fixing up paging issues

2026-06-15 18:09:04 -04:00
parent ac4b510221
commit 25da0f6a71
7 changed files with 101 additions and 85 deletions
--- a/kernel/boot/boot.S
+++ b/kernel/boot/boot.S
@@ -4,18 +4,38 @@
 .set MAGIC,    0x1BADB002       /* 'magic number' lets bootloader find the header */
 .set CHECKSUM, -(MAGIC + FLAGS) /* checksum of above, to prove we are multiboot */

-.section .multiboot
+.section .multiboot, "a"
 .align 4
 .long MAGIC
 .long FLAGS
 .long CHECKSUM

-.section .bss
-.align 4096
-boot_page_directory:
-    .skip 4096
-boot_page_table1:
-    .skip 4096
+.section .text
+.global _start
+_start:
+	cli
+
+	mov $(page_directory - 0xC0000000), %ecx
+
+	mov %cr4, %edx
+    or $0x00000010, %edx
+    mov %edx, %cr4
+
+	mov %ecx, %cr3
+
+	mov %cr0, %edx
+    or $0x80000000, %edx
+    mov %edx, %cr0
+
+	lea higher, %ecx
+    jmp *%ecx
+higher:
+	mov $stack_top, %esp
+	push %ebx
+	push %eax
+	call kmain
+loop:
+	jmp loop

 .section .bss
 .align 16
@@ -23,13 +43,11 @@ stack_bottom:
 .skip 16384 # 16 KiB
 stack_top:

-.section .text
-.global _start
-_start:
-	cli
-	mov $stack_top, %esp
-	push %ebx
-	push %eax
-	call kmain
-loop:
-	jmp loop
+.section .data, "a"
+.align 4096
+.global page_directory
+page_directory:
+	.long 0x00000083
+	.skip 3068
+	.long 0x00000083
+	.skip 1020
--- a/kernel/kmain.c
+++ b/kernel/kmain.c
@@ -18,6 +18,9 @@ extern void enable_interrupts();

 void* page = NULL;

+extern char __kernel_start;
+extern char __kernel_end;
+
 void kmain(uint32_t magic, multiboot_info* mbi)  {
  extern print_stream_t vga_print_stream;
  extern print_stream_t* kout;
@@ -49,16 +52,19 @@ void kmain(uint32_t magic, multiboot_info* mbi)  {
    return;
  }

-  init_mm((void*)mbi->mmap_addr, mbi->mmap_length);
+  init_pmm((void*)mbi->mmap_addr, mbi->mmap_length);
  uint32_t mem_size = total_free_memory();
  kprintf("Total available memory: %d MB\n", mem_size / 1024 / 1024);
  
-  init_paging();
-  enable_paging();
-  kprintf("Paging enabled\n");
+  kprintf("__kernel_start: 0x%x\n", &__kernel_start);
+  kprintf("__kernel_end: 0x%x\n", &__kernel_end);
+  extern uint32_t page_directory[1024];
+  kprintf("page directory: 0x%x\n", &page_directory);
+  uint32_t size = (&__kernel_end - &__kernel_start) / 1024;
+  kprintf("kernel size: %dKB\n", size);

-  // enable_interrupts();
-  // kprintf("Interrupts enabled\n");
+  init_page_tables();
+  kprintf("Page tables reloaded");

  while(1);
 }
--- a/kernel/linker.ld
+++ b/kernel/linker.ld
@@ -1,30 +1,35 @@
 ENTRY(_start)

+KERNEL_VMA = 0xC0000000;
+KERNEL_LMA = 0x00200000;
+
 SECTIONS
 {
-	. = 0xC0100000;
+    . = KERNEL_VMA + KERNEL_LMA;
 	__kernel_start = .;
-
-	.text BLOCK(4K) : ALIGN(4K)
+    .text : AT(ADDR(.text) - KERNEL_VMA)
    {
        *(.multiboot)
-		*(.text)
+        *(.text*)
    }

-	.rodata BLOCK(4K) : ALIGN(4K)
+    .rodata : AT(ADDR(.rodata) - KERNEL_VMA)
    {
-		*(.rodata)
+        *(.rodata*)
    }

-	.data BLOCK(4K) : ALIGN(4K)
+    .data : AT(ADDR(.data) - KERNEL_VMA)
    {
-		*(.data)
+        *(.data*)
    }

-	.bss BLOCK(4K) : ALIGN(4K)
+    .bss : AT(ADDR(.bss) - KERNEL_VMA)
    {
+        __bss_start = .;
+        *(.bss*)
        *(COMMON)
-		*(.bss)
+        __bss_end = .;
    }
+
    __kernel_end = .;
 }
--- a/kernel/memory/mm.c
+++ b/kernel/memory/mm.c
@@ -13,8 +13,6 @@ static uint32_t max_address = 0;
 static uint32_t total_available_memory = 0;
 static uint8_t memory_bitmap[BITMAP_SIZE];

-uint32_t* page_directory;
-
 static void mark_free(uint32_t addr) {
    uint32_t page_index = addr / PAGE_SIZE;
    uint32_t byte_index = page_index / 8;
@@ -56,8 +54,10 @@ static void parse_multiboot_mmap(void* base, uint32_t limit) {
                continue;
            }

+            uint32_t kernel_phys_start = (uint32_t)&__kernel_start - 0xC0000000;
+            uint32_t kernel_phys_end   = (uint32_t)&__kernel_end - 0xC0000000;
            for (uint32_t addr = usable_start; addr < usable_end; addr += 4096) {
-                if (addr <= (uint32_t)&__kernel_end && addr >= (uint32_t)&__kernel_start) {
+                if (addr <= (uint32_t)&kernel_phys_end && addr >= (uint32_t)&kernel_phys_start) {
                    continue;
                }

@@ -78,7 +78,7 @@ static void parse_multiboot_mmap(void* base, uint32_t limit) {
    }
 }

-void init_mm(void* mmap_base, uint32_t mmap_limit) {
+void init_pmm(void* mmap_base, uint32_t mmap_limit) {
    for (int i = 0; i < BITMAP_SIZE; i++) {
        memory_bitmap[i] = 0xFF;
    }
@@ -92,7 +92,8 @@ uint32_t total_free_memory() {
    return total_available_memory;
 }

-void* alloc_page() {
+// this returns the virtual address of the physical page allocated
+void* alloc_phys_page() {
    for (uint32_t i = 0; i < BITMAP_SIZE; i++) {
        uint8_t b = memory_bitmap[i];
        if (b == 0xFF) {
@@ -103,7 +104,7 @@ void* alloc_page() {
            if ((b & (1 << bit)) == 0) {
                uint32_t page_addr = (i * 8 + bit) * PAGE_SIZE;
                mark_used(page_addr);
-                return (void*)page_addr;
+                return (void*)(page_addr + 0xC0000000);
            }
        }
    }
@@ -111,22 +112,19 @@ void* alloc_page() {
    return 0;
 }

-void free_page(void* addr) {
+void free_phys_page(void* addr) {
    mark_free((uint32_t)addr);
 }

-void init_paging() {
-    page_directory = alloc_page();
+extern uint32_t page_directory[1024];
+extern void flush_tlb();
+extern void disable_pae();
+void init_page_tables() {
+    uint32_t* kernel_table = alloc_phys_page();
    for (int i = 0; i < 1024; i++) {
-        page_directory[i] = 0x0; 
+        kernel_table[i] = (i * PAGE_SIZE) | 0x3;
    }
-
-    uint32_t* page_table = alloc_page();
-    page_directory[0] = (uint32_t)(page_table) | 0x3;
-    for (int i = 0; i < 1024; i++) {
-        page_table[i] = (i * PAGE_SIZE) | 0x3;
-    }
-
-    extern void load_page_directory(uint32_t* pd);
-    load_page_directory(page_directory);
+    uint32_t* phys_table = kernel_table - 0xC000000;
+    page_directory[768] = (uint32_t)(phys_table) | 0x3;
+    flush_tlb();
 }
--- a/kernel/memory/mm.h
+++ b/kernel/memory/mm.h
@@ -7,13 +7,12 @@ typedef struct __attribute__((packed)) {
    uint32_t addr;
 } mem_page_t;

-void init_mm(void* mmap_base, uint32_t mmap_limit);
+void init_pmm(void* mmap_base, uint32_t mmap_limit);
 uint32_t total_free_memory();

 void* alloc_page();
 void free_page(void* addr);

-void init_paging();
-void enable_paging();
+void init_page_tables();

 #endif 
--- a/kernel/memory/mm_stubs.S
+++ b/kernel/memory/mm_stubs.S
@@ -1,21 +1,11 @@
 .code32
-.global load_page_directory
-load_page_directory: 
-    push %ebp 
-    mov %esp, %ebp 
-    
-    mov 8(%ebp), %eax
+.global flush_tlb
+flush_tlb:
+    mov %cr3, %eax
    mov %eax, %cr3
-
-    leave 
    ret
     
-.global enable_paging
-enable_paging:
-    mov %eax, %cr0
-    orl $0x80000000, %eax
-    mov %cr0, %eax
-    jmp 1f
-1:
+.global disable_pae
+disable_pae: 
    ret
    
--- a/2
+++ b/2
@@ -16,7 +16,7 @@ LDFLAGS := -T kernel/linker.ld

 all: $(OSNAME).iso

-$(OSNAME).bin: $(OBJECTS)
+$(OSNAME).bin: $(OBJECTS) kernel/linker.ld
 	$(LD) $(LDFLAGS) -o $@ $(OBJECTS)

 $(OSNAME).iso: $(OSNAME).bin grub.cfg