diff --git a/src/c_interface.rs b/src/c_interface.rs
index 822dd55..f18553c 100644
--- a/src/c_interface.rs
+++ b/src/c_interface.rs
@@ -19,10 +19,10 @@ mod lang {
     #[lang = "panic_fmt"]
     #[no_mangle]
     extern fn panic_fmt(fmt: core::fmt::Arguments, file: &'static str, line: u32) -> ! {
-        eprintln!("\n\nPANIC in {} at line {}:", file, line);
-        eprintln!("    {}", fmt);
         use super::ucore::__panic;
-        unsafe{ __panic() };
+        // FIXME: can not use `format`, will cause page fault
+        // let mut s = fmt::format(fmt);
+        unsafe{ __panic(file.as_ptr(), line as i32, "Rust panic\0".as_ptr()) };
         unreachable!()
     }
 }
@@ -35,9 +35,15 @@ mod ucore {
         pub fn inode_init(inode: &mut INode, ops: &INodeOps, fs: &mut Fs);
         pub fn inode_kill(inode: &mut INode);
         pub fn __alloc_fs(type_: i32) -> *mut Fs;
-        pub fn __panic();
+        pub fn __panic(file: *const u8, line: i32, fmt: *const u8);
+        fn cputchar(c: i32);
     }
     pub const SFS_TYPE: i32 = 0; // TODO
+    pub fn print(s: &str) {
+        for c in s.chars() {
+            unsafe{ cputchar(c as i32);}
+        }
+    }
 }
 
 // Exports for ucore
@@ -48,6 +54,7 @@ static SFS_INODE_OPS: INodeOps = INodeOps::from_rust_inode::<sfs::INode>();
 #[no_mangle]
 pub extern fn sfs_do_mount(dev: *mut Device, fs_store: &mut *mut Fs) -> ErrorCode {
     use self::ucore::*;
+    panic!("sfs_do_mount");
     let fs = unsafe{__alloc_fs(SFS_TYPE)};
     let device = unsafe{ Box::from_raw(dev) };  // TODO: fix unsafe
     unsafe{&mut (*fs)}.fs = sfs::SimpleFileSystem::open(device).unwrap();
@@ -311,21 +318,23 @@ mod allocator {
     use alloc::heap::{Alloc, AllocErr, Layout};
     use core::ptr::NonNull;
 
-    pub struct UcoreAllocator {
-        pub malloc: unsafe extern fn(size: usize) -> *mut u8,
-        pub free: unsafe extern fn(*mut u8),
+    extern {
+        fn kmalloc(size: usize) -> *mut u8;
+        fn kfree(ptr: *mut u8);
     }
 
+    pub struct UcoreAllocator;
+
     unsafe impl<'a> Alloc for &'a UcoreAllocator {
         unsafe fn alloc(&mut self, layout: Layout) -> Result<*mut u8, AllocErr> {
             const NULL: *mut u8 = 0 as *mut u8;
-            match (self.malloc)(layout.size()) {
+            match kmalloc(layout.size()) {
                 NULL => Err(AllocErr::Exhausted { request: layout }),
                 ptr => Ok(ptr),
             }
         }
         unsafe fn dealloc(&mut self, ptr: *mut u8, layout: Layout) {
-            (self.free)(ptr);
+            kfree(ptr);
         }
     }
 }
\ No newline at end of file
diff --git a/src/lib.rs b/src/lib.rs
index f67c072..2532a4c 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -7,6 +7,7 @@
 #[macro_use]
 extern crate std;
 extern crate spin;
+#[macro_use]
 extern crate alloc;
 extern crate bit_set;
 
@@ -16,6 +17,12 @@ macro_rules! eprintln {
     ($fmt:expr) => ();
     ($fmt:expr, $($arg:tt)*) => ();
 }
+#[cfg(feature = "ucore")]
+macro_rules! eprintln {
+    () => (::c_interface::ucore::print("\n"));
+    ($fmt:expr) => (::c_interface::ucore::print($fmt); ::c_interface::ucore::print("\n"););
+//    ($fmt:expr, $($arg:tt)*) => ();
+}
 
 mod dirty;
 mod vfs;
@@ -28,10 +35,4 @@ mod tests;
 
 #[cfg(feature = "ucore")]
 #[global_allocator]
-pub static UCORE_ALLOCATOR: c_interface::UcoreAllocator = {
-    extern {
-        fn kmalloc(size: usize) -> *mut u8;
-        fn kfree(ptr: *mut u8);
-    }
-    c_interface::UcoreAllocator{malloc: kmalloc, free: kfree}
-};
\ No newline at end of file
+pub static UCORE_ALLOCATOR: c_interface::UcoreAllocator = c_interface::UcoreAllocator{};
\ No newline at end of file