fix(fspy): allocate a slot for the NULL terminator in execl with 32+ arguments

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 - **Perf** When tasks miss the cache, `vp run` no longer waits for the disk after saving each task's result, so the run finishes sooner. If the computer loses power or the operating system crashes during `vp run`, the cache entries that the run saved can be lost, and those tasks run again next time instead of hitting the cache ([#871](https://github.com/voidzero-dev/vite-task/pull/871)).
 - **Fixed** Running `vp run` in a package that sits inside a workspace folder but isn't listed in its `pnpm-workspace.yaml` `packages` or `package.json` `workspaces` now runs that package's own tasks, instead of treating the enclosing workspace as its root. When both configurations exist, `pnpm-workspace.yaml` takes precedence ([#859](https://github.com/voidzero-dev/vite-task/pull/859)).
+- **Fixed** On Linux and macOS, programs using automatic file-access tracking no longer abort when they call `execl`, `execlp`, or `execle` with 32 or more arguments ([#699](https://github.com/voidzero-dev/vite-task/issues/699), [#865](https://github.com/voidzero-dev/vite-task/pull/865)).
 - **Fixed** A mistyped or misplaced setting in a task now gets an error that names it. For example, `cache: { outputs: [...] }` now fails with an `unknown field` error that names `outputs` and lists the accepted settings, instead of `data did not match any variant of untagged enum UserTaskDefinition` ([vite-plus#2635](https://github.com/voidzero-dev/vite-plus/issues/2635), [#815](https://github.com/voidzero-dev/vite-task/pull/815)).
 - **Fixed** In cached tasks on Linux and macOS, programs that pass `-1` as a directory descriptor to calls such as `openat` no longer abort. For example, `ps -p <pid>` from procps-ng 4.0.6 or later aborted when the process had already exited ([#862](https://github.com/voidzero-dev/vite-task/pull/862)).
 - **Fixed** `vp run` no longer panics before running a script that contains non-ASCII characters, such as `echo こんにちは`, and no longer cuts off such commands where it displays them ([#861](https://github.com/voidzero-dev/vite-task/pull/861)).

crates/fspy/tests/execl_many_args.rs

@@ -0,0 +1,95 @@
+//! `execl`, `execlp`, and `execle` take a variable number of arguments. The
+//! interposer stores them in a stack array for fewer than 32 arguments and a
+//! heap allocation otherwise. A call with 32 or more arguments used to write
+//! the NULL terminator past the end of that allocation, aborting the program.
+//!
+//! `exec` replaces the process, so the call runs in a forked child; the parent
+//! waits for the child and checks that the program ran successfully.
+#![cfg(unix)]
+
+mod test_utils;
+
+use std::{ffi::CString, io::Error};
+
+use test_log::test;
+
+#[test(tokio::test)]
+async fn execl_with_many_arguments() -> anyhow::Result<()> {
+    let program = which::which("true")?;
+    track_fn!(program.to_str().unwrap().to_owned(), |program: String| {
+        let program = CString::new(program).unwrap();
+        let args: Vec<CString> = (0..40)
+            .map(
+                |i| if i == 0 { program.clone() } else { CString::new(format!("arg{i}")).unwrap() },
+            )
+            .collect();
+
+        // SAFETY: the tracked test process is single-threaded here, and the
+        // child and parent only call async-signal-safe functions below.
+        let pid = unsafe { libc::fork() };
+        assert!(pid >= 0, "fork failed: {}", Error::last_os_error());
+
+        if pid == 0 {
+            // SAFETY: every pointer is a valid NUL-terminated C string and the
+            // argument list is NULL-terminated.
+            unsafe {
+                libc::execl(
+                    program.as_ptr(),
+                    args[0].as_ptr(),
+                    args[1].as_ptr(),
+                    args[2].as_ptr(),
+                    args[3].as_ptr(),
+                    args[4].as_ptr(),
+                    args[5].as_ptr(),
+                    args[6].as_ptr(),
+                    args[7].as_ptr(),
+                    args[8].as_ptr(),
+                    args[9].as_ptr(),
+                    args[10].as_ptr(),
+                    args[11].as_ptr(),
+                    args[12].as_ptr(),
+                    args[13].as_ptr(),
+                    args[14].as_ptr(),
+                    args[15].as_ptr(),
+                    args[16].as_ptr(),
+                    args[17].as_ptr(),
+                    args[18].as_ptr(),
+                    args[19].as_ptr(),
+                    args[20].as_ptr(),
+                    args[21].as_ptr(),
+                    args[22].as_ptr(),
+                    args[23].as_ptr(),
+                    args[24].as_ptr(),
+                    args[25].as_ptr(),
+                    args[26].as_ptr(),
+                    args[27].as_ptr(),
+                    args[28].as_ptr(),
+                    args[29].as_ptr(),
+                    args[30].as_ptr(),
+                    args[31].as_ptr(),
+                    args[32].as_ptr(),
+                    args[33].as_ptr(),
+                    args[34].as_ptr(),
+                    args[35].as_ptr(),
+                    args[36].as_ptr(),
+                    args[37].as_ptr(),
+                    args[38].as_ptr(),
+                    args[39].as_ptr(),
+                    core::ptr::null::<libc::c_char>(),
+                );
+                libc::_exit(127);
+            }
+        }
+
+        let mut status = 0;
+        // SAFETY: `pid` is the child process created above, and `status` is
+        // writable storage for the wait status.
+        let waited = unsafe { libc::waitpid(pid, &raw mut status, 0) };
+        assert_eq!(waited, pid, "waitpid failed: {}", Error::last_os_error());
+        assert!(libc::WIFEXITED(status), "child did not exit normally: {status}");
+        assert_eq!(libc::WEXITSTATUS(status), 0);
+    })
+    .await?;
+
+    Ok(())
+}

crates/fspy/tests/test_utils/mod.rs

@@ -23,6 +23,11 @@ pub use vt_subprocess_test::command_for_fn;
 /// # Panics
 ///
 /// Panics if the path was not accessed, or was accessed in another way.
+#[expect(
+    clippy::allow_attributes,
+    reason = "allow attribute required for conditionally-used helper"
+)]
+#[allow(dead_code, reason = "not all test files use this helper")]
 #[track_caller]
 pub fn assert_contains<'a>(
     accesses: &'a PathAccessIterable,

crates/fspy_preload_unix/src/interceptions/spawn/exec/with_argv.rs

@@ -31,14 +31,14 @@ pub unsafe fn with_argv(
         stack.as_mut_slice()
     } else if argc < 4096 {
         // TODO: Use ARG_MAX, not this hardcoded constant
-        // SAFETY: requesting a heap allocation of the correct size for argc pointers
-        let ptr = unsafe { libc::malloc(argc * mem::size_of::<*const c_char>()) };
+        // SAFETY: requesting a heap allocation of the correct size for argc + 1 pointers, including the NULL terminator
+        let ptr = unsafe { libc::malloc((argc + 1) * mem::size_of::<*const c_char>()) };
         if ptr.is_null() {
             Error::ENOMEM.set();
             return -1;
         }
-        // SAFETY: ptr is non-null (checked above), properly aligned, and points to argc elements worth of allocated memory
-        unsafe { slice::from_raw_parts_mut(ptr.cast::<MaybeUninit<*const c_char>>(), argc) }
+        // SAFETY: ptr is non-null (checked above), properly aligned, and points to argc + 1 elements worth of allocated memory
+        unsafe { slice::from_raw_parts_mut(ptr.cast::<MaybeUninit<*const c_char>>(), argc + 1) }
     } else {
         Error::E2BIG.set();
         return -1;