sseg and eseg

[zhang jin]

In minix 3.1 text book version, consider the following code

         .align 16 

06788 errexception: 

06789 sseg pop (ex_number) 

06790 sseg pop (trap_errno) 

06791 exception1:   ! Common for all exceptions. 

06792 push eax ! eax is scratch register 

06793 mov eax, 0+4(esp) ! old eip 

06794 sseg mov (old_eip), eax 

06795 movzx eax, 4+4(esp) ! old cs 

06796 sseg mov (old_cs), eax 

06797 mov eax, 8+4(esp) ! old eflags 

06798 sseg mov (old_eflags), eax 

06799 pop eax 06800 call save 

06801 push (old_eflags)  

why is sseg necessary? because pop automatically work with stack esp ? so why is sseg needed here?

also I have seen eseg being used? why are they needed