1 files changed, 68 insertions, 52 deletions
diff --git a/kernel/asm.s b/kernel/asm.s
index 4abe607..0bf9067 100644
--- a/kernel/asm.s
+++ b/kernel/asm.s
@@ -1,60 +1,76 @@
+global clear_tss
 global switch_to
+global set_tss
+extern cstate
 extern ctask
-extern tss
+extern gdt
+extern save_state
 
+; void switch_to(int n, struct task_struct *task);
 switch_to:
   push ebp
   mov ebp, esp
-  mov eax, [ebp+8]
-  mov [ctask], eax
-  mov esi, [ebp+12]
-  mov ecx, 13
-.loop:
-  lodsd
-  push eax
-  dec ecx
-  jz .end
-  jmp .loop
-.end:
-  mov ax, 0x23
-  mov ds, ax
-  mov es, ax
-  mov fs, ax
-  mov gs, ax
-  popa
-  iret
+  ; abort if we're switching to the current task
+  mov ebx, [ctask]
+  cmp ebx, [ebp+12]
+  jne .skip
+  pop ebp
+  ret
+.skip:
+  ; clear the busy flag in the current TSS
+  mov eax, 0
+  str ax
+  add ax, gdt+5
+  mov byte [eax], 0x89
+  ; set the current TSS to null so it won't be overwritten by the switch
+  mov ax, 0
+  ltr ax
+  ; copy the saved state into the previous TSS
+  call save_state
+  ; update ctask
+  mov ebx, [ebp+12]
+  mov [ctask], ebx
+  ; calculate the task segment index and jump to it
+  mov ebx, [ebp+8]
+  add ebx, 5
+  shl ebx, 3
+  mov [.tmp+4], bx
+  jmp far [.tmp]
+.tmp:
+  dq 0
 
-; uint32_t ss;
-; uint32_t esp;
-; uint32_t eflags;
-; uint32_t cs;
-; uint32_t eip;
-; uint32_t eax;
-; uint32_t ecx;
-; uint32_t edx;
-; uint32_t ebx;
-; uint32_t esp_garbage;
-; uint32_t ebp;
-; uint32_t esi;
-; uint32_t edi;
+; void set_tss(unsigned int n, void *tss);
+set_tss:
+  push ebp
+  mov ebp, esp
+  push ebx
+  mov eax, [ebp+12]
+  mov ebx, [ebp+8]
+  shl ebx, 3
+  add ebx, gdt+40
+  mov [ebx+2], ax
+  shr eax, 16
+  mov [ebx+4], al
+  mov [ebx+7], ah
+  mov eax, 103 ; limit - 1
+  mov [ebx], ax
+  shr eax, 16
+  and al, 0x0F
+  mov [ebx+6], al
+  mov byte [ebx+5], 0x89
+  pop ebx
+  pop ebp
+  ret
 
-; switch_to:
-  ; push ebp
-  ; mov ebp, esp
-  ; cli
-  ; mov ax, 0x23
-  ; mov ds, ax
-  ; mov es, ax
-  ; mov fs, ax
-  ; mov gs, ax
-  ; mov eax, esp
-  ; ; save ESP in the TSS
-  ; mov [tss+4], eax
-  ; push dword 0x23
-  ; push dword 0x00180000
-  ; pushf
-  ; push dword 0x1B
-  ; push dword 0x00100000
-  ; iret
-  ; pop ebp
-  ; ret
+; void clear_tss(unsigned int n);
+clear_tss:
+  push ebp
+  mov ebp, esp
+  push ebx
+  mov ebx, [ebp+8]
+  shl ebx, 3
+  add ebx, gdt+40
+  mov byte [ebx+5], 0
+  pop ebx
+  pop ebp
+  ret