Add: userland hello world code

Makefile

@@ -11,8 +11,8 @@ install:
 
 bin:
 	$(MAKE) -C $(LIB)
-	gcc -c test.c -Ilibk -Llibk -lk -m32
-	ld -m elf_i386 -Ttext=0x6000000 --entry=main test.o -L./libk/ -lk
+	gcc -c ./app/$(APP).c -Ilibk -Llibk -lk -m32
+	ld -m elf_i386 -Ttext=0x6000000 --entry=main ./$(APP).o -L./libk/ -lk
 	objcopy --input binary --output elf32-i386 --binary-architecture i386 --rename-section .data=.rodata,CONTENTS,ALLOC,LOAD,READONLY,DATA a.out myfile.o
 	cp myfile.o $(SOURCEDIR)/myfile.o
 

Makefile.common

@@ -5,3 +5,4 @@ GRUBDIR = iso
 SOURCEDIR = src
 TARGET = kernel
 LIB=libk
+APP=hello_world

app/hello_world.c

@@ -0,0 +1,10 @@
+#include <syscall.h>
+
+static char s[] = "Hello from userland!\n";
+
+int main(void)
+{
+    write(1, s, 21);
+    while (1);
+    return 0;
+}