build.rs

use std::fmt::Write;
use std::time::{SystemTime, UNIX_EPOCH};
use std::{env, error::Error, fs, path::PathBuf, process::Command};

fn get_output(cmd: &mut Command) -> Result<String, Box<dyn Error>> {
    let output = cmd.output()?;
    assert!(output.status.success());
    Ok(String::from_utf8(output.stdout)?.trim().into())
}

fn binstring(len: usize, s: String) -> String {
    let b = s.as_bytes();
    let mut res: String = "[".into();
    for i in 0..len {
        write!(res, "0x{:x},", b.get(i).cloned().unwrap_or(0)).unwrap()
    }
    write!(res, "]").unwrap();
    res
}

fn main() -> Result<(), Box<dyn Error>> {
    let out = &PathBuf::from(env::var("OUT_DIR").unwrap());

    let git_commit = get_output(Command::new("git").args(&["rev-parse", "HEAD"])).unwrap();
    let git_diff = get_output(Command::new("git").args(&["diff-index", "HEAD"])).unwrap();
    let build_user = binstring(16, get_output(&mut Command::new("whoami")).unwrap());
    let build_hostname = binstring(16, get_output(&mut Command::new("hostname")).unwrap());

    let mut flags = 0;
    if !git_diff.is_empty() {
        flags |= 1; // GIT_DIRTY
    }

    let timestamp = SystemTime::now().duration_since(UNIX_EPOCH).unwrap().as_secs();

    fs::write(
        out.join("build_info_generated.rs"),
        format!(
            r#"
const FLAGS: u32 = {};
const TIMESTAMP: u32 = {};
const GIT_COMMIT: [u8;20] = hex!("{}");
const USER: [u8;16] = {};
const HOSTNAME: [u8;16] = {};
            "#,
            flags, timestamp, git_commit, build_user, build_hostname,
        ),
    )
    .unwrap();

    Ok(())
}

build_info.rs

use hex_literal::hex;

pub const MAGIC: u32 = 0x12341234;
pub const FLAG_GIT_DIRTY: u32 = 1;
include!(concat!(env!("OUT_DIR"), "/build_info_generated.rs"));

#[repr(C)]
#[derive(Debug)]
#[cfg_attr(feature = "defmt", derive(defmt::Format))]
pub struct BuildInfo {
    magic: u32,
    hardware_code: u32,
    timestamp: u32,
    flags: u32,
    git_commit: [u8; 20],
    user: [u8; 16],
    hostname: [u8; 16],
}

#[used]
#[no_mangle]
#[link_section = ".build_info"]
static BUILD_INFO: BuildInfo = BuildInfo {
    magic: MAGIC,
    hardware_code: crate::hardware_codes::HARDWARE_CODE,
    timestamp: TIMESTAMP,
    flags: FLAGS,
    git_commit: GIT_COMMIT,
    user: USER,
    hostname: HOSTNAME,
};