only identity map the start of the kernel

src/arch/x86_64/boot/boot.asm

@@ -1,6 +1,7 @@
 global _start
 global pml4
 extern x86_64_main
+extern kernel_end
 
 %define FLAGS       0b10
 %define MAGIC       0x1BADB002
@@ -43,6 +44,8 @@ section .data
         dd 0
     multiboot_magic:
         dd 0
+    kernel_page_count:
+        dd 0
 
 section .text
     bits 32
@@ -98,10 +101,18 @@ section .text
         mov eax, pd
         or eax, 0x03
         mov [pdpt], eax
-        ; Map first 32 2mb pages for the kernel for a total of 64mb
+
+        ; Calculate how many 2mb pages we need to identity map
+        mov ecx, kernel_end
+        add ecx, 0x1FFFFF               ; Page align end of kernel
+        shr ecx, 21                     ; ecx now holds the required pages
+
+        ; Save the page count so we can pass it to c later
+        mov [kernel_page_count], ecx
+
+        ; Identity map the 0x0 to kernel_end
         mov edi, pd
         mov eax, 0x83
-        mov ecx, 32
     .setup_pd:
         mov [edi], eax
         add eax, 0x200000
@@ -150,6 +161,7 @@ section .text
         ; Finally, we call in to c
         mov edi, [multiboot_magic]
         mov esi, [multiboot_info]
+        mov edx, [kernel_page_count]
         call x86_64_main
     .hang:
         hlt