ext/caos-with-snake
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Use xv6 macros for gdt init.

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This commit is contained in:
Alexander Myltsev 2022-11-22 21:43:13 +03:00
parent fb88c62f67
commit 1e326bddc1
3 changed files with 12 additions and 25 deletions
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2
Makefile
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@ -46,7 +46,7 @@ kernel.bin: kernel.o console.o drivers/vga.o drivers/keyboard.o \
$(CC) -m32 -ffreestanding -Wall -Werror -c -g $< -o $@
%.o: %.S
$(AS) --32 -g $^ -o $@
$(CC) -m32 -ffreestanding -c -g $^ -o $@
mbr.bin: mbr.o
$(LD) -m elf_i386 -Ttext=0x7c00 --oformat=binary $^ -o $@

5
cpu/gdt.h
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@ -12,6 +12,11 @@
#define SEG_UDATA 4
#define SEG_TSS 5
#define SEG_ASM(type,base,lim) \
.word (((lim) >> 12) & 0xffff), ((base) & 0xffff); \
.byte (((base) >> 16) & 0xff), (0x90 | (type)), \
(0xC0 | (((lim) >> 28) & 0xf)), (((base) >> 24) & 0xff)
#define USER_BASE 0x400000 // 4 MB
#ifndef __ASSEMBLER__

30
mbr.S
View File

@ -1,3 +1,5 @@
#include "cpu/gdt.h"
.code16
.global _start
_start:
@ -102,12 +104,12 @@ switch_to_32bit:
mov %cr0, %eax
or $1, %eax // 3. enable protected mode
mov %eax, %cr0
ljmp $CODE_SEG, $init_32bit // 4. far jump
ljmp $SEG_KCODE << 3, $init_32bit // 4. far jump
.code32
init_32bit:
mov $DATA_SEG, %ax // 5. update segment registers
mov $SEG_KDATA << 3, %ax // 5. update segment registers
mov %ax, %ds
mov %ax, %ss
mov %ax, %es
@ -155,25 +157,8 @@ sectors_per_track:
.balign 4
gdt_start:
.quad 0x0 // null descriptor
// code segment descriptor
gdt_code:
.word 0xffff // segment length, bits 0-15
.word 0x0 // segment base, bits 0-15
.byte 0x0 // segment base, bits 16-23
.byte 0b10011010 // flags (8 bits)
.byte 0b11001111 // flags (4 bits) + segment length, bits 16-19
.byte 0x0 // segment base, bits 24-31
// data segment descriptor
gdt_data:
.word 0xffff // segment length, bits 0-15
.word 0x0 // segment base, bits 0-15
.byte 0x0 // segment base, bits 16-23
.byte 0b10010010 // flags (8 bits)
.byte 0b11001111 // flags (4 bits) + segment length, bits 16-19
.byte 0x0 // segment base, bits 24-31
SEG_ASM(STA_X|STA_R, 0x0, 0xffffffff) # code seg
SEG_ASM(STA_W, 0x0, 0xffffffff) # data seg
gdt_end:
// GDT descriptor
@ -181,8 +166,5 @@ gdt_descriptor:
.word gdt_end - gdt_start - 1 // size (16 bit)
.int gdt_start // address (32 bit)
.equ CODE_SEG, gdt_code - gdt_start
.equ DATA_SEG, gdt_data - gdt_start
. = _start + 510 # pad to 510 bytes
.byte 0x55, 0xaa # boot sector magic value