diff --git a/src/libos/src/exception/cpuid.rs b/src/libos/src/exception/cpuid.rs
index dac435cb..b8580ac6 100644
--- a/src/libos/src/exception/cpuid.rs
+++ b/src/libos/src/exception/cpuid.rs
@@ -253,9 +253,12 @@ pub fn setup_cpuid_info() {
 }
 
 pub fn handle_cpuid_exception(user_context: &mut CpuContext) -> Result<isize> {
-    debug!("handle CPUID exception");
     let leaf = user_context.rax as u32;
     let subleaf = user_context.rcx as u32;
+    debug!(
+        "handle CPUID exception: leaf = 0x{:x?}, subleaf = 0x{:x?}",
+        leaf, subleaf
+    );
     let cpuid_result = CPUID.get_cpuid_info(leaf, subleaf);
     trace!("cpuid result: {:?}", cpuid_result);
     user_context.rax = cpuid_result.eax as u64;
diff --git a/src/libos/src/exception/syscall.rs b/src/libos/src/exception/syscall.rs
index 09750f04..7c00a5de 100644
--- a/src/libos/src/exception/syscall.rs
+++ b/src/libos/src/exception/syscall.rs
@@ -5,8 +5,6 @@ use sgx_types::*;
 pub const SYSCALL_OPCODE: u16 = 0x050F;
 
 pub fn handle_syscall_exception(user_context: &mut CpuContext) -> ! {
-    debug!("handle SYSCALL exception");
-
     // SYSCALL instruction saves RIP into RCX and RFLAGS into R11. This is to
     // comply with hardware's behavoir. Not useful for us.
     user_context.rcx = user_context.rip;
@@ -19,6 +17,7 @@ pub fn handle_syscall_exception(user_context: &mut CpuContext) -> ! {
 
     let num = user_context.rax as u32;
     assert!(num != SyscallNum::HandleException as u32);
+    debug!("handle SYSCALL exception: syscall number = {:?}", num);
 
     // FIXME: occlum syscall must use Linux ABI
     occlum_syscall(user_context);
diff --git a/src/libos/src/fs/file_ops/open.rs b/src/libos/src/fs/file_ops/open.rs
index 91156b14..a2da2d1a 100644
--- a/src/libos/src/fs/file_ops/open.rs
+++ b/src/libos/src/fs/file_ops/open.rs
@@ -19,5 +19,7 @@ pub fn do_openat(fs_path: &FsPath, flags: u32, mode: FileMode) -> Result<FileDes
         let creation_flags = CreationFlags::from_bits_truncate(flags);
         current.add_file(file_ref, creation_flags.must_close_on_spawn())
     };
+
+    debug!("openat: result fd: {:?}", fd);
     Ok(fd)
 }