Re add program build into makefile

Makefile

@@ -15,11 +15,15 @@ debug: os.iso kernel/kernel.elf
 	qemu-system-i386 -s $(QFLAGS) &
 	$(GDB) -ex "target remote localhost:1234" -ex "symbol-file kernel/kernel.elf"
 
-os.iso: kernel/kernel.elf initrd/*
+os.iso: kernel/kernel.elf initrd/* initrd/prog.elf
 	cp kernel/kernel.elf iso/boot
 	ruby makeinitrd.rb initrd iso/boot/initrd
 	grub-mkrescue -o $@ iso
 
+initrd/prog.elf: prog/*
+	cd prog && make
+	cp prog/prog.elf initrd
+
 kernel/kernel.elf: $(OBJ)
 	i386-elf-ld -T linker.ld -o $@ $^
 

prog/Makefile

@@ -0,0 +1,13 @@
+C_SOURCES = $(wildcard *.c)
+OBJ = $(C_SOURCES:.c=.o)
+CFLAGS = -Wall -g -ffreestanding
+CC = i386-elf-gcc
+
+prog.elf: $(OBJ)
+	i386-elf-ld -o $@ $^
+
+%.o: %.c
+	$(CC) $(CFLAGS)  -c $< -o $@
+
+clean:
+	rm -rf *.o prog.elf

prog/main.c

@@ -0,0 +1,4 @@
+int _start() {
+  int x=17;
+  return x+3;
+}