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;;
;; Copyright (c) 2025 Ian Marco Moffett and the Osmora Team.
;; All rights reserved.
;;
;; Redistribution and use in source and binary forms, with or without
;; modification, are permitted provided that the following conditions are met:
;;
;; 1. Redistributions of source code must retain the above copyright notice,
;; this list of conditions and the following disclaimer.
;; 2. Redistributions in binary form must reproduce the above copyright
;; notice, this list of conditions and the following disclaimer in the
;; documentation and/or other materials provided with the distribution.
;; 3. Neither the name of Hyra nor the names of its
;; contributors may be used to endorse or promote products derived from
;; this software without specific prior written permission.
;;
;; THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
;; AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
;; IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
;; ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
;; LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
;; CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
;; SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
;; INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
;; CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
;; ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
;; POSSIBILITY OF SUCH DAMAGE.
;;
[bits 16]
[org 0x8000]
%define AP_BUDA 0x9000
%define IA32_EFER 0xC0000080
[bits 16]
_start:
cli
mov al, 0xFF ;; Mask i8259 inputs
out 0x21, al ;; Disable master PIC
out 0xA1, al ;; Disable slave PIC
mov eax, cr4 ;; CR4 -> EAX
or eax, 0xA0 ;; Enable physical address extension + PGE
mov cr4, eax ;; Write it back
mov eax, dword [AP_BUDA] ;; BUDA.CR3 -> EAX
mov cr3, eax ;; EAX -> CR3
mov ecx, IA32_EFER ;; Read IA32_EFER
rdmsr ;; -> EAX
or eax, 0xD00 ;; Set EFER.LME + defaults
wrmsr ;; Write it back
mov eax, cr0 ;; CR0 -> EAX
or eax, 0x80000001 ;; CR0 |= PG/PM
mov cr0, eax ;; Write it back
lgdt [GDTR]
jmp 0x08:thunk64
GDT:
.NULL:
dq 0x0000000000000000 ;; NULL DESCRIPTOR
.CODE: ;; ---------------
dq 0x00209A0000000000 ;; CODE DESCRIPTOR
.DATA: ;; ---------------
dq 0x0000920000000000 ;; DATA DESCRIPTOR
GDTR: ;; ---------------
dw $ - GDT - 1 ;; LIMIT
dq GDT ;; OFFSET
[bits 64]
thunk64:
mov ax, 0x10
mov ds, ax
mov es, ax
mov fs, ax
mov ss, ax
xor ax, ax
mov gs, ax
mov rsp, qword [AP_BUDA + 0x08]
mov rbx, qword [AP_BUDA + 0x10]
mov rax, 1
xchg qword [AP_BUDA + 0x18], rax
cld
jmp rbx
times 4096 - ($ - $$) db 0
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