find_kernel: give values meaningful names

src/arch/x86_64/multiboot.rs

@@ -131,26 +131,29 @@ pub fn find_kernel() -> &'static [u8] {
 	let elf_len = end_address - start_address;
 	info!("Module length: {:#x}", elf_len);
 
+	// The mapping functions use `PhysAlloc`, even when the range they map
+	// is not covered by it, so it needs to be initialized before
+	// the mappings happen.
 	let free_memory_address = end_address.align_up(Size2MiB::SIZE as usize);
 	// TODO: Workaround for https://github.com/hermitcore/loader/issues/96
 	let free_memory_address = cmp::max(free_memory_address, 0x800000);
 	// Memory after the highest end address is unused and available for the physical memory manager.
 	PhysAlloc::init(free_memory_address);
 
 	// Identity-map the ELF header of the first module.
+	let first_module_mapping_end = start_address.align_up(Size2MiB::SIZE as usize);
 	paging::map_range::<Size4KiB>(
 		start_address,
 		start_address,
-		start_address.align_up(Size2MiB::SIZE as usize),
+		first_module_mapping_end,
 		PageTableFlags::empty(),
 	);
 
 	// map also the rest of the module
-	let address = start_address.align_up(Size2MiB::SIZE as usize);
 	paging::map_range::<Size2MiB>(
-		address,
-		address,
-		end_address.align_up(Size2MiB::SIZE as usize),
+		first_module_mapping_end,
+		first_module_mapping_end,
+		free_memory_address,
 		PageTableFlags::empty(),
 	);