add a function to read the instruction pointer

arch/x86/include/asm/processor.h

@@ -119,6 +119,8 @@ static inline void tlb_flush(void)
 		write_cr3(val);
 }
 
+void read_eip(void);
+
 /*
  * invalidate (not flush!) lines in L1 that map to MPB lines
  */

arch/x86/kernel/entry.asm

@@ -106,6 +106,12 @@ idt_load:
     lidt [idtp]
     ret
 
+global read_eip
+read_eip:
+    pop eax                     ; Get the return address
+    jmp eax                     ; Return. Can't use RET because return
+                                ; address popped off the stack.
+
 ; In just a few pages in this tutorial, we will add our Interrupt
 ; Service Routines (ISRs) right here!
 global isr0
@@ -141,6 +147,7 @@ global isr29
 global isr30
 global isr31
 global isrsyscall
+global jump_to_child
 
 ;  0: Divide By Zero Exception
 isr0:
@@ -446,6 +453,17 @@ isrsyscall:
     pop ebp
     iret
 
+jump_to_child:
+    add esp, 4
+    mov eax, 0 ; child got always zero as return value
+    pop ebx
+    pop ecx
+    pop edx
+    pop esi
+    pop edi
+    pop ebp
+    iret
+
 global irq0
 global irq1
 global irq2
@@ -791,7 +809,6 @@ apic_svr:
     push byte 127
     jmp irq_common_stub
 
-
 irq_common_stub:
     pusha