'Better' task management, needs more testing

task.nasm

@@ -0,0 +1,46 @@
+task_ptr: equ (0x310000-4)
+
+global save_current_task
+save_current_task:
+push ebx
+mov ebx, esp
+mov esp, dword [task_ptr] ; load current task pointer
+push ss
+push ebp ; return stack
+pushfd
+push cs
+push eax ; return address
+push ds ; other segs, pop
+push es ; before iret
+push fs ; in exit handler
+push gs
+mov dword [task_ptr], esp ; save new task pointer
+mov esp, ebx
+pop ebx
+ret
+
+global return_prev_task
+return_prev_task:
+mov edi, eax ; save for later
+mov esi, dword [task_ptr] ; load current task pointer
+add dword [task_ptr], 36 ; adjust to last task pointer
+mov eax, [esi+0] ; gs
+mov gs, ax
+mov eax, [esi+4] ; fs
+mov fs, ax
+mov eax, [esi+8] ; es
+mov es, ax
+mov ebx, [esi+16] ; eip
+mov ecx, [esi+20] ; cs
+mov edx, [esi+24] ; eflags
+; SS:ESP <- return stack
+mov esp, [esi+28] ; esp
+mov eax, [esi+32] ; ss
+mov ss, ax
+mov eax, [esi+12] ; ds
+mov ds, ax
+push edx ; eflags
+push ecx ; cs
+push ebx ; eip
+mov eax, edi ; restore return value
+iret