Fixed some Task stuff, added DOSFS filesystem

task.nasm

@@ -1,12 +1,16 @@
 task_ptr: equ (0x310000-4)
 
+; return address in EAX
+; return stack in ECX
+; we can modify EAX, ECX, EDX
+; i.e. save all others in task
 global save_current_task
 save_current_task:
-push ebx
-mov ebx, esp
+push edx
+mov edx, esp ; EDX holds our tmp stack, unsaved
 mov esp, dword [task_ptr] ; load current task pointer
 push ss
-push ebp ; return stack
+push ecx ; return stack
 pushfd
 push cs
 push eax ; return address
@@ -14,33 +18,41 @@ push ds ; other segs, pop
 push es ; before iret
 push fs ; in exit handler
 push gs
+push ebp ; saved
+push ebx ; saved
+push esi ; saved
+push edi ; saved
 mov dword [task_ptr], esp ; save new task pointer
-mov esp, ebx
-pop ebx
+mov esp, edx
+pop edx
 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 ecx, eax ; save return value for later
+mov edx, dword [task_ptr] ; load current task pointer
+add dword [task_ptr], 52 ; adjust to last task pointer
+mov edi, [edx+0]
+mov esi, [edx+4]
+mov ebx, [edx+8]
+mov ebp, [edx+12]
+mov eax, [edx+0+16] ; gs
 mov gs, ax
-mov eax, [esi+4] ; fs
+mov eax, [edx+4+16] ; fs
 mov fs, ax
-mov eax, [esi+8] ; es
+mov eax, [edx+8+16] ; 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 esp, [edx+28+16] ; esp
+mov eax, [edx+32+16] ; ss
 mov ss, ax
-mov eax, [esi+12] ; ds
+mov eax, [edx+24+16] ; eflags
+push eax
+mov eax, [edx+20+16] ; cs
+push eax
+mov eax, [edx+16+16] ; eip
+push eax
+mov eax, [edx+12+16] ; ds
 mov ds, ax
-push edx ; eflags
-push ecx ; cs
-push ebx ; eip
-mov eax, edi ; restore return value
+mov eax, ecx ; restore return value
 iret