diff --git a/src/libos/src/fs.rs b/src/libos/src/fs.rs
index 4d8ff7f0..a40f8b0b 100644
--- a/src/libos/src/fs.rs
+++ b/src/libos/src/fs.rs
@@ -51,7 +51,7 @@ pub fn do_write(fd: FileDesc, buf: &[u8]) -> Result<usize, Error> {
     let current_ref = process::get_current();
     let current_process = current_ref.lock().unwrap();
     let file_ref = current_process.file_table.get(fd)
-        .ok_or_else(|| Error::new(Errno::EBADF, "Invalid file descriptor"))?;
+        .ok_or_else(|| Error::new(Errno::EBADF, "Invalid file descriptor [do_write]"))?;
     file_ref.write(buf)
 }
 
@@ -59,7 +59,7 @@ pub fn do_read(fd: FileDesc, buf: &mut [u8]) -> Result<usize, Error> {
     let current_ref = process::get_current();
     let current_process = current_ref.lock().unwrap();
     let file_ref = current_process.file_table.get(fd)
-        .ok_or_else(|| Error::new(Errno::EBADF, "Invalid file descriptor"))?;
+        .ok_or_else(|| Error::new(Errno::EBADF, "Invalid file descriptor [do_read]"))?;
     file_ref.read(buf)
 }
 
@@ -69,6 +69,6 @@ pub fn do_close(fd: FileDesc) -> Result<(), Error> {
     let file_table = &mut current_process.file_table;
     match file_table.del(fd) {
         Some(_) => Ok(()),
-        None => Err(Error::new(Errno::EBADF, "Invalid file descriptor")),
+        None => Err(Error::new(Errno::EBADF, "Invalid file descriptor [do_close]")),
     }
 }
diff --git a/src/libos/src/syscall.h b/src/libos/src/syscall.h
index ff0820dc..494901c0 100644
--- a/src/libos/src/syscall.h
+++ b/src/libos/src/syscall.h
@@ -18,6 +18,7 @@ extern int occlum_spawn(int* child_pid, const char* path,
 extern int occlum_wait4(int child_pid, int* status, int options/*, struct rusage* rusage*/);
 extern unsigned int occlum_getpid(void);
 extern void occlum_exit(int status);
+extern int occlum_unknown(int num);
 
 #ifdef __cplusplus
 }
diff --git a/src/libos/src/syscall.rs b/src/libos/src/syscall.rs
index db5cbb6b..80d51a60 100644
--- a/src/libos/src/syscall.rs
+++ b/src/libos/src/syscall.rs
@@ -85,6 +85,12 @@ pub extern "C" fn occlum_exit(status: i32)
     process::do_exit(status);
 }
 
+#[no_mangle]
+pub extern "C" fn occlum_unknown(num: u32)
+{
+    println!("[WARNING] Unknown syscall (num = {})", num);
+}
+
 #[no_mangle]
 pub extern "C" fn occlum_spawn(child_pid: *mut c_int, path: *const c_char,
     argv: *const *const c_char, envp: *const *const c_char) -> c_int
diff --git a/src/libos/src/syscall_entry.c b/src/libos/src/syscall_entry.c
index 96dab001..aef447ef 100644
--- a/src/libos/src/syscall_entry.c
+++ b/src/libos/src/syscall_entry.c
@@ -61,7 +61,7 @@ long dispatch_syscall(int num, long arg0, long arg1, long arg2, long arg3, long
         break;
     }
     default:
-        ret = -1;
+        ret = occlum_unknown(num);
         break;
     }
 
diff --git a/test/Makefile b/test/Makefile
index a16384a2..8b8fd16b 100644
--- a/test/Makefile
+++ b/test/Makefile
@@ -1,7 +1,7 @@
 CUR_DIR := $(shell dirname $(realpath $(lastword $(MAKEFILE_LIST))))
 PROJECT_DIR := $(realpath $(CUR_DIR)/../)
 
-TEST_SUITES := hello_world_raw spawn_and_wait4_raw getpid file_io
+TEST_SUITES := empty
 BUILD_TEST_SUITES := $(TEST_SUITES:%=%)
 RUN_TEST_SUITES := $(TEST_SUITES:%=run-%)
 CLEAN_TEST_SUITES := $(TEST_SUITES:%=clean-%)
@@ -14,10 +14,7 @@ CLEAN_TEST_SUITES := $(TEST_SUITES:%=clean-%)
 
 all: build
 
-build: build_rusgx_stub $(BUILD_TEST_SUITES)
-
-build_rusgx_stub:
-	@$(MAKE) -C rusgx_stub
+build: $(BUILD_TEST_SUITES)
 
 $(BUILD_TEST_SUITES): %:
 	@$(MAKE) -C $@
@@ -42,7 +39,6 @@ $(RUN_TEST_SUITES): run-%: % pal libocclum.signed.so
 #############################################################################
 
 clean: $(CLEAN_TEST_SUITES)
-	@$(MAKE) -C rusgx_stub clean
 	@$(RM) -f pal libocclum.signed.so
 
 $(CLEAN_TEST_SUITES): clean-%:
diff --git a/test/empty/Makefile b/test/empty/Makefile
new file mode 100644
index 00000000..b71a4d49
--- /dev/null
+++ b/test/empty/Makefile
@@ -0,0 +1,4 @@
+include ../test_common.mk
+
+EXTRA_C_FLAGS :=
+EXTRA_LINK_FLAGS :=
diff --git a/test/empty/empty.c b/test/empty/empty.c
new file mode 100644
index 00000000..9b6bdc2e
--- /dev/null
+++ b/test/empty/empty.c
@@ -0,0 +1,3 @@
+int main(void) {
+    return 0;
+}
diff --git a/test/file_io/Makefile b/test/file_io/Makefile
deleted file mode 100644
index 593ab76d..00000000
--- a/test/file_io/Makefile
+++ /dev/null
@@ -1,4 +0,0 @@
-include ../test_common.mk
-
-EXTRA_C_FLAGS := -fno-builtin
-EXTRA_LINK_FLAGS := -nostdlib
diff --git a/test/file_io/main.c b/test/file_io/main.c
deleted file mode 100644
index 99acb7b3..00000000
--- a/test/file_io/main.c
+++ /dev/null
@@ -1,66 +0,0 @@
-#include "rusgx_stub.h"
-
-static char success_str_buf[] = "Success!\n";
-static unsigned long success_str_size = sizeof(success_str_buf);
-
-static void print_ok(void) {
-    __rusgx_write(1, success_str_buf, success_str_size);
-}
-
-
-static int test_write(const char* file_path) {
-    int write_fd = __rusgx_open(file_path, O_WRONLY | O_CREAT | O_TRUNC, 0666);
-    if (write_fd < 0) {
-        return -1;
-    }
-
-    char write_buf[] = "Hello World!\n";
-    size_t write_len = sizeof(write_buf);
-    if (__rusgx_write(write_fd, write_buf, write_len) != write_len) {
-        return -2;
-    }
-
-    if (__rusgx_close(write_fd) < 0) {
-        return -3;
-    }
-
-    return 0;
-}
-
-static int test_read(const char* file_path) {
-    int read_fd = __rusgx_open(file_path, O_RDONLY, 0);
-    if (read_fd < 0) {
-        return -1;
-    }
-
-    char read_buf[256] = { 0 };
-    size_t read_len;
-    if ((read_len = __rusgx_read(read_fd, read_buf, 256)) < 0 ) {
-        return -2;
-    }
-
-    __rusgx_write(1, read_buf, read_len);
-
-    if (__rusgx_close(read_fd) < 0) {
-        return -3;
-    }
-
-    return 0;
-}
-
-void _start(void) {
-    int ret = 0;
-    const char* file_path = "tmp.txt.protected";
-
-    if ((ret = test_write(file_path)) < 0) {
-        goto on_exit;
-    }
-
-    if ((ret = test_read(file_path)) < 0) {
-        goto on_exit;
-    }
-
-    print_ok();
-on_exit:
-    __rusgx_exit(ret);
-}
diff --git a/test/getpid/Makefile b/test/getpid/Makefile
deleted file mode 100644
index 593ab76d..00000000
--- a/test/getpid/Makefile
+++ /dev/null
@@ -1,4 +0,0 @@
-include ../test_common.mk
-
-EXTRA_C_FLAGS := -fno-builtin
-EXTRA_LINK_FLAGS := -nostdlib
diff --git a/test/getpid/main.c b/test/getpid/main.c
deleted file mode 100644
index 270be522..00000000
--- a/test/getpid/main.c
+++ /dev/null
@@ -1,8 +0,0 @@
-#include "rusgx_stub.h"
-
-void _start(void) {
-    int pid = __rusgx_getpid();
-    (void)pid;
-
-    __rusgx_exit(0);
-}
diff --git a/test/hello_world_raw/Makefile b/test/hello_world_raw/Makefile
deleted file mode 100644
index 593ab76d..00000000
--- a/test/hello_world_raw/Makefile
+++ /dev/null
@@ -1,4 +0,0 @@
-include ../test_common.mk
-
-EXTRA_C_FLAGS := -fno-builtin
-EXTRA_LINK_FLAGS := -nostdlib
diff --git a/test/hello_world_raw/main.c b/test/hello_world_raw/main.c
deleted file mode 100644
index 127d511c..00000000
--- a/test/hello_world_raw/main.c
+++ /dev/null
@@ -1,9 +0,0 @@
-#include "rusgx_stub.h"
-
-char str_buf[] = "Hello World!\n";
-unsigned long str_size = sizeof(str_buf);
-
-void _start(void) {
-    __rusgx_write(1, str_buf, str_size);
-    __rusgx_exit(0);
-}
diff --git a/test/include/rusgx_stub.h b/test/include/rusgx_stub.h
deleted file mode 100644
index e925c600..00000000
--- a/test/include/rusgx_stub.h
+++ /dev/null
@@ -1,99 +0,0 @@
-#ifndef __RUSGX_STUB__
-#define __RUSGX_STUB__
-
-#include <stddef.h>
-#include <sys/types.h>
-
-/*
- * Stub for Rusgx syscalls
- *
- * Executables built with Rusgx's toolchain are dynamically linked with this
- * stub library. This stub library serves two purposes:
- *
- *  1) Enable Rusgx's syscalls. Since this library is dynamically linked with
- *  executables, the compile-time linker generates proper dynamic linking
- *  information. Using this information, the program loader of Rusgx can do
- *  runtime relocation so that user programs can make syscalls to the library
- *  OS.
- *
- *  2) Run without Rusgx. When not running upon Rusgx, the executables can use the
- *  host syscalls provided by the default implementation of this library.
- */
-
-#define SYS_read    0
-#define SYS_write   1
-#define SYS_open    2
-#define SYS_close   3
-#define SYS_getpid  39
-#define SYS_exit    60
-#define SYS_wait4   61
-#define SYS_spawn   360
-
-#define O_RDONLY        0x00000000U
-#define O_WRONLY        0x00000001U
-#define O_RDWR          0x00000002U
-#define O_CREAT         0x00000040U
-#define O_EXCL          0x00000080U
-#define O_NOCTTY        0x00000100U
-#define O_TRUNC         0x00000200U
-#define O_APPEND        0x00000400U
-#define O_NONBLOCK      0x00000800U
-#define O_NDELAY        0x00000800U
-#define O_DSYNC         0x00001000U
-#define O_DIRECTORY     0x00010000U
-#define O_NOFOLLOW      0x00020000U
-#define O_CLOEXEC       0x00080000U
-#define O_SYNC          0x00101000U
-
-
-long __occlum_syscall(int num, long arg0, long arg1, long arg2, long arg3, long arg4);
-
-#define RUSGX_SYSCALL0(num) \
-    __occlum_syscall((num), (long)0, (long)0, (long)0, (long)0, (long)0)
-#define RUSGX_SYSCALL1(num, arg0) \
-    __occlum_syscall((num), (long)(arg0), (long)0, (long)0, (long)0, (long)0)
-#define RUSGX_SYSCALL2(num, arg0, arg1) \
-    __occlum_syscall((num), (long)(arg0), (long)(arg1), (long)0, (long)0, (long)0)
-#define RUSGX_SYSCALL3(num, arg0, arg1, arg2) \
-    __occlum_syscall((num), (long)(arg0), (long)(arg1), (long)(arg2), (long)0, (long)0)
-#define RUSGX_SYSCALL4(num, arg0, arg1, arg2, arg3) \
-    __occlum_syscall((num), (long)(arg0), (long)(arg1), (long)(arg2), (long)(arg3), (long)0)
-#define RUSGX_SYSCALL5(num, arg0, arg1, arg2, arg3, arg4) \
-    __occlum_syscall((num), (long)(arg0), (long)(arg1), (long)(arg2), (long)(arg3), (long)(arg4))
-
-
-static inline ssize_t __rusgx_read(int fd, void* buf, unsigned long size) {
-    return (ssize_t) RUSGX_SYSCALL3(SYS_read, fd, buf, size);
-}
-
-static inline ssize_t __rusgx_write(int fd, const void* buf, unsigned long size) {
-    return (ssize_t) RUSGX_SYSCALL3(SYS_write, fd, buf, size);
-}
-
-static inline int __rusgx_open(const void* buf, int flags, int mode) {
-    return (int) RUSGX_SYSCALL3(SYS_open, buf, flags, mode);
-}
-
-static inline int __rusgx_close(int fd) {
-    return (int) RUSGX_SYSCALL1(SYS_close, fd);
-}
-
-
-static inline unsigned int __rusgx_getpid(void) {
-    return (unsigned int) RUSGX_SYSCALL0(SYS_getpid);
-}
-
-static inline void __rusgx_exit(int status) {
-    RUSGX_SYSCALL1(SYS_exit, status);
-}
-
-static inline int __rusgx_spawn(int* child_pid, const char* path,
-                        const char** argv, const char** envp) {
-    return (int) RUSGX_SYSCALL4(SYS_spawn, child_pid, path, argv, envp);
-}
-
-static inline int __rusgx_wait4(int child_pid, int* status, int options/*, struct rusage* rusage*/) {
-    return (int) RUSGX_SYSCALL3(SYS_wait4, child_pid, status, options);
-}
-
-#endif /* __RUSGX_STUB__ */
diff --git a/test/rusgx_stub/Makefile b/test/rusgx_stub/Makefile
deleted file mode 100644
index 3e5821da..00000000
--- a/test/rusgx_stub/Makefile
+++ /dev/null
@@ -1,23 +0,0 @@
-C_SRCS := $(wildcard *.c)
-S_FILES := $(C_SRCS:%.c=%.S)
-C_OBJS := $(C_SRCS:%.c=%.o)
-LIB_NAME := librusgx_stub.so
-
-C_FLAGS := -Wall -fno-builtin -fno-stack-protector -fverbose-asm -fpic -I../include
-C_FLAGS += -O0
-LINK_FLAGS := -nostdlib
-
-.PHONY: all clean
-all: $(LIB_NAME)
-
-$(LIB_NAME): $(C_OBJS)
-	$(CC) $^ $(LINK_FLAGS) -shared -o $(LIB_NAME)
-
-$(C_OBJS): %.o: %.S
-	$(CC) $(C_FLAGS) -c $< -o $@
-
-$(S_FILES): %.S: %.c
-	$(CC) $(C_FLAGS) -S $< -o $@
-
-clean:
-	$(RM) -f *.o *.S $(LIB_NAME)
diff --git a/test/rusgx_stub/stub_impl.c b/test/rusgx_stub/stub_impl.c
deleted file mode 100644
index 47899d0d..00000000
--- a/test/rusgx_stub/stub_impl.c
+++ /dev/null
@@ -1,77 +0,0 @@
-#include "rusgx_stub.h"
-
-static long __read(int fd, void* buf, unsigned long size) {
-    long ret;
-    __asm__ __volatile__ (
-        "syscall"
-        : "=a" (ret)
-        : "0" (SYS_read), "D" (fd), "S" (buf), "d" (size)
-        : "cc", "rcx", "r11", "memory"
-    );
-    return ret;
-}
-
-static long __write(int fd, const void* buf, unsigned long size) {
-    long ret;
-    __asm__ __volatile__ (
-        "syscall"
-        : "=a" (ret)
-        : "0" (SYS_write), "D" (fd), "S" (buf), "d" (size)
-        : "cc", "rcx", "r11", "memory"
-    );
-    return ret;
-}
-
-static long __open(const char* path, int flags, int mode) {
-    long ret;
-    __asm__ __volatile__ (
-        "syscall"
-        : "=a" (ret)
-        : "0" (SYS_open), "D" (path), "S" (flags), "d" (mode)
-        : "cc", "rcx", "r11", "memory"
-    );
-    return ret;
-}
-
-static long __close(int fd) {
-    long ret;
-    __asm__ __volatile__ (
-        "syscall"
-        : "=a" (ret)
-        : "a" (SYS_close), "D" (fd)
-        : "cc", "rcx", "r11", "memory" );
-    return ret;
-}
-
-static void __exit(int status) {
-    __asm__ __volatile__ (
-        "syscall"
-        :
-        : "a" (SYS_exit), "D" (status)
-        : "cc", "rcx", "r11", "memory" );
-    return;
-}
-
-long __occlum_syscall(int num, long arg0, long arg1, long arg2, long arg3, long arg4) {
-    long ret = 0;
-    switch (num) {
-    case SYS_exit:
-        __exit((int)arg0);
-        break;
-    case SYS_read:
-        ret = __read((int)arg0, (void*)arg1, (unsigned long)arg2);
-        break;
-    case SYS_write:
-        ret = __write((int)arg0, (const void*)arg1, (unsigned long)arg2);
-        break;
-    case SYS_open:
-        ret = __open((const char*)arg0, (int)arg1, (int)arg2);
-        break;
-    case SYS_close:
-        ret = __close((int)arg0);
-        break;
-    default:
-        break;
-    }
-    return ret;
-}
diff --git a/test/spawn_and_wait4_raw/Makefile b/test/spawn_and_wait4_raw/Makefile
deleted file mode 100644
index 593ab76d..00000000
--- a/test/spawn_and_wait4_raw/Makefile
+++ /dev/null
@@ -1,4 +0,0 @@
-include ../test_common.mk
-
-EXTRA_C_FLAGS := -fno-builtin
-EXTRA_LINK_FLAGS := -nostdlib
diff --git a/test/spawn_and_wait4_raw/main.c b/test/spawn_and_wait4_raw/main.c
deleted file mode 100644
index 793730fa..00000000
--- a/test/spawn_and_wait4_raw/main.c
+++ /dev/null
@@ -1,28 +0,0 @@
-#include "rusgx_stub.h"
-
-static char success_str_buf[] = "A child process starts and exits!\n";
-static unsigned long success_str_size = sizeof(success_str_buf);
-
-static void print_ok(void) {
-    __rusgx_write(1, success_str_buf, success_str_size);
-}
-
-#define NUM_CHILDREN            10
-
-void _start(void) {
-    for (int ci = 0; ci < NUM_CHILDREN; ci++) {
-        int ret = 0;
-        int pid = 0;
-
-        ret = __rusgx_spawn(&pid, "hello_world_raw/bin.encrypted", NULL, NULL);
-        if (ret < 0) { __rusgx_exit(0); }
-
-        int status;
-        ret = __rusgx_wait4(pid, &status, 0);
-        if (ret < 0) { __rusgx_exit(0); }
-
-        //print_ok();
-    }
-
-    __rusgx_exit(0);
-}
diff --git a/test/test_common.mk b/test/test_common.mk
index 8d094dac..94eaef1e 100644
--- a/test/test_common.mk
+++ b/test/test_common.mk
@@ -3,6 +3,7 @@ INCLUDE_MAKEFILE := $(lastword $(MAKEFILE_LIST))
 CUR_DIR := $(shell dirname $(realpath $(MAIN_MAKEFILE)))
 PROJECT_DIR := $(realpath $(CUR_DIR)/../../)
 
+CC := /usr/local/occlum/bin/musl-gcc
 C_SRCS := $(wildcard *.c)
 S_FILES := $(C_SRCS:%.c=%.S)
 C_OBJS := $(C_SRCS:%.c=%.o)
@@ -11,14 +12,10 @@ BIN_ENC_NAME := bin.encrypted
 OBJDUMP_FILE := bin.objdump
 READELF_FILE := bin.readelf
 
-C_FLAGS = -Wall -fno-stack-protector -fverbose-asm -fpic \
-		  -I../include -L../rusgx_stub -lrusgx_stub \
-		  -O0 \
-		  $(EXTRA_C_FLAGS)
-LINK_FLAGS = -pie -L../rusgx_stub -lrusgx_stub \
-			$(EXTRA_LINK_FLAGS)
+C_FLAGS = -Wall -fverbose-asm -O0 $(EXTRA_C_FLAGS)
+LINK_FLAGS = $(EXTRA_LINK_FLAGS)
 
-.PHONY: all run run-without-rusgx debug clean
+.PHONY: all run debug clean
 
 #############################################################################
 # Build
@@ -55,9 +52,6 @@ $(S_FILES): %.S: %.c
 run: $(BIN_ENC_NAME)
 	cd ../ && RUST_BACKTRACE=1 ./pal $(CUR_DIR)/$(BIN_ENC_NAME)
 
-run-without-rusgx:
-	cd ../ && LD_LIBRARY_PATH=./rusgx_stub/ ./$(BIN_NAME)
-
 #############################################################################
 # Misc
 #############################################################################