Hi all,
I am trying to set up a dylib project that is intended to work as a LD_PRELOAD shared object. While the unit tests of what I'm implementing generally work fine, I'm having issues when running a simple integration test (the ones in ./tests directory) of this form:
fn preload_lib_path() -> PathBuf {
let path = [
env!("CARGO_MANIFEST_DIR"),
format!("target/debug/lib{}.so", env!("CARGO_PKG_NAME")).as_str(),
]
.into_iter()
.collect::<PathBuf>();
// File must exist for the integration tests that rely on it to succeed! Just in case...
assert!(path.is_file(), "Preload .so does not exist at {path:?}. Please compile the project first and then run these tests!");
path
}
#[test]
fn preload_works_via_logs() {
// We create a random command with `assert_cmd` and pass LD_PRELOAD as an env var to it
let command = Command::new("ls")
.arg("-l")
.env("LD_PRELOAD", preload_lib_path())
.output()
.expect("failed to execute process");
// Running a innocuous command expected to work without issues
command
.assert()
.success();
// ... there are some example logs that I print, so I test that they are emitted here
}
I'm trying to set up a minimal reproducer but I haven't managed yet (I'll share as soon as I do), but the basic structure of the project has an entrypoint like this one:
#[cfg_attr(target_os = "linux", link_section = ".init_array")]
pub static LD_PRELOAD_INITIALIZE: extern "C" fn() = self::ld_preload_initialize;
extern "C" fn ld_preload_initialize() { /* logic here */ }
And performs some operations like:
- Setting up a logger with
env_logger. - Read files and parse them with
serde. - Manipulate a non-trivial collection (
HashMap) inside aMutex.
Although by the logs that are emitted indicate that the ld_preload_initialize reaches the end, the actual command executed in the test (ls) doesn't get to run, and instead I get this error:
fatal runtime error: thread::set_current should only be called once per thread
error: test failed, to rerun pass `--lib`
Caused by:
process didn't exit successfully: `/<PROJECT_PATH>/target/debug/deps/<PROJECT_NAME>-5f5c39d631f618e1` (signal: 6, SIGABRT: process abort signal)
I don't spawn any threads explicitly in all the logic (but I assume env_logger might), nor call set_current.
I have seen that if I compile the project with the static conditionally compiled to be absent in test builds the integration tests actually succeed:
#[cfg(not(test))]
#[cfg_attr(target_os = "linux", link_section = ".init_array")]
pub static LD_PRELOAD_INITIALIZE: extern "C" fn() = self::ld_preload_initialize;
extern "C" fn ld_preload_initialize() { ... }
So I suspect some kind of this PRELOAD .init_array section is being initialised more than once when running the "test binary"... but I don't know if testing like this is even advisable or if it should be working at all anyways. The code I'm writing tries its best to not have any panics (handling all Result::Err, Option::None and so on) and doesn't include any explicit unsafe code.
As I said above, I'm trying to set up a minimal reproducer but I haven't been able to do so. As soon as I have it I'll either add more data here or even post the solution if I find it.
It's my first time exploring this, so there's quite a bit that I don't know yet. I wonder if there's anything in what I report that points to a possible root cause? Any recommendations when developing programs like this that leverage .init_array and are intended to run as LD_PRELOAD shared objects? Let me know if there's more information I can provide to help figuring out the issue, I'll try to share the details I can.
Thanks a lot!