Re-wrote interrupt handling. Now, flush_idt only initializes IDT entries

32-255. A separate routine in the new file traps.s initializes the first
32 entries with addresses pointing to exception handlers within said
file.

Modified the register_isr function to now accept a descriptor privilege
level which it will assign to the modified IDT entry.

Added a task state segment and corresponding entry to the GDT. The TSS
will store the kernel's stack pointer and stack segment when switching
to userspace. NOTE: The stack pointer MUST be saved manually before
switching to userspace!

Added the framework for a system call interface at interrupt vector 0x80
(128).

1 files changed, 227 insertions, 0 deletions

diff --git a/kernel/traps.s b/kernel/traps.s
new file mode 100644
index 0000000..7b7446b
--- /dev/null
+++ b/kernel/traps.s
@@ -0,0 +1,227 @@
+;
+; traps.s provides entry points to the exception handlers
+; as well as the system call interface.
+;
+
+global syscall_init
+global traps_init
+extern idt
+extern register_isr
+extern syscall
+
+%macro SAVE 0
+  pusha
+  ; save the data segment selectors
+  mov ax, ds
+  push ax
+  ; switch to kernel data segments
+  mov ax, 0x10
+  mov ds, ax
+  mov es, ax
+  mov fs, ax
+  mov gs, ax
+%endmacro
+
+%macro SAVE_ERR 0
+  pusha
+  ; fetch the error code that was pushed
+  mov ebx, [esp+32]
+  ; save the data segment selectors
+  mov ax, ds
+  push ax
+  ; switch to kernel data segments
+  mov ax, 0x10
+  mov ds, ax
+  mov es, ax
+  mov fs, ax
+  mov gs, ax
+%endmacro
+
+%macro RESTORE 0
+  ; restore the data segment selectors
+  pop ax
+  mov ds, ax
+  mov es, ax
+  mov fs, ax
+  mov gs, ax
+  popa
+  iret
+%endmacro
+
+%macro RESTORE_ERR 0
+  ; restore the data segment selectors
+  pop ax
+  mov ds, ax
+  mov es, ax
+  mov fs, ax
+  mov gs, ax
+  popa
+  add esp, 4
+  iret
+%endmacro
+
+traps:
+  dd exc_div
+  dd exc_debug
+  dd exc_nmi
+  dd exc_brk
+  dd exc_ovf
+  dd exc_bounds
+  dd exc_invop
+  dd exc_nomath
+  dd exc_dbf
+  dd exc_coseg
+  dd exc_invtss
+  dd exc_segnotpres
+  dd exc_stackf
+  dd exc_gprot
+  dd exc_pagef
+  dd exc_reserved
+  dd exc_mathf
+  dd exc_alignchk
+  dd exc_machinechk
+  dd exc_simdfp
+  dd exc_virt
+  dd exc_reserved
+  dd exc_reserved
+  dd exc_reserved
+  dd exc_reserved
+  dd exc_reserved
+  dd exc_reserved
+  dd exc_reserved
+  dd exc_reserved
+  dd exc_reserved
+  dd exc_reserved
+  dd exc_reserved
+
+traps_init:
+  push ebp
+  mov ebp, esp
+  mov ecx, 0
+  mov edx, idt
+.loop:
+  mov eax, ecx
+  shl eax, 2
+  add eax, traps
+  mov eax, [eax]
+  mov [edx], ax
+  shr eax, 16
+  mov [edx+6], ax
+  mov word [edx+2], 0x08
+  mov byte [edx+4], 0x00
+  mov byte [edx+5], 0x8E
+  inc ecx
+  cmp ecx, 32
+  je .end
+  add edx, 8
+  jmp .loop
+.end:
+  pop ebp
+  ret
+
+exc_div:
+  SAVE
+  RESTORE
+
+exc_debug:
+  SAVE
+  RESTORE
+
+exc_nmi:
+  SAVE
+  RESTORE
+
+exc_brk:
+  SAVE
+  RESTORE
+
+exc_ovf:
+  SAVE
+  RESTORE
+
+exc_bounds:
+  SAVE
+  RESTORE
+
+exc_invop:
+  SAVE
+  RESTORE
+
+exc_nomath:
+  SAVE
+  RESTORE
+
+exc_dbf:
+  SAVE_ERR
+  RESTORE_ERR
+
+exc_coseg:
+  SAVE
+  RESTORE
+
+exc_invtss:
+  SAVE_ERR
+  RESTORE_ERR
+
+exc_segnotpres:
+  SAVE_ERR
+  RESTORE_ERR
+
+exc_stackf:
+  SAVE_ERR
+  RESTORE_ERR
+
+exc_gprot:
+  SAVE_ERR
+  RESTORE_ERR
+
+exc_pagef:
+  SAVE_ERR
+  RESTORE_ERR
+
+exc_mathf:
+  SAVE
+  RESTORE
+
+exc_alignchk:
+  SAVE
+  RESTORE
+
+exc_machinechk:
+  SAVE
+  RESTORE
+
+exc_simdfp:
+  SAVE
+  RESTORE
+
+exc_virt:
+  SAVE
+  RESTORE
+
+exc_reserved:
+  SAVE
+  RESTORE
+
+syscall_handler:
+  SAVE
+
+  ; pass the saved ESP value to the REAL handler
+  mov eax, [esp+46]
+  push eax
+  call syscall
+  add esp, 4
+
+  RESTORE
+
+
+syscall_init:
+  push ebp
+  mov ebp, esp
+  push syscall_handler
+  push dword 3
+  push dword 0x80
+  call register_isr
+  add esp, 12
+  pop ebp
+  ret