Add writing to screen and print function

.gitignore

@@ -0,0 +1,2 @@
+build/
+bin/

Makefile

@@ -1,4 +1,6 @@
-FILES = ./build/kernel.asm.o
+FILES = ./build/kernel.asm.o ./build/kernel.o
+INCLUDES = -I./src
+FLAGS = -g -ffreestanding -falign-jumps -falign-functions -falign-labels -falign-loops -fstrength-reduce -fomit-frame-pointer -finline-functions -Wno-unused-function -fno-builtin -Werror -Wno-unused-label -Wno-cpp -Wno-unused-parameter -nostdlib -nostartfiles -nodefaultlibs -Wall -O0 -Iinc
 
 all: ./bin/boot.bin ./bin/kernel.bin
 	rm -rf ./bin/os.bin
@@ -8,12 +10,15 @@ all: ./bin/boot.bin ./bin/kernel.bin
 
 ./bin/kernel.bin: $(FILES)
 	i686-elf-ld -g -relocatable $(FILES) -o ./build/kernelfull.o
-	i686-elf-gcc -T ./src/linker.ld -o ./bin/kernel.bin -ffreestanding -O0 -nostdlib ./build/kernelfull.o
+	i686-elf-gcc $(FLAGS) -T ./src/linker.ld -o ./bin/kernel.bin -ffreestanding -O0 -nostdlib ./build/kernelfull.o
 
 ./bin/boot.bin: ./src/boot/boot.asm
 	nasm -f bin ./src/boot/boot.asm -o ./bin/boot.bin
 ./build/kernel.asm.o: ./src/kernel.asm
 	nasm -f elf -g ./src/kernel.asm -o ./build/kernel.asm.o
+./build/kernel.o: ./src/kernel.c
+	i686-elf-gcc $(INCLUDES) $(FLAGS) -std=gnu99 -c ./src/kernel.c -o ./build/kernel.o
+
 clean:
 	rm -rf ./bin/boot.bin
 	rm -rf ./bin/kernel.bin

run.sh

@@ -0,0 +1,3 @@
+#/bin/bash
+./build.sh
+qemu-system-x86_64 -hda bin/os.bin

src/kernel.asm

@@ -1,6 +1,6 @@
 BITS 32
 global _start
-
+extern kernel_main
 CODE_SEG equ 0x08
 DATA_SEG equ 0x10
 
@@ -19,6 +19,7 @@ _start:
     or al, 2
     out 0x92, al
 
+    call kernel_main
     jmp $
 
 times 512-($-$$) db 0

src/kernel.c

@@ -0,0 +1,71 @@
+#include "kernel.h"
+#include <stdint.h>
+#include <stddef.h>
+
+uint16_t *video_mem = 0;
+uint16_t terminal_row = 0;
+uint16_t terminal_col = 0;
+
+uint16_t terminal_make_char(char c, char color)
+{
+    return (color << 8) | c;
+}
+
+void terminal_putchar(int x, int y, char c, char color)
+{
+    video_mem[(y * VGA_WIDTH + x)] = terminal_make_char(c, color);
+}
+
+void terminal_writechar(char c, char color)
+{
+    if (c == '\n')
+    {
+        terminal_row += 1;
+        terminal_col = 0;
+        return;
+    }
+    terminal_putchar(terminal_col, terminal_row, c, color);
+    terminal_col += 1;
+    if (terminal_col >= VGA_WIDTH)
+    {
+        terminal_col = 0;
+        terminal_row += 1;
+    }
+}
+
+void terminal_initialize()
+{
+    video_mem = (uint16_t *)(0xB8000);
+    for (int y = 0; y < VGA_HEIGHT; y++)
+    {
+        for (int x = 0; x < VGA_WIDTH; x++)
+        {
+            terminal_putchar(x, y, ' ', 0);
+        }
+    }
+}
+
+size_t strlen(const char *str)
+{
+    size_t len = 0;
+    while (str[len])
+    {
+        len++;
+    }
+
+    return len;
+}
+
+void print(const char *str)
+{
+    size_t len = strlen(str);
+    for (int i = 0; i < len; i++)
+    {
+        terminal_writechar(str[i], 15);
+    }
+}
+void kernel_main()
+{
+    terminal_initialize();
+    print("Hello World!\nThis is fun");
+}

src/kernel.h

@@ -0,0 +1,9 @@
+#ifndef KERNEL_H
+#define KERNEL_H
+
+#define VGA_WIDTH 80
+#define VGA_HEIGHT 80
+
+void kernel_main();
+
+#endif