...

.vscode/launch.json

@@ -0,0 +1,18 @@
+{
+    "version": "0.2.0",
+    "configurations": [
+        {
+            "type": "gdb",
+            "request": "attach",
+            "name": "Attach to QEMU",
+            "executable": "${workspaceFolder}/.build/kernel/kernel",
+            "target": "localhost:1234",
+            "remote": true,
+            "cwd": "${workspaceRoot}",
+            "gdbpath": "/usr/bin/gdb",
+            "autorun": [
+                "b _start"
+            ]
+        }
+    ]
+}

.vscode/settings.json

@@ -0,0 +1,7 @@
+{
+    "files.associations": {
+        "bitset": "c",
+        "algorithm": "c",
+        "format": "c"
+    }
+}

README.md

@@ -31,5 +31,5 @@ qemu-system-x86_64 -cdrom .build/nub-os.iso
 
 ```sh
 qemu-system-x86_64 -s -S -cdrom .build/nub-os.iso
-gdb -tui .build/kernel -ex "target remote localhost:1234"
+gdb -tui .build/kernel/kernel -ex "target remote localhost:1234"
 ```

linker.ld

@@ -3,6 +3,7 @@ ENTRY(_start)
 SECTIONS
 {
 	. = 2M;
+	kernel_start = .;
 
 	.text BLOCK(4K) : ALIGN(4K)
 	{
@@ -25,4 +26,6 @@ SECTIONS
 		*(COMMON)
 		*(.bss)
 	}
+
+	kernel_end = .;
 }

src/arch/x86_64/boot/boot.asm

@@ -108,7 +108,7 @@ section .text
         add edi, 8
         loop .setup_pd
 
-        ; Load cr3 with the address of pml4
+        ; Tell the cpu where pml4 is
         mov eax, pml4
         mov cr3, eax
 

src/arch/x86_64/mem.c

@@ -18,14 +18,29 @@ typedef struct
 static memory_region_t usable_regions[USABLE_REGION_SIZE];
 static size_t num_regions = 0;
 
-#define BITMAP_SIZE 32768 // Supports up to 1GB of RAM
-#define USABLE_REGION_SIZE 32
-#define PAGE_SIZE 4096
+#define KiB(count) ((u64)count * 1024)
+#define MiB(count) (KiB((u64)count) * 1024)
+#define GiB(count) (MiB((u64)count) * 1024)
+#define TiB(count) (GiB((u64)count) * 1024)
+
+// Fixed at 2mb for now
+#define PAGE_SIZE MiB(2)
+
+// Defines the theoretical max memory the kernel can allocate, not the actual memory of the system
+#define MAX_MEMORY GiB(64)
+
+#define BITMAP_PAGE_COUNT (MAX_MEMORY / PAGE_SIZE)
+#define BITMAP_SIZE (BITMAP_PAGE_COUNT / 8)
 
 static u8 page_bitmap[BITMAP_SIZE];
 static u64 total_pages = 0;
 static u64 free_pages = 0;
 
+#define PTE_MASK 0x00000000FFFFF000
+#define PTE_PRESENT 1
+
+extern u64* pml4;
+
 void mem_init(multiboot_info_t* info)
 {
     if (!(info->flags & (1 << 6)))
@@ -51,7 +66,7 @@ void mem_init(multiboot_info_t* info)
             }
             else
             {
-                printf("System has more memory than the memory map can hold\n");
+                printf("System has more memory than the usable memory map can hold\n");
                 break;
             }
         }
@@ -84,11 +99,11 @@ void mem_init(multiboot_info_t* info)
         }
     }
 
-    // Reserve first 64MB which is reserved by boot code
-    // todo(nub31): Later we should only identity map only the kernel pages or make a higher half kernel
-    for (u64 page = 0; page < (64 * 1024 * 1024) / PAGE_SIZE; page++)
+    // Mark first 32 pages (64mb) as unusable since it is reserved by the bootloader
+    // todo(nub31): This should be revisited. Maybe do a higher half kernel?
+    for (u64 page = 0; page < 32; page++)
     {
-        if (page < BITMAP_SIZE * 8)
+        if (page < BITMAP_PAGE_COUNT)
         {
             if (!(page_bitmap[page / 8] & (1 << (page % 8))))
             {
@@ -96,6 +111,10 @@ void mem_init(multiboot_info_t* info)
                 free_pages--;
             }
         }
+        else
+        {
+            panic("Bitmap is not large enough to hold the bootloader reserved memory");
+        }
     }
 }