root/swtch.S

/*   */

   1 # Context switch
   2 #
   3 #   void swtch(struct context **old, struct context *new);
   4 # 
   5 # Save the current registers on the stack, creating
   6 # a struct context, and save its address in *old.
   7 # Switch stacks to new and pop previously-saved registers.
   8 
   9 .globl swtch
  10 swtch:
  11   movl 4(%esp), %eax
  12   movl 8(%esp), %edx
  13 
  14   # Save old callee-saved registers
  15   pushl %ebp
  16   pushl %ebx
  17   pushl %esi
  18   pushl %edi
  19 
  20   # Switch stacks
  21   movl %esp, (%eax)
  22   movl %edx, %esp
  23 
  24   # Load new callee-saved registers
  25   popl %edi
  26   popl %esi
  27   popl %ebx
  28   popl %ebp
  29   ret

/*   */