EQ(TRAP_HWBKPT, siginfo.si_code);
+#if defined(__arm__) || defined(__aarch64__)
+  ASSERT_EQ(&data, siginfo.si_addr);
+#endif
+}
+
+static void run_watchpoint_test(unsigned cpu) {
+  run_watchpoint_test_impl<uint8_t>(cpu);
+  run_watchpoint_test_impl<uint16_t>(cpu);
+  run_watchpoint_test_impl<uint32_t>(cpu);
+#if __LP64__
+  run_watchpoint_test_impl<uint64_t>(cpu);
+#endif
+}
+
+// Test watchpoint API. The test is considered successful if our watchpoints get hit OR the
+// system reports that watchpoint support is not present. We run the test for different
+// watchpoint sizes, while pinning the process to each cpu in turn, for better coverage.
+TEST(ptrace, watchpoint_stress) {
+  cpu_set_t available_cpus;
+  ASSERT_EQ(0, sched_getaffinity(0, sizeof available_cpus, &available_cpus));
+
+  for (size_t cpu = 0; cpu < CPU_SETSIZE; ++cpu) {
+    if (!CPU_ISSET(cpu, &available_cpus)) continue;
+    run_watchpoint_test(cpu);
+  }
+}