Rollup merge of #104110 - krasimirgg:msan-16, r=nagisa

prevent uninitialized access in black_box for zero-sized-types

Don't read the pointer location in black_box for zero sized types, just emit a memory clobber instead. Addresses  https://github.com/rust-lang/rust/issues/103304 when rust is build against LLVM at HEAD.

Zulip thread: https://rust-lang.zulipchat.com/#narrow/stream/187780-t-compiler.2Fwg-llvm/topic/.28with.20llvm.20at.20HEAD.29.3A.20msan.20error.20in.20core.3A.3Ahint.3A.3Ablack_box

1 files changed, 32 insertions, 0 deletions

diff --git a/src/test/ui/sanitize/memory-passing.rs b/src/test/ui/sanitize/memory-passing.rs
new file mode 100644
index 00000000000..6d9b70ad6b1
--- /dev/null
+++ b/src/test/ui/sanitize/memory-passing.rs
@@ -0,0 +1,32 @@
+// needs-sanitizer-support
+// needs-sanitizer-memory
+//
+// revisions: unoptimized optimized
+//
+// [optimized]compile-flags: -Z sanitizer=memory -Zsanitizer-memory-track-origins -O
+// [unoptimized]compile-flags: -Z sanitizer=memory -Zsanitizer-memory-track-origins
+//
+// run-pass
+//
+// This test case intentionally limits the usage of the std,
+// since it will be linked with an uninstrumented version of it.
+
+#![feature(core_intrinsics)]
+#![feature(start)]
+#![allow(invalid_value)]
+
+use std::hint::black_box;
+
+fn calling_black_box_on_zst_ok() {
+    // It's OK to call black_box on a value of a zero-sized type, even if its
+    // underlying the memory location is uninitialized. For non-zero-sized types,
+    // this would be an MSAN error.
+    let zst = ();
+    black_box(zst);
+}
+
+#[start]
+fn main(_: isize, _: *const *const u8) -> isize {
+    calling_black_box_on_zst_ok();
+    0
+}