whisker_dev_server/hotpatch/

runner.rs

//! Spawn-side companions to [`super::thin_build::build_obj_plan`]
//! and [`super::link_plan::build_link_plan`].
//!
//! Two stages, one helper that wires them together:
//!
//!   - [`run_obj_plan`] — invoke rustc with an [`ObjBuildPlan`] and
//!     return the path of the emitted object file.
//!   - [`run_link_plan`] — invoke the linker driver with a
//!     [`LinkPlan`] and return the path of the produced
//!     `.so` / `.dylib`.
//!   - [`thin_rebuild_obj`] — composes both: build the obj plan,
//!     spawn rustc, build the link plan, spawn the linker, return
//!     the dylib path.
//!
//! All three inherit stdout/stderr so compile / link errors land
//! in the dev-server's terminal instead of being swallowed.

use anyhow::{Context, Result};
use std::path::{Path, PathBuf};

use super::link_plan::{build_link_plan, LinkPlan, LinkerOs};
use super::thin_build::{build_obj_plan, ObjBuildPlan};
use super::wrapper::CapturedRustcInvocation;

/// Spawn rustc with `plan.args` from `cwd`. On success, returns
/// the path of the emitted object (= `plan.expected_object`).
///
/// rustc with `--emit=obj <path>` writes exactly one `.o`; we don't
/// need to scan the directory after the fact.
pub async fn run_obj_plan(plan: &ObjBuildPlan, rustc_path: &Path, cwd: &Path) -> Result<PathBuf> {
    std::fs::create_dir_all(&plan.output_dir)
        .with_context(|| format!("create out dir {}", plan.output_dir.display()))?;
    let status = tokio::process::Command::new(rustc_path)
        .args(&plan.args)
        .current_dir(cwd)
        .status()
        .await
        .with_context(|| format!("spawn {}", rustc_path.display()))?;
    if !status.success() {
        anyhow::bail!(
            "rustc exited {} during obj rebuild (out_dir={})",
            status,
            plan.output_dir.display(),
        );
    }
    if !plan.expected_object.is_file() {
        anyhow::bail!(
            "rustc succeeded but `{}` was not produced",
            plan.expected_object.display(),
        );
    }
    Ok(plan.expected_object.clone())
}

/// Spawn the linker driver with `plan.args` from `cwd`. On success,
/// returns the path of the produced shared object (= `plan.output`).
///
/// `linker_path` is typically the same `cc`/`clang` rustc would use.
/// On macOS, `xcrun -f clang` resolves to the active toolchain's
/// driver. On Linux/Android, the NDK ships a per-API-level wrapper
/// (e.g. `aarch64-linux-android21-clang`).
pub async fn run_link_plan(plan: &LinkPlan, linker_path: &Path, cwd: &Path) -> Result<PathBuf> {
    if let Some(parent) = plan.output.parent() {
        std::fs::create_dir_all(parent)
            .with_context(|| format!("create out dir {}", parent.display()))?;
    }
    // Capture stderr so a failed link surfaces *why* (e.g. unresolved
    // symbols, missing libraries) instead of just "exit 1". stdout is
    // inherited so progress / warnings remain visible.
    let out = tokio::process::Command::new(linker_path)
        .args(&plan.args)
        .current_dir(cwd)
        .stderr(std::process::Stdio::piped())
        .output()
        .await
        .with_context(|| format!("spawn {}", linker_path.display()))?;
    if !out.status.success() {
        let stderr = String::from_utf8_lossy(&out.stderr);
        anyhow::bail!(
            "linker `{}` exited {} during patch link (output={})\n\
             argv: {:?}\n\
             stderr:\n{}",
            linker_path.display(),
            out.status,
            plan.output.display(),
            plan.args,
            stderr.trim_end(),
        );
    }
    if !plan.output.is_file() {
        anyhow::bail!(
            "linker succeeded but `{}` was not produced",
            plan.output.display(),
        );
    }
    Ok(plan.output.clone())
}

/// Compose [`run_obj_plan`] and [`run_link_plan`] into the full
/// hot-patch rebuild.
///
/// Inputs are the **captured** rustc + linker calls from the fat
/// build, plus where the patch should land and which OS the patch
/// is going to run on. Returns the final `.so`/`.dylib` path that
/// can be packaged into a `JumpTable` and sent to the device.
///
/// This function is the "happy path" — the production code (Patcher,
/// I4g-X3) calls this directly when neither captured call is missing
/// and the target is supported.
///
/// `aslr_stub` is an optional pre-built jump-stub object
/// ([`crate::hotpatch::create_undefined_symbol_stub`]). When `Some`,
/// it gets linked into the patch dylib alongside the freshly rebuilt
/// `.o`, supplying every host symbol the patch references as a
/// hardcoded runtime-address trampoline. When `None`, the patch is
/// linked with `--unresolved-symbols=ignore-all` only — fine for
/// host-only fixtures where the test process satisfies the patch via
/// `dynamic_lookup`.
#[allow(clippy::too_many_arguments)]
pub async fn thin_rebuild_obj(
    captured_rustc: &CapturedRustcInvocation,
    captured_linker_args: &[String],
    output_dir: &Path,
    output_dylib: &Path,
    rustc_path: &Path,
    linker_path: &Path,
    cwd: &Path,
    target_os: LinkerOs,
    aslr_stub: Option<&Path>,
) -> Result<PathBuf> {
    let obj_plan = build_obj_plan(captured_rustc, output_dir);
    let object = run_obj_plan(&obj_plan, rustc_path, cwd).await?;
    let extras: Vec<PathBuf> = aslr_stub.map(|p| vec![p.to_path_buf()]).unwrap_or_default();
    let link_plan = build_link_plan(
        captured_linker_args,
        &object,
        output_dylib,
        target_os,
        &extras,
        &[],
    );
    run_link_plan(&link_plan, linker_path, cwd).await
}

// ============================================================================
// Tests
// ============================================================================

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

    fn s(v: &[&str]) -> Vec<String> {
        v.iter().map(|s| s.to_string()).collect()
    }

    fn unique_tempdir() -> PathBuf {
        use std::sync::atomic::{AtomicU64, Ordering};
        static SEQ: AtomicU64 = AtomicU64::new(0);
        let n = SEQ.fetch_add(1, Ordering::Relaxed);
        let pid = std::process::id();
        let p = std::env::temp_dir().join(format!("whisker-runner-test-{pid}-{n}"));
        let _ = std::fs::remove_dir_all(&p);
        std::fs::create_dir_all(&p).unwrap();
        p
    }

    // ----- run_obj_plan ------------------------------------------------

    #[tokio::test]
    async fn run_obj_plan_surfaces_rustc_failure_with_path_context() {
        // Plan that will fail because the source file doesn't exist.
        let dir = unique_tempdir();
        let plan = ObjBuildPlan {
            args: s(&[
                "--edition=2021",
                "--crate-name",
                "demo",
                "--crate-type",
                "rlib",
                "--out-dir",
                dir.to_string_lossy().as_ref(),
                "/nope/this/source/does/not/exist.rs",
                "--emit",
                &format!("obj={}/demo.o", dir.display()),
            ]),
            output_dir: dir.clone(),
            expected_object: dir.join("demo.o"),
        };
        let res = run_obj_plan(&plan, Path::new("rustc"), &dir).await;
        let err = res.unwrap_err();
        let msg = format!("{err:#}");
        assert!(
            msg.contains("rustc exited") || msg.contains("spawn"),
            "msg should mention rustc exit or spawn: {msg}",
        );
        let _ = std::fs::remove_dir_all(&dir);
    }

    #[tokio::test]
    async fn run_obj_plan_errors_when_rustc_binary_doesnt_exist() {
        let dir = unique_tempdir();
        let plan = ObjBuildPlan {
            args: vec![],
            output_dir: dir.clone(),
            expected_object: dir.join("demo.o"),
        };
        let res = run_obj_plan(&plan, Path::new("/nope/no-such-rustc"), &dir).await;
        assert!(res.is_err());
        let _ = std::fs::remove_dir_all(&dir);
    }

    // ----- run_link_plan -----------------------------------------------

    #[tokio::test]
    async fn run_link_plan_creates_output_parent_dir() {
        // The linker call will fail (we use /usr/bin/true so it
        // returns success without writing anything), then run_link_plan
        // surfaces "succeeded but file not produced". The test's
        // load-bearing claim is "parent dir was created up front
        // even though the call ultimately failed".
        let dir = unique_tempdir();
        let nested_out = dir.join("nested/sub").join("libfoo.dylib");
        let plan = LinkPlan {
            args: vec![],
            output: nested_out.clone(),
        };
        let res = run_link_plan(&plan, Path::new("/usr/bin/true"), &dir).await;
        assert!(res.is_err(), "true returns success but writes no file");
        let parent = nested_out.parent().unwrap();
        assert!(parent.is_dir(), "parent should have been created");
        let _ = std::fs::remove_dir_all(&dir);
    }

    #[tokio::test]
    async fn run_link_plan_surfaces_linker_nonzero_exit() {
        // /usr/bin/false exits 1 — we want a clear error, not a
        // "file not found" misdirection.
        let dir = unique_tempdir();
        let plan = LinkPlan {
            args: vec![],
            output: dir.join("libfoo.dylib"),
        };
        let res = run_link_plan(&plan, Path::new("/usr/bin/false"), &dir).await;
        let err = res.unwrap_err();
        let msg = format!("{err:#}");
        assert!(msg.contains("linker"), "msg: {msg}");
        let _ = std::fs::remove_dir_all(&dir);
    }
}