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banan-os
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Kernel: We now identity map full GiB in boot.S 

The paging structure is pre-built so no unnecessary calculations are done
This commit is contained in:
Bananymous 2023-05-30 00:08:52 +03:00
parent 3b9d60d7cb
commit 265fe9c62e
1 changed files with 25 additions and 28 deletions
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41
kernel/arch/x86_64/boot.S
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@ -37,19 +37,6 @@
g_kernel_cmdline:
.skip 4096
# Reserve memory for paging structures,
# we will identity map first 4 MiB
# 0 MiB -> 1 MiB: bootloader stuff
# 1 MiB -> : kernel
.align 4096
boot_pml4:
.skip 512 * 8
boot_pdpt1:
.skip 512 * 8
boot_pd1:
.skip 512 * 8
.global g_multiboot_info
g_multiboot_info:
.skip 8
@ -59,6 +46,25 @@ g_multiboot_magic:
.section .text
# Identity map first GiB
.align 4096
boot_pml4:
.quad boot_pdpt + (PG_READ_WRITE | PG_PRESENT)
.rept 511
.quad 0
.endr
boot_pdpt:
.quad boot_pd + (PG_READ_WRITE | PG_PRESENT)
.rept 511
.quad 0
.endr
boot_pd:
.set i, 0
.rept 512
.quad i + (PG_PAGE_SIZE | PG_READ_WRITE | PG_PRESENT)
.set i, i + 0x00200000
.endr
boot_gdt:
.quad 0x0000000000000000 # null descriptor
.quad 0x00AF9A000000FFFF # kernel code
@ -125,15 +131,6 @@ enable_sse:
ret
initialize_paging:
# identity map first 6 MiB
movl $(0x00000000 + PG_PAGE_SIZE + PG_READ_WRITE + PG_PRESENT), boot_pd1 + 0
movl $(0x00200000 + PG_PAGE_SIZE + PG_READ_WRITE + PG_PRESENT), boot_pd1 + 8
movl $(0x00400000 + PG_PAGE_SIZE + PG_READ_WRITE + PG_PRESENT), boot_pd1 + 16
# set pdpte1 and pml4e1
movl $(boot_pd1 + PG_READ_WRITE + PG_PRESENT), boot_pdpt1
movl $(boot_pdpt1 + PG_READ_WRITE + PG_PRESENT), boot_pml4
# enable PAE
movl %cr4, %ecx
orl $0x20, %ecx