diff --git a/src/libos/src/process/mod.rs b/src/libos/src/process/mod.rs
index 37539bc1..8ec293ec 100644
--- a/src/libos/src/process/mod.rs
+++ b/src/libos/src/process/mod.rs
@@ -6,7 +6,7 @@ pub mod table {
 pub use self::exit::{do_exit, do_wait4, ChildProcessFilter};
 pub use self::spawn::{do_spawn, FileAction};
 pub use self::wait::{WaitQueue, Waiter};
-pub use self::thread::{do_clone, CloneFlags, ThreadGroup};
+pub use self::thread::{do_clone, CloneFlags, ThreadGroup, do_set_tid_address};
 pub use self::futex::{FutexOp, FutexFlags, futex_op_and_flags_from_u32, futex_wake, futex_wait};
 pub use self::arch_prctl::{ArchPrctlCode, do_arch_prctl};
 
@@ -24,6 +24,7 @@ pub struct Process {
     // TODO: move cwd, root_inode into a FileSystem structure
     // TODO: should cwd be a String or INode?
     cwd: String,
+    clear_child_tid: Option<*mut pid_t>,
     parent: Option<ProcessRef>,
     children: Vec<ProcessWeakRef>,
     waiting_children: Option<WaitQueue<ChildProcessFilter, pid_t>>,
@@ -42,7 +43,13 @@ pub fn do_getpid() -> pid_t {
     current.get_pid()
 }
 
-pub fn do_getgpid() -> pid_t {
+pub fn do_gettid() -> pid_t {
+    let current_ref = get_current();
+    let current = current_ref.lock().unwrap();
+    current.get_tid()
+}
+
+pub fn do_getpgid() -> pid_t {
     let current_ref = get_current();
     let current = current_ref.lock().unwrap();
     current.get_pgid()
diff --git a/src/libos/src/process/process.rs b/src/libos/src/process/process.rs
index 2a203d0f..e932b081 100644
--- a/src/libos/src/process/process.rs
+++ b/src/libos/src/process/process.rs
@@ -14,6 +14,7 @@ lazy_static! {
             tgid: 0,
             exit_status: 0,
             cwd: "/".to_owned(),
+            clear_child_tid: None,
             parent: None,
             children: Vec::new(),
             waiting_children: Default::default(),
@@ -38,6 +39,7 @@ impl Process {
             pgid: new_pid,
             tgid: new_pid,
             cwd: cwd.to_owned(),
+            clear_child_tid: None,
             exit_status: 0,
             parent: None,
             children: Vec::new(),
@@ -54,15 +56,17 @@ impl Process {
     pub fn get_task_mut(&mut self) -> &mut Task {
         &mut self.task
     }
+    /// pid as seen by the user is actually the thread group ID
     pub fn get_pid(&self) -> pid_t {
+        self.tgid
+    }
+    /// tid as seen by the user is actually the process ID
+    pub fn get_tid(&self) -> pid_t {
         self.pid
     }
     pub fn get_pgid(&self) -> pid_t {
         self.pgid
     }
-    pub fn get_tgid(&self) -> pid_t {
-        self.tgid
-    }
     pub fn get_status(&self) -> Status {
         self.status
     }
@@ -101,6 +105,9 @@ impl Drop for Process {
     }
 }
 
+unsafe impl Send for Process {}
+unsafe impl Sync for Process {}
+
 #[derive(Clone, Copy, Debug, PartialEq)]
 pub enum Status {
     RUNNING,
diff --git a/src/libos/src/process/thread.rs b/src/libos/src/process/thread.rs
index b1efeda1..52ba10a5 100644
--- a/src/libos/src/process/thread.rs
+++ b/src/libos/src/process/thread.rs
@@ -82,3 +82,11 @@ fn new_thread_task(user_stack: usize, new_tls: usize) -> Result<Task, Error> {
         ..Default::default()
     })
 }
+
+pub fn do_set_tid_address(tidptr: *mut pid_t) -> Result<pid_t, Error> {
+    info!("set_tid_address: tidptr: {:#x}", tidptr as usize);
+    let current_ref = get_current();
+    let mut current = current_ref.lock().unwrap();
+    current.clear_child_tid = Some(tidptr);
+    Ok(current.get_tid())
+}
diff --git a/src/libos/src/syscall/mod.rs b/src/libos/src/syscall/mod.rs
index d7828303..ebd39052 100644
--- a/src/libos/src/syscall/mod.rs
+++ b/src/libos/src/syscall/mod.rs
@@ -79,6 +79,10 @@ pub extern "C" fn dispatch_syscall(
             arg3 as *const *const i8,
             arg4 as *const FdOp,
         ),
+        SYS_WAIT4 => do_wait4(arg0 as i32, arg1 as *mut i32),
+        SYS_GETPID => do_getpid(),
+        SYS_GETPPID => do_getppid(),
+
         SYS_CLONE => do_clone(
             arg0 as u32,
             arg1 as usize,
@@ -86,15 +90,14 @@ pub extern "C" fn dispatch_syscall(
             arg3 as *mut i32,
             arg4 as usize,
         ),
-        SYS_WAIT4 => do_wait4(arg0 as i32, arg1 as *mut i32),
         SYS_FUTEX => do_futex(
             arg0 as *const i32,
             arg1 as u32,
             arg2 as i32,
             // TODO: accept other optional arguments
         ),
-        SYS_GETPID => do_getpid(),
-        SYS_GETPPID => do_getppid(),
+        SYS_ARCH_PRCTL => do_arch_prctl(arg0 as u32, arg1 as *mut usize),
+        SYS_SET_TID_ADDRESS => do_set_tid_address(arg0 as *mut pid_t),
 
         SYS_MMAP => do_mmap(
             arg0 as usize,
@@ -122,8 +125,6 @@ pub extern "C" fn dispatch_syscall(
 
         SYS_GETTIMEOFDAY => do_gettimeofday(arg0 as *mut timeval_t),
 
-        SYS_ARCH_PRCTL => do_arch_prctl(arg0 as u32, arg1 as *mut usize),
-
         _ => do_unknown(num, arg0, arg1, arg2, arg3, arg4, arg5),
     };
     debug!("syscall return: {:?}", ret);
@@ -506,8 +507,8 @@ fn do_wait4(pid: i32, _exit_status: *mut i32) -> Result<isize, Error> {
         pid if pid < -1 => process::ChildProcessFilter::WithPGID((-pid) as pid_t),
         -1 => process::ChildProcessFilter::WithAnyPID,
         0 => {
-            let gpid = process::do_getgpid();
-            process::ChildProcessFilter::WithPGID(gpid)
+            let pgid = process::do_getpgid();
+            process::ChildProcessFilter::WithPGID(pgid)
         }
         pid if pid > 0 => process::ChildProcessFilter::WithPID(pid as pid_t),
         _ => {
@@ -663,3 +664,7 @@ fn do_arch_prctl(code: u32, addr: *mut usize) -> Result<isize, Error> {
     process::do_arch_prctl(code, addr).map(|_| 0)
 }
 
+fn do_set_tid_address(tidptr: *mut pid_t) -> Result<isize, Error> {
+    check_mut_ptr(tidptr)?;
+    process::do_set_tid_address(tidptr).map(|tid| tid as isize)
+}