avr: Provide abort()

Author: Patryk27

compiler-builtins/src/avr.rs

@@ -0,0 +1,22 @@
+intrinsics! {
+    pub unsafe extern "C" fn abort() -> ! {
+        // On AVRs, an architecture that doesn't support traps, unreachable code
+        // paths get lowered into calls to `abort`:
+        //
+        // https://github.com/llvm/llvm-project/blob/cbe8f3ad7621e402b050e768f400ff0d19c3aedd/llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp#L4462
+        //
+        // When control gets here, it means an undefined behavior has occurred, so
+        // there's really not that much we can do to recover - we can't reliably
+        // `panic!()`, because for all we know the environment is gone, so panicking
+        // might end up with us getting back to this very function.
+        //
+        // So let's do the next best thing, loop.
+        //
+        // Alternatively we could (try to) restart the program, but since undefined
+        // behavior is undefined, there's really no obligation for us to do anything
+        // here - for all we care, we could just set the chip on fire; but that'd be
+        // bad for the environment.
+
+        loop {}
+    }
+}

compiler-builtins/src/lib.rs

@@ -63,6 +63,9 @@ pub mod aarch64_linux;
 ))]
 pub mod arm_linux;
 
+#[cfg(target_arch = "avr")]
+pub mod avr;
+
 #[cfg(target_arch = "hexagon")]
 pub mod hexagon;