diff --git a/src/lib.rs b/src/lib.rs
index c616a81..463503d 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -8,6 +8,8 @@ pub use self::flag::*;
 pub use self::number::*;
 pub use self::scheme::*;
 
+use core::mem;
+
 #[cfg(target_arch = "x86")]
 #[path="x86.rs"]
 mod arch;
@@ -67,7 +69,7 @@ pub fn fpath(fd: usize, buf: &mut [u8]) -> Result<usize> {
 }
 
 pub fn fstat(fd: usize, stat: &mut Stat) -> Result<usize> {
-    unsafe { syscall2(SYS_FSTAT, fd, stat as *mut Stat as usize) }
+    unsafe { syscall3(SYS_FSTAT, fd, stat as *mut Stat as usize, mem::size_of::<Stat>()) }
 }
 
 pub fn fsync(fd: usize) -> Result<usize> {
diff --git a/src/number.rs b/src/number.rs
index 718f75f..525da1c 100644
--- a/src/number.rs
+++ b/src/number.rs
@@ -1,38 +1,52 @@
-pub const SYS_BRK: usize = 45;
-pub const SYS_CHDIR: usize = 12;
-pub const SYS_CLONE: usize = 120;
-pub const SYS_CLOSE: usize = 6;
+pub const SYS_CLASS: usize =    0xF000_0000;
+pub const SYS_CLASS_PATH: usize=0x1000_0000;
+pub const SYS_CLASS_FILE: usize=0x2000_0000;
+
+pub const SYS_ARG: usize =      0x0F00_0000;
+pub const SYS_ARG_SLICE: usize =0x0100_0000;
+pub const SYS_ARG_MSLICE: usize=0x0200_0000;
+pub const SYS_ARG_PATH: usize = 0x0300_0000;
+
+pub const SYS_RET: usize =      0x00F0_0000;
+pub const SYS_RET_FILE: usize = 0x0010_0000;
+
+pub const SYS_LINK: usize =     SYS_CLASS_PATH | SYS_ARG_PATH | 9;
+pub const SYS_OPEN: usize =     SYS_CLASS_PATH | SYS_RET_FILE | 5;
+pub const SYS_MKDIR: usize =    SYS_CLASS_PATH | 39;
+pub const SYS_RMDIR: usize =    SYS_CLASS_PATH | 84;
+pub const SYS_UNLINK: usize =   SYS_CLASS_PATH | 10;
+
+pub const SYS_CLOSE: usize =    SYS_CLASS_FILE | 6;
+pub const SYS_DUP: usize =      SYS_CLASS_FILE | SYS_RET_FILE | 41;
+pub const SYS_READ: usize =     SYS_CLASS_FILE | SYS_ARG_MSLICE | 3;
+pub const SYS_WRITE: usize =    SYS_CLASS_FILE | SYS_ARG_SLICE | 4;
+pub const SYS_FEVENT: usize =   SYS_CLASS_FILE | 927;
+pub const SYS_LSEEK: usize =    SYS_CLASS_FILE | 19;
+pub const SYS_FPATH: usize =    SYS_CLASS_FILE | SYS_ARG_MSLICE | 928;
+pub const SYS_FSTAT: usize =    SYS_CLASS_FILE | SYS_ARG_MSLICE | 28;
+pub const SYS_FSYNC: usize =    SYS_CLASS_FILE | 118;
+pub const SYS_FTRUNCATE: usize =SYS_CLASS_FILE | 93;
+
+pub const SYS_BRK: usize =      45;
+pub const SYS_CHDIR: usize =    12;
 pub const SYS_CLOCK_GETTIME: usize = 265;
-pub const SYS_DUP: usize = 41;
-pub const SYS_EXECVE: usize = 11;
-pub const SYS_EXIT: usize = 1;
-pub const SYS_FEVENT: usize = 927;
-pub const SYS_FPATH: usize = 928;
-pub const SYS_FSTAT: usize = 28;
-pub const SYS_FSYNC: usize = 118;
-pub const SYS_FTRUNCATE: usize = 93;
-pub const SYS_FUTEX: usize = 240;
-pub const SYS_GETCWD: usize = 183;
-pub const SYS_GETGID: usize = 200;
-pub const SYS_GETPID: usize = 20;
-pub const SYS_GETUID: usize = 199;
-pub const SYS_IOPL: usize = 110;
-pub const SYS_LINK: usize = 9;
-pub const SYS_LSEEK: usize = 19;
-pub const SYS_MKDIR: usize = 39;
-pub const SYS_NANOSLEEP: usize = 162;
-pub const SYS_OPEN: usize = 5;
-pub const SYS_PHYSALLOC: usize = 945;
+pub const SYS_CLONE: usize =    120;
+pub const SYS_EXECVE: usize =   11;
+pub const SYS_EXIT: usize =     1;
+pub const SYS_FUTEX: usize =    240;
+pub const SYS_GETCWD: usize =   183;
+pub const SYS_GETGID: usize =   200;
+pub const SYS_GETPID: usize =   20;
+pub const SYS_GETUID: usize =   199;
+pub const SYS_IOPL: usize =     110;
+pub const SYS_NANOSLEEP: usize =162;
+pub const SYS_PHYSALLOC: usize =945;
 pub const SYS_PHYSFREE: usize = 946;
-pub const SYS_PHYSMAP: usize = 947;
-pub const SYS_PHYSUNMAP: usize = 948;
-pub const SYS_VIRTTOPHYS: usize = 949;
-pub const SYS_PIPE2: usize = 331;
-pub const SYS_READ: usize = 3;
-pub const SYS_RMDIR: usize = 84;
-pub const SYS_SETGID: usize = 214;
-pub const SYS_SETUID: usize = 213;
-pub const SYS_UNLINK: usize = 10;
-pub const SYS_WAITPID: usize = 7;
-pub const SYS_WRITE: usize = 4;
-pub const SYS_YIELD: usize = 158;
+pub const SYS_PHYSMAP: usize =  947;
+pub const SYS_PHYSUNMAP: usize =948;
+pub const SYS_VIRTTOPHYS: usize=949;
+pub const SYS_PIPE2: usize =    331;
+pub const SYS_SETGID: usize =   214;
+pub const SYS_SETUID: usize =   213;
+pub const SYS_WAITPID: usize =  7;
+pub const SYS_YIELD: usize =    158;