attempt to clarify what the backtrace belongs to when there could be ambiguity

90 files changed, 93 insertions, 90 deletions

diff --git a/src/tools/miri/src/diagnostics.rs b/src/tools/miri/src/diagnostics.rs
index 6f94d57bcc0..2087d0cb548 100644
--- a/src/tools/miri/src/diagnostics.rs
+++ b/src/tools/miri/src/diagnostics.rs
@@ -362,9 +362,11 @@ fn report_msg<'tcx>(
     }
 
     // Show note and help messages.
+    let mut extra_span = false;
     for (span_data, note) in &notes {
         if let Some(span_data) = span_data {
             err.span_note(span_data.span(), note);
+            extra_span = true;
         } else {
             err.note(note);
         }
@@ -372,13 +374,14 @@ fn report_msg<'tcx>(
     for (span_data, help) in &helps {
         if let Some(span_data) = span_data {
             err.span_help(span_data.span(), help);
+            extra_span = true;
         } else {
             err.help(help);
         }
     }
     if notes.len() + helps.len() > 0 {
         // Add visual separator before backtrace.
-        err.note("BACKTRACE:");
+        err.note(if extra_span { "BACKTRACE (of the first span):" } else { "BACKTRACE:" });
     }
     // Add backtrace
     for (idx, frame_info) in stacktrace.iter().enumerate() {
diff --git a/src/tools/miri/tests/fail/box-cell-alias.stderr b/src/tools/miri/tests/fail/box-cell-alias.stderr
index f57b52c4bda..fc946d6d39b 100644
--- a/src/tools/miri/tests/fail/box-cell-alias.stderr
+++ b/src/tools/miri/tests/fail/box-cell-alias.stderr
@@ -19,7 +19,7 @@ help: <TAG> was later invalidated at offsets [0x0..0x1] by a Unique retag
    |
 LL |     let res = helper(val, ptr);
    |                      ^^^
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside `helper` at $DIR/box-cell-alias.rs:LL:CC
 note: inside `main`
   --> $DIR/box-cell-alias.rs:LL:CC
diff --git a/src/tools/miri/tests/fail/data_race/alloc_read_race.stderr b/src/tools/miri/tests/fail/data_race/alloc_read_race.stderr
index 38b1ad3cfef..59b38024161 100644
--- a/src/tools/miri/tests/fail/data_race/alloc_read_race.stderr
+++ b/src/tools/miri/tests/fail/data_race/alloc_read_race.stderr
@@ -11,7 +11,7 @@ LL |             pointer.store(Box::into_raw(Box::new_uninit()), Ordering::Relax
    |                                         ^^^^^^^^^^^^^^^^^
    = 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 (of the first span):
    = note: inside closure at $DIR/alloc_read_race.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
diff --git a/src/tools/miri/tests/fail/data_race/alloc_write_race.stderr b/src/tools/miri/tests/fail/data_race/alloc_write_race.stderr
index 473a6945226..0564e4b5bf5 100644
--- a/src/tools/miri/tests/fail/data_race/alloc_write_race.stderr
+++ b/src/tools/miri/tests/fail/data_race/alloc_write_race.stderr
@@ -11,7 +11,7 @@ LL |                 .store(Box::into_raw(Box::<usize>::new_uninit()) as *mut us
    |                                      ^^^^^^^^^^^^^^^^^^^^^^^^^^
    = 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 (of the first span):
    = note: inside closure at $DIR/alloc_write_race.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
diff --git a/src/tools/miri/tests/fail/data_race/atomic_read_na_write_race1.stderr b/src/tools/miri/tests/fail/data_race/atomic_read_na_write_race1.stderr
index 565fba32808..ab7a6178102 100644
--- a/src/tools/miri/tests/fail/data_race/atomic_read_na_write_race1.stderr
+++ b/src/tools/miri/tests/fail/data_race/atomic_read_na_write_race1.stderr
@@ -11,7 +11,7 @@ LL |             *(c.0 as *mut usize) = 32;
    |             ^^^^^^^^^^^^^^^^^^^^^^^^^
    = 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 (of the first span):
    = note: inside closure at $DIR/atomic_read_na_write_race1.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
diff --git a/src/tools/miri/tests/fail/data_race/atomic_read_na_write_race2.stderr b/src/tools/miri/tests/fail/data_race/atomic_read_na_write_race2.stderr
index 753a2961b49..cd8e095a6e2 100644
--- a/src/tools/miri/tests/fail/data_race/atomic_read_na_write_race2.stderr
+++ b/src/tools/miri/tests/fail/data_race/atomic_read_na_write_race2.stderr
@@ -11,7 +11,7 @@ LL |             atomic_ref.load(Ordering::SeqCst)
    |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    = 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 (of the first span):
    = note: inside closure at $DIR/atomic_read_na_write_race2.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
diff --git a/src/tools/miri/tests/fail/data_race/atomic_write_na_read_race1.stderr b/src/tools/miri/tests/fail/data_race/atomic_write_na_read_race1.stderr
index 5be597b7f56..b339e5adf8f 100644
--- a/src/tools/miri/tests/fail/data_race/atomic_write_na_read_race1.stderr
+++ b/src/tools/miri/tests/fail/data_race/atomic_write_na_read_race1.stderr
@@ -11,7 +11,7 @@ LL |             atomic_ref.store(32, Ordering::SeqCst)
    |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    = 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 (of the first span):
    = note: inside closure at $DIR/atomic_write_na_read_race1.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
diff --git a/src/tools/miri/tests/fail/data_race/atomic_write_na_read_race2.stderr b/src/tools/miri/tests/fail/data_race/atomic_write_na_read_race2.stderr
index 2c21337029a..39686203491 100644
--- a/src/tools/miri/tests/fail/data_race/atomic_write_na_read_race2.stderr
+++ b/src/tools/miri/tests/fail/data_race/atomic_write_na_read_race2.stderr
@@ -11,7 +11,7 @@ LL |             let _val = *(c.0 as *mut usize);
    |                        ^^^^^^^^^^^^^^^^^^^^
    = 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 (of the first span):
    = note: inside closure at $DIR/atomic_write_na_read_race2.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
diff --git a/src/tools/miri/tests/fail/data_race/atomic_write_na_write_race1.stderr b/src/tools/miri/tests/fail/data_race/atomic_write_na_write_race1.stderr
index b10724aa67e..fd360797d34 100644
--- a/src/tools/miri/tests/fail/data_race/atomic_write_na_write_race1.stderr
+++ b/src/tools/miri/tests/fail/data_race/atomic_write_na_write_race1.stderr
@@ -11,7 +11,7 @@ LL |             *(c.0 as *mut usize) = 32;
    |             ^^^^^^^^^^^^^^^^^^^^^^^^^
    = 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 (of the first span):
    = note: inside closure at $DIR/atomic_write_na_write_race1.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
diff --git a/src/tools/miri/tests/fail/data_race/atomic_write_na_write_race2.stderr b/src/tools/miri/tests/fail/data_race/atomic_write_na_write_race2.stderr
index 63393a2a8bd..4e2494cf57b 100644
--- a/src/tools/miri/tests/fail/data_race/atomic_write_na_write_race2.stderr
+++ b/src/tools/miri/tests/fail/data_race/atomic_write_na_write_race2.stderr
@@ -11,7 +11,7 @@ LL |             atomic_ref.store(64, Ordering::SeqCst);
    |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    = 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 (of the first span):
    = note: inside closure at $DIR/atomic_write_na_write_race2.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
diff --git a/src/tools/miri/tests/fail/data_race/dangling_thread_async_race.stderr b/src/tools/miri/tests/fail/data_race/dangling_thread_async_race.stderr
index 26ab3c16735..aba051a2b63 100644
--- a/src/tools/miri/tests/fail/data_race/dangling_thread_async_race.stderr
+++ b/src/tools/miri/tests/fail/data_race/dangling_thread_async_race.stderr
@@ -11,7 +11,7 @@ LL |             *c.0 = 32;
    |             ^^^^^^^^^
    = 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 (of the first span):
    = note: inside closure at $DIR/dangling_thread_async_race.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
diff --git a/src/tools/miri/tests/fail/data_race/dangling_thread_race.stderr b/src/tools/miri/tests/fail/data_race/dangling_thread_race.stderr
index 23ccb33e9a9..dc35ccf3545 100644
--- a/src/tools/miri/tests/fail/data_race/dangling_thread_race.stderr
+++ b/src/tools/miri/tests/fail/data_race/dangling_thread_race.stderr
@@ -11,7 +11,7 @@ LL |             *c.0 = 32;
    |             ^^^^^^^^^
    = 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 (of the first span):
    = note: inside `main` at $DIR/dangling_thread_race.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
diff --git a/src/tools/miri/tests/fail/data_race/dealloc_read_race1.stderr b/src/tools/miri/tests/fail/data_race/dealloc_read_race1.stderr
index baf3f852164..fbeab37e17f 100644
--- a/src/tools/miri/tests/fail/data_race/dealloc_read_race1.stderr
+++ b/src/tools/miri/tests/fail/data_race/dealloc_read_race1.stderr
@@ -16,7 +16,7 @@ LL |             let _val = *ptr.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 (of the first span):
    = note: inside closure at $DIR/dealloc_read_race1.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
diff --git a/src/tools/miri/tests/fail/data_race/dealloc_read_race_stack.stderr b/src/tools/miri/tests/fail/data_race/dealloc_read_race_stack.stderr
index 94d95d44ac8..9ef9bf35ae7 100644
--- a/src/tools/miri/tests/fail/data_race/dealloc_read_race_stack.stderr
+++ b/src/tools/miri/tests/fail/data_race/dealloc_read_race_stack.stderr
@@ -11,7 +11,7 @@ LL |             *pointer.load(Ordering::Acquire)
    |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    = 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 (of the first span):
    = note: inside closure at $DIR/dealloc_read_race_stack.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
diff --git a/src/tools/miri/tests/fail/data_race/dealloc_write_race1.stderr b/src/tools/miri/tests/fail/data_race/dealloc_write_race1.stderr
index cce2701a03c..75a98cc5d7d 100644
--- a/src/tools/miri/tests/fail/data_race/dealloc_write_race1.stderr
+++ b/src/tools/miri/tests/fail/data_race/dealloc_write_race1.stderr
@@ -16,7 +16,7 @@ LL |             *ptr.0 = 2;
    |             ^^^^^^^^^^
    = 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 (of the first span):
    = note: inside closure at $DIR/dealloc_write_race1.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
diff --git a/src/tools/miri/tests/fail/data_race/dealloc_write_race_stack.stderr b/src/tools/miri/tests/fail/data_race/dealloc_write_race_stack.stderr
index 0f60926fb5b..f2fc338b33f 100644
--- a/src/tools/miri/tests/fail/data_race/dealloc_write_race_stack.stderr
+++ b/src/tools/miri/tests/fail/data_race/dealloc_write_race_stack.stderr
@@ -11,7 +11,7 @@ LL |             *pointer.load(Ordering::Acquire) = 3;
    |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    = 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 (of the first span):
    = note: inside closure at $DIR/dealloc_write_race_stack.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
diff --git a/src/tools/miri/tests/fail/data_race/enable_after_join_to_main.stderr b/src/tools/miri/tests/fail/data_race/enable_after_join_to_main.stderr
index e608342f8d7..620cb37859c 100644
--- a/src/tools/miri/tests/fail/data_race/enable_after_join_to_main.stderr
+++ b/src/tools/miri/tests/fail/data_race/enable_after_join_to_main.stderr
@@ -11,7 +11,7 @@ LL |             *c.0 = 32;
    |             ^^^^^^^^^
    = 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 (of the first span):
    = note: inside closure at $DIR/enable_after_join_to_main.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
diff --git a/src/tools/miri/tests/fail/data_race/fence_after_load.stderr b/src/tools/miri/tests/fail/data_race/fence_after_load.stderr
index 9c1d92d14f8..0bd36067d95 100644
--- a/src/tools/miri/tests/fail/data_race/fence_after_load.stderr
+++ b/src/tools/miri/tests/fail/data_race/fence_after_load.stderr
@@ -11,7 +11,7 @@ LL |         unsafe { V = 1 }
    |                  ^^^^^
    = 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 (of the first span):
    = note: inside `main` at $DIR/fence_after_load.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
diff --git a/src/tools/miri/tests/fail/data_race/read_write_race.stderr b/src/tools/miri/tests/fail/data_race/read_write_race.stderr
index e31bc5fbb4a..0c0d2fa32c3 100644
--- a/src/tools/miri/tests/fail/data_race/read_write_race.stderr
+++ b/src/tools/miri/tests/fail/data_race/read_write_race.stderr
@@ -11,7 +11,7 @@ LL |             let _val = *c.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 (of the first span):
    = note: inside closure at $DIR/read_write_race.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
diff --git a/src/tools/miri/tests/fail/data_race/read_write_race_stack.stderr b/src/tools/miri/tests/fail/data_race/read_write_race_stack.stderr
index 09b704e0631..e1d0a52d42a 100644
--- a/src/tools/miri/tests/fail/data_race/read_write_race_stack.stderr
+++ b/src/tools/miri/tests/fail/data_race/read_write_race_stack.stderr
@@ -11,7 +11,7 @@ LL |             *pointer.load(Ordering::Acquire) = 3;
    |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    = 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 (of the first span):
    = note: inside closure at $DIR/read_write_race_stack.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
diff --git a/src/tools/miri/tests/fail/data_race/relax_acquire_race.stderr b/src/tools/miri/tests/fail/data_race/relax_acquire_race.stderr
index a996fc35002..fdf0e4917df 100644
--- a/src/tools/miri/tests/fail/data_race/relax_acquire_race.stderr
+++ b/src/tools/miri/tests/fail/data_race/relax_acquire_race.stderr
@@ -11,7 +11,7 @@ LL |             *c.0 = 1;
    |             ^^^^^^^^
    = 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 (of the first span):
    = note: inside closure at $DIR/relax_acquire_race.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
diff --git a/src/tools/miri/tests/fail/data_race/release_seq_race.stderr b/src/tools/miri/tests/fail/data_race/release_seq_race.stderr
index 8b27a188563..234ce48e76a 100644
--- a/src/tools/miri/tests/fail/data_race/release_seq_race.stderr
+++ b/src/tools/miri/tests/fail/data_race/release_seq_race.stderr
@@ -11,7 +11,7 @@ LL |             *c.0 = 1;
    |             ^^^^^^^^
    = 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 (of the first span):
    = note: inside closure at $DIR/release_seq_race.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
diff --git a/src/tools/miri/tests/fail/data_race/release_seq_race_same_thread.stderr b/src/tools/miri/tests/fail/data_race/release_seq_race_same_thread.stderr
index a3561b1a269..8e95d3593b0 100644
--- a/src/tools/miri/tests/fail/data_race/release_seq_race_same_thread.stderr
+++ b/src/tools/miri/tests/fail/data_race/release_seq_race_same_thread.stderr
@@ -11,7 +11,7 @@ LL |             *c.0 = 1;
    |             ^^^^^^^^
    = 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 (of the first span):
    = note: inside closure at $DIR/release_seq_race_same_thread.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
diff --git a/src/tools/miri/tests/fail/data_race/rmw_race.stderr b/src/tools/miri/tests/fail/data_race/rmw_race.stderr
index 9448d9059bf..6252cd5a71f 100644
--- a/src/tools/miri/tests/fail/data_race/rmw_race.stderr
+++ b/src/tools/miri/tests/fail/data_race/rmw_race.stderr
@@ -11,7 +11,7 @@ LL |             *c.0 = 1;
    |             ^^^^^^^^
    = 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 (of the first span):
    = note: inside closure at $DIR/rmw_race.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
diff --git a/src/tools/miri/tests/fail/data_race/stack_pop_race.stderr b/src/tools/miri/tests/fail/data_race/stack_pop_race.stderr
index 0e2e2029009..6cb0270b3da 100644
--- a/src/tools/miri/tests/fail/data_race/stack_pop_race.stderr
+++ b/src/tools/miri/tests/fail/data_race/stack_pop_race.stderr
@@ -11,7 +11,7 @@ LL |         let _val = unsafe { *ptr.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 (of the first span):
    = note: inside `race` at $DIR/stack_pop_race.rs:LL:CC
 note: inside `main`
   --> $DIR/stack_pop_race.rs:LL:CC
diff --git a/src/tools/miri/tests/fail/data_race/write_write_race.stderr b/src/tools/miri/tests/fail/data_race/write_write_race.stderr
index dcc94a9d255..e9055932c55 100644
--- a/src/tools/miri/tests/fail/data_race/write_write_race.stderr
+++ b/src/tools/miri/tests/fail/data_race/write_write_race.stderr
@@ -11,7 +11,7 @@ LL |             *c.0 = 32;
    |             ^^^^^^^^^
    = 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 (of the first span):
    = note: inside closure at $DIR/write_write_race.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
diff --git a/src/tools/miri/tests/fail/data_race/write_write_race_stack.stderr b/src/tools/miri/tests/fail/data_race/write_write_race_stack.stderr
index 8b0250593d5..d156ece4a1e 100644
--- a/src/tools/miri/tests/fail/data_race/write_write_race_stack.stderr
+++ b/src/tools/miri/tests/fail/data_race/write_write_race_stack.stderr
@@ -11,7 +11,7 @@ LL |             *pointer.load(Ordering::Acquire) = 3;
    |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    = 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 (of the first span):
    = note: inside closure at $DIR/write_write_race_stack.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
diff --git a/src/tools/miri/tests/fail/function_calls/exported_symbol_clashing.stderr b/src/tools/miri/tests/fail/function_calls/exported_symbol_clashing.stderr
index 8eb9fa4ff5c..09e4157b31f 100644
--- a/src/tools/miri/tests/fail/function_calls/exported_symbol_clashing.stderr
+++ b/src/tools/miri/tests/fail/function_calls/exported_symbol_clashing.stderr
@@ -14,7 +14,7 @@ help: then it's defined here again, in crate `exported_symbol_clashing`
    |
 LL | fn bar() {}
    | ^^^^^^^^
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside `main` at $DIR/exported_symbol_clashing.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
diff --git a/src/tools/miri/tests/fail/function_calls/exported_symbol_shim_clashing.stderr b/src/tools/miri/tests/fail/function_calls/exported_symbol_shim_clashing.stderr
index 58a996e6453..0d0055bb85c 100644
--- a/src/tools/miri/tests/fail/function_calls/exported_symbol_shim_clashing.stderr
+++ b/src/tools/miri/tests/fail/function_calls/exported_symbol_shim_clashing.stderr
@@ -12,7 +12,7 @@ LL | |
 LL | |     unreachable!()
 LL | | }
    | |_^
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside `main` at $DIR/exported_symbol_shim_clashing.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
diff --git a/src/tools/miri/tests/fail/stacked_borrows/alias_through_mutation.stderr b/src/tools/miri/tests/fail/stacked_borrows/alias_through_mutation.stderr
index 461275c3fa3..b22db3eb121 100644
--- a/src/tools/miri/tests/fail/stacked_borrows/alias_through_mutation.stderr
+++ b/src/tools/miri/tests/fail/stacked_borrows/alias_through_mutation.stderr
@@ -19,7 +19,7 @@ help: <TAG> was later invalidated at offsets [0x0..0x4] by a write access
    |
 LL |     *target = 13;
    |     ^^^^^^^^^^^^
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside `main` at $DIR/alias_through_mutation.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
diff --git a/src/tools/miri/tests/fail/stacked_borrows/aliasing_mut1.stderr b/src/tools/miri/tests/fail/stacked_borrows/aliasing_mut1.stderr
index 4514abb4ab2..3ce39968cbb 100644
--- a/src/tools/miri/tests/fail/stacked_borrows/aliasing_mut1.stderr
+++ b/src/tools/miri/tests/fail/stacked_borrows/aliasing_mut1.stderr
@@ -16,7 +16,7 @@ help: <TAG> is this argument
    |
 LL | pub fn safe(_x: &mut i32, _y: &mut i32) {}
    |             ^^
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside `safe` at $DIR/aliasing_mut1.rs:LL:CC
 note: inside `main`
   --> $DIR/aliasing_mut1.rs:LL:CC
diff --git a/src/tools/miri/tests/fail/stacked_borrows/aliasing_mut2.stderr b/src/tools/miri/tests/fail/stacked_borrows/aliasing_mut2.stderr
index 9ca9743cbd9..df4b6cf0256 100644
--- a/src/tools/miri/tests/fail/stacked_borrows/aliasing_mut2.stderr
+++ b/src/tools/miri/tests/fail/stacked_borrows/aliasing_mut2.stderr
@@ -16,7 +16,7 @@ help: <TAG> is this argument
    |
 LL | pub fn safe(_x: &i32, _y: &mut i32) {}
    |             ^^
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside `safe` at $DIR/aliasing_mut2.rs:LL:CC
 note: inside `main`
   --> $DIR/aliasing_mut2.rs:LL:CC
diff --git a/src/tools/miri/tests/fail/stacked_borrows/aliasing_mut3.stderr b/src/tools/miri/tests/fail/stacked_borrows/aliasing_mut3.stderr
index b504097a3c9..55aaed62f4f 100644
--- a/src/tools/miri/tests/fail/stacked_borrows/aliasing_mut3.stderr
+++ b/src/tools/miri/tests/fail/stacked_borrows/aliasing_mut3.stderr
@@ -19,7 +19,7 @@ help: <TAG> was later invalidated at offsets [0x0..0x4] by a Unique FnEntry reta
    |
 LL |     safe_raw(xraw, xshr);
    |     ^^^^^^^^^^^^^^^^^^^^
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside `safe` at $DIR/aliasing_mut3.rs:LL:CC
 note: inside `main`
   --> $DIR/aliasing_mut3.rs:LL:CC
diff --git a/src/tools/miri/tests/fail/stacked_borrows/aliasing_mut4.stderr b/src/tools/miri/tests/fail/stacked_borrows/aliasing_mut4.stderr
index 6fe0d709029..ddf197bc639 100644
--- a/src/tools/miri/tests/fail/stacked_borrows/aliasing_mut4.stderr
+++ b/src/tools/miri/tests/fail/stacked_borrows/aliasing_mut4.stderr
@@ -16,7 +16,7 @@ help: <TAG> is this argument
    |
 LL | pub fn safe(_x: &i32, _y: &mut Cell<i32>) {}
    |             ^^
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside `safe` at $DIR/aliasing_mut4.rs:LL:CC
 note: inside `main`
   --> $DIR/aliasing_mut4.rs:LL:CC
diff --git a/src/tools/miri/tests/fail/stacked_borrows/box_exclusive_violation1.stderr b/src/tools/miri/tests/fail/stacked_borrows/box_exclusive_violation1.stderr
index f114130f6fa..76f4e81f71b 100644
--- a/src/tools/miri/tests/fail/stacked_borrows/box_exclusive_violation1.stderr
+++ b/src/tools/miri/tests/fail/stacked_borrows/box_exclusive_violation1.stderr
@@ -19,7 +19,7 @@ help: <TAG> was later invalidated at offsets [0x0..0x4] by a write access
    |
 LL |     *our = 5;
    |     ^^^^^^^^
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside `unknown_code_2` at $DIR/box_exclusive_violation1.rs:LL:CC
 note: inside `demo_box_advanced_unique`
   --> $DIR/box_exclusive_violation1.rs:LL:CC
diff --git a/src/tools/miri/tests/fail/stacked_borrows/box_noalias_violation.stderr b/src/tools/miri/tests/fail/stacked_borrows/box_noalias_violation.stderr
index 139fcd0ca45..59377aeb971 100644
--- a/src/tools/miri/tests/fail/stacked_borrows/box_noalias_violation.stderr
+++ b/src/tools/miri/tests/fail/stacked_borrows/box_noalias_violation.stderr
@@ -16,7 +16,7 @@ help: <TAG> is this argument
    |
 LL | unsafe fn test(mut x: Box<i32>, y: *const i32) -> i32 {
    |                ^^^^^
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside `test` at $DIR/box_noalias_violation.rs:LL:CC
 note: inside `main`
   --> $DIR/box_noalias_violation.rs:LL:CC
diff --git a/src/tools/miri/tests/fail/stacked_borrows/buggy_as_mut_slice.stderr b/src/tools/miri/tests/fail/stacked_borrows/buggy_as_mut_slice.stderr
index 6aa14361287..fa3d7ca3676 100644
--- a/src/tools/miri/tests/fail/stacked_borrows/buggy_as_mut_slice.stderr
+++ b/src/tools/miri/tests/fail/stacked_borrows/buggy_as_mut_slice.stderr
@@ -19,7 +19,7 @@ help: <TAG> was later invalidated at offsets [0x0..0xc] by a Unique retag
    |
 LL |         unsafe { from_raw_parts_mut(self_.as_ptr() as *mut T, self_.len()) }
    |                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside `main` at $DIR/buggy_as_mut_slice.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
diff --git a/src/tools/miri/tests/fail/stacked_borrows/buggy_split_at_mut.stderr b/src/tools/miri/tests/fail/stacked_borrows/buggy_split_at_mut.stderr
index cdeccc0855a..c75d8cab3fc 100644
--- a/src/tools/miri/tests/fail/stacked_borrows/buggy_split_at_mut.stderr
+++ b/src/tools/miri/tests/fail/stacked_borrows/buggy_split_at_mut.stderr
@@ -19,7 +19,7 @@ help: <TAG> was later invalidated at offsets [0x0..0x10] by a Unique retag
    |
 LL |                 from_raw_parts_mut(ptr.offset(mid as isize), len - mid),
    |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside `main` at $DIR/buggy_split_at_mut.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
diff --git a/src/tools/miri/tests/fail/stacked_borrows/disable_mut_does_not_merge_srw.stderr b/src/tools/miri/tests/fail/stacked_borrows/disable_mut_does_not_merge_srw.stderr
index e05f44fac9d..bd79b401f66 100644
--- a/src/tools/miri/tests/fail/stacked_borrows/disable_mut_does_not_merge_srw.stderr
+++ b/src/tools/miri/tests/fail/stacked_borrows/disable_mut_does_not_merge_srw.stderr
@@ -19,7 +19,7 @@ help: <TAG> was later invalidated at offsets [0x0..0x4] by a write access
    |
 LL |         *base = 1;
    |         ^^^^^^^^^
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside `main` at $DIR/disable_mut_does_not_merge_srw.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
diff --git a/src/tools/miri/tests/fail/stacked_borrows/fnentry_invalidation.stderr b/src/tools/miri/tests/fail/stacked_borrows/fnentry_invalidation.stderr
index e81411bbdd8..e3bffde1f01 100644
--- a/src/tools/miri/tests/fail/stacked_borrows/fnentry_invalidation.stderr
+++ b/src/tools/miri/tests/fail/stacked_borrows/fnentry_invalidation.stderr
@@ -19,7 +19,7 @@ help: <TAG> was later invalidated at offsets [0x0..0x4] by a Unique FnEntry reta
    |
 LL |     x.do_bad();
    |     ^^^^^^^^^^
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside `main` at $DIR/fnentry_invalidation.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
diff --git a/src/tools/miri/tests/fail/stacked_borrows/fnentry_invalidation2.stderr b/src/tools/miri/tests/fail/stacked_borrows/fnentry_invalidation2.stderr
index d6d0084fa2a..b104de4b8d9 100644
--- a/src/tools/miri/tests/fail/stacked_borrows/fnentry_invalidation2.stderr
+++ b/src/tools/miri/tests/fail/stacked_borrows/fnentry_invalidation2.stderr
@@ -19,7 +19,7 @@ help: <TAG> was later invalidated at offsets [0x0..0xc] by a Unique FnEntry reta
    |
 LL |     let _ = t.sli.as_mut_ptr();
    |             ^^^^^^^^^^^^^^^^^^
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside `main` at $DIR/fnentry_invalidation2.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
diff --git a/src/tools/miri/tests/fail/stacked_borrows/illegal_dealloc1.stderr b/src/tools/miri/tests/fail/stacked_borrows/illegal_dealloc1.stderr
index f2f13d0d559..7fff60f25fb 100644
--- a/src/tools/miri/tests/fail/stacked_borrows/illegal_dealloc1.stderr
+++ b/src/tools/miri/tests/fail/stacked_borrows/illegal_dealloc1.stderr
@@ -16,7 +16,7 @@ help: <TAG> was later invalidated at offsets [0x0..0x1] by a write access
    |
 LL |         ptr1.write(0);
    |         ^^^^^^^^^^^^^
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside `std::alloc::dealloc` at RUSTLIB/alloc/src/alloc.rs:LL:CC
 note: inside `main`
   --> $DIR/illegal_deALLOC.rs:LL:CC
diff --git a/src/tools/miri/tests/fail/stacked_borrows/illegal_read1.stderr b/src/tools/miri/tests/fail/stacked_borrows/illegal_read1.stderr
index 95ff05d70c3..7a159c9d3fe 100644
--- a/src/tools/miri/tests/fail/stacked_borrows/illegal_read1.stderr
+++ b/src/tools/miri/tests/fail/stacked_borrows/illegal_read1.stderr
@@ -19,7 +19,7 @@ help: <TAG> was later invalidated at offsets [0x0..0x4] by a read access
    |
 LL |     let _val = unsafe { *xraw };
    |                         ^^^^^
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside `main` at $DIR/illegal_read1.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
diff --git a/src/tools/miri/tests/fail/stacked_borrows/illegal_read2.stderr b/src/tools/miri/tests/fail/stacked_borrows/illegal_read2.stderr
index 5cfdf77dee4..e3e79f6f0f0 100644
--- a/src/tools/miri/tests/fail/stacked_borrows/illegal_read2.stderr
+++ b/src/tools/miri/tests/fail/stacked_borrows/illegal_read2.stderr
@@ -19,7 +19,7 @@ help: <TAG> was later invalidated at offsets [0x0..0x4] by a SharedReadOnly reta
    |
 LL |     let shr = unsafe { &*xraw };
    |                        ^^^^^^
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside `main` at $DIR/illegal_read2.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
diff --git a/src/tools/miri/tests/fail/stacked_borrows/illegal_read3.stderr b/src/tools/miri/tests/fail/stacked_borrows/illegal_read3.stderr
index dacf71fa3ee..3a8687ad9aa 100644
--- a/src/tools/miri/tests/fail/stacked_borrows/illegal_read3.stderr
+++ b/src/tools/miri/tests/fail/stacked_borrows/illegal_read3.stderr
@@ -19,7 +19,7 @@ help: <TAG> was later invalidated at offsets [0x0..0x4] by a read access
    |
 LL |     let _val = unsafe { *xref1.r };
    |                         ^^^^^^^^
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside `main` at $DIR/illegal_read3.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
diff --git a/src/tools/miri/tests/fail/stacked_borrows/illegal_read4.stderr b/src/tools/miri/tests/fail/stacked_borrows/illegal_read4.stderr
index 5ce0cba6179..dcf37b26901 100644
--- a/src/tools/miri/tests/fail/stacked_borrows/illegal_read4.stderr
+++ b/src/tools/miri/tests/fail/stacked_borrows/illegal_read4.stderr
@@ -19,7 +19,7 @@ help: <TAG> was later invalidated at offsets [0x0..0x4] by a read access
    |
 LL |     let _val = unsafe { *xraw }; // use the raw again, this invalidates xref2 *even* with the special read except for uniq refs
    |                         ^^^^^
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside `main` at $DIR/illegal_read4.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
diff --git a/src/tools/miri/tests/fail/stacked_borrows/illegal_read5.stderr b/src/tools/miri/tests/fail/stacked_borrows/illegal_read5.stderr
index 63532f87944..1793798d15f 100644
--- a/src/tools/miri/tests/fail/stacked_borrows/illegal_read5.stderr
+++ b/src/tools/miri/tests/fail/stacked_borrows/illegal_read5.stderr
@@ -19,7 +19,7 @@ help: <TAG> was later invalidated at offsets [$HEX..$HEX] by a read access
    |
 LL |     mem::forget(unsafe { ptr::read(xshr) }); // but after reading through the shared ref
    |                          ^^^^^^^^^^^^^^^
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside `main` at $DIR/illegal_read5.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
diff --git a/src/tools/miri/tests/fail/stacked_borrows/illegal_read6.stderr b/src/tools/miri/tests/fail/stacked_borrows/illegal_read6.stderr
index 93a96ab601e..17b28dee3c7 100644
--- a/src/tools/miri/tests/fail/stacked_borrows/illegal_read6.stderr
+++ b/src/tools/miri/tests/fail/stacked_borrows/illegal_read6.stderr
@@ -19,7 +19,7 @@ help: <TAG> was later invalidated at offsets [0x0..0x4] by a Unique retag
    |
 LL |         let x = &mut *x; // kill `raw`
    |                 ^^^^^^^
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside `main` at $DIR/illegal_read6.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
diff --git a/src/tools/miri/tests/fail/stacked_borrows/illegal_read7.stderr b/src/tools/miri/tests/fail/stacked_borrows/illegal_read7.stderr
index 2e8ac207bea..b76446d60f6 100644
--- a/src/tools/miri/tests/fail/stacked_borrows/illegal_read7.stderr
+++ b/src/tools/miri/tests/fail/stacked_borrows/illegal_read7.stderr
@@ -19,7 +19,7 @@ help: <TAG> was later invalidated at offsets [0x0..0x4] by a read access
    |
 LL |         let _val = ptr::read(raw);
    |                    ^^^^^^^^^^^^^^
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside `main` at $DIR/illegal_read7.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
diff --git a/src/tools/miri/tests/fail/stacked_borrows/illegal_read8.stderr b/src/tools/miri/tests/fail/stacked_borrows/illegal_read8.stderr
index c34fa2d8955..b43079c3b7f 100644
--- a/src/tools/miri/tests/fail/stacked_borrows/illegal_read8.stderr
+++ b/src/tools/miri/tests/fail/stacked_borrows/illegal_read8.stderr
@@ -19,7 +19,7 @@ help: <TAG> was later invalidated at offsets [0x0..0x4] by a write access
    |
 LL |         *y2 += 1;
    |         ^^^^^^^^
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside `main` at $DIR/illegal_read8.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
diff --git a/src/tools/miri/tests/fail/stacked_borrows/illegal_read_despite_exposed1.stderr b/src/tools/miri/tests/fail/stacked_borrows/illegal_read_despite_exposed1.stderr
index 43b4ec2ba65..fbd5d8b956d 100644
--- a/src/tools/miri/tests/fail/stacked_borrows/illegal_read_despite_exposed1.stderr
+++ b/src/tools/miri/tests/fail/stacked_borrows/illegal_read_despite_exposed1.stderr
@@ -19,7 +19,7 @@ help: <TAG> was later invalidated at offsets [0x0..0x4] by a write access
    |
 LL |         *exposed_ptr = 0;
    |         ^^^^^^^^^^^^^^^^
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside `main` at $DIR/illegal_read_despite_exposed1.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
diff --git a/src/tools/miri/tests/fail/stacked_borrows/illegal_read_despite_exposed2.stderr b/src/tools/miri/tests/fail/stacked_borrows/illegal_read_despite_exposed2.stderr
index 832320fc202..19e4cbdb938 100644
--- a/src/tools/miri/tests/fail/stacked_borrows/illegal_read_despite_exposed2.stderr
+++ b/src/tools/miri/tests/fail/stacked_borrows/illegal_read_despite_exposed2.stderr
@@ -19,7 +19,7 @@ help: <TAG> was later invalidated at offsets [0x0..0x4] by a read access
    |
 LL |         let _val = *exposed_ptr;
    |                    ^^^^^^^^^^^^
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside `main` at $DIR/illegal_read_despite_exposed2.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
diff --git a/src/tools/miri/tests/fail/stacked_borrows/illegal_write1.stderr b/src/tools/miri/tests/fail/stacked_borrows/illegal_write1.stderr
index 3bf27f4815e..c1e49181465 100644
--- a/src/tools/miri/tests/fail/stacked_borrows/illegal_write1.stderr
+++ b/src/tools/miri/tests/fail/stacked_borrows/illegal_write1.stderr
@@ -14,7 +14,7 @@ help: <TAG> was created by a SharedReadOnly retag at offsets [0x0..0x4]
    |
 LL |         let x: *mut u32 = xref as *const _ as *mut _;
    |                           ^^^^
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside `main` at $DIR/illegal_write1.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
diff --git a/src/tools/miri/tests/fail/stacked_borrows/illegal_write2.stderr b/src/tools/miri/tests/fail/stacked_borrows/illegal_write2.stderr
index a9fe8cb6ccc..3e11e86eb81 100644
--- a/src/tools/miri/tests/fail/stacked_borrows/illegal_write2.stderr
+++ b/src/tools/miri/tests/fail/stacked_borrows/illegal_write2.stderr
@@ -19,7 +19,7 @@ help: <TAG> was later invalidated at offsets [0x0..0x4] by a Unique retag
    |
 LL |     drop(&mut *target); // reborrow
    |          ^^^^^^^^^^^^
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside `main` at $DIR/illegal_write2.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
diff --git a/src/tools/miri/tests/fail/stacked_borrows/illegal_write3.stderr b/src/tools/miri/tests/fail/stacked_borrows/illegal_write3.stderr
index d64f2ddd876..4053325821e 100644
--- a/src/tools/miri/tests/fail/stacked_borrows/illegal_write3.stderr
+++ b/src/tools/miri/tests/fail/stacked_borrows/illegal_write3.stderr
@@ -14,7 +14,7 @@ help: <TAG> was created by a SharedReadOnly retag at offsets [0x0..0x4]
    |
 LL |     let ptr = r#ref as *const _ as *mut _; // raw ptr, with raw tag
    |               ^^^^^
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside `main` at $DIR/illegal_write3.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
diff --git a/src/tools/miri/tests/fail/stacked_borrows/illegal_write4.stderr b/src/tools/miri/tests/fail/stacked_borrows/illegal_write4.stderr
index e3b8621eb74..fceda8db4ce 100644
--- a/src/tools/miri/tests/fail/stacked_borrows/illegal_write4.stderr
+++ b/src/tools/miri/tests/fail/stacked_borrows/illegal_write4.stderr
@@ -19,7 +19,7 @@ help: <TAG> was later invalidated at offsets [0x0..0x4] by a Unique retag
    |
 LL |     let _mut_ref: &mut i32 = unsafe { mem::transmute(raw) }; // &mut, with raw tag
    |                                       ^^^^^^^^^^^^^^^^^^^
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside `main` at $DIR/illegal_write4.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
diff --git a/src/tools/miri/tests/fail/stacked_borrows/illegal_write5.stderr b/src/tools/miri/tests/fail/stacked_borrows/illegal_write5.stderr
index bbeb81258bd..c71780b7e03 100644
--- a/src/tools/miri/tests/fail/stacked_borrows/illegal_write5.stderr
+++ b/src/tools/miri/tests/fail/stacked_borrows/illegal_write5.stderr
@@ -19,7 +19,7 @@ help: <TAG> was later invalidated at offsets [0x0..0x4] by a write access
    |
 LL |     unsafe { *xraw = 15 };
    |              ^^^^^^^^^^
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside `main` at $DIR/illegal_write5.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
diff --git a/src/tools/miri/tests/fail/stacked_borrows/illegal_write6.stderr b/src/tools/miri/tests/fail/stacked_borrows/illegal_write6.stderr
index 49d9050f309..3d3d2a24c28 100644
--- a/src/tools/miri/tests/fail/stacked_borrows/illegal_write6.stderr
+++ b/src/tools/miri/tests/fail/stacked_borrows/illegal_write6.stderr
@@ -16,7 +16,7 @@ help: <TAG> is this argument
    |
 LL | fn foo(a: &mut u32, y: *mut u32) -> u32 {
    |        ^
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside `foo` at $DIR/illegal_write6.rs:LL:CC
 note: inside `main`
   --> $DIR/illegal_write6.rs:LL:CC
diff --git a/src/tools/miri/tests/fail/stacked_borrows/illegal_write_despite_exposed1.stderr b/src/tools/miri/tests/fail/stacked_borrows/illegal_write_despite_exposed1.stderr
index 87ddf61d758..1bb3afe483e 100644
--- a/src/tools/miri/tests/fail/stacked_borrows/illegal_write_despite_exposed1.stderr
+++ b/src/tools/miri/tests/fail/stacked_borrows/illegal_write_despite_exposed1.stderr
@@ -19,7 +19,7 @@ help: <TAG> was later invalidated at offsets [0x0..0x4] by a write access
    |
 LL |         *exposed_ptr = 0;
    |         ^^^^^^^^^^^^^^^^
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside `main` at $DIR/illegal_write_despite_exposed1.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
diff --git a/src/tools/miri/tests/fail/stacked_borrows/interior_mut1.stderr b/src/tools/miri/tests/fail/stacked_borrows/interior_mut1.stderr
index 1d68727c82a..da55e724fd8 100644
--- a/src/tools/miri/tests/fail/stacked_borrows/interior_mut1.stderr
+++ b/src/tools/miri/tests/fail/stacked_borrows/interior_mut1.stderr
@@ -19,7 +19,7 @@ help: <TAG> was later invalidated at offsets [0x0..0x4] by a write access
    |
 LL |         *c.get() = UnsafeCell::new(1); // invalidates inner_shr
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside `main` at $DIR/interior_mut1.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
diff --git a/src/tools/miri/tests/fail/stacked_borrows/interior_mut2.stderr b/src/tools/miri/tests/fail/stacked_borrows/interior_mut2.stderr
index 8a335714226..8c8a96cbbbd 100644
--- a/src/tools/miri/tests/fail/stacked_borrows/interior_mut2.stderr
+++ b/src/tools/miri/tests/fail/stacked_borrows/interior_mut2.stderr
@@ -19,7 +19,7 @@ help: <TAG> was later invalidated at offsets [0x0..0x4] by a write access
    |
 LL |         *c.get() = UnsafeCell::new(0); // now inner_shr gets invalidated
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside `main` at $DIR/interior_mut2.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
diff --git a/src/tools/miri/tests/fail/stacked_borrows/invalidate_against_protector1.stderr b/src/tools/miri/tests/fail/stacked_borrows/invalidate_against_protector1.stderr
index a53c633c381..95fa4c51d12 100644
--- a/src/tools/miri/tests/fail/stacked_borrows/invalidate_against_protector1.stderr
+++ b/src/tools/miri/tests/fail/stacked_borrows/invalidate_against_protector1.stderr
@@ -16,7 +16,7 @@ help: <TAG> is this argument
    |
 LL | fn inner(x: *mut i32, _y: &mut i32) {
    |                       ^^
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside `inner` at $DIR/invalidate_against_protector1.rs:LL:CC
 note: inside `main`
   --> $DIR/invalidate_against_protector1.rs:LL:CC
diff --git a/src/tools/miri/tests/fail/stacked_borrows/invalidate_against_protector2.stderr b/src/tools/miri/tests/fail/stacked_borrows/invalidate_against_protector2.stderr
index 6ee78d1aac6..8f677bd547c 100644
--- a/src/tools/miri/tests/fail/stacked_borrows/invalidate_against_protector2.stderr
+++ b/src/tools/miri/tests/fail/stacked_borrows/invalidate_against_protector2.stderr
@@ -16,7 +16,7 @@ help: <TAG> is this argument
    |
 LL | fn inner(x: *mut i32, _y: &i32) {
    |                       ^^
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside `inner` at $DIR/invalidate_against_protector2.rs:LL:CC
 note: inside `main`
   --> $DIR/invalidate_against_protector2.rs:LL:CC
diff --git a/src/tools/miri/tests/fail/stacked_borrows/invalidate_against_protector3.stderr b/src/tools/miri/tests/fail/stacked_borrows/invalidate_against_protector3.stderr
index 2b38dea9dbb..1648ca9e58b 100644
--- a/src/tools/miri/tests/fail/stacked_borrows/invalidate_against_protector3.stderr
+++ b/src/tools/miri/tests/fail/stacked_borrows/invalidate_against_protector3.stderr
@@ -16,7 +16,7 @@ help: <TAG> is this argument
    |
 LL | fn inner(x: *mut i32, _y: &i32) {
    |                       ^^
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside `inner` at $DIR/invalidate_against_protector3.rs:LL:CC
 note: inside `main`
   --> $DIR/invalidate_against_protector3.rs:LL:CC
diff --git a/src/tools/miri/tests/fail/stacked_borrows/load_invalid_mut.stderr b/src/tools/miri/tests/fail/stacked_borrows/load_invalid_mut.stderr
index 08dc171c9ee..7aca065ca0d 100644
--- a/src/tools/miri/tests/fail/stacked_borrows/load_invalid_mut.stderr
+++ b/src/tools/miri/tests/fail/stacked_borrows/load_invalid_mut.stderr
@@ -19,7 +19,7 @@ help: <TAG> was later invalidated at offsets [0x0..0x4] by a read access
    |
 LL |     let _val = unsafe { *xraw }; // invalidate xref
    |                         ^^^^^
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside `main` at $DIR/load_invalid_mut.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
diff --git a/src/tools/miri/tests/fail/stacked_borrows/load_invalid_shr.stderr b/src/tools/miri/tests/fail/stacked_borrows/load_invalid_shr.stderr
index 50bbed2b295..7eb973ae7f2 100644
--- a/src/tools/miri/tests/fail/stacked_borrows/load_invalid_shr.stderr
+++ b/src/tools/miri/tests/fail/stacked_borrows/load_invalid_shr.stderr
@@ -19,7 +19,7 @@ help: <TAG> was later invalidated at offsets [0x0..0x4] by a write access
    |
 LL |     unsafe { *xraw = 42 }; // unfreeze
    |              ^^^^^^^^^^
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside `main` at $DIR/load_invalid_shr.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
diff --git a/src/tools/miri/tests/fail/stacked_borrows/mut_exclusive_violation1.stderr b/src/tools/miri/tests/fail/stacked_borrows/mut_exclusive_violation1.stderr
index 2f3900c40d7..3e7fe11b520 100644
--- a/src/tools/miri/tests/fail/stacked_borrows/mut_exclusive_violation1.stderr
+++ b/src/tools/miri/tests/fail/stacked_borrows/mut_exclusive_violation1.stderr
@@ -19,7 +19,7 @@ help: <TAG> was later invalidated at offsets [0x0..0x4] by a write access
    |
 LL |     *our = 5;
    |     ^^^^^^^^
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside `unknown_code_2` at $DIR/mut_exclusive_violation1.rs:LL:CC
 note: inside `demo_mut_advanced_unique`
   --> $DIR/mut_exclusive_violation1.rs:LL:CC
diff --git a/src/tools/miri/tests/fail/stacked_borrows/mut_exclusive_violation2.stderr b/src/tools/miri/tests/fail/stacked_borrows/mut_exclusive_violation2.stderr
index 43b5325fc54..30ce698761f 100644
--- a/src/tools/miri/tests/fail/stacked_borrows/mut_exclusive_violation2.stderr
+++ b/src/tools/miri/tests/fail/stacked_borrows/mut_exclusive_violation2.stderr
@@ -19,7 +19,7 @@ help: <TAG> was later invalidated at offsets [0x0..0x4] by a Unique retag
    |
 LL |         let _raw2 = ptr2.as_mut();
    |                     ^^^^^^^^^^^^^
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside `main` at $DIR/mut_exclusive_violation2.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
diff --git a/src/tools/miri/tests/fail/stacked_borrows/newtype_pair_retagging.stderr b/src/tools/miri/tests/fail/stacked_borrows/newtype_pair_retagging.stderr
index 90677dfaf55..0cba380ea1a 100644
--- a/src/tools/miri/tests/fail/stacked_borrows/newtype_pair_retagging.stderr
+++ b/src/tools/miri/tests/fail/stacked_borrows/newtype_pair_retagging.stderr
@@ -16,7 +16,7 @@ help: <TAG> is this argument
    |
 LL | fn dealloc_while_running(_n: Newtype<'_>, dealloc: impl FnOnce()) {
    |                          ^^
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside `std::boxed::Box::<i32>::from_raw_in` at RUSTLIB/alloc/src/boxed.rs:LL:CC
    = note: inside `std::boxed::Box::<i32>::from_raw` at RUSTLIB/alloc/src/boxed.rs:LL:CC
 note: inside closure
diff --git a/src/tools/miri/tests/fail/stacked_borrows/newtype_retagging.stderr b/src/tools/miri/tests/fail/stacked_borrows/newtype_retagging.stderr
index f189d0483d1..f76b6a57eac 100644
--- a/src/tools/miri/tests/fail/stacked_borrows/newtype_retagging.stderr
+++ b/src/tools/miri/tests/fail/stacked_borrows/newtype_retagging.stderr
@@ -16,7 +16,7 @@ help: <TAG> is this argument
    |
 LL | fn dealloc_while_running(_n: Newtype<'_>, dealloc: impl FnOnce()) {
    |                          ^^
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside `std::boxed::Box::<i32>::from_raw_in` at RUSTLIB/alloc/src/boxed.rs:LL:CC
    = note: inside `std::boxed::Box::<i32>::from_raw` at RUSTLIB/alloc/src/boxed.rs:LL:CC
 note: inside closure
diff --git a/src/tools/miri/tests/fail/stacked_borrows/outdated_local.stderr b/src/tools/miri/tests/fail/stacked_borrows/outdated_local.stderr
index 8c2bba53918..ad366bdabce 100644
--- a/src/tools/miri/tests/fail/stacked_borrows/outdated_local.stderr
+++ b/src/tools/miri/tests/fail/stacked_borrows/outdated_local.stderr
@@ -19,7 +19,7 @@ help: <TAG> was later invalidated at offsets [0x0..0x4] by a write access
    |
 LL |     x = 1; // this invalidates y by reactivating the lowermost uniq borrow for this local
    |     ^^^^^
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside `main` at $DIR/outdated_local.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
diff --git a/src/tools/miri/tests/fail/stacked_borrows/pass_invalid_mut.stderr b/src/tools/miri/tests/fail/stacked_borrows/pass_invalid_mut.stderr
index d7ab930aa37..96cec327b9d 100644
--- a/src/tools/miri/tests/fail/stacked_borrows/pass_invalid_mut.stderr
+++ b/src/tools/miri/tests/fail/stacked_borrows/pass_invalid_mut.stderr
@@ -19,7 +19,7 @@ help: <TAG> was later invalidated at offsets [0x0..0x4] by a read access
    |
 LL |     let _val = unsafe { *xraw }; // invalidate xref
    |                         ^^^^^
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside `main` at $DIR/pass_invalid_mut.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
diff --git a/src/tools/miri/tests/fail/stacked_borrows/pass_invalid_shr.stderr b/src/tools/miri/tests/fail/stacked_borrows/pass_invalid_shr.stderr
index c14b35c75c8..5243858a91a 100644
--- a/src/tools/miri/tests/fail/stacked_borrows/pass_invalid_shr.stderr
+++ b/src/tools/miri/tests/fail/stacked_borrows/pass_invalid_shr.stderr
@@ -19,7 +19,7 @@ help: <TAG> was later invalidated at offsets [0x0..0x4] by a write access
    |
 LL |     unsafe { *xraw = 42 }; // unfreeze
    |              ^^^^^^^^^^
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside `main` at $DIR/pass_invalid_shr.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
diff --git a/src/tools/miri/tests/fail/stacked_borrows/pointer_smuggling.stderr b/src/tools/miri/tests/fail/stacked_borrows/pointer_smuggling.stderr
index 7d58d1aebbe..e20b5b89a2f 100644
--- a/src/tools/miri/tests/fail/stacked_borrows/pointer_smuggling.stderr
+++ b/src/tools/miri/tests/fail/stacked_borrows/pointer_smuggling.stderr
@@ -19,7 +19,7 @@ help: <TAG> was later invalidated at offsets [0x0..0x1] by a write access
    |
 LL |     *val = 2; // this invalidates any raw ptrs `fun1` might have created.
    |     ^^^^^^^^
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside `fun2` at $DIR/pointer_smuggling.rs:LL:CC
 note: inside `main`
   --> $DIR/pointer_smuggling.rs:LL:CC
diff --git a/src/tools/miri/tests/fail/stacked_borrows/raw_tracking.stderr b/src/tools/miri/tests/fail/stacked_borrows/raw_tracking.stderr
index d75934445e6..9f7e7a058df 100644
--- a/src/tools/miri/tests/fail/stacked_borrows/raw_tracking.stderr
+++ b/src/tools/miri/tests/fail/stacked_borrows/raw_tracking.stderr
@@ -19,7 +19,7 @@ help: <TAG> was later invalidated at offsets [0x0..0x4] by a Unique retag
    |
 LL |     let raw2 = &mut l as *mut _; // invalidates raw1
    |                ^^^^^^
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside `main` at $DIR/raw_tracking.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
diff --git a/src/tools/miri/tests/fail/stacked_borrows/retag_data_race_read.stderr b/src/tools/miri/tests/fail/stacked_borrows/retag_data_race_read.stderr
index 790fd51ec37..26607e1a690 100644
--- a/src/tools/miri/tests/fail/stacked_borrows/retag_data_race_read.stderr
+++ b/src/tools/miri/tests/fail/stacked_borrows/retag_data_race_read.stderr
@@ -11,7 +11,7 @@ LL |         let _r = &*p;
    |                  ^^^
    = 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 (of the first span):
    = note: inside `thread_2` at $DIR/retag_data_race_read.rs:LL:CC
 note: inside closure
   --> $DIR/retag_data_race_read.rs:LL:CC
diff --git a/src/tools/miri/tests/fail/stacked_borrows/retag_data_race_write.stderr b/src/tools/miri/tests/fail/stacked_borrows/retag_data_race_write.stderr
index c5b8b4c41f5..33839d2647d 100644
--- a/src/tools/miri/tests/fail/stacked_borrows/retag_data_race_write.stderr
+++ b/src/tools/miri/tests/fail/stacked_borrows/retag_data_race_write.stderr
@@ -11,7 +11,7 @@ LL |         let _r = &mut *p;
    |                  ^^^^^^^
    = 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 (of the first span):
    = note: inside `thread_2` at $DIR/retag_data_race_write.rs:LL:CC
 note: inside closure
   --> $DIR/retag_data_race_write.rs:LL:CC
diff --git a/src/tools/miri/tests/fail/stacked_borrows/return_invalid_mut.stderr b/src/tools/miri/tests/fail/stacked_borrows/return_invalid_mut.stderr
index 1b28f780c1c..2bf91b676c4 100644
--- a/src/tools/miri/tests/fail/stacked_borrows/return_invalid_mut.stderr
+++ b/src/tools/miri/tests/fail/stacked_borrows/return_invalid_mut.stderr
@@ -19,7 +19,7 @@ help: <TAG> was later invalidated at offsets [0x0..0x8] by a read access
    |
 LL |     let _val = unsafe { *xraw }; // invalidate xref
    |                         ^^^^^
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside `foo` at $DIR/return_invalid_mut.rs:LL:CC
 note: inside `main`
   --> $DIR/return_invalid_mut.rs:LL:CC
diff --git a/src/tools/miri/tests/fail/stacked_borrows/return_invalid_mut_option.stderr b/src/tools/miri/tests/fail/stacked_borrows/return_invalid_mut_option.stderr
index db14dcafa00..ff00c54570c 100644
--- a/src/tools/miri/tests/fail/stacked_borrows/return_invalid_mut_option.stderr
+++ b/src/tools/miri/tests/fail/stacked_borrows/return_invalid_mut_option.stderr
@@ -19,7 +19,7 @@ help: <TAG> was later invalidated at offsets [0x0..0x8] by a read access
    |
 LL |     let _val = unsafe { *xraw }; // invalidate xref
    |                         ^^^^^
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside `foo` at $DIR/return_invalid_mut_option.rs:LL:CC
 note: inside `main`
   --> $DIR/return_invalid_mut_option.rs:LL:CC
diff --git a/src/tools/miri/tests/fail/stacked_borrows/return_invalid_mut_tuple.stderr b/src/tools/miri/tests/fail/stacked_borrows/return_invalid_mut_tuple.stderr
index 81ed4218aad..61d041a8816 100644
--- a/src/tools/miri/tests/fail/stacked_borrows/return_invalid_mut_tuple.stderr
+++ b/src/tools/miri/tests/fail/stacked_borrows/return_invalid_mut_tuple.stderr
@@ -19,7 +19,7 @@ help: <TAG> was later invalidated at offsets [0x0..0x8] by a read access
    |
 LL |     let _val = unsafe { *xraw }; // invalidate xref
    |                         ^^^^^
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside `foo` at $DIR/return_invalid_mut_tuple.rs:LL:CC
 note: inside `main`
   --> $DIR/return_invalid_mut_tuple.rs:LL:CC
diff --git a/src/tools/miri/tests/fail/stacked_borrows/return_invalid_shr.stderr b/src/tools/miri/tests/fail/stacked_borrows/return_invalid_shr.stderr
index 9c8cc50b2d7..d3a73a00fa6 100644
--- a/src/tools/miri/tests/fail/stacked_borrows/return_invalid_shr.stderr
+++ b/src/tools/miri/tests/fail/stacked_borrows/return_invalid_shr.stderr
@@ -19,7 +19,7 @@ help: <TAG> was later invalidated at offsets [0x0..0x8] by a write access
    |
 LL |     unsafe { *xraw = (42, 23) }; // unfreeze
    |              ^^^^^^^^^^^^^^^^
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside `foo` at $DIR/return_invalid_shr.rs:LL:CC
 note: inside `main`
   --> $DIR/return_invalid_shr.rs:LL:CC
diff --git a/src/tools/miri/tests/fail/stacked_borrows/return_invalid_shr_option.stderr b/src/tools/miri/tests/fail/stacked_borrows/return_invalid_shr_option.stderr
index 00ce6f6cd5f..f14e8b8532f 100644
--- a/src/tools/miri/tests/fail/stacked_borrows/return_invalid_shr_option.stderr
+++ b/src/tools/miri/tests/fail/stacked_borrows/return_invalid_shr_option.stderr
@@ -19,7 +19,7 @@ help: <TAG> was later invalidated at offsets [0x0..0x8] by a write access
    |
 LL |     unsafe { *xraw = (42, 23) }; // unfreeze
    |              ^^^^^^^^^^^^^^^^
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside `foo` at $DIR/return_invalid_shr_option.rs:LL:CC
 note: inside `main`
   --> $DIR/return_invalid_shr_option.rs:LL:CC
diff --git a/src/tools/miri/tests/fail/stacked_borrows/return_invalid_shr_tuple.stderr b/src/tools/miri/tests/fail/stacked_borrows/return_invalid_shr_tuple.stderr
index bbd17b1284c..9ddaad4d1be 100644
--- a/src/tools/miri/tests/fail/stacked_borrows/return_invalid_shr_tuple.stderr
+++ b/src/tools/miri/tests/fail/stacked_borrows/return_invalid_shr_tuple.stderr
@@ -19,7 +19,7 @@ help: <TAG> was later invalidated at offsets [0x0..0x8] by a write access
    |
 LL |     unsafe { *xraw = (42, 23) }; // unfreeze
    |              ^^^^^^^^^^^^^^^^
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside `foo` at $DIR/return_invalid_shr_tuple.rs:LL:CC
 note: inside `main`
   --> $DIR/return_invalid_shr_tuple.rs:LL:CC
diff --git a/src/tools/miri/tests/fail/stacked_borrows/shared_rw_borrows_are_weak1.stderr b/src/tools/miri/tests/fail/stacked_borrows/shared_rw_borrows_are_weak1.stderr
index 3a139c3ab21..589e1291ba7 100644
--- a/src/tools/miri/tests/fail/stacked_borrows/shared_rw_borrows_are_weak1.stderr
+++ b/src/tools/miri/tests/fail/stacked_borrows/shared_rw_borrows_are_weak1.stderr
@@ -19,7 +19,7 @@ help: <TAG> was later invalidated at offsets [0x0..0x4] by a Unique retag
    |
 LL |         shr_rw.set(1);
    |         ^^^^^^^^^^^^^
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside `main` at $DIR/shared_rw_borrows_are_weak1.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
diff --git a/src/tools/miri/tests/fail/stacked_borrows/shared_rw_borrows_are_weak2.stderr b/src/tools/miri/tests/fail/stacked_borrows/shared_rw_borrows_are_weak2.stderr
index 0609a73e793..0e37c4ffb39 100644
--- a/src/tools/miri/tests/fail/stacked_borrows/shared_rw_borrows_are_weak2.stderr
+++ b/src/tools/miri/tests/fail/stacked_borrows/shared_rw_borrows_are_weak2.stderr
@@ -19,7 +19,7 @@ help: <TAG> was later invalidated at offsets [$HEX..$HEX] by a Unique retag
    |
 LL |         shr_rw.replace(1);
    |         ^^^^^^^^^^^^^^^^^
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside `main` at $DIR/shared_rw_borrows_are_weak2.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
diff --git a/src/tools/miri/tests/fail/stacked_borrows/shr_frozen_violation1.stderr b/src/tools/miri/tests/fail/stacked_borrows/shr_frozen_violation1.stderr
index fe0ac211318..a69116f2afa 100644
--- a/src/tools/miri/tests/fail/stacked_borrows/shr_frozen_violation1.stderr
+++ b/src/tools/miri/tests/fail/stacked_borrows/shr_frozen_violation1.stderr
@@ -14,7 +14,7 @@ help: <TAG> was created by a SharedReadOnly retag at offsets [0x0..0x4]
    |
 LL |         *(x as *const i32 as *mut i32) = 7;
    |           ^
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside `unknown_code` at $DIR/shr_frozen_violation1.rs:LL:CC
 note: inside `foo`
   --> $DIR/shr_frozen_violation1.rs:LL:CC
diff --git a/src/tools/miri/tests/fail/stacked_borrows/track_caller.stderr b/src/tools/miri/tests/fail/stacked_borrows/track_caller.stderr
index 6f1d0ccd348..05be0d3f1e9 100644
--- a/src/tools/miri/tests/fail/stacked_borrows/track_caller.stderr
+++ b/src/tools/miri/tests/fail/stacked_borrows/track_caller.stderr
@@ -19,7 +19,7 @@ help: <TAG> was later invalidated at offsets [0x0..0x4] by a read access
    |
 LL |     callee(xraw);
    |     ^^^^^^^^^^^^
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside `main` at $DIR/track_caller.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
diff --git a/src/tools/miri/tests/fail/stacked_borrows/transmute-is-no-escape.stderr b/src/tools/miri/tests/fail/stacked_borrows/transmute-is-no-escape.stderr
index a2ecb07fd31..ac962311d42 100644
--- a/src/tools/miri/tests/fail/stacked_borrows/transmute-is-no-escape.stderr
+++ b/src/tools/miri/tests/fail/stacked_borrows/transmute-is-no-escape.stderr
@@ -14,7 +14,7 @@ help: <TAG> was created by a SharedReadWrite retag at offsets [0x4..0x8]
    |
 LL |     let raw = (&mut x[1] as *mut i32).wrapping_offset(-1);
    |                ^^^^^^^^^
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside `main` at $DIR/transmute-is-no-escape.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
diff --git a/src/tools/miri/tests/fail/stacked_borrows/unescaped_static.stderr b/src/tools/miri/tests/fail/stacked_borrows/unescaped_static.stderr
index 01a4bf4340c..7a40d1078b3 100644
--- a/src/tools/miri/tests/fail/stacked_borrows/unescaped_static.stderr
+++ b/src/tools/miri/tests/fail/stacked_borrows/unescaped_static.stderr
@@ -14,7 +14,7 @@ help: <TAG> was created by a SharedReadOnly retag at offsets [0x0..0x1]
    |
 LL |     let ptr_to_first = &ARRAY[0] as *const u8;
    |                        ^^^^^^^^^
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside `main` at $DIR/unescaped_static.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
diff --git a/src/tools/miri/tests/fail/stacked_borrows/zst_slice.stderr b/src/tools/miri/tests/fail/stacked_borrows/zst_slice.stderr
index e134ee2845d..950abc4cbcf 100644
--- a/src/tools/miri/tests/fail/stacked_borrows/zst_slice.stderr
+++ b/src/tools/miri/tests/fail/stacked_borrows/zst_slice.stderr
@@ -14,7 +14,7 @@ help: <TAG> would have been created here, but this is a zero-size retag ([0x0..0
    |
 LL |         assert_eq!(*s.get_unchecked(1), 2);
    |                     ^^^^^^^^^^^^^^^^^^
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside `core::slice::<impl [i32]>::get_unchecked::<usize>` at RUSTLIB/core/src/slice/mod.rs:LL:CC
 note: inside `main`
   --> $DIR/zst_slice.rs:LL:CC