handle_sys question

[Songmao Tian <kingkongmao@xxxxxxxxx>]

Hello all:
   In handle_sys there's a 
  50         sw      a3, PT_R26(sp)          # save a3 for syscall restarting

I woner why it need to save  a3 in R26(k0) slot in the stack?

Thanks,
songmao