OSDev.org

Code: Select all

static void do_switch(kDispatcher *me, kThread *from, kThread* to)
{
  static kThread *checkme;

  checkme=from;
  dumpDispatcher();
  if (from!=to && to!=NULL) {

   switching++;

   kSaveCpuCtx(&(from->cpuState),from->ptrTss);
   kRestoreCpuCtx(to->ptrTss,&(to->cpuState));

   if (!(to->stat & KT_TSSOWNER))
       to->ptrTss->eip=(dword)resume_switch;


      if (from->TSS_ID != to->TSS_ID) {
          task_switch(0,to->TSS_ID,&(from->cpuState));
      } else {
          stack_switch(&(from->cpuState),&(to->cpuState));
      }
      switching--;
  }
}

_task_switch:
   push ebp
   mov ebp, esp
   pushfd
   push fs
   pushad
   mov eax,[ebp+16]
   mov [eax],esp
   mov [eax+4],ss

   jmp far [ebp+8]
_resume_switch:
   popad
   pop fs
   popfd
   pop ebp
   ret


;;--------------------------------------------------------------------------
;; performs a stack-switch for multi-threading.
;; cs:   don't need to be saved: =0x08 for every thread in kernel mode.
;; ds,es,gs:    don't need to be saved: =0x10/0x18 for every thread.
;; fs:   this holds the selector for user data segment. same for all threads
;;   within a given process, but should better be saved in case a thread
;;   changed it for special purpose
;; eax:   return value, don't need to be saved.
;; edx,ecx: callee-clobbered register: the compiler will assume we overwrote
;;   them after function returns.
;; -------------------------------------------------------------------------
;;; cpu_context* stack_switch(cpu_context *saveto, cpu_context *getfrom)
_stack_switch:
   push ebp
   mov ebp,esp
   pushfd
   push fs
   pushad

   mov eax,[ebp+8]
   mov edx,[ebp+12]
   mov [eax],esp
   mov [eax+4],ss
   lss esp,[edx]

   popad
   pop fs
   popfd
   pop ebp
   ret