add simple puts function for testing

Makefile

@@ -5,6 +5,8 @@ SRC_DIR=src
 BUILD_DIR=build
 ISO_DIR=$(BUILD_DIR)/iso
 
+INCLUDE_DIR=$(SRC_DIR)/kernel/include
+
 KERNEL_ASM		:= $(shell find $(SRC_DIR)/kernel -name "*.asm")
 KERNEL_C		:= $(shell find $(SRC_DIR)/kernel -name "*.c")
 
@@ -31,7 +33,7 @@ $(BUILD_DIR)/%.asm.o: $(SRC_DIR)/%.asm
 
 $(BUILD_DIR)/%.c.o: $(SRC_DIR)/%.c
 	@mkdir -p "$(@D)"
-	$(CC) -c $< -o $@ -std=gnu99 -ffreestanding -O2 -Wall -Wextra
+	$(CC) -c $< -o $@ -I$(INCLUDE_DIR) -std=gnu99 -ffreestanding -O2 -Wall -Wextra
 
 clean:
 	rm -rf $(BUILD_DIR)/*

src/kernel/include/string.h

@@ -0,0 +1,7 @@
+#ifndef _CLIPPER_STRING_H_
+#define _CLIPPER_STRING_H_
+
+void putch(char c);
+void puts(const char* str);
+
+#endif 

src/kernel/kmain.c

@@ -10,6 +10,9 @@
 #	error "Please use an ix86-elf compiler"
 #endif
 
+#include "string.h"
+
 void kmain(void) {
+	puts("Clipper has booted!\r\n");
 	return;
 }

src/kernel/lib/string.c

@@ -0,0 +1,44 @@
+#include "string.h"
+
+#include <stdint.h>
+
+static volatile char* video = (volatile char*)0xB8000;
+static uint8_t cursor_x = 0, cursor_y = 0;
+
+#define SCREEN_WIDTH 80
+#define SCREEN_HEIGHT 25
+
+static inline void advance_cursor(void) {
+	cursor_x++;
+	if (cursor_x >= SCREEN_WIDTH) {
+		cursor_x = 0;
+		cursor_y++;
+
+		if (cursor_y >= SCREEN_HEIGHT) {
+			cursor_y = 0;
+		}
+	}
+}
+
+static inline void linefeed(void) {
+	cursor_y++;
+	if (cursor_y >= SCREEN_HEIGHT) {
+		cursor_y = 0;
+	}
+}
+
+void putch(char c) {
+	switch(c) {
+	case '\r':	cursor_x = 0; return;
+	case '\n':	linefeed(); return;
+	}
+
+	video[cursor_y * (SCREEN_WIDTH * 2) + (cursor_x * 2)] = c;
+	advance_cursor();
+}
+
+void puts(const char* str) {
+	for (const char* c = str; *c != '\0'; c++) {
+		putch(*c);
+	}
+}