; Copyright 2015 Philipp Oppermann
;
; Licensed under the Apache License, Version 2.0 (the "License");
; you may not use this file except in compliance with the License.
; You may obtain a copy of the License at
;
;    http://www.apache.org/licenses/LICENSE-2.0
;
; Unless required by applicable law or agreed to in writing, software
; distributed under the License is distributed on an "AS IS" BASIS,
; WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
; See the License for the specific language governing permissions and
; limitations under the License.

global long_mode_start
extern main

section .text
bits 64
long_mode_start:
    call setup_SSE

    ; call rust main
    call main
    ; print `OKAY` to screen
    mov rax, 0x2f592f412f4b2f4f
    mov qword [0xb8000], rax
    hlt

; Check for SSE and enable it. If it's not supported throw error "a".
setup_SSE:
    ; check for SSE
    mov rax, 0x1
    cpuid
    test edx, 1<<25
    jz .no_SSE

    ; enable SSE
    mov rax, cr0
    and ax, 0xFFFB      ; clear coprocessor emulation CR0.EM
    or ax, 0x2          ; set coprocessor monitoring  CR0.MP
    mov cr0, rax
    mov rax, cr4
    or ax, 3 << 9       ; set CR4.OSFXSR and CR4.OSXMMEXCPT at the same time
    mov cr4, rax

    ret
.no_SSE:
    mov al, "a"
    jmp error

; Prints `ERROR: ` and the given error code to screen and hangs.
; parameter: error code (in ascii) in al
error:
    mov rbx, 0x4f4f4f524f524f45
    mov [0xb8000], rbx
    mov rbx, 0x4f204f204f3a4f52
    mov [0xb8008], rbx
    mov byte [0xb800e], al
    hlt
    jmp error