add weak memcpy et al (take 2)

Cargo.toml

@@ -2,3 +2,6 @@
 authors = ["Jorge Aparicio <[email protected]>"]
 name = "rustc_builtins"
 version = "0.1.0"
+
+[dependencies]
+rlibc = { path = "rlibc" }

rlibc/Cargo.toml

@@ -0,0 +1,6 @@
+[package]
+name = "rlibc"
+version = "0.1.0"
+authors = ["Jorge Aparicio <[email protected]>"]
+
+[dependencies]

rlibc/src/lib.rs

@@ -0,0 +1,46 @@
+#![feature(linkage)]
+#![no_builtins]
+#![no_std]
+
+#[linkage = "weak"]
+#[no_mangle]
+pub unsafe extern fn memcpy(dest: *mut u8, src: *const u8,
+                            n: usize) -> *mut u8 {
+    let mut i = 0;
+    while i < n {
+        *dest.offset(i as isize) = *src.offset(i as isize);
+        i += 1;
+    }
+    return dest;
+}
+
+#[linkage = "weak"]
+#[no_mangle]
+pub unsafe extern fn memmove(dest: *mut u8, src: *const u8,
+                             n: usize) -> *mut u8 {
+    if src < dest as *const u8 { // copy from end
+        let mut i = n;
+        while i != 0 {
+            i -= 1;
+            *dest.offset(i as isize) = *src.offset(i as isize);
+        }
+    } else { // copy from beginning
+        let mut i = 0;
+        while i < n {
+            *dest.offset(i as isize) = *src.offset(i as isize);
+            i += 1;
+        }
+    }
+    return dest;
+}
+
+#[linkage = "weak"]
+#[no_mangle]
+pub unsafe extern fn memset(s: *mut u8, c: i32, n: usize) -> *mut u8 {
+    let mut i = 0;
+    while i < n {
+        *s.offset(i as isize) = c as u8;
+        i += 1;
+    }
+    return s;
+}

src/lib.rs

@@ -9,6 +9,8 @@
 #[cfg(test)]
 extern crate core;
 
+extern crate rlibc;
+
 use core::mem;
 
 #[cfg(target_arch = "arm")]