xen/include/asm-x86/current.h
  1.  #define reset_stack_and_jump(__fn)              \
    2. 

  2.      __asm__ __volatile__ (                      \
    3. 

  3.          "mov %0,%%"__OP"sp; jmp "STR(__fn)      \
    4. 

  4.          : : "r" (guest_cpu_user_regs()) : "memory" )