Fix up intrinsic implementation

src/libcore/intrinsics.rs

@@ -1352,7 +1352,7 @@ pub fn volatile_copy_nonoverlapping_memory<T>(dst: *mut T, src: *const T,
     /// Internal hook used by Miri to implement unwinding.
     /// Perma-unstable: do not use
     #[cfg(not(bootstrap))]
-    pub fn miri_start_panic(data: *mut (dyn crate::any::Any + Send)) -> !;
+    pub fn miri_start_panic(data: u128) -> !;
 }
 
 // Some functions are defined here because they accidentally got made

src/libpanic_unwind/miri.rs

@@ -1,9 +1,13 @@
+use core::any::Any;
+use alloc::boxed::Box;
+
 pub fn payload() -> *mut u8 {
     core::ptr::null_mut()
 }
 
-pub unsafe fn panic(data: Box<dyn Any + Send>) -> u32 {
-    core::intrinsics::miri_start_panic(Box::into_raw(data))
+pub unsafe fn panic(data: Box<dyn Any + Send>) -> ! {
+    let raw_val = core::mem::transmute::<_, u128>(Box::into_raw(data));
+    core::intrinsics::miri_start_panic(raw_val)
 }
 
 pub unsafe fn cleanup(ptr: *mut u8) -> Box<dyn Any + Send> {

src/librustc_codegen_ssa/mir/block.rs

@@ -528,6 +528,16 @@ fn codegen_call_terminator<'b>(
             _ => FnAbi::new(&bx, sig, &extra_args)
         };
 
+        // This should never be reachable at runtime:
+        // We should only emit a call to this intrinsic in #[cfg(miri)] mode,
+        // which means that we will never actually use the generate object files
+        // (we will just be interpreting the MIR)
+        if intrinsic == Some("miri_start_panic") {
+            bx.abort();
+            bx.unreachable();
+            return;
+        }
+
         // Emit a panic or a no-op for `panic_if_uninhabited`.
         if intrinsic == Some("panic_if_uninhabited") {
             let ty = instance.unwrap().substs.type_at(0);

src/librustc_typeck/check/intrinsic.rs

@@ -384,6 +384,10 @@ pub fn check_intrinsic_type(tcx: TyCtxt<'_>, it: &hir::ForeignItem) {
                 (1, vec![ tcx.mk_mut_ptr(param(0)), param(0) ], tcx.mk_unit())
             }
 
+            "miri_start_panic" => {
+                (0, vec![tcx.types.u128], tcx.types.never)
+            }
+
             ref other => {
                 struct_span_err!(tcx.sess, it.span, E0093,
                                  "unrecognized intrinsic function: `{}`",