minor optimizations and code cleanups

arch/x86/kernel/entry32.asm

@@ -436,9 +436,11 @@ isr31:
 extern syscall_handler
 
 ; used to realize system calls
+; by entering the handler, the interrupt flag is not cleared
 isrsyscall:
-    push ds
+    cli
     push es
+    push ds
     push ebp
     push edi
     push esi
@@ -446,21 +448,27 @@ isrsyscall:
     push ecx
     push ebx
     push eax
+
+    ; set kernel data segmenets
     mov ax, 0x10
     mov ds, ax
     mov es, ax
     mov eax, [esp]
+    sti
+
     call syscall_handler
+
+    cli
     add esp, 4 ; eax contains the return value
-	       ; => we did not restore eax
+               ; => we did not restore eax
     pop ebx 
     pop ecx
     pop edx
     pop esi
     pop edi
     pop ebp
-    pop es
     pop ds
+    pop es
     iret
 
 global irq0
@@ -766,8 +774,8 @@ switch_context:
     push DWORD 0x0              ; Interrupt number
     push DWORD 0x00edbabe       ; Error code
     pusha                       ; Registers...
-    push es
-    push ds
+    push 0x10                   ; kernel data segment
+    push 0x10                   ; kernel data segment
 
     jmp common_switch