Changed into higher half kernel

https://wiki.osdev.org/Higher_Half_x86_Bare_Bones

kernel/arch/i386/boot.s

@@ -1,38 +1,114 @@
-/* Declare constants for the multiboot header. */
-.set ALIGN,    1<<0             /* align loaded modules on page boundaries */
-.set MEMINFO,  1<<1             /* provide memory map */
-.set MB_FLAGS,    ALIGN | MEMINFO  /* this is the Multiboot 'flag' field */
-.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 */
- 
- /* Multiboot header */
-.section .multiboot
+# Declare constants for the multiboot header
+.set ALIGN,			1<<0					# align loaded modules on page boundaries
+.set MEMINFO,		1<<1					# provide memory map
+.set MB_FLAGS,		ALIGN | MEMINFO			# this is the Multiboot 'flag' field
+.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
+
+# Multiboot header
+.section .multiboot.data, "aw"
 	.align 4
 	.long MB_MAGIC
 	.long MB_FLAGS
 	.long MB_CHECKSUM
- 
- /* Create stack */
-.section .bss
-	.align 16
+
+ # Create stack
+.section .bootstrap_stack, "aw", @nobits
 	stack_bottom:
-	.skip 16384 # 16 KiB
+	.skip 16384		# 16 KiB
 	stack_top:
- 
-/* Entrypoint */
-.section .text
+
+# Preallocate pages
+.section .bss, "aw", @nobits
+	.align 4096
+	boot_page_directory:
+		.skip 4096
+	boot_page_table1:
+		.skip 4096
+
+# Kernel entrypoint
+.section .multiboot.text, "a"
 .global _start
 .type _start, @function
 _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
  
-	/* Call into C code */
+	# Call into C code
 	call kernel_main
  
-	/* Hang if kernel_main returns */
+	# Hang if kernel_main returns
 	cli
 1:	hlt
 	jmp 1b
- 
-.size _start, . - _start

kernel/arch/i386/linker.ld

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

kernel/arch/i386/tty.c

@@ -6,10 +6,9 @@
 #include <stddef.h>
 #include <stdint.h>
 
-
 static const size_t VGA_WIDTH = 80;
 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_col;

kernel/kernel/kernel.cpp

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