...

src/boot/boot.asm

@@ -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
+    %define BOOTLOADER_MAGIC    0x36d76289
-    call c_start
+
-    add esp, 8
+    ; 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

src/boot/mem.c

@@ -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;
+    }
+}

src/boot/start.c

@@ -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) {
+void c_start() {
-    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) {
     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);
-    }
 }