Don't spill operands onto the stack in naked functions

Currently, the code spills operands onto the stack for the purpose of
debuginfo. However, naked functions can only contain an asm block. Therefore,
attempting to spill the operands on the stack is undefined behavior.

Fixes https://github.com/rust-lang/rust/issues/42779
cc https://github.com/rust-lang/rust/issues/32408

1 files changed, 8 insertions, 0 deletions

diff --git a/src/librustc_codegen_ssa/mir/debuginfo.rs b/src/librustc_codegen_ssa/mir/debuginfo.rs
index d166a27b5a9..d8a530d98fa 100644
--- a/src/librustc_codegen_ssa/mir/debuginfo.rs
+++ b/src/librustc_codegen_ssa/mir/debuginfo.rs
@@ -1,6 +1,7 @@
 use crate::traits::*;
 use rustc_hir::def_id::CrateNum;
 use rustc_index::vec::IndexVec;
+use rustc_middle::middle::codegen_fn_attrs::CodegenFnAttrFlags;
 use rustc_middle::mir;
 use rustc_middle::ty;
 use rustc_session::config::DebugInfo;
@@ -216,6 +217,13 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
             LocalRef::Operand(None) => return,
 
             LocalRef::Operand(Some(operand)) => {
+                // Don't spill operands onto the stack in naked functions.
+                // See: https://github.com/rust-lang/rust/issues/42779
+                let attrs = bx.tcx().codegen_fn_attrs(self.instance.def_id());
+                if attrs.flags.contains(CodegenFnAttrFlags::NAKED) {
+                    return;
+                }
+
                 // "Spill" the value onto the stack, for debuginfo,
                 // without forcing non-debuginfo uses of the local
                 // to also load from the stack every single time.