allocate backtrace strings mutably

Author: RalfJung

src/shims/backtrace.rs

@@ -119,8 +119,10 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
         // `lo.col` is 0-based - add 1 to make it 1-based for the caller.
         let colno: u32 = lo.col.0 as u32 + 1;
 
-        let name_alloc = this.allocate_str(&name, MiriMemoryKind::Rust.into());
-        let filename_alloc = this.allocate_str(&filename, MiriMemoryKind::Rust.into());
+        // These are "mutable" allocations as we consider them to be owned by the callee.
+        let name_alloc = this.allocate_str(&name, MiriMemoryKind::Rust.into(), Mutability::Mut);
+        let filename_alloc =
+            this.allocate_str(&filename, MiriMemoryKind::Rust.into(), Mutability::Mut);
         let lineno_alloc = Scalar::from_u32(lineno);
         let colno_alloc = Scalar::from_u32(colno);
 

src/shims/panic.rs

@@ -13,6 +13,7 @@
 
 use log::trace;
 
+use rustc_ast::Mutability;
 use rustc_middle::{mir, ty};
 use rustc_target::spec::abi::Abi;
 use rustc_target::spec::PanicStrategy;
@@ -169,7 +170,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
         let this = self.eval_context_mut();
 
         // First arg: message.
-        let msg = this.allocate_str(msg, MiriMemoryKind::Machine.into());
+        let msg = this.allocate_str(msg, MiriMemoryKind::Machine.into(), Mutability::Not);
 
         // Call the lang item.
         let panic = this.tcx.lang_items().panic_fn().unwrap();