From df3664c4c7e21a82c4bed0a6cb7bd2139237aa36 Mon Sep 17 00:00:00 2001
From: Andrew Drake <adrake@adrake.org>
Date: Sun, 22 Jun 2025 14:58:27 -0700
Subject: [PATCH 1/3] Enforce minimum alignment on entries to fix tagged
 pointer unsoundness

---
 src/raw/mod.rs          | 5 +++--
 src/raw/utils/tagged.rs | 3 +++
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/src/raw/mod.rs b/src/raw/mod.rs
index 79eb825..4fc5ac7 100644
--- a/src/raw/mod.rs
+++ b/src/raw/mod.rs
@@ -118,8 +118,9 @@ pub enum RawInsertResult<'g, K, V> {
     },
 }
 
-// An entry in the hash-table.
-#[repr(C)]
+// An entry in the hash-table. We force a minimum of 8-byte alignment because
+// we store entry flags in the low 3 bits of pointers to this type.
+#[repr(C, align(8))]
 pub struct Entry<K, V> {
     /// The key for this entry.
     pub key: K,
diff --git a/src/raw/utils/tagged.rs b/src/raw/utils/tagged.rs
index 793ebfb..4ab0120 100644
--- a/src/raw/utils/tagged.rs
+++ b/src/raw/utils/tagged.rs
@@ -33,6 +33,9 @@ unsafe impl<T> StrictProvenance<T> for *mut T {
     where
         T: Unpack,
     {
+        // This assert will fail at compile time if T doesn't have an alignment that
+        // guarantees all valid pointers have zero in the bits excluded by T::MASK.
+        const { assert!(align_of::<T>() > !T::MASK) };
         Tagged {
             raw: self,
             ptr: self.map_addr(|addr| addr & T::MASK),

From fdb0aad9a510b79ad3b1869f70371484921a095f Mon Sep 17 00:00:00 2001
From: Andrew Drake <adrake@adrake.org>
Date: Sun, 22 Jun 2025 21:08:32 -0700
Subject: [PATCH 2/3] Fix Rust 1.72 compatibility

---
 src/raw/utils/tagged.rs | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/src/raw/utils/tagged.rs b/src/raw/utils/tagged.rs
index 4ab0120..962a6c5 100644
--- a/src/raw/utils/tagged.rs
+++ b/src/raw/utils/tagged.rs
@@ -1,3 +1,4 @@
+use std::mem::align_of;
 use std::sync::atomic::{AtomicPtr, Ordering};
 
 // Polyfill for the unstable strict-provenance APIs.
@@ -17,6 +18,16 @@ pub trait Unpack {
     const MASK: usize;
 }
 
+// This function does nothing, but will fail to compile if T doesn't have an alignment
+// that guarantees all valid pointers have zero in the bits excluded by T::MASK.
+const fn static_assert_align_of<T: Unpack>() {
+    struct Dummy<T>(T);
+    impl<T: Unpack> Dummy<T> {
+        const ASSERT: () = assert!(align_of::<T>() > !T::MASK);
+    }
+    Dummy::<T>::ASSERT
+}
+
 unsafe impl<T> StrictProvenance<T> for *mut T {
     #[inline(always)]
     fn addr(self) -> usize {
@@ -33,9 +44,7 @@ unsafe impl<T> StrictProvenance<T> for *mut T {
     where
         T: Unpack,
     {
-        // This assert will fail at compile time if T doesn't have an alignment that
-        // guarantees all valid pointers have zero in the bits excluded by T::MASK.
-        const { assert!(align_of::<T>() > !T::MASK) };
+        static_assert_align_of::<T>();
         Tagged {
             raw: self,
             ptr: self.map_addr(|addr| addr & T::MASK),

From 2851f093ed30e613feaf655d14f6eb50f73de73f Mon Sep 17 00:00:00 2001
From: Andrew Drake <adrake@adrake.org>
Date: Tue, 24 Jun 2025 02:59:09 -0700
Subject: [PATCH 3/3] Move assertion const to Unpack trait

---
 src/raw/utils/tagged.rs | 16 +++++-----------
 1 file changed, 5 insertions(+), 11 deletions(-)

diff --git a/src/raw/utils/tagged.rs b/src/raw/utils/tagged.rs
index 962a6c5..c92de4b 100644
--- a/src/raw/utils/tagged.rs
+++ b/src/raw/utils/tagged.rs
@@ -13,19 +13,13 @@ pub unsafe trait StrictProvenance<T>: Sized {
 }
 
 // Unpack a tagged pointer.
-pub trait Unpack {
+pub trait Unpack: Sized {
     // A mask for the pointer tag bits.
     const MASK: usize;
-}
 
-// This function does nothing, but will fail to compile if T doesn't have an alignment
-// that guarantees all valid pointers have zero in the bits excluded by T::MASK.
-const fn static_assert_align_of<T: Unpack>() {
-    struct Dummy<T>(T);
-    impl<T: Unpack> Dummy<T> {
-        const ASSERT: () = assert!(align_of::<T>() > !T::MASK);
-    }
-    Dummy::<T>::ASSERT
+    // This constant, if used, will fail to compile if T doesn't have an alignment
+    // that guarantees all valid pointers have zero in the bits excluded by T::MASK.
+    const ASSERT_ALIGNMENT: () = assert!(align_of::<Self>() > !Self::MASK);
 }
 
 unsafe impl<T> StrictProvenance<T> for *mut T {
@@ -44,7 +38,7 @@ unsafe impl<T> StrictProvenance<T> for *mut T {
     where
         T: Unpack,
     {
-        static_assert_align_of::<T>();
+        let () = T::ASSERT_ALIGNMENT;
         Tagged {
             raw: self,
             ptr: self.map_addr(|addr| addr & T::MASK),