adjust frame_in_std to recognize std tests

Author: RalfJung

src/tools/miri/src/helpers.rs

@@ -968,10 +968,6 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
 
     fn frame_in_std(&self) -> bool {
         let this = self.eval_context_ref();
-        let Some(start_fn) = this.tcx.lang_items().start_fn() else {
-            // no_std situations
-            return false;
-        };
         let frame = this.frame();
         // Make an attempt to get at the instance of the function this is inlined from.
         let instance: Option<_> = try {
@@ -982,13 +978,15 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
         };
         // Fall back to the instance of the function itself.
         let instance = instance.unwrap_or(frame.instance);
-        // Now check if this is in the same crate as start_fn.
-        // As a special exception we also allow unit tests from
-        // <https://github.com/rust-lang/miri-test-libstd/tree/master/std_miri_test> to call these
-        // shims.
+        // Now check the crate it is in. We could try to be clever here and e.g. check if this is
+        // the same crate as `start_fn`, but that would not work for running std tests in Miri, so
+        // we'd need some more hacks anyway. So we just check the name of the crate. If someone
+        // calls their crate `std` then we'll just let them keep the pieces.
         let frame_crate = this.tcx.def_path(instance.def_id()).krate;
-        frame_crate == this.tcx.def_path(start_fn).krate
-            || this.tcx.crate_name(frame_crate).as_str() == "std_miri_test"
+        let crate_name = this.tcx.crate_name(frame_crate);
+        let crate_name = crate_name.as_str();
+        // On miri-test-libstd, the name of the crate is different.
+        crate_name == "std" || crate_name == "std_miri_test"
     }
 
     /// Handler that should be called when unsupported functionality is encountered.