os/cpu/i386/tasking_helpers.s

.section .text
.global switchTask
switchTask:
    pusha
    pushf
    push %eax
    mov 44(%esp), %eax #The first argument, where to save
    mov %ebx, 4(%eax)
    mov %ecx, 8(%eax)
    mov %edx, 12(%eax)
    mov %esi, 16(%eax)
    mov %edi, 20(%eax)
    mov 36(%esp), %ebx #EAX
    mov 40(%esp), %ecx #IP
    mov 20(%esp), %edx #ESP
    add $4, %edx #Remove the return value ;)
    mov 16(%esp), %esi #EBP
    mov 4(%esp), %edi #EFLAGS
    mov %ebx, (%eax)
    mov %edx, 24(%eax)
    mov %esi, 28(%eax)
    mov %ecx, 32(%eax)
    mov %edi, 36(%eax)
    pop %ebx
    push %ebx #Goodbye again ;)
    mov 48(%esp), %eax #Now it is the new object
    mov 4(%eax), %ebx #EBX
    mov 8(%eax), %ecx #ECX
    mov 12(%eax), %edx #EDX
    mov 16(%eax), %esi #ESI
    mov 20(%eax), %edi #EDI
    mov 28(%eax), %ebp #EBP
    push %eax
    mov 36(%eax), %eax #EFLAGS
    push %eax
    popf
    pop %eax
    mov 24(%eax), %esp #ESP
    push %eax
    pop %eax
    push %eax
    mov 32(%eax), %eax #EIP
    xchg (%esp), %eax #We do not have any more registers to use as tmp storage
    mov (%eax), %eax #EAX
    ret #This ends all!
.global readEip
readEip:
  pop %eax
  jmp %eax