...

makefile

@@ -17,13 +17,13 @@ iso: .build/nub-os.iso
 clean:
 	@rm -r .build 2>/dev/null || true
 
-.build/nub-os.iso: .build/kernel grub.cfg
+.build/nub-os.iso: .build/kernel/kernel grub.cfg
 	mkdir -p .build/nub-os/boot/grub
 	cp grub.cfg .build/nub-os/boot/grub
-	cp .build/kernel .build/nub-os/boot/
+	cp .build/kernel/kernel .build/nub-os/boot/
 	grub-mkrescue -o .build/nub-os.iso .build/nub-os/
 
-.build/kernel: $(OBJS)
+.build/kernel/kernel: $(OBJS)
 	$(LD) $(LDFLAGS) -T linker.ld -o $@ $^
 
 .build/%.o: src/%.c

src/arch/x86_64/entry.c

@@ -1,4 +1,4 @@
-#include "../../kernel.h"
+#include "../../kernel/kernel.h"
 #include "../arch.h"
 #include "interrupts/idt.h"
 #include "interrupts/irq.h"

src/kernel/kernel.c

@@ -5,5 +5,8 @@
 void main()
 {
     pmm_init();
+
+    uint64_t page = pmm_alloc_page();
+    printf("page: %u\n", page);
     printf("Welcome to nub OS :)\n");
 }

src/kernel/pmm.c

@@ -1,5 +1,5 @@
 #include "pmm.h"
-#include "arch/arch.h"
+#include "../arch/arch.h"
 #include <stddef.h>
 #include <stdio.h>
 #include <string.h>
@@ -52,6 +52,7 @@ void pmm_init()
     }
 }
 
+// Returns the address of first free physical page
 uint64_t pmm_alloc_page()
 {
     for (size_t i = 0; i < BITMAP_SIZE; i++)
@@ -73,6 +74,7 @@ uint64_t pmm_alloc_page()
     return 0;
 }
 
+// Frees the physical page at the specified address
 void pmm_free_page(uint64_t addr)
 {
     uint64_t page = addr / PAGE_SIZE;