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kstart.S: remove leftovers from the 64-bit version.

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This commit is contained in:
Alexander Myltsev 2025-01-18 01:11:31 +04:00
parent e1bcd70747
commit 5a05c48afc
1 changed files with 8 additions and 40 deletions
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48
kernel/kstart.S
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@ -12,36 +12,22 @@
.global _start
.asciz "kernel start\n"
_start:
.code32
mov dword ptr [patch_addr - KERNBASE], offset gdt32_begin - KERNBASE
lgdt gdtr32 - KERNBASE
// zero our PD at 0x1000 and PT at 0x2000
// zero out PD at 0x1000
xor eax, eax
mov ecx, 2048
mov ecx, 1024
rep stosd
// Set up the page table for the lowest 4 MiB: PD[0] -> PT
mov dword ptr [0x1000], 0x2000 | 0x3
// KERNBASE = 0x8000_0000
// Use the same page table for the first 4 MiB after KERNBASE: PD[0x200] -> PT
mov dword ptr [0x1000 + ((KERNBASE >> 22) * 4)], 0x2000 | 0x3
// Enable 4 MiB pages
mov eax, cr4
or eax, 0x10 // Set the PSE bit (bit 4)
mov cr4, eax
// Identity map the first 2 MiB
mov edi, 0x2000 // Start of the PT
mov ebx, 0x00000003 // Present, R/W
mov ecx, 512 // 2 MiB / 4 KiB = 512
SetEntry:
mov dword ptr [edi], ebx
add ebx, 0x1000
add edi, 4
loop SetEntry
// Identity map low 4 MiB
mov dword ptr [0x1000], 0 | PTE_P | PTE_W | PTE_PS
// KERNBASE = 0x8000_0000
// Same mapping for the first 4 MiB after KERNBASE
mov dword ptr [0x1000 + ((KERNBASE >> 22) * 4)], 0 | PTE_P | PTE_W | PTE_PS
// Load physical address of PD into CR3
mov edi, 0x1000
@ -52,25 +38,7 @@ SetEntry:
or eax, 1 << 31 // Set the PG bit
mov cr0, eax
.att_syntax
jmp $0x8, $loadseg - KERNBASE
.intel_syntax noprefix
loadseg:
// jump to the high half
add esp, KERNBASE
lea eax, kmain
jmp eax
.align 16
gdtr32:
.word gdt32_end - gdt32_begin - 1
patch_addr:
.long gdt32_begin - KERNBASE
.align 16
gdt32_begin:
.long 0x00000000, 0x00000000 # Null descriptor
.long 0x0000ffff, 0x00cf9a00 # Code segment
.long 0x0000ffff, 0x00cf9200 # Data segment
gdt32_end: