Changed into higher half kernel

https://wiki.osdev.org/Higher_Half_x86_Bare_Bones
This commit is contained in:
Bananymous 2022-11-13 01:04:10 +02:00
parent e9f029696f
commit fd13f74bbf
4 changed files with 126 additions and 33 deletions

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@ -1,38 +1,114 @@
/* Declare constants for the multiboot header. */ # Declare constants for the multiboot header
.set ALIGN, 1<<0 /* align loaded modules on page boundaries */ .set ALIGN, 1<<0 # align loaded modules on page boundaries
.set MEMINFO, 1<<1 /* provide memory map */ .set MEMINFO, 1<<1 # provide memory map
.set MB_FLAGS, ALIGN | MEMINFO /* this is the Multiboot 'flag' field */ .set MB_FLAGS, ALIGN | MEMINFO # this is the Multiboot 'flag' field
.set MB_MAGIC, 0x1BADB002 /* 'magic number' lets bootloader find the header */ .set MB_MAGIC, 0x1BADB002 # 'magic number' lets bootloader find the header
.set MB_CHECKSUM, -(MB_MAGIC + MB_FLAGS) /* checksum of above, to prove we are multiboot */ .set MB_CHECKSUM, -(MB_MAGIC + MB_FLAGS) #checksum of above, to prove we are multiboot
/* Multiboot header */ # Multiboot header
.section .multiboot .section .multiboot.data, "aw"
.align 4 .align 4
.long MB_MAGIC .long MB_MAGIC
.long MB_FLAGS .long MB_FLAGS
.long MB_CHECKSUM .long MB_CHECKSUM
/* Create stack */ # Create stack
.section .bss .section .bootstrap_stack, "aw", @nobits
.align 16
stack_bottom: stack_bottom:
.skip 16384 # 16 KiB .skip 16384 # 16 KiB
stack_top: stack_top:
/* Entrypoint */ # Preallocate pages
.section .text .section .bss, "aw", @nobits
.align 4096
boot_page_directory:
.skip 4096
boot_page_table1:
.skip 4096
# Kernel entrypoint
.section .multiboot.text, "a"
.global _start .global _start
.type _start, @function .type _start, @function
_start: _start:
/* Setup stack */ # Physical address of boot_page_table1
movl $(boot_page_table1 - 0xC0000000), %edi
# First address to map is 0
movl $0, %esi
# Map 1023 pages, 1024th will be VGA memory
movl $1023, %ecx
1:
# Only map the kernel
cmpl $_kernel_start, %esi
jl 2f
cmpl $(_kernel_end - 0xC0000000), %esi
jge 3f
# Map physical address as "present, writable"
# Note that this maps .text and .rodata as writable. Mind security and map them as non-writable.
movl %esi, %edx
orl $0x003, %edx
movl %edx, (%edi)
2:
# Size of page is 4096 bytes
addl $4096, %esi
# Size of entry in boot_page_table1 is 4 bytes
addl $4, %edi
# Loop to next entry if we haven't finished
loop 1b
3:
# Map VGA memory to 0xC03FF000 as "present, writable"
movl $(0x000B8000 | 0x003), boot_page_table1 - 0xC0000000 + 1023 * 4
# The page table is used at both page directory entry 0 (virtually from 0x0
# to 0x3FFFFF) (thus identity mapping the kernel) and page directory entry
# 768 (virtually from 0xC0000000 to 0xC03FFFFF) (thus mapping it in the
# higher half). The kernel is identity mapped because enabling paging does
# not change the next instruction, which continues to be physical. The CPU
# would instead page fault if there was no identity mapping.
# Map the page table to virtual addresses 0x00000000 and 0xC0000000
movl $(boot_page_table1 - 0xC0000000 + 0x003), boot_page_directory - 0xC0000000 + 0
movl $(boot_page_table1 - 0xC0000000 + 0x003), boot_page_directory - 0xC0000000 + 768 * 4
# Set cr3 to the address of the boot_page_directory
movl $(boot_page_directory - 0xC0000000), %ecx
movl %ecx, %cr3
# Enable paging and the write-protect bit
movl %cr0, %ecx
orl $0x80010000, %ecx
movl %ecx, %cr0
# Jump to higher half with an absolute jump
lea 4f, %ecx
jmp *%ecx
.section .text
4:
# Now paging is fully set up and enabled
# Unmap the identity mapping since it is not unnecessary
movl $0, boot_page_directory + 0
# Reload crc3 to force a TLB flush for the changes to take effect
movl %cr3, %ecx
movl %ecx, %cr3
# Setup stack
mov $stack_top, %esp mov $stack_top, %esp
/* Call into C code */ # Call into C code
call kernel_main call kernel_main
/* Hang if kernel_main returns */ # Hang if kernel_main returns
cli cli
1: hlt 1: hlt
jmp 1b jmp 1b
.size _start, . - _start

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@ -2,27 +2,37 @@ ENTRY(_start)
SECTIONS SECTIONS
{ {
. = 1M; . = 0x00100000;
.text BLOCK(4K) : ALIGN(4K) _kernel_start = .;
{ .multiboot.data : {
*(.multiboot) *(.multiboot.data)
*(.text)
} }
.rodata BLOCK(4K) : ALIGN(4K) .multiboot.text : {
*(.multiboot.text)
}
. += 0xC0000000;
.text ALIGN(4K) : AT(ADDR(.text) - 0xC0000000)
{
*(.text)
}
.rodata ALIGN(4K) : AT(ADDR(.rodata) - 0xC0000000)
{ {
*(.rodata) *(.rodata)
} }
.data ALIGN(4K) : AT(ADDR(.data) - 0xC0000000)
.data BLOCK(4K) : ALIGN(4K)
{ {
*(.data) *(.data)
} }
.bss ALIGN(4K) : AT(ADDR(.bss) - 0xC0000000)
.bss BLOCK(4K) : ALIGN(4K)
{ {
*(COMMON) *(COMMON)
*(.bss) *(.bss)
*(.bootstrap_stack)
} }
_kernel_end = .;
} }

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@ -6,10 +6,9 @@
#include <stddef.h> #include <stddef.h>
#include <stdint.h> #include <stdint.h>
static const size_t VGA_WIDTH = 80; static const size_t VGA_WIDTH = 80;
static const size_t VGA_HEIGHT = 25; static const size_t VGA_HEIGHT = 25;
static uint16_t* const VGA_MEMORY = (uint16_t*)0xB8000; static uint16_t* const VGA_MEMORY = (uint16_t*)0xC03FF000;
static size_t terminal_row; static size_t terminal_row;
static size_t terminal_col; static size_t terminal_col;

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@ -1,10 +1,18 @@
#include <kernel/tty.h> #include <kernel/tty.h>
#include <stdio.h> #include <stdio.h>
#include <stdint.h>
extern "C" extern "C"
void kernel_main() void kernel_main()
{ {
terminal_initialize(); terminal_initialize();
printf("Hello from the kernel!\n"); printf("Hello from the kernel!\n");
printf("%p\n", kernel_main);
int a = 10;
printf("%p\n", &a);
} }