Fix prctl SET_NAME and GET_NAME behaviour.

src/shims/thread.rs

@@ -99,11 +99,17 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
         let option = this.read_scalar(option)?.to_i32()?;
         if option == this.eval_libc_i32("PR_SET_NAME")? {
             let address = this.read_scalar(arg2)?.not_undef()?;
-            let name = this.memory.read_c_str(address)?.to_owned();
+            let mut name = this.memory.read_c_str(address)?.to_owned();
+            // The name should be no more than 16 bytes, including the null
+            // byte. Since `read_c_str` returns the string without the null
+            // byte, we need to truncate to 15.
+            name.truncate(15);
             this.set_active_thread_name(name)?;
         } else if option == this.eval_libc_i32("PR_GET_NAME")? {
             let address = this.read_scalar(arg2)?.not_undef()?;
-            let name = this.get_active_thread_name()?.to_vec();
+            let mut name = this.get_active_thread_name()?.to_vec();
+            name.push(0u8);
+            assert!(name.len() <= 16);
             this.memory.write_bytes(address, name)?;
         } else {
             throw_unsup_format!("unsupported prctl option {}", option);

src/thread.rs

@@ -313,11 +313,11 @@ impl<'mir, 'tcx: 'mir> ThreadManager<'mir, 'tcx> {
     }
 
     /// Get the name of the active thread.
-    fn get_thread_name(&self) -> InterpResult<'tcx, &[u8]> {
+    fn get_thread_name(&self) -> &[u8] {
         if let Some(ref thread_name) = self.active_thread_ref().thread_name {
-            Ok(thread_name)
+            thread_name
         } else {
-            throw_ub_format!("thread {:?} has no name set", self.active_thread)
+            b"<unnamed>"
         }
     }
 
@@ -574,7 +574,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
         'mir: 'c,
     {
         let this = self.eval_context_ref();
-        this.machine.threads.get_thread_name()
+        Ok(this.machine.threads.get_thread_name())
     }
 
     #[inline]

tests/run-pass/libc.rs

@@ -147,12 +147,21 @@ fn test_rwlock_libc_static_initializer() {
 #[cfg(target_os = "linux")]
 fn test_prctl_thread_name() {
     use std::ffi::CString;
+    use libc::c_long;
     unsafe {
+        let mut buf = [255; 10];
+        assert_eq!(libc::prctl(libc::PR_GET_NAME, buf.as_mut_ptr() as c_long, 0 as c_long, 0 as c_long, 0 as c_long), 0);
+        assert_eq!(b"<unnamed>\0", &buf);
         let thread_name = CString::new("hello").expect("CString::new failed");
-        assert_eq!(libc::prctl(libc::PR_SET_NAME, thread_name.as_ptr() as libc::c_long, 0 as libc::c_long, 0 as libc::c_long, 0 as libc::c_long), 0);
-        let mut buf = [0; 6];
-        assert_eq!(libc::prctl(libc::PR_GET_NAME, buf.as_mut_ptr() as libc::c_long, 0 as libc::c_long, 0 as libc::c_long, 0 as libc::c_long), 0);
-        assert_eq!(thread_name.as_bytes_with_nul(), buf);
+        assert_eq!(libc::prctl(libc::PR_SET_NAME, thread_name.as_ptr() as c_long, 0 as c_long, 0 as c_long, 0 as c_long), 0);
+        let mut buf = [255; 6];
+        assert_eq!(libc::prctl(libc::PR_GET_NAME, buf.as_mut_ptr() as c_long, 0 as c_long, 0 as c_long, 0 as c_long), 0);
+        assert_eq!(b"hello\0", &buf);
+        let long_thread_name = CString::new("01234567890123456789").expect("CString::new failed");
+        assert_eq!(libc::prctl(libc::PR_SET_NAME, long_thread_name.as_ptr() as c_long, 0 as c_long, 0 as c_long, 0 as c_long), 0);
+        let mut buf = [255; 16];
+        assert_eq!(libc::prctl(libc::PR_GET_NAME, buf.as_mut_ptr() as c_long, 0 as c_long, 0 as c_long, 0 as c_long), 0);
+        assert_eq!(b"012345678901234\0", &buf);
     }
 }