lib.rs

#![no_std]
#![feature(alloc_system, lang_items)]
extern crate alloc_system;

pub fn foo() -> u32 {
    42
}

#[lang = "eh_personality"] extern fn eh_personality() {}
#[lang = "panic_fmt"] extern fn panic_fmt() -> ! { loop {} }

log.txt

mbrubeck@p50:~/src/test$ rustc -V
rustc 1.18.0-nightly (2bd4b5c6d 2017-04-23)

mbrubeck@p50:~/src/test$ rustc -C lto --crate-type=staticlib -C opt-level=z -C panic=abort lib.rs && strip liblib.a 
note: link against the following native artifacts when linking against this static library

note: the order and any duplication can be significant on some platforms, and so may need to be preserved

note: library: c

note: library: m

note: library: rt

note: library: pthread

note: library: util

mbrubeck@p50:~/src/test$ ls -lh liblib.a 
-rw-r--r-- 1 mbrubeck mbrubeck 428 Apr 27 17:58 liblib.a