link_map/
link_map.rs

1//! Captures the link map a link would print, and shows what a library link
2//! takes from the process: nothing, unless it is asked to.
3//!
4//! ```sh
5//! cargo run --example link_map
6//! ```
7//!
8//! A link writes to the process's standard output only through
9//! [`LinkOptions::map_output`], and reads the environment only through the
10//! fields [`LinkOptions::use_process_defaults`] fills. Both are empty in
11//! [`LinkOptions::new`], so a library link is hermetic and silent; the
12//! `qld` binary — and [`qld::parse_gnu`], which describes the link the
13//! binary runs — opts into both.
14
15#[path = "support/objects.rs"]
16mod objects;
17
18use std::sync::{Arc, Mutex};
19
20use qld::args::{InputAttrs, InputKind, LinkOptions, OutputKind, TextOutput};
21use qld::diag::Collect;
22
23fn main() -> qld::Result<()> {
24    let mut options = LinkOptions::new();
25    options.kind = OutputKind::StaticExecutable;
26    options.push_input(
27        InputKind::bytes("main.o", objects::main_object()),
28        InputAttrs::default(),
29    );
30    options.push_input(
31        InputKind::bytes("answer.o", objects::answer_object(42)),
32        InputAttrs::default(),
33    );
34
35    // `-M` and `--cref`, into a string instead of standard output.
36    options.print_map = true;
37    options.cref = true;
38    let map = Arc::new(Mutex::new(String::new()));
39    let collected = Arc::clone(&map);
40    options.map_output = Some(TextOutput::new(move |text| {
41        collected.lock().unwrap().push_str(text);
42    }));
43
44    let image = qld::link_to_memory(&options, &Collect::new())?;
45    let map = map.lock().unwrap();
46    println!("linked {} bytes, {} of map", image.len(), map.len());
47    for line in map.lines().take(8) {
48        println!("  {line}");
49    }
50
51    // What the same options would take from the process, if asked.
52    let mut as_the_binary = options.clone();
53    as_the_binary.use_process_defaults();
54    println!(
55        "\nhermetic: map_output {}, LD_LIBRARY_PATH {} entries, timing {}",
56        if options.map_output.is_some() {
57            "set by this program"
58        } else {
59            "unset"
60        },
61        options.env_library_path.len(),
62        if options.timing.is_some() {
63            "on"
64        } else {
65            "off"
66        },
67    );
68    println!(
69        "as the binary: LD_LIBRARY_PATH {} entries, timing {}",
70        as_the_binary.env_library_path.len(),
71        if as_the_binary.timing.is_some() {
72            "on"
73        } else {
74            "off"
75        },
76    );
77    Ok(())
78}
link_map/link_map.rs

link_map/
link_map.rs
