initial commit

5 files changed, 261 insertions, 0 deletions

diff --git a/kernel/Makefile b/kernel/Makefile
new file mode 100644
index 0000000..cc03386
--- /dev/null
+++ b/kernel/Makefile
@@ -0,0 +1,16 @@
+all: kernel.elf
+
+kernel.elf: kernel.o entry.o
+	ld -Tlinker.ld -melf_i386 entry.o kernel.o -o kernel.elf
+
+kernel.o: kernel.c
+	gcc -std=gnu99 -m32 -fno-builtin -ffreestanding -nostdlib -Wall -Wextra -c kernel.c
+
+# entry.o: entry.S
+# 	as -32 $< -o entry.o
+
+entry.o: entry.asm
+	nasm -f elf32 $<
+
+clean:
+	rm -f *.o kernel.elf
diff --git a/kernel/entry.S b/kernel/entry.S
new file mode 100644
index 0000000..5b16b30
--- /dev/null
+++ b/kernel/entry.S
@@ -0,0 +1,42 @@
+# declare some constants
+.set ALIGN,    1<<0             # align loaded modules on page boundaries
+.set MEMINFO,  1<<1             # provide memory map
+.set FLAGS,    ALIGN | MEMINFO  # this is the Multiboot 'flag' field
+.set MAGIC,    0x1BADB002       # 'magic number' lets bootloader find the header
+.set CHECKSUM, -(MAGIC + FLAGS) # checksum of above, to prove we are multiboot
+
+# the bootloader will search for this magic sequence
+# and recognize us as a multiboot kernel
+.section .multiboot
+.align 4
+.long MAGIC
+.long FLAGS
+.long CHECKSUM
+
+# allocatable, writable, contains no data
+.section .bootstrap_stack, "aw", @nobits
+stack_bottom:
+.skip 16384         # 16 KiB
+stack_top:
+
+# the linker script specifies _start as the entry point to the kernel and the
+# bootloader will jump to this position once the kernel has been loaded
+.section .text
+.global _start
+.type _start, @function
+_start:
+    movl $stack_top, %esp
+    push %eax
+    push %ebx
+
+    call kernel_main
+
+    cli
+
+hang:
+    hlt
+    jmp hang
+
+# Set the size of the _start symbol to the current location '.' minus its start.
+# This is useful when debugging or when you implement call tracing.
+.size _start, . - _start
diff --git a/kernel/entry.asm b/kernel/entry.asm
new file mode 100644
index 0000000..28e491a
--- /dev/null
+++ b/kernel/entry.asm
@@ -0,0 +1,43 @@
+global _start
+global stack_ptr
+
+extern kernel_main
+
+; declare some constants
+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 of above, to prove we are multiboot
+
+; the bootloader will search for this magic sequence
+; and recognize us as a multiboot kernel
+section .multiboot
+align 4
+MultiBootHeader:
+  dd MAGIC
+  dd FLAGS
+  dd CHECKSUM
+
+section .code
+; setup the stack
+STACKSIZE equ 0x16384
+
+_start:
+  mov esp, stack+STACKSIZE
+  push eax
+  push ebx
+
+  call kernel_main
+
+  cli
+
+hang:
+  hlt
+  jmp hang
+
+section .bss
+align 4
+stack:
+  resb STACKSIZE
+stack_ptr:
diff --git a/kernel/kernel.c b/kernel/kernel.c
new file mode 100644
index 0000000..5054231
--- /dev/null
+++ b/kernel/kernel.c
@@ -0,0 +1,114 @@
+#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 we are targeting the wrong operating system. */
+#if defined(__linux__)
+/* TODO how does this check for a cross compiler? It was failing. */
+/*#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
+
+/* 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,
+};
+
+static uint8_t make_color(enum vga_color fg, enum vga_color bg)
+{
+    return fg | bg << 4;
+}
+
+static uint16_t make_vgaentry(char c, uint8_t color)
+{
+    uint16_t c16 = c;
+    uint16_t color16 = color;
+    return c16 | color16 << 8;
+}
+
+/* static size_t strlen(const char* str) */
+/* { */
+/*     size_t ret = 0; */
+/*     for (const char* p = str; *p != 0; p++, 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;
+
+static void terminal_initialize()
+{
+    terminal_row = 0;
+    terminal_column = 0;
+    terminal_color = make_color(COLOR_LIGHT_GREY, COLOR_BLACK);
+    terminal_buffer = (uint16_t*) 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);
+        }
+    }
+}
+
+/* static void terminal_setcolor(uint8_t color) */
+/* { */
+/*     terminal_color = color; */
+/* } */
+
+static 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);
+}
+
+static 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;
+        }
+    }
+}
+
+static void terminal_writestring(const char* data)
+{
+    for (const char* p = data; *p != 0; p++)
+        terminal_putchar(*p);
+}
+
+#if defined(__cplusplus)
+extern "C" /* Use C linkage for kernel_main. */
+#endif
+void kernel_main()
+{
+    terminal_initialize();
+    terminal_writestring("Hello, kernel World!\n");
+}
diff --git a/kernel/linker.ld b/kernel/linker.ld
new file mode 100644
index 0000000..3f1fe9d
--- /dev/null
+++ b/kernel/linker.ld
@@ -0,0 +1,46 @@
+/* the entry point */
+ENTRY(_start)
+
+SECTIONS
+{
+    /* all sections located above 1MB */
+    . = 0x100000;
+
+    /* multiboot header first (needs to reside within the first 8KB),
+     * then the code itself
+     */
+    .text BLOCK(4K) : ALIGN(4K)
+    {
+        *(.multiboot)
+        *(.code)
+    }
+
+    /* to be sure that this kernel is identified as a multiboot one,
+     * the GNU notes information should be placed inside the first 8K.
+     * another option is to exclude this unqiue header with -Wl,--build-id=none
+     */
+    .note.gnu.build-id BLOCK(4K) : ALIGN(4K)
+    {
+        *(.note.gnu.build-id)
+    }
+
+    /* read-only data */
+    .rodata BLOCK(4K) : ALIGN(4K)
+    {
+        *(.rodata*)
+    }
+
+    /* read-write data (initialized) */
+    .data BLOCK(4K) : ALIGN(4K)
+    {
+        *(.data*)
+    }
+
+    /* read-write data (uninitialized) and stack */
+    .bss BLOCK(4K) : ALIGN(4K)
+    {
+        *(COMMON)
+        *(.bss)
+        *(.bootstrap_stack)
+    }
+}