From 66289aa8ecfa07b20bad424eb9860b196641ef52 Mon Sep 17 00:00:00 2001
From: Brett Weiland <brett_weiland@bpcspace.com>
Date: Fri, 19 Mar 2021 10:54:25 -0500
Subject: first commit

---
 src/bootloader/enter_kernel_backup | 87 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 87 insertions(+)
 create mode 100644 src/bootloader/enter_kernel_backup

(limited to 'src/bootloader/enter_kernel_backup')

diff --git a/src/bootloader/enter_kernel_backup b/src/bootloader/enter_kernel_backup
new file mode 100644
index 0000000..7631f20
--- /dev/null
+++ b/src/bootloader/enter_kernel_backup
@@ -0,0 +1,87 @@
+[extern main]
+[extern _kernel_stack_loc]
+enter_longmode:
+cli
+
+; TODO check if a20 is already set
+mov al, 0x92
+or al, 2
+out 0x92, al
+
+lgdt [protected_gdt.descriptor]
+mov eax, cr0
+or eax, 0x1
+mov cr0, eax
+
+mov eax, 0x8
+mov ds, eax
+
+jmp 0x8:init_longmode
+
+bits 32
+init_longmode:
+mov ebp, 0xffff
+mov esp, ebp
+mov ax, PROTECTED_DATA_SEGMENT
+mov ds, ax
+mov ss, ax
+mov es, ax
+mov fs, ax
+mov gs, ax
+
+mov edi, 0x3000 ; this is where our page tables will be
+mov cr3, edi     
+mov eax, 0      ; what we'll be putting there
+mov ecx, 4096   ; how many times we'll put it there
+rep stosd       ; kinda like memset(&edi, ecx, edi)
+mov edi, cr3
+
+mov DWORD [edi], 0x4003 ; pml4e[0] = pdpe
+add edi, 0x1000
+mov DWORD [edi], 0x5003 ; pdpe[0] = pde
+add edi, 0x1000
+mov DWORD [edi], 0x6003 ; pde[0] = pte
+add edi, 0x1000
+
+mov ebx, 0x00000003 ; the flags
+mov ecx, 512; the loop counter, will map 2 mib
+
+.idmap_pte_loop:
+mov DWORD [edi], ebx
+add ebx, 0x1000 ; physical address. Should leave us at 0x7000
+add edi, 8      ; position in page table
+loop .idmap_pte_loop
+
+mov eax, cr4         
+or eax, 1 << 5     
+mov cr4, eax         
+
+mov ecx, 0xc0000080
+rdmsr
+or eax, 1 << 8
+wrmsr
+
+mov eax, cr0
+or eax, 1 << 31 | 1 << 0 ; this is where we set paging and protected mode (respectively)!
+mov cr0, eax
+
+
+mov ecx, 0xc0000080
+rdmsr
+or eax, 1 << 8
+wrmsr
+
+mov eax, cr0
+or eax, 1 << 31
+mov cr0, eax
+
+lgdt [long_gdt.descriptor]
+
+jmp LONG_CODE_SEGMENT:enter_kernel
+enter_kernel:
+bits 64
+mov rbp, _kernel_stack_loc
+mov rsp, _kernel_stack_loc
+call main ; where we actually call the kernel
+jmp $
+ret
-- 
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