From ce6c25da5887dcdb446b56892ace1d2463a743f3 Mon Sep 17 00:00:00 2001
From: Oliver Scherer <github35764891676564198441@oli-obk.de>
Date: Wed, 30 Sep 2020 10:40:49 +0200
Subject: [PATCH] References to ZSTs may be at arbitrary aligned addresses
---
compiler/rustc_mir/src/const_eval/eval_queries.rs | 10 +++++-----
src/test/ui/match/const_non_normal_zst_ref_pattern.rs | 9 +++++++++
2 files changed, 14 insertions(+), 5 deletions(-)
create mode 100644 src/test/ui/match/const_non_normal_zst_ref_pattern.rs
diff --git a/compiler/rustc_mir/src/const_eval/eval_queries.rs b/compiler/rustc_mir/src/const_eval/eval_queries.rs
index a0ee7fdc072ef..57aa216850aab 100644
--- a/compiler/rustc_mir/src/const_eval/eval_queries.rs
+++ b/compiler/rustc_mir/src/const_eval/eval_queries.rs
@@ -14,7 +14,7 @@ use rustc_middle::ty::print::with_no_trimmed_paths;
use rustc_middle::ty::{self, subst::Subst, TyCtxt};
use rustc_span::source_map::Span;
use rustc_target::abi::{Abi, LayoutOf};
-use std::convert::TryInto;
+use std::convert::{TryFrom, TryInto};
pub fn note_on_undefined_behavior_error() -> &'static str {
"The rules on what exactly is undefined behavior aren't clear, \
@@ -148,10 +148,10 @@ pub(super) fn op_to_const<'tcx>(
Scalar::Raw { data, .. } => {
assert!(mplace.layout.is_zst());
assert_eq!(
- data,
- mplace.layout.align.abi.bytes().into(),
- "this MPlaceTy must come from `try_as_mplace` being used on a zst, so we know what
- value this integer address must have",
+ u64::try_from(data).unwrap() % mplace.layout.align.abi.bytes(),
+ 0,
+ "this MPlaceTy must come from a validated constant, thus we can assume the \
+ alignment is correct",
);
ConstValue::Scalar(Scalar::zst())
}
diff --git a/src/test/ui/match/const_non_normal_zst_ref_pattern.rs b/src/test/ui/match/const_non_normal_zst_ref_pattern.rs
new file mode 100644
index 0000000000000..a114fafb64730
--- /dev/null
+++ b/src/test/ui/match/const_non_normal_zst_ref_pattern.rs
@@ -0,0 +1,9 @@
+// check-pass
+
+const FOO: isize = 10;
+const ZST: &() = unsafe { std::mem::transmute(FOO) };
+fn main() {
+ match &() {
+ ZST => 9,
+ };
+}