Bare bones.

2 files changed, 195 insertions, 0 deletions

diff --git a/kernel/l0/kmain.c b/kernel/l0/kmain.c
new file mode 100644
index 0000000..9139856
--- /dev/null
+++ b/kernel/l0/kmain.c
@@ -0,0 +1,126 @@
+#if !defined(__cplusplus)
+#include <stdbool.h> /* C doesn't have booleans by default. */
+#endif
+#include <stddef.h>
+#include <stdint.h>
+ 
+/* Check if the compiler thinks if we are targeting the wrong operating system. */
+#if defined(__linux__)
+#error "You are not using a cross-compiler, you will most certainly run into trouble"
+#endif
+ 
+/* This tutorial will only work for the 32-bit ix86 targets. */
+#if !defined(__i386__)
+#error "This tutorial needs to be compiled with a ix86-elf compiler"
+#endif
+
+#include "multiboot.h"
+ 
+extern void k_highhalf_addr;
+
+/* Hardware text mode color constants. */
+enum vga_color
+{
+	COLOR_BLACK = 0,
+	COLOR_BLUE = 1,
+	COLOR_GREEN = 2,
+	COLOR_CYAN = 3,
+	COLOR_RED = 4,
+	COLOR_MAGENTA = 5,
+	COLOR_BROWN = 6,
+	COLOR_LIGHT_GREY = 7,
+	COLOR_DARK_GREY = 8,
+	COLOR_LIGHT_BLUE = 9,
+	COLOR_LIGHT_GREEN = 10,
+	COLOR_LIGHT_CYAN = 11,
+	COLOR_LIGHT_RED = 12,
+	COLOR_LIGHT_MAGENTA = 13,
+	COLOR_LIGHT_BROWN = 14,
+	COLOR_WHITE = 15,
+};
+ 
+uint8_t make_color(enum vga_color fg, enum vga_color bg)
+{
+	return fg | bg << 4;
+}
+ 
+uint16_t make_vgaentry(char c, uint8_t color)
+{
+	uint16_t c16 = c;
+	uint16_t color16 = color;
+	return c16 | color16 << 8;
+}
+ 
+size_t strlen(const char* str)
+{
+	size_t ret = 0;
+	while ( str[ret] != 0 )
+		ret++;
+	return ret;
+}
+ 
+static const size_t VGA_WIDTH = 80;
+static const size_t VGA_HEIGHT = 25;
+ 
+size_t terminal_row;
+size_t terminal_column;
+uint8_t terminal_color;
+uint16_t* terminal_buffer;
+ 
+void terminal_initialize()
+{
+	terminal_row = 0;
+	terminal_column = 0;
+	terminal_color = make_color(COLOR_LIGHT_GREY, COLOR_BLACK);
+	terminal_buffer = (uint16_t*) (&k_highhalf_addr + 0xB8000);
+	for ( size_t y = 0; y < VGA_HEIGHT; y++ )
+	{
+		for ( size_t x = 0; x < VGA_WIDTH; x++ )
+		{
+			const size_t index = y * VGA_WIDTH + x;
+			terminal_buffer[index] = make_vgaentry(' ', terminal_color);
+		}
+	}
+}
+ 
+void terminal_setcolor(uint8_t color)
+{
+	terminal_color = color;
+}
+ 
+void terminal_putentryat(char c, uint8_t color, size_t x, size_t y)
+{
+	const size_t index = y * VGA_WIDTH + x;
+	terminal_buffer[index] = make_vgaentry(c, color);
+}
+ 
+void terminal_putchar(char c)
+{
+	terminal_putentryat(c, terminal_color, terminal_column, terminal_row);
+	if ( ++terminal_column == VGA_WIDTH )
+	{
+		terminal_column = 0;
+		if ( ++terminal_row == VGA_HEIGHT )
+		{
+			terminal_row = 0;
+		}
+	}
+}
+ 
+void terminal_writestring(const char* data)
+{
+	size_t datalen = strlen(data);
+	for ( size_t i = 0; i < datalen; i++ )
+		terminal_putchar(data[i]);
+}
+ 
+#if defined(__cplusplus)
+extern "C" /* Use C linkage for kernel_main. */
+#endif
+void kmain(struct multiboot_info_t *mbd, int32_t mb_magic)
+{
+	terminal_initialize();
+	/* Since there is no support for newlines in terminal_putchar yet, \n will
+	   produce some VGA specific character instead. This is normal. */
+	terminal_writestring("Hello, kernel World!\n");
+}
diff --git a/kernel/l0/loader.s b/kernel/l0/loader.s
new file mode 100644
index 0000000..a31fcf5
--- /dev/null
+++ b/kernel/l0/loader.s
@@ -0,0 +1,69 @@
+[EXTERN k_highhalf_addr]
+
+[GLOBAL loader]           ; making entry point visible to linker
+
+[EXTERN kmain]            ; kmain is defined in kmain.c
+
+; loader stack size
+LOADER_STACK_SIZE	equ		0x8000		; 8Kb
+
+; setting up the Multiboot header - see GRUB docs for details
+MODULEALIGN equ  1<<0                   ; align loaded modules on page boundaries
+MEMINFO     equ  1<<1                   ; provide memory map
+FLAGS       equ  MODULEALIGN | MEMINFO  ; this is the Multiboot 'flag' field
+MAGIC       equ    0x1BADB002           ; 'magic number' lets bootloader find the header
+CHECKSUM    equ -(MAGIC + FLAGS)        ; checksum required
+ 
+section .text
+align 4
+MultiBootHeader:
+   dd MAGIC
+   dd FLAGS
+   dd CHECKSUM
+ 
+section .setup
+loader:		;here, we load our false GDT, used for having the kernel in higher half
+	lgdt [trickgdt]
+	mov cx, 0x10;
+	mov ds, cx;
+	mov es, cx;
+	mov fs, cx;
+	mov gs, cx;
+	mov ss, cx;
+
+	jmp 0x08:higherhalf
+
+section .text
+higherhalf:		; now we're running in higher half
+   mov esp, stack_top                 ; set up the stack
+
+   push eax                           ; pass Multiboot magic number
+   add ebx, k_highhalf_addr			  ; update the MB info structure so that it is in the new seg
+   push ebx                           ; pass Multiboot info structure
+
+   call  kmain                       ; call kernel proper
+
+   cli		; disable interupts
+
+hang:
+   hlt                                ; halt machine should kernel return
+   jmp   hang
+
+[section .setup]	; this is included in the .setup section, so that it thinks it is at 0x00100000
+
+trickgdt:		; our false GDT
+   dw gdt_end - gdt - 1		; gdt limit
+   dd gdt					; gdt base
+
+gdt:
+   dd 0, 0					; null GDT entry
+   db 0xFF, 0xFF, 0, 0, 0, 10011010b, 11001111b, 0x40	; kernel code segment
+   db 0xFF, 0xFF, 0, 0, 0, 10010010b, 11001111b, 0x40	; kernel data segment
+
+gdt_end:
+
+[section .bss]
+align 4
+stack_bottom:
+	resb LOADER_STACK_SIZE
+stack_top: