#[lang="exchange_malloc"] seems to be broken

[snare]

Adding the #[lang="exchange_malloc"] directive to a function causes an assertion failure in the compiler. Tested with the latest version (746d086)

$ cat ex.rs
#![no_std]
#![no_main]

#[no_split_stack]
#[no_mangle]
pub fn thing()->int {
    let y = box 10;
    0
}

#[lang="exchange_malloc"]
pub fn malloc(size: uint) -> *mut u8 {
    0 as *mut u8
}

$ rustc --crate-type=lib ex.rs
ex.rs:7:6: 7:7 warning: unused variable: `y`, #[warn(unused_variable)] on by default
ex.rs:7     let y = box 10;
                ^
ex.rs:12:15: 12:19 warning: unused variable: `size`, #[warn(unused_variable)] on by default
ex.rs:12 pub fn malloc(size: uint) -> *mut u8 {
                       ^~~~
Assertion failed: ((Args.size() == FTy->getNumParams() || (FTy->isVarArg() && Args.size() > FTy->getNumParams())) && "Calling a function with bad signature!"), function init, file /<redacted>/rust/src/llvm/lib/IR/Instructions.cpp, line 276.
zsh: abort      ~/rust/bin/rustc --crate-type=lib ex.rs     zsh: abort      rustc --crate-type=lib ex.rs

[alexcrichton]

Closing, it was changed recently to take an align parameter as well:

#[lang="exchange_malloc"]
pub fn malloc(size: uint, align: uint) -> *mut u8 { /* ... */ }

Making this a first class error is covered by #9307