Add explicit Miri support to libpanic_unwind

Author: Aaron1011

src/libcore/intrinsics.rs

@@ -1348,6 +1348,11 @@ extern "rust-intrinsic" {
     /// See documentation of `<*const T>::offset_from` for details.
     #[cfg(not(bootstrap))]
     pub fn ptr_offset_from<T>(ptr: *const T, base: *const T) -> isize;
+
+    /// 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)) -> !;
 }
 
 // Some functions are defined here because they accidentally got made

src/libpanic_unwind/lib.rs

@@ -36,7 +36,10 @@ use core::raw;
 use core::panic::BoxMeUp;
 
 cfg_if::cfg_if! {
-    if #[cfg(target_os = "emscripten")] {
+    if #[cfg(miri)] {
+        #[path = "miri.rs"]
+        mod imp;
+    } else if #[cfg(target_os = "emscripten")] {
         #[path = "emcc.rs"]
         mod imp;
     } else if #[cfg(target_arch = "wasm32")] {

src/libpanic_unwind/miri.rs

@@ -0,0 +1,12 @@
+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 cleanup(ptr: *mut u8) -> Box<dyn Any + Send> {
+    Box::from_raw(ptr)
+}
+