Ensure that memory::init is only called once

Cargo.toml

@@ -7,6 +7,7 @@ authors = ["Philipp Oppermann <dev@phil-opp.com>"]
 crate-type = ["staticlib"]
 
 [dependencies]
+once = "0.2.1"
 rlibc = "0.1.4"
 spin = "0.3.4"
 bump_allocator = {path="libs/bump_allocator"}

src/lib.rs

@@ -18,6 +18,8 @@ extern crate multiboot2;
 #[macro_use]
 extern crate bitflags;
 extern crate x86;
+#[macro_use]
+extern crate once;
 
 extern crate bump_allocator;
 extern crate alloc;

src/memory/mod.rs

@@ -18,6 +18,8 @@ mod paging;
 pub const PAGE_SIZE: usize = 4096;
 
 pub fn init(boot_info: &BootInformation) {
+    assert_has_not_been_called!("memory::init must be called only once");
+
     let memory_map_tag = boot_info.memory_map_tag().expect(
         "Memory map tag required");
     let elf_sections_tag = boot_info.elf_sections_tag().expect(