add getting memory map from grub

src/kernel/kernel.c

@@ -144,10 +144,43 @@ void kmain(unsigned int magic, unsigned int info)
 	terminal_initialize();
 	printf("KatauOS booting up\n");
 
+	if(magic != MULTIBOOT_BOOTLOADER_MAGIC) {
+        printf("invalid magic number!\n");
+		while(1){}
+    }
+
 	if(mbi.flags & MULTIBOOT_INFO_BOOT_LOADER_NAME) {
                 printf("bootloader: %s\n", mbi.boot_loader_name);
 	}
 
+	/* Check bit 6 to see if we have a valid memory map */
+    if(!(mbi.flags >> 6 & 0x1)) {
+        printf("invalid memory map given by GRUB bootloader\n");
+		while(1){}
+    }
+
+	/* Loop through the memory map and display the values */
+    int i;
+    for(i = 0; i < mbi.mmap_length; 
+        i += sizeof(multiboot_memory_map_t)) 
+    {
+        multiboot_memory_map_t* mmmt = 
+            (multiboot_memory_map_t*) (mbi.mmap_addr + i);
+
+        printf("Start Addr: %x | Length: %x | Size: %x | Type: %x\n",
+            mmmt->addr, mmmt->len, mmmt->size, mmmt->type);
+
+        if(mmmt->type == MULTIBOOT_MEMORY_AVAILABLE) {
+            /* 
+             * Do something with this memory block!
+             * BE WARNED that some of memory shown as availiable is actually 
+             * actively being used by the kernel! You'll need to take that
+             * into account before writing to memory!
+             */
+			printf("available\n");
+        }
+    }
+
 
 	isr_install();
 	pic_remap(0x20, 0x28);