lib.rs

// Copyright Kani Contributors
// SPDX-License-Identifier: Apache-2.0 OR MIT

//! This crate includes two "proxy binaries": `kani` and `cargo-kani`.
//! These are conveniences to make it easy to:
//!
//! ```bash
//! cargo install --locked kani-verifer
//! ```
//!
//! Upon first run, or upon running `cargo-kani setup`, these proxy
//! binaries will download the appropriate Kani release bundle and invoke
//! the "real" `kani` and `cargo-kani` binaries.

mod cmd;
mod os_hacks;
mod setup;

use std::ffi::OsString;
use std::os::unix::prelude::CommandExt;
use std::path::{Path, PathBuf};
use std::process::Command;
use std::{env, fs};

use anyhow::{bail, Context, Result};

/// Effectively the entry point (i.e. `main` function) for both our proxy binaries.
/// `bin` should be either `kani` or `cargo-kani`
pub fn proxy(bin: &str) -> Result<()> {
    match parse_args(env::args_os().collect()) {
        ArgsResult::ExplicitSetup { use_local_bundle } => setup::setup(use_local_bundle),
        ArgsResult::Default => {
            fail_if_in_dev_environment()?;
            if !setup::appears_setup() {
                setup::setup(None)?;
            } else {
                // This handles cases where the setup was left incomplete due to an interrupt
                // For example - https://github.com/model-checking/kani/issues/1545
                if let Some(path_to_bundle) = setup::appears_incomplete() {
                    setup::setup(Some(path_to_bundle.clone().into_os_string()))?;
                    // Suppress warning with unused assignment
                    // and remove the bundle if it still exists
                    let _ = fs::remove_file(path_to_bundle);
                }
            }
            exec(bin)
        }
    }
}

/// Minimalist argument parsing result type
#[derive(PartialEq, Eq, Debug)]
enum ArgsResult {
    ExplicitSetup { use_local_bundle: Option<OsString> },
    Default,
}

/// Parse `args` and decide what to do.
fn parse_args(args: Vec<OsString>) -> ArgsResult {
    // In an effort to keep our dependencies minimal, we do the bare minimum argument parsing manually.
    // `args_ez` makes it easy to do crude arg parsing with match.
    let args_ez: Vec<Option<&str>> = args.iter().map(|x| x.to_str()).collect();
    // "cargo kani setup" comes in as "cargo-kani kani setup"
    // "cargo-kani setup" comes in as "cargo-kani setup"
    match &args_ez[..] {
        &[_, Some("setup"), Some("--use-local-bundle"), _] => {
            ArgsResult::ExplicitSetup { use_local_bundle: Some(args[3].clone()) }
        }
        &[_, Some("kani"), Some("setup"), Some("--use-local-bundle"), _] => {
            ArgsResult::ExplicitSetup { use_local_bundle: Some(args[4].clone()) }
        }
        &[_, Some("setup")] | &[_, Some("kani"), Some("setup")] => {
            ArgsResult::ExplicitSetup { use_local_bundle: None }
        }
        _ => ArgsResult::Default,
    }
}

/// In dev environments, this proxy shouldn't be used.
/// But accidentally using it (with the test suite) can fire off
/// hundreds of HTTP requests trying to download a non-existent release bundle.
/// So if we positively detect a dev environment, raise an error early.
fn fail_if_in_dev_environment() -> Result<()> {
    if let Ok(exe) = std::env::current_exe() {
        if let Some(path) = exe.parent() {
            if path.ends_with("target/debug") || path.ends_with("target/release") {
                bail!(
                    "Running a release-only executable, {}, from a development environment. This is usually caused by PATH including 'target/release' erroneously.",
                    exe.file_name().unwrap().to_string_lossy()
                )
            }
        }
    }

    Ok(())
}

/// Executes `kani-driver` in `bin` mode (kani or cargo-kani)
/// augmenting environment variables to accomodate our release environment
fn exec(bin: &str) -> Result<()> {
    let kani_dir = setup::kani_dir()?;
    let program = kani_dir.join("bin").join("kani-driver");
    let pyroot = kani_dir.join("pyroot");
    let bin_kani = kani_dir.join("bin");
    let bin_pyroot = pyroot.join("bin");

    // Allow python scripts to find dependencies under our pyroot
    let pythonpath = prepend_search_path(&[pyroot], env::var_os("PYTHONPATH"))?;
    // Add: kani, cbmc, viewer (pyroot), and our rust toolchain directly to our PATH
    let path = prepend_search_path(&[bin_kani, bin_pyroot], env::var_os("PATH"))?;

    // Ensure our environment variables for linker search paths won't cause failures, before we execute:
    fixup_dynamic_linking_environment();
    // Override our `RUSTUP_TOOLCHAIN` with the version Kani links against
    set_kani_rust_toolchain(&kani_dir)?;

    let mut cmd = Command::new(program);
    cmd.args(env::args_os().skip(1)).env("PYTHONPATH", pythonpath).env("PATH", path).arg0(bin);

    let result = cmd.status().context("Failed to invoke kani-driver")?;

    std::process::exit(result.code().expect("No exit code?"));
}

/// Prepend paths to an environment variable search string like PATH
fn prepend_search_path(paths: &[PathBuf], original: Option<OsString>) -> Result<OsString> {
    match original {
        None => Ok(env::join_paths(paths)?),
        Some(original) => {
            let orig = env::split_paths(&original);
            let new_iter = paths.iter().cloned().chain(orig);
            Ok(env::join_paths(new_iter)?)
        }
    }
}

/// `rustup` sets dynamic linker paths when it proxies to the target Rust toolchain. It's not fully
/// clear why. `rustup run` exists, which may aid in running Rust binaries that dynamically link to
/// the Rust standard library with `-C prefer-dynamic`. This might be why. All toolchain binaries
/// have `RUNPATH` set, so it's not needed by e.g. rustc. (Same for Kani)
///
/// However, this causes problems for us when the default Rust toolchain is nightly. Then
/// `LD_LIBRARY_PATH` is set to a nightly `lib` that may contain a different version of
/// `librustc_driver-*.so` that might have the same name. This takes priority over the `RUNPATH` of
/// `kani-compiler` and causes the linker to use a slightly different version of rustc than Kani
/// was built against. This manifests in errors like:
/// `kani-compiler: symbol lookup error: ... undefined symbol`
///
/// Consequently, let's remove from our linking environment anything that looks like a toolchain
/// path that rustup set. Then we can safely invoke our binaries. Note also that we update
/// `PATH` in [`exec`] to include our favored Rust toolchain, so we won't re-drive `rustup` when
/// `kani-driver` later invokes `cargo`.
fn fixup_dynamic_linking_environment() {
    #[cfg(not(target_os = "macos"))]
    const LOADER_PATH: &str = "LD_LIBRARY_PATH";
    #[cfg(target_os = "macos")]
    const LOADER_PATH: &str = "DYLD_FALLBACK_LIBRARY_PATH";

    if let Some(paths) = env::var_os(LOADER_PATH) {
        // unwrap safety: we're just filtering, so it should always succeed
        let new_val =
            env::join_paths(env::split_paths(&paths).filter(unlike_toolchain_path)).unwrap();
        env::set_var(LOADER_PATH, new_val);
    }
}

/// Determines if a path looks unlike a toolchain library path. These often looks like:
/// `/home/user/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib`
// Ignore this lint (recommending Path instead of PathBuf),
// we want to take the right argument type for use in `filter` above.
#[allow(clippy::ptr_arg)]
fn unlike_toolchain_path(path: &PathBuf) -> bool {
    let mut components = path.iter().rev();

    // effectively matching `*/toolchains/*/lib`
    !(components.next() == Some(std::ffi::OsStr::new("lib"))
        && components.next().is_some()
        && components.next() == Some(std::ffi::OsStr::new("toolchains")))
}

/// We should currently see a `RUSTUP_TOOLCHAIN` that was set by whatever default
/// toolchain the user has. We override our own environment variable (that is passed
/// down to children) with the toolchain Kani uses instead.
fn set_kani_rust_toolchain(kani_dir: &Path) -> Result<()> {
    let toolchain_verison = setup::get_rust_toolchain_version(kani_dir)?;
    env::set_var("RUSTUP_TOOLCHAIN", toolchain_verison);
    Ok(())
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn check_unlike_toolchain_path() {
        fn trial(s: &str) -> bool {
            unlike_toolchain_path(&PathBuf::from(s))
        }
        // filter these out:
        assert!(!trial("/home/user/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib"));
        assert!(!trial("/home/user/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/"));
        assert!(!trial("/home/user/.rustup/toolchains/nightly/lib"));
        assert!(!trial("/home/user/.rustup/toolchains/stable/lib"));
        // minimally:
        assert!(!trial("toolchains/nightly/lib"));
        // keep these:
        assert!(trial("/home/user/.rustup/toolchains"));
        assert!(trial("/usr/lib"));
        assert!(trial("/home/user/lib/toolchains"));
        // don't error on these:
        assert!(trial(""));
        assert!(trial("/"));
    }

    #[test]
    fn check_arg_parsing() {
        fn trial(args: &[&str]) -> ArgsResult {
            parse_args(args.iter().map(OsString::from).collect())
        }
        {
            let e = ArgsResult::Default;
            assert_eq!(e, trial(&["cargo-kani", "kani"]));
            assert_eq!(e, trial(&[]));
        }
        {
            let e = ArgsResult::ExplicitSetup { use_local_bundle: None };
            assert_eq!(e, trial(&["cargo-kani", "kani", "setup"]));
            assert_eq!(e, trial(&["cargo", "kani", "setup"]));
            assert_eq!(e, trial(&["cargo-kani", "setup"]));
        }
        {
            let e = ArgsResult::ExplicitSetup { use_local_bundle: Some(OsString::from("FILE")) };
            assert_eq!(e, trial(&["cargo-kani", "kani", "setup", "--use-local-bundle", "FILE"]));
            assert_eq!(e, trial(&["cargo", "kani", "setup", "--use-local-bundle", "FILE"]));
            assert_eq!(e, trial(&["cargo-kani", "setup", "--use-local-bundle", "FILE"]));
        }
    }
}