diff --git a/src/apis/emscripten/lock.rs b/src/apis/emscripten/lock.rs
index 5ac0f83e0..9067be99e 100644
--- a/src/apis/emscripten/lock.rs
+++ b/src/apis/emscripten/lock.rs
@@ -2,7 +2,11 @@ use crate::webassembly::Instance;
 use libc::c_int;
 
 // NOTE: Not implemented by Emscripten
-pub extern "C" fn ___lock(_which: c_int, _varargs: c_int, _instance: &mut Instance) {}
+pub extern "C" fn ___lock(_which: c_int, _varargs: c_int, _instance: &mut Instance) {
+    debug!("emscripten::___lock");
+}
 
 // NOTE: Not implemented by Emscripten
-pub extern "C" fn ___unlock(_which: c_int, _varargs: c_int, _instance: &mut Instance) {}
+pub extern "C" fn ___unlock(_which: c_int, _varargs: c_int, _instance: &mut Instance) {
+    debug!("emscripten::___unlock");
+}
diff --git a/src/apis/emscripten/signal.rs b/src/apis/emscripten/signal.rs
index ff7c9c115..71584db1e 100644
--- a/src/apis/emscripten/signal.rs
+++ b/src/apis/emscripten/signal.rs
@@ -16,6 +16,7 @@ pub extern "C" fn _sigaction(_signum: u32, _act: u32, _oldact: u32, _instance: &
 }
 
 pub extern "C" fn _sigaddset(set: u32, signum: u32, instance: &mut Instance) -> i32 {
+    debug!("emscripten::_sigaddset");
     let set_addr = instance.memory_offset_addr(0, set as _) as *mut u32;
     unsafe {
         *set_addr |= 1 << (signum - 1);
@@ -24,5 +25,6 @@ pub extern "C" fn _sigaddset(set: u32, signum: u32, instance: &mut Instance) ->
 }
 
 pub extern "C" fn _sigprocmask() -> i32 {
+    debug!("emscripten::_sigprocmask");
     0
 }
diff --git a/src/apis/emscripten/syscalls.rs b/src/apis/emscripten/syscalls.rs
index 7be897c6a..795ab3297 100644
--- a/src/apis/emscripten/syscalls.rs
+++ b/src/apis/emscripten/syscalls.rs
@@ -626,6 +626,7 @@ pub extern "C" fn ___syscall221(
     mut varargs: VarArgs,
     instance: &mut Instance,
 ) -> c_int {
+    debug!("emscripten::___syscall221 (fcntl64)");
     // fcntl64
     let _fd: i32 = varargs.get(instance);
     let cmd: u32 = varargs.get(instance);
diff --git a/src/apis/emscripten/time.rs b/src/apis/emscripten/time.rs
index 926370574..e8aa2d06c 100644
--- a/src/apis/emscripten/time.rs
+++ b/src/apis/emscripten/time.rs
@@ -16,6 +16,7 @@ use crate::webassembly::Instance;
 
 /// emscripten: _gettimeofday
 pub extern "C" fn _gettimeofday(tp: c_int, tz: c_int, instance: &mut Instance) -> c_int {
+    debug!("emscripten::_gettimeofday {} {}", tp, tz);
     #[repr(C)]
     struct GuestTimeVal {
         tv_sec: i32,
@@ -39,6 +40,7 @@ pub extern "C" fn _gettimeofday(tp: c_int, tz: c_int, instance: &mut Instance) -
 
 /// emscripten: _clock_gettime
 pub extern "C" fn _clock_gettime(clk_id: c_int, tp: c_int, instance: &mut Instance) -> c_int {
+    debug!("emscripten::_clock_gettime {} {}", clk_id, tp);
     #[repr(C)]
     struct GuestTimeSpec {
         tv_sec: i32,