Never start the Stack::retain loop at offset 0 so that the left element is always inbounds

1 files changed, 21 insertions, 0 deletions

diff --git a/src/tools/miri/tests/pass/stacked-borrows/unknown-bottom-gc.rs b/src/tools/miri/tests/pass/stacked-borrows/unknown-bottom-gc.rs
new file mode 100644
index 00000000000..e62ee528686
--- /dev/null
+++ b/src/tools/miri/tests/pass/stacked-borrows/unknown-bottom-gc.rs
@@ -0,0 +1,21 @@
+//@compile-flags: -Zmiri-permissive-provenance
+#![feature(strict_provenance)]
+
+use std::ptr;
+
+fn main() {
+    let mut v = 1u8;
+    let ptr = &mut v as *mut u8;
+
+    // Expose the allocation and use the exposed pointer, creating an unknown bottom
+    unsafe {
+        let p: *mut u8 = ptr::from_exposed_addr::<u8>(ptr.expose_addr()) as *mut u8;
+        *p = 1;
+    }
+
+    // Pile on a lot of SharedReadOnly at the top of the stack
+    let r = &v;
+    for _ in 0..1024 {
+        let _x = &*r;
+    }
+}