Fixed get thread name behavior for FreeBSD

src/shims/unix/freebsd/foreign_items.rs

@@ -34,12 +34,15 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
             "pthread_get_name_np" => {
                 let [thread, name, len] =
                     this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
-                // FreeBSD's pthread_get_name_np does not return anything.
+                // FreeBSD's pthread_get_name_np does not return anything
+                // and uses strlcpy, which truncates the resulting value,
+                // but always adds a null terminator (except for zero-sized buffers).
+                // https://github.com/freebsd/freebsd-src/blob/c2d93a803acef634bd0eede6673aeea59e90c277/lib/libthr/thread/thr_info.c#L119-L144
                 this.pthread_getname_np(
                     this.read_scalar(thread)?,
                     this.read_scalar(name)?,
                     this.read_scalar(len)?,
-                    false,
+                    /* truncate */ true,
                 )?;
             }
 

tests/pass-dep/libc/pthread-threadname.rs

@@ -79,10 +79,9 @@ fn main() {
             // if the buffer is shorter than the thread name.
             #[cfg(any(target_os = "illumos", target_os = "solaris"))]
             assert_eq!(get_thread_name(&mut buf[..4]), libc::ERANGE);
-
-            // For libc implementation for macOS it's not an error
-            // for a buffer being too short for the thread name.
-            #[cfg(target_os = "macos")]
+            // On macOS and FreeBSD it's not an error for the buffer to be
+            // too short for the thread name -- they truncate instead.
+            #[cfg(any(target_os = "freebsd", target_os = "macos"))]
             {
                 // Ensure that a zero sized buffer returns no error.
                 assert_eq!(get_thread_name(&mut buf[..0]), 0);
@@ -123,8 +122,8 @@ fn main() {
             // Also test directly calling pthread_setname to check its return value.
             assert_eq!(set_thread_name(&cstr), 0);
 
-            // But with a too long name it should fail (except on FreeBSD where the
-            // function has no return, hence cannot indicate failure).
+            // But with a too long name it should fail (except on FreeBSD where
+            // names of arbitrary size seem to be supported).
             // On macOS, the error code is different.
             #[cfg(not(any(target_os = "freebsd", target_os = "macos")))]
             assert_eq!(set_thread_name(&CString::new(long_name).unwrap()), libc::ERANGE);