cargo-show-asm

A cargo subcommand that displays the Assembly, LLVM-IR and MIR generated for Rust source code.

Install

console $ cargo install cargo-show-asm

Features

• Platform support:

  • OS: Linux and MacOSX. Limited support for Windows
  • Rust: nightly and stable.
  • Architectures: x86, x86_64, aarch64, probably more but untested.
  • Cross-compilation support.

Missing operating systems and architectures might be supported by accident, please make a ticket if something not working for your favorite platform

• Displaying:

  • Assembly in Intel or AT&T syntax.
  • Corresponding Rust source code alongside assembly.
  • llvm-ir.
  • rustc MIR

Usage:

You can start by running cargo asm with no parameters - it will suggests how to narrow the search scope - for workspace crates you need to specify a crate to work with, for crates defining several targets (lib, binaries, examples) you need to specify exactly which target to use. In a workspace cargo asm lists only workspace members as suggestions but any crate from workspace tree is available.

Once cargo asm focuses on a single target it will run rustc producing assembly file and will try to list of available public functions:

```console,ignore $ cargo asm --lib Try one of those "<&T as core::fmt::Display>::fmt" [17, 12, 12, 12, 12, 19, 19, 12] "<&mut W as core::fmt::Write>::writechar" [20] "<&mut W as core::fmt::Write>::writefmt" [38] "<&mut W as core::fmt::Write>::write_str" [90] ">::parse" [263]

...

```

Name in quotes is demangled rust name, numbers in square brackets represent number of lines in asm file. Function with the same name can be present in several instances.

Specifying exact function name will print its assembly code

console,ignore $ cargo asm --lib "cargo_show_asm::opts::focus::{{closure}}" To pick between different alternatives you can either specify the index

console,ignore $ cargo asm --lib "cargo_show_asm::opts::focus::{{closure}}" 2 Or start using full names with hex included:

```console,ignore $ cargo asm --lib --full-name

...

$ cargo asm --lib "once_cell::imp::OnceCell::initialize::h9c5c7d5bd745000b" ```

cargo-show-asm comes with a built in search function. Just pass partial name instead of a full one and only matching functions will be listed

console $ cargo asm --lib Debug

What about cargo-asm?

cargo-asm is not maintained: https://github.com/gnzlbg/cargo-asm/issues/244. This crate is a reimplementation which addresses a number of its shortcomings, including:

• cargo-asm calls rustc directly. It recompiles everything every time with 1 codegen unit, which is slow and also not necessarily what is in your release profile. cargo-show-asm lets cargo run rustc.

• Because of how cargo-asm handles demangling the output looks like asm but isn't actually asm. It contains a whole bunch of extra commas which makes reusing it more annoying.

• cargo-asm always uses colors unless you pass a flag while cargo-show-asm changes its default behavior if output is not sent to a terminal.

• cargo-show-asm also supports MIR (note that the formatting of human-readable MIR is not stable).

I'm on MacOS and cargo-show-asm fails to compile for me

In case you encounter a problem with openssl and libgit - you can try enabling one or both: ```console cargo install cargo-show-asm --features vendored-openssl,vendored-libgit2

```

License

This project is licensed under either of

• Apache License, Version 2.0, (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
• MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT)

at your option.

Contribution

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in this project by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.