test(ffi): assert cdylib exists and is readable before ELF inspection

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: yannham

libdd-otel-thread-ctx-ffi/build.rs

@@ -25,18 +25,5 @@ fn main() {
         println!(
             "cargo:rustc-cdylib-link-arg=-Wl,--version-script={manifest_dir}/tls-dynamic-list.txt"
         );
-
-        // Expose the profile output directory to integration tests so they can
-        // locate the cdylib without fragile path-walking.
-        // OUT_DIR = <target>/[<triple>/]<profile>/build/<pkg>-<hash>/out
-        // Three levels up lands on <target>/[<triple>/]<profile>.
-        let profile_dir = std::path::PathBuf::from(&env::var("OUT_DIR").unwrap())
-            .ancestors()
-            .nth(3)
-            .unwrap()
-            .to_str()
-            .unwrap()
-            .to_owned();
-        println!("cargo:rustc-env=CDYLIB_PROFILE_DIR={profile_dir}");
     }
 }

libdd-otel-thread-ctx-ffi/tests/elf_properties.rs

@@ -8,7 +8,9 @@
 //! - `otel_thread_ctx_v1` is accessed via TLSDESC relocations (R_X86_64_TLSDESC or
 //!   R_AARCH64_TLSDESC), as required by the OTel thread-level context sharing spec.
 //!
-//! The cdylib path is injected at compile time via `build.rs` from `OUT_DIR`.
+//! The cdylib path is derived at runtime from the test executable location:
+//! the test binary lives in `target/<[triple/]profile>/deps/`, so the cdylib
+//! is one level up at `target/<[triple/]profile>/liblibdd_otel_thread_ctx_ffi.so`.
 
 #![cfg(target_os = "linux")]
 
@@ -18,22 +20,43 @@ use std::process::Command;
 const SYMBOL: &str = "otel_thread_ctx_v1";
 
 fn cdylib_path() -> PathBuf {
-    PathBuf::from(env!("CDYLIB_PROFILE_DIR")).join("liblibdd_otel_thread_ctx_ffi.so")
+    // test binary: target/<[triple/]profile>/deps/<name>
+    // cdylib:      target/<[triple/]profile>/liblibdd_otel_thread_ctx_ffi.so
+    let exe = std::env::current_exe().expect("failed to read current executable path");
+    exe.parent() // deps/
+        .and_then(|p| p.parent()) // <profile>/
+        .expect("unexpected test executable path structure")
+        .join("liblibdd_otel_thread_ctx_ffi.so")
+}
+
+fn check_cdylib_exists(path: &PathBuf) {
+    assert!(
+        path.exists(),
+        "cdylib not found at {}: \
+         ensure `cargo build -p libdd-otel-thread-ctx-ffi` has been run for this profile",
+        path.display()
+    );
+    assert!(
+        std::fs::File::open(path).is_ok(),
+        "cdylib exists at {} but could not be opened for reading",
+        path.display()
+    );
 }
 
 fn readelf(args: &[&str], path: &PathBuf) -> String {
     let out = Command::new("readelf")
         .args(args)
         .arg(path)
         .output()
-        .expect("failed to run readelf — is binutils installed?");
+        .expect("failed to run readelf. Is binutils installed?");
     String::from_utf8_lossy(&out.stdout).into_owned()
 }
 
 #[test]
 #[cfg_attr(miri, ignore)]
 fn otel_thread_ctx_v1_in_dynsym() {
     let path = cdylib_path();
+    check_cdylib_exists(&path);
     let output = readelf(&["-W", "--dyn-syms"], &path);
     let line = output
         .lines()
@@ -49,6 +72,7 @@ fn otel_thread_ctx_v1_in_dynsym() {
 #[cfg_attr(miri, ignore)]
 fn otel_thread_ctx_v1_tlsdesc_reloc() {
     let path = cdylib_path();
+    check_cdylib_exists(&path);
     let output = readelf(&["-W", "--relocs"], &path);
     let found = output.lines().any(|l| {
         l.contains(SYMBOL) && (l.contains("R_X86_64_TLSDESC") || l.contains("R_AARCH64_TLSDESC"))