[feature] higher half kernel

boot/loader.asm

@@ -5,41 +5,79 @@
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 
 [BITS 32]
-[global loader]
-[extern kernel_main] ; comes from kernel.c
-[extern end_of_kernel] ; comes from linker.ld
+global loader                           ; the entry point for the linker
 
+extern kernel_main                            ; kmain is defined in kmain.c
+extern end_of_kernel
 
-; Setting up multibootheaders for GRUB
-MODULEALIGN equ 1<<0 ; align loaded modules on page boundary
+; setting up the multiboot headers for GRUB
+MODULEALIGN equ 1<<0                    ; align loaded modules on page 
+                                        ; boundaries
+MEMINFO     equ 1<<1                    ; provide memory map
+FLAGS       equ MODULEALIGN | MEMINFO   ; the multiboot flag field
+MAGIC       equ 0x1BADB002              ; magic number for bootloader to 
+                                        ; find the header
+CHECKSUM    equ -(MAGIC + FLAGS)        ; checksum required
 
-MEMINFO equ 1<<1 ; provide memory map
-FLAGS equ MODULEALIGN | MEMINFO
-MAGIC equ 0x1BADB002
+; paging for the kernel
+KERNEL_VIRTUAL_BASE     equ 0xC0000000                  ; we start at 3GB
+KERNEL_PAGE_IDX         equ (KERNEL_VIRTUAL_BASE >> 22) ; PDT index for 4MB PDE
 
-CHECKSUM equ -(MAGIC + FLAGS) ; checksum required
+; the page directory used to boot the kernel into the higher half
+section .data
+align 4096                               ; align on 4kB blocks
+boot_page_directory:
+    dd 00000000000000000000000010001011b ; identity mapped first 4MB
+    times (KERNEL_PAGE_IDX-1) dd 0       ; no pages here
+    dd 00000000000000000000000010001011b ; map 0xC0000000 to the first 4MB
+    times (1024-KERNEL_PAGE_IDX-1) dd 0  ; no more pages
 
-section .text
 
+section .text
 align 4
     dd MAGIC
     dd FLAGS
     dd CHECKSUM
 
+; the entry point, called by GRUB
 loader:
-    mov esp, stack+STACKSIZE ; set up the stack pointer
-    push end_of_kernel
-    push eax ; eax holds the MAGIC number
-    push ebx ; ebx holds the Multiboot info
+    mov ecx, (boot_page_directory-KERNEL_VIRTUAL_BASE)
+    and ecx, 0xFFFFF000     ; we only care about the upper 20 bits
+    or  ecx, 0x08           ; PWT, enable page write through?
+    mov cr3, ecx            ; load pdt
+
+    mov ecx, cr4            ; read current config from cr4
+    or  ecx, 0x00000010     ; set bit enabling 4MB pages
+    mov cr4, ecx            ; enable it by writing to cr4
 
-    call kernel_main
+    mov	ecx, cr0		    ; read current config from cr0
+	or	ecx, 0x80000000	    ; the highest bit controls paging
+	mov cr0, ecx		    ; enable paging by writing config to cr0
+
+    lea ecx, [higher_half]  ; store the address higher_half in ecx
+    jmp ecx                 ; now we jump into 0xC0100000
+
+; code executing from here on uses the page table, and is accessed through
+; the upper half, 0xC0100000
+higher_half:
+    mov     DWORD [boot_page_directory], 0  ; erase identity mapping of kernel
+    invlpg  [0]                             ; and flush any tlb-references to it
+
+    mov esp, stack+STACKSIZE            ; sets up the stack pointer
+    push end_of_kernel
+    push eax                            ; eax contains the MAGIC number
+    push ebx                            ; ebx contains the multiboot data 
+                                        ; structure
+    call kernel_main                          ; call the main function of the kernel
 
 hang:
-    jmp hang ; loop forever
+    jmp hang                            ; loop forever
 
-; reserving initial stack size
-STACKSIZE equ 0x4000 ; 16kB
+; reserve initial stack space
+STACKSIZE equ 0x4000                    ; 16kB
 
+section .bss
 align 4
 stack:
-    resb STACKSIZE ; reserve memory for stack on doubleworded memory
+    resb STACKSIZE                      ; reserve memory for stack on 
+                                        ; doubleworded memory

kernel/include/common.h

@@ -0,0 +1,7 @@
+#ifndef _COMMON_H_
+#define _COMMON_H_
+
+#define UNUSED_ARGUMENT(x) (void)x;
+#define KERNEL_BASE_ADDR 0xC0000000
+
+#endif

kernel/include/kernel.h

@@ -3,6 +3,7 @@
 
 #include "multiboot_util.h"
 #include "system.h"
+#include "common.h"
 #include "../libc/include/stdio.h"
 #include "tty.h"
 #include "qemu_debug.h"
@@ -19,6 +20,6 @@
 #include "../../gui/render_image.h"
 #include "options.h"
 
-void kernel_main(multiboot_info_t *, uint32_t, uint32_t);
+void kernel_main(uint32_t, uint32_t, uint32_t);
 
 #endif

kernel/include/multiboot_util.h

@@ -3,11 +3,13 @@
 
 #include <stdbool.h>
 #include "multiboot.h"
+#include "common.h"
 #include "../libc/include/stdio.h"
 #include "qemu_debug.h"
 #include "panic.h"
 
 void display_memory_info(multiboot_info_t *, uint32_t);
 void check_mboot_bootloader_magic(uint32_t);
+multiboot_info_t *remap_multiboot_info(uint32_t);
 
 #endif

kernel/include/tty.h

@@ -5,10 +5,11 @@
 #include "../libc/include/stdio.h"
 #include "qemu_debug.h"
 #include "config.h"
+#include "common.h"
 #include <stddef.h>
 #include <stdint.h>
 
-#define VIDEO_MEM_ADDRESS 0xB8000
+#define VIDEO_MEM_ADDRESS 0xB8000 + KERNEL_BASE_ADDR
 #define VGA_WIDTH 80
 #define VGA_HEIGHT 25
 

kernel/src/kernel.c

@@ -5,9 +5,9 @@ void test_idt()
 	__asm__("int $0x04");
 }
 
-void kernel_main(multiboot_info_t *mbinfo, uint32_t mbmagic,
-		 uint32_t end_of_kernel)
+void kernel_main(uint32_t mbaddr, uint32_t mbmagic, uint32_t end_of_kernel)
 {
+	multiboot_info_t *mbinfo = remap_multiboot_info(mbaddr);
 	terminal_init();
 	gdt_init();
 	idt_init();
@@ -24,7 +24,7 @@ void kernel_main(multiboot_info_t *mbinfo, uint32_t mbmagic,
 	keyboard_init();
 	check_mboot_bootloader_magic(mbmagic);
 	display_memory_info(mbinfo, end_of_kernel);
-	paging_init(end_of_kernel);
+	//paging_init(end_of_kernel);
 
 #if TEST_IDT
 	test_idt();

kernel/src/multiboot_util.c

@@ -1,5 +1,15 @@
 #include "../include/multiboot_util.h"
 
+multiboot_info_t *remap_multiboot_info(uint32_t mbinfo_addr)
+{
+	multiboot_info_t *mbinfo =
+		(multiboot_info_t *)(mbinfo_addr + KERNEL_BASE_ADDR);
+
+	mbinfo->mmap_addr += KERNEL_BASE_ADDR;
+
+	return mbinfo;
+}
+
 void display_memory_info(multiboot_info_t *mbinfo, uint32_t end_of_kernel)
 {
 	qemu_write_string("\n%s %s START\n", DEBUG_OUTPUT, MEMORY_OUTPUT);

linker.ld

@@ -2,31 +2,27 @@ ENTRY(loader)
 
 SECTIONS
 {
-    . = 0x00100000;
+    . = 0xC0100000;
 
-    .text ALIGN (0x1000) :
+    .text ALIGN (0x1000) : AT(ADDR(.text)-0xC0000000)
     {
         *(.text)
     }
 
-    .rodata ALIGN (0x1000) :
+    .rodata ALIGN (0x1000) : AT(ADDR(.rodata)-0xC0000000)
     {
         *(.rodata*)
     }
 
-    .data ALIGN (0x1000) :
+    .data ALIGN (0x1000) : AT(ADDR(.data)-0xC0000000)
     {
         *(.data)
     }
 
-    .bss :
+    .bss : AT(ADDR(.bss)-0xC0000000)
     {
         *(COMMON)
         *(.bss)
-    }
-
-    . :
-    {
-        end_of_kernel = ALIGN(0x1000);
+        end_of_kernel = .;
     }
 }