libafl_libfuzzer 0.16.0

use core::error::Error;
#[cfg(unix)]
use std::os::unix::fs::symlink;
use std::{
    fs,
    fs::File,
    io::{BufRead, BufReader, BufWriter, Write},
    path::{Path, PathBuf},
    process::{Command, Stdio},
};

#[cfg(feature = "rabbit")]
const NAMESPACE: &str = "🐇";
#[cfg(not(feature = "rabbit"))]
const NAMESPACE: &str = "__libafl";
const NAMESPACE_LEN: usize = NAMESPACE.len();
const RUNTIME_CRATE_NAME: &str = "libafl_libfuzzer_runtime";

#[expect(clippy::too_many_lines)]
#[cfg(any(target_os = "linux", target_os = "macos"))]
fn build() -> Result<(), Box<dyn Error>> {
    println!("cargo:rerun-if-changed=libafl_libfuzzer_runtime/src");
    println!("cargo:rerun-if-changed=libafl_libfuzzer_runtime/build.rs");

    let custom_lib_dir =
        AsRef::<Path>::as_ref(&std::env::var_os("OUT_DIR").unwrap()).join("libafl_libfuzzer");
    let custom_lib_target = custom_lib_dir.join("target");
    fs::create_dir_all(&custom_lib_target)
        .expect("Couldn't create the output directory for the fuzzer runtime build");

    let manifest_dir = PathBuf::from(std::env::var_os("CARGO_MANIFEST_DIR").unwrap());

    let mut command = Command::new(std::env::var_os("CARGO").unwrap());
    command
        .env_remove("RUSTFLAGS")
        .env_remove("CARGO_ENCODED_RUSTFLAGS");

    for (var, _) in std::env::vars() {
        if var.starts_with("CARGO_PKG_") || var.starts_with("CARGO_FEATURE_") {
            command.env_remove(var);
        }
    }

    command.env("PATH", std::env::var_os("PATH").unwrap());

    command.arg("build");

    let mut features = vec![];

    if cfg!(any(feature = "fork")) {
        features.push("fork");
    }

    if !features.is_empty() {
        command.arg("--features").arg(features.join(","));
    }

    command
        .arg("--release")
        .arg("--no-default-features")
        .arg("--target-dir")
        .arg(&custom_lib_target)
        .arg("--target")
        .arg(std::env::var_os("TARGET").unwrap());

    // detect if we are a version or path/git dep, or testing version-based behavior
    let runtime_dir = manifest_dir.ancestors().find_map(|ancestor| {
        let direct = ancestor.join(RUNTIME_CRATE_NAME);
        if fs::exists(&direct).unwrap_or(false) {
            return Some(direct);
        }
        let under_crates = ancestor.join("crates").join(RUNTIME_CRATE_NAME);
        if fs::exists(&under_crates).unwrap_or(false) {
            return Some(under_crates);
        }
        None
    });

    if let Some(runtime_dir) =
        runtime_dir.filter(|_| !cfg!(feature = "libafl-libfuzzer-use-version"))
    {
        command.current_dir(runtime_dir);
    } else {
        // we are being used as a version dep; we need to create the package virtually

        // remove old files; we need to trigger a rebuild if our path changes!
        let _ = fs::remove_file(custom_lib_dir.join("src"));
        let _ = fs::remove_dir_all(custom_lib_dir.join("src")); // maybe a dir in windows
        let _ = fs::remove_file(custom_lib_dir.join("build.rs"));
        let _ = fs::remove_file(custom_lib_dir.join("Cargo.toml"));

        // create symlinks for all the source files
        // canonicalize can theoretically fail if we are within a non-executable directory?
        symlink(fs::canonicalize("runtime/src")?, custom_lib_dir.join("src"))?;
        symlink(
            fs::canonicalize("runtime/build.rs")?,
            custom_lib_dir.join("build.rs"),
        )?;

        let mut template: toml::Value =
            toml::from_str(&fs::read_to_string("runtime/Cargo.toml.template")?)?;
        let toml::Value::Table(root) = &mut template else {
            unreachable!("Invalid Cargo.toml");
        };
        root.insert(
            "workspace".to_string(),
            toml::Value::Table(toml::Table::new()),
        );
        let Some(toml::Value::Table(deps)) = root.get_mut("dependencies") else {
            unreachable!("Invalid Cargo.toml");
        };
        let version = env!("CARGO_PKG_VERSION");
        for (_name, spec) in deps {
            if let toml::Value::Table(spec) = spec {
                // replace all path deps with version deps
                if spec.remove("path").is_some() {
                    spec.insert(
                        "version".to_string(),
                        toml::Value::String(version.to_string()),
                    );
                }
            }
        }

        let serialized = toml::to_string(&template)?;
        fs::write(custom_lib_dir.join("Cargo.toml"), serialized)?;

        // build in this filled out template
        command.current_dir(custom_lib_dir);
    }

    assert!(
        command.status().is_ok_and(|s| s.success()),
        "Couldn't build runtime crate! Did you remember to use nightly? (`rustup default nightly` to install)"
    );

    let redefined_archive_path = rename_symbols(&custom_lib_target);

    if cfg!(feature = "embed-runtime") {
        // NOTE: lib, .a are added always on unix-like systems as described in:
        // https://gist.github.com/novafacing/1389cbb2f0a362d7eb103e67b4468e2b
        println!(
            "cargo:rustc-env=LIBAFL_LIBFUZZER_RUNTIME_PATH={}",
            redefined_archive_path.display()
        );
    }

    println!(
        "cargo:rustc-link-search=native={}",
        custom_lib_target.to_str().unwrap()
    );
    println!("cargo:rustc-link-lib=static=Fuzzer");

    if cfg!(target_os = "macos") {
        println!("cargo:rustc-link-lib=c++");
    } else {
        println!("cargo:rustc-link-lib=stdc++");
        println!("cargo:rustc-link-arg=-Wl,--allow-multiple-definition");
    }
    Ok(())
}

fn main() {
    if cfg!(any(clippy, docsrs)) {
        return; // skip when clippy or docs is running
    }

    #[cfg(not(any(target_os = "linux", target_os = "macos")))]
    println!(
        "cargo:warning=The libafl_libfuzzer runtime may only be built for linux or macos; failing fast."
    );

    #[cfg(any(target_os = "linux", target_os = "macos"))]
    build().expect("Failed to build libafl_libfuzzer runtime");
}

/// This function creates a copy of the libfuzzer runtime with all the symbols renamed to avoid
/// a conflict with whatever we link to. It should be compatible with legacy and v0 mangling.
#[cfg(any(target_os = "linux", target_os = "macos"))]
fn rename_symbols(custom_lib_target: &Path) -> PathBuf {
    let mut archive_path = custom_lib_target.join(std::env::var_os("TARGET").unwrap());
    archive_path.push("release");

    archive_path.push("libafl_libfuzzer_runtime.a");
    let target_libdir = Command::new("rustc")
        .args(["--print", "target-libdir"])
        .output()
        .expect("Couldn't find rustc's target-libdir");
    let target_libdir = String::from_utf8(target_libdir.stdout).unwrap();
    let target_libdir = Path::new(target_libdir.trim());

    // NOTE: depends on llvm-tools
    let rust_objcopy = target_libdir.join("../bin/llvm-objcopy");
    let nm = target_libdir.join("../bin/llvm-nm");

    let nm = if nm.exists() {
        nm.to_str().unwrap().to_string()
    } else {
        libafl_build::find_llvm_tool("llvm-nm").expect("Could not find llvm-nm")
    };

    let rust_objcopy = if rust_objcopy.exists() {
        rust_objcopy.to_str().unwrap().to_string()
    } else {
        libafl_build::find_llvm_tool("llvm-objcopy").expect("Could not find llvm-objcopy")
    };

    let redefined_archive_path = custom_lib_target.join("libFuzzer.a");
    let redefined_symbols = custom_lib_target.join("redefs.txt");

    let mut nm_child = Command::new(nm)
        .arg(&archive_path)
        .stdout(Stdio::piped())
        .spawn()
        .expect("llvm-nm does not work (are you using nightly? or did you install by rustup component add llvm-tools?)");

    let mut redefinitions_file = BufWriter::new(File::create(&redefined_symbols).unwrap());

    let rn_prefix = if cfg!(target_os = "macos") {
        // macOS symbols have an extra `_`
        "__RN"
    } else {
        "_RN"
    };
    let r_prefix = if cfg!(target_os = "macos") {
        // macOS symbols have an extra `_`
        "__R"
    } else {
        "_R"
    };

    let zn_prefix = if cfg!(target_os = "macos") {
        // macOS symbols have an extra `_`
        "__ZN"
    } else {
        "_ZN"
    };

    let replacement = format!("{zn_prefix}{NAMESPACE_LEN}{NAMESPACE}");

    // redefine all the rust-mangled symbols we can
    for line in BufReader::new(nm_child.stdout.take().unwrap()).lines() {
        let line = line.unwrap();

        // Skip headers
        if line.ends_with(':') || line.is_empty() {
            continue;
        }
        let (_, symbol) = line.rsplit_once(' ').unwrap();

        if symbol.starts_with(rn_prefix) {
            if let Some((_prefix, renamed)) = symbol.split_once("__rustc") {
                let (size, renamed) = renamed.split_once('_').unwrap();
                writeln!(redefinitions_file, "{symbol} {replacement}{size}{renamed}E").unwrap();
            } else {
                // v0 mangling: this uses the vendor-specific suffix model
                writeln!(redefinitions_file, "{symbol} {symbol}${NAMESPACE}").unwrap();
            }
        } else if symbol.starts_with(zn_prefix) {
            writeln!(
                redefinitions_file,
                "{symbol} {}",
                symbol.replacen(zn_prefix, &replacement, 1)
            )
            .unwrap();
        } else if symbol.starts_with(r_prefix) {
            // v0 mangling (not in namespace): this uses the vendor-specific suffix model
            writeln!(redefinitions_file, "{symbol} {symbol}${NAMESPACE}").unwrap();
        }
    }
    redefinitions_file.flush().unwrap();
    drop(redefinitions_file);

    assert!(
        nm_child.wait().is_ok_and(|s| s.success()),
        "Couldn't link runtime crate! Do you have the llvm-tools component installed? (`rustup component add llvm-tools-preview` to install)"
    );

    let mut objcopy_command = Command::new(rust_objcopy);

    for symbol in [
        "__rust_drop_panic",
        "__rust_foreign_exception",
        "rust_begin_unwind",
        "rust_panic",
        "rust_eh_personality",
        "__rg_oom",
        "__rdl_oom",
        "__rdl_alloc",
        "__rust_alloc",
        "__rdl_dealloc",
        "__rust_dealloc",
        "__rdl_realloc",
        "__rust_realloc",
        "__rdl_alloc_zeroed",
        "__rust_alloc_zeroed",
        "__rust_alloc_error_handler",
        "__rust_no_alloc_shim_is_unstable",
        "__rust_alloc_error_handler_should_panic",
    ] {
        let mut symbol = symbol.to_string();
        // macOS symbols have an extra `_`
        if cfg!(target_os = "macos") {
            symbol.insert(0, '_');
        }

        objcopy_command
            .arg("--redefine-sym")
            .arg(format!("{symbol}={symbol}_libafl_libfuzzer_runtime"));
    }

    objcopy_command
        .arg("--redefine-syms")
        .arg(redefined_symbols)
        .args([&archive_path, &redefined_archive_path]);

    assert!(
        objcopy_command.status().is_ok_and(|s| s.success()),
        "Couldn't rename allocators in the runtime crate! Do you have the llvm-tools component installed? (`rustup component add llvm-tools-preview` to install)"
    );
    redefined_archive_path
}