nub31/nub-os-2
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nub31
2025-12-30 02:54:54 +01:00
parent 8340de0ad1
commit cd31762fb0
3 changed files with 141 additions and 72 deletions
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85
src/boot/boot.asm
View File

@@ -1,5 +1,4 @@
global _start
extern c_start
%define MAGIC 0xe85250d6
%define ARCH 0x0
@@ -19,6 +18,10 @@ header:
dd 8
.end:
section .data
align 8
multiboot_info: dd 0
section .bss
align 4096
stack:
@@ -26,13 +29,85 @@ stack:
resb 1024 * 16
.top:
align 4096
pml4t: resb 4096
pdpt: resb 4096
pdt: resb 4096
pt: resb 4096
section .text
_start:
mov esp, stack.top
push ebx
push eax
call c_start
add esp, 8
%define BOOTLOADER_MAGIC 0x36d76289
; Make sure we booted with multiboot 2
cmp eax, BOOTLOADER_MAGIC
jne .halt
; Save pointer to info gathered by multiboot
mov [multiboot_info], ebx
; Tell the cpu where the pages area
mov edi, pml4t
mov cr3, edi
%define PT_PRESENT 1
%define PT_READABLE 2
; pml4t[0] -> pdpt
mov edi, pdpt
or edi, PT_PRESENT | PT_READABLE
mov [pml4t], edi
; pdpt[0] -> pdt
mov edi, pdt
or edi, PT_PRESENT | PT_READABLE
mov [pdpt], edi
; pdt[0] -> pt
mov edi, pt
or edi, PT_PRESENT | PT_READABLE
mov [pdt], edi
%define ENTRIES_PER_PT 512
%define SIZEOF_PT_ENTRY 8
%define PAGE_SIZE 0x1000
%define START_ADDRESS 0x0
; Identity map first 2mb of memory
mov edi, pt
mov ebx, START_ADDRESS | PT_PRESENT | PT_READABLE
mov ecx, ENTRIES_PER_PT
.set_pt_entry:
mov [edi], ebx
add ebx, PAGE_SIZE
add edi, SIZEOF_PT_ENTRY
loop .set_pt_entry
%define CR4_PAE_ENABLE 1 << 5
; Enable pae
mov eax, cr4
or eax, CR4_PAE_ENABLE
mov cr4, eax
%define EFER_MSR 0xc0000080
%define EFER_LM_ENABLE 1 << 8
; Switch to compatibility mode
mov ecx, EFER_MSR
rdmsr
or eax, EFER_LM_ENABLE
wrmsr
%define CR0_PG_ENABLE 1 << 31
; Enable paging
mov eax, cr0
or eax, CR0_PG_ENABLE
mov cr0, eax
.halt:
cli
hlt

60
src/boot/mem.c Normal file
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@@ -0,0 +1,60 @@
#include <def.h>
#include "console.h"
#include "multiboot2.h"
#include "panic.h"
#include "util.h"
static void *multiboot_find_tag(uptr multiboot_info, u32 type) {
uptr next = multiboot_info + 8;
while (true) {
multiboot_tag *tag = (multiboot_tag*)next;
if (tag->type == MULTIBOOT_TAG_TYPE_END) {
return NULL;
}
if (tag->type == type) {
return tag;
}
next = align(next + tag->size, MULTIBOOT_TAG_ALIGN);
}
}
#define MAX_REGIONS 64
typedef struct {
u64 base_address;
u64 length;
} region;
extern uptr kernel_start;
extern uptr kernel_end;
static region regions[MAX_REGIONS] = {0};
static size_t region_count = 0;
static void find_memory_regions(uptr multiboot_info) {
multiboot_tag_mmap *tag = multiboot_find_tag(multiboot_info, MULTIBOOT_TAG_TYPE_MMAP);
if (tag == NULL) {
boot_panic("Multiboot did not provide mmap tag");
}
u32 entry_count = (tag->size - 16) / tag->entry_size;
u8 *entry_ptr = (u8*)tag->entries;
for (u32 i = 0; i < entry_count; ++i) {
multiboot_mmap_entry *entry = (multiboot_mmap_entry*)entry_ptr;
if (entry->type == MULTIBOOT_MEMORY_AVAILABLE) {
if (region_count >= MAX_REGIONS) {
boot_panic("Too many memory regions");
}
regions[region_count++] = (region){ entry->base_address, entry->length };
}
entry_ptr += tag->entry_size;
}
}

68
src/boot/start.c
View File

@@ -2,73 +2,7 @@
#include "console.h"
#include "multiboot2.h"
#include "panic.h"
#include "util.h"
static void *multiboot_find_tag(uptr multiboot_info, u32 type) {
uptr next = multiboot_info + 8;
while (true) {
multiboot_tag *tag = (multiboot_tag*)next;
if (tag->type == MULTIBOOT_TAG_TYPE_END) {
return NULL;
}
if (tag->type == type) {
return tag;
}
next = align(next + tag->size, MULTIBOOT_TAG_ALIGN);
}
}
#define MAX_REGIONS 64
typedef struct {
u64 base_address;
u64 length;
} region;
extern uptr kernel_start;
extern uptr kernel_end;
static region regions[MAX_REGIONS] = {0};
static size_t region_count = 0;
static void find_memory_regions(uptr multiboot_info) {
multiboot_tag_mmap *tag = multiboot_find_tag(multiboot_info, MULTIBOOT_TAG_TYPE_MMAP);
if (tag == NULL) {
boot_panic("Multiboot did not provide mmap tag");
}
u32 entry_count = (tag->size - 16) / tag->entry_size;
u8 *entry_ptr = (u8*)tag->entries;
for (u32 i = 0; i < entry_count; ++i) {
multiboot_mmap_entry *entry = (multiboot_mmap_entry*)entry_ptr;
if (entry->type == MULTIBOOT_MEMORY_AVAILABLE) {
if (region_count >= MAX_REGIONS) {
boot_panic("Too many memory regions");
}
regions[region_count++] = (region){ entry->base_address, entry->length };
}
entry_ptr += tag->entry_size;
}
}
void c_start(u32 magic, uptr multiboot_info) {
void c_start() {
console_clear();
if (magic != MULTIBOOT_BOOTLOADER_MAGIC) {
boot_panic("Expected bootloader magic 0x%x, got 0x%x", MULTIBOOT_BOOTLOADER_MAGIC, magic);
}
find_memory_regions(multiboot_info);
for (size_t i = 0; i < region_count; i++) {
kprintf("Memory region %d: base=0x%X, length=0x%X\n", i, regions[i].base_address, regions[i].length);
}
}