print thread name in miri error backtraces

Author: RalfJung

src/tools/miri/src/concurrency/data_race.rs

@@ -1673,8 +1673,8 @@ impl GlobalState {
         vector: VectorIdx,
     ) -> String {
         let thread = self.vector_info.borrow()[vector];
-        let thread_name = thread_mgr.get_thread_name(thread);
-        format!("thread `{}`", String::from_utf8_lossy(thread_name))
+        let thread_name = thread_mgr.get_thread_display_name(thread);
+        format!("thread `{thread_name}`")
     }
 
     /// Acquire a lock, express that the previous call of

src/tools/miri/src/concurrency/thread.rs

@@ -160,9 +160,18 @@ pub type StackEmptyCallback<'mir, 'tcx> =
     Box<dyn FnMut(&mut MiriInterpCx<'mir, 'tcx>) -> InterpResult<'tcx, Poll<()>>>;
 
 impl<'mir, 'tcx> Thread<'mir, 'tcx> {
-    /// Get the name of the current thread, or `<unnamed>` if it was not set.
-    fn thread_name(&self) -> &[u8] {
-        if let Some(ref thread_name) = self.thread_name { thread_name } else { b"<unnamed>" }
+    /// Get the name of the current thread if it was set.
+    fn thread_name(&self) -> Option<&[u8]> {
+        self.thread_name.as_deref()
+    }
+
+    /// Get the name of the current thread for display purposes; will include thread ID if not set.
+    fn thread_display_name(&self, id: ThreadId) -> String {
+        if let Some(ref thread_name) = self.thread_name {
+            String::from_utf8_lossy(thread_name).into_owned()
+        } else {
+            format!("unnamed-{}", id.index())
+        }
     }
 
     /// Return the top user-relevant frame, if there is one.
@@ -205,7 +214,7 @@ impl<'mir, 'tcx> std::fmt::Debug for Thread<'mir, 'tcx> {
         write!(
             f,
             "{}({:?}, {:?})",
-            String::from_utf8_lossy(self.thread_name()),
+            String::from_utf8_lossy(self.thread_name().unwrap_or(b"<unnamed>")),
             self.state,
             self.join_status
         )
@@ -572,10 +581,14 @@ impl<'mir, 'tcx: 'mir> ThreadManager<'mir, 'tcx> {
     }
 
     /// Get the name of the given thread.
-    pub fn get_thread_name(&self, thread: ThreadId) -> &[u8] {
+    pub fn get_thread_name(&self, thread: ThreadId) -> Option<&[u8]> {
         self.threads[thread].thread_name()
     }
 
+    pub fn get_thread_display_name(&self, thread: ThreadId) -> String {
+        self.threads[thread].thread_display_name(thread)
+    }
+
     /// Put the thread into the blocked state.
     fn block_thread(&mut self, thread: ThreadId) {
         let state = &mut self.threads[thread].state;
@@ -980,7 +993,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
     }
 
     #[inline]
-    fn get_thread_name<'c>(&'c self, thread: ThreadId) -> &'c [u8]
+    fn get_thread_name<'c>(&'c self, thread: ThreadId) -> Option<&[u8]>
     where
         'mir: 'c,
     {

src/tools/miri/src/diagnostics.rs

@@ -477,7 +477,6 @@ pub fn report_msg<'tcx>(
 
     // Show note and help messages.
     let mut extra_span = false;
-    let notes_len = notes.len();
     for (span_data, note) in notes {
         if let Some(span_data) = span_data {
             err.span_note(span_data.span(), note);
@@ -486,7 +485,6 @@ pub fn report_msg<'tcx>(
             err.note(note);
         }
     }
-    let helps_len = helps.len();
     for (span_data, help) in helps {
         if let Some(span_data) = span_data {
             err.span_help(span_data.span(), help);
@@ -495,12 +493,20 @@ pub fn report_msg<'tcx>(
             err.help(help);
         }
     }
-    if notes_len + helps_len > 0 {
-        // Add visual separator before backtrace.
-        err.note(if extra_span { "BACKTRACE (of the first span):" } else { "BACKTRACE:" });
-    }
 
     // Add backtrace
+    let mut backtrace_title = String::from("BACKTRACE");
+    if extra_span {
+        write!(backtrace_title, " (of the first span)").unwrap();
+    }
+    let thread_name =
+        machine.threads.get_thread_display_name(machine.threads.get_active_thread_id());
+    if thread_name != "main" {
+        // Only print thread name if it is not `main`.
+        write!(backtrace_title, " on thread `{thread_name}`").unwrap();
+    };
+    write!(backtrace_title, ":").unwrap();
+    err.note(backtrace_title);
     for (idx, frame_info) in stacktrace.iter().enumerate() {
         let is_local = machine.is_local(frame_info);
         // No span for non-local frames and the first frame (which is the error site).

src/tools/miri/src/shims/unix/thread.rs

@@ -104,7 +104,8 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
         let name_out = name_out.to_pointer(this)?;
         let len = len.to_target_usize(this)?;
 
-        let name = this.get_thread_name(thread).to_owned();
+        // FIXME: we should use the program name if the thread name is not set
+        let name = this.get_thread_name(thread).unwrap_or(b"<unnamed>").to_owned();
         let (success, _written) = this.write_c_str(&name, name_out, len)?;
 
         Ok(if success { Scalar::from_u32(0) } else { this.eval_libc("ERANGE") })

src/tools/miri/tests/compiletest.rs

@@ -172,6 +172,8 @@ regexes! {
     r"\.rs:[0-9]+:[0-9]+(: [0-9]+:[0-9]+)?" => ".rs:LL:CC",
     // erase alloc ids
     "alloc[0-9]+"                    => "ALLOC",
+    // erase thread ids
+    r"unnamed-[0-9]+"               => "unnamed-ID",
     // erase borrow tags
     "<[0-9]+>"                       => "<TAG>",
     "<[0-9]+="                       => "<TAG=",

src/tools/miri/tests/fail-dep/concurrency/libc_pthread_create_too_few_args.stderr

@@ -6,7 +6,7 @@ LL |     panic!()
    |
    = help: this indicates a bug in the program: it performed an invalid operation, and caused Undefined Behavior
    = help: see https://doc.rust-lang.org/nightly/reference/behavior-considered-undefined.html for further information
-   = note: BACKTRACE:
+   = note: BACKTRACE on thread `unnamed-ID`:
    = note: inside `thread_start` at RUSTLIB/core/src/panic.rs:LL:CC
    = note: this error originates in the macro `$crate::panic::panic_2021` which comes from the expansion of the macro `panic` (in Nightly builds, run with -Z macro-backtrace for more info)
 

src/tools/miri/tests/fail-dep/concurrency/libc_pthread_create_too_many_args.stderr

@@ -6,7 +6,7 @@ LL |     panic!()
    |
    = help: this indicates a bug in the program: it performed an invalid operation, and caused Undefined Behavior
    = help: see https://doc.rust-lang.org/nightly/reference/behavior-considered-undefined.html for further information
-   = note: BACKTRACE:
+   = note: BACKTRACE on thread `unnamed-ID`:
    = note: inside `thread_start` at RUSTLIB/core/src/panic.rs:LL:CC
    = note: this error originates in the macro `$crate::panic::panic_2021` which comes from the expansion of the macro `panic` (in Nightly builds, run with -Z macro-backtrace for more info)
 

src/tools/miri/tests/fail-dep/concurrency/libc_pthread_join_main.stderr

@@ -6,7 +6,7 @@ LL |             assert_eq!(libc::pthread_join(thread_id, ptr::null_mut()), 0);
    |
    = help: this indicates a bug in the program: it performed an invalid operation, and caused Undefined Behavior
    = help: see https://doc.rust-lang.org/nightly/reference/behavior-considered-undefined.html for further information
-   = note: BACKTRACE:
+   = note: BACKTRACE on thread `unnamed-ID`:
    = note: inside closure at $DIR/libc_pthread_join_main.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace

src/tools/miri/tests/fail-dep/concurrency/libc_pthread_join_multiple.stderr

@@ -6,7 +6,7 @@ LL | ...   assert_eq!(libc::pthread_join(native_copy, ptr::null_mut()), 0);
    |
    = help: this indicates a bug in the program: it performed an invalid operation, and caused Undefined Behavior
    = help: see https://doc.rust-lang.org/nightly/reference/behavior-considered-undefined.html for further information
-   = note: BACKTRACE:
+   = note: BACKTRACE on thread `unnamed-ID`:
    = note: inside closure at $DIR/libc_pthread_join_multiple.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace

src/tools/miri/tests/fail-dep/concurrency/libc_pthread_join_self.stderr

@@ -6,7 +6,7 @@ LL |             assert_eq!(libc::pthread_join(native, ptr::null_mut()), 0);
    |
    = help: this indicates a bug in the program: it performed an invalid operation, and caused Undefined Behavior
    = help: see https://doc.rust-lang.org/nightly/reference/behavior-considered-undefined.html for further information
-   = note: BACKTRACE:
+   = note: BACKTRACE on thread `unnamed-ID`:
    = note: inside closure at $DIR/libc_pthread_join_self.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace