do.sh

cargo add alloc-cortex-m
xargo build --example hello
arm-none-eabi-gdb ..
# output: https://i.imgur.com/31iWvIc.png

hello.rs

// modified examples/hello.rs that uses the allocator

#![feature(collections)]
#![feature(used)]
#![no_std]

extern crate alloc_cortex_m;
#[macro_use]
extern crate collections;
#[macro_use]
extern crate cortex_m;
extern crate cortex_m_rt;

use cortex_m::asm;

fn main() {
    extern {
        // HEAP START
        static mut _edata: usize;
    }

    // 1 KiB heap
    unsafe {
        alloc_cortex_m::init(&mut _edata, (&mut _edata as *mut _).offset(256));
    }

    let xs = vec![0, 1, 2];

    hprintln!("{:?}", xs);
}

// As we are not using interrupts, we just register a dummy catch all handler
#[allow(dead_code)]
#[used]
#[link_section = ".rodata.interrupts"]
static INTERRUPTS: [extern "C" fn(); 240] = [default_handler; 240];

extern "C" fn default_handler() {
    asm::bkpt();
}

Xargo.toml

[dependencies.collections] # <- this changed

[dependencies.compiler_builtins]
features = ["mem"]
git = "https://github.com/rust-lang-nursery/compiler-builtins"
stage = 1