diff --git a/src/ec.cc b/src/ec.cc
index 2fa08fe..0a091ef 100644
--- a/src/ec.cc
+++ b/src/ec.cc
@@ -94,7 +94,12 @@ void Ec::root_invoke()
 
     printf ("iret to user ...\n");
 
-    // TODO prepare stack and iret to user
+    mword stack[] = { code, SEL_USER_CODE, 0x200, 2 * PAGE_SIZE, SEL_USER_DATA };
+
+    asm volatile (
+        "mov %0, %%esp   ;"
+        "iret            ;"
+        : : "r" (&stack) : "memory");
 
     UNREACHED;
 }
@@ -106,7 +111,23 @@ void Ec::handle_tss()
 
 void Ec::syscall_handler (uint8 number)
 {
-    printf ("syscall %d\n", number);
+    Sys_regs * r = current->sys_regs();
+
+    switch (number) {
+
+    case 0: // nop
+        printf ("syscall %d - nop\n", number);
+        break;
+
+    case 1: // add
+        printf ("syscall %d - add : %lu + %lu\n", number, r->esi, r->edi);
+        r->esi += r->edi;
+        break;
+
+    default:
+        printf ("syscall %d - unknown\n", number);
+        break;
+    };

     ret_user_sysexit();
 
diff --git a/src/usercode.cc b/src/usercode.cc
index a3acf93..6a27426 100644
--- a/src/usercode.cc
+++ b/src/usercode.cc
@@ -1,12 +1,48 @@
 #include "compiler.h"
 
+USER
+unsigned syscall1 (unsigned w0)
+{
+    asm volatile (
+        "   mov %%esp, %%ecx    ;"
+        "   mov $1f, %%edx      ;"
+        "   and $0xfff, %%edx   ;"
+        "   add $0x2000, %%edx  ;"
+        "   sysenter            ;"
+        "1:                     ;"
+        : "+a" (w0) : : "ecx", "edx");
+    return w0;
+}
+
+USER
+unsigned syscall3 (unsigned w0, unsigned w1, unsigned w2)
+{
+    asm volatile (
+        "   mov %%esp, %%ecx    ;"
+        "   mov $1f, %%edx      ;"
+        "   and $0xfff, %%edx   ;"
+        "   add $0x2000, %%edx  ;"
+        "   sysenter            ;"
+        "1:                     ;"
+        : "+a" (w0) : "S" (w1), "D" (w2) : "ecx", "edx");
+    return w0;
+}
+
+unsigned sys_nop()
+{
+    return syscall1 (0);
+}
+
+unsigned sys_add (unsigned a, unsigned b)
+{
+    return syscall3 (1,a,b);
+}
+
 EXTERN_C REGPARM(1) NORETURN USER
 void usercode (unsigned)
 {
-    // TODO
-    // - 1st : ud2 or force page fault here
-    // - 2nd : reenter the kernel via sysenter
-    // - 3rd : so some simple system calls, like adding two numbers
+    sys_nop();
+    sys_add(2,3);
 
     while (1) ;
 }