From 44acdd7873a624eb7cdcc2ba3a5965c870d631e7 Mon Sep 17 00:00:00 2001
From: Janis <janis@nirgendwo.xyz>
Date: Fri, 21 Feb 2025 23:55:05 +0100
Subject: [PATCH] aligned function pointers

---
 src/lib.rs         |  1 +
 src/praetor/mod.rs | 16 ++++++++++++++--
 2 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/src/lib.rs b/src/lib.rs
index 1250cd7..5bea4f0 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -4,6 +4,7 @@
     debug_closure_helpers,
     cell_update,
     cold_path,
+    fn_align,
     let_chains
 )]
 
diff --git a/src/praetor/mod.rs b/src/praetor/mod.rs
index 0a06d4c..fb59fe7 100644
--- a/src/praetor/mod.rs
+++ b/src/praetor/mod.rs
@@ -66,6 +66,10 @@ mod util {
         }
     }
 
+    // Miri doesn't like tagging pointers that it doesn't know the alignment of.
+    // This includes function pointers, which aren't guaranteed to be aligned to
+    // anything, but generally have an alignment of 8, and can be specified to
+    // be aligned to `n` with `#[repr(align(n))]`.
     #[repr(transparent)]
     pub struct TaggedAtomicPtr<T, const BITS: usize>(AtomicPtr<()>, PhantomData<T>);
 
@@ -85,7 +89,12 @@ mod util {
 
         pub fn ptr(&self, order: Ordering) -> NonNull<T> {
             unsafe {
-                NonNull::new_unchecked(self.0.load(order).map_addr(|addr| addr & !Self::mask()) as _)
+                NonNull::new_unchecked(
+                    self.0
+                        .load(order)
+                        .map_addr(|addr| addr & !Self::mask())
+                        .cast(),
+                )
             }
         }
 
@@ -180,7 +189,7 @@ mod util {
             let mask = Self::mask();
             loop {
                 let ptr = self.0.load(failure);
-                let new = ptr.with_addr((ptr.addr() & !mask) | (tag & mask));
+                let new = ptr.map_addr(|addr| (addr & !mask) | (tag & mask));
 
                 if self
                     .0
@@ -823,6 +832,7 @@ mod job {
             F: FnOnce(&super::Scope) -> T + Send,
             T: Send,
         {
+            #[repr(align(8))]
             unsafe fn harness<F, T>(this: *const (), job: *const Job<()>, scope: &super::Scope)
             where
                 F: FnOnce(&super::Scope) -> T + Send,
@@ -864,6 +874,7 @@ mod job {
             F: FnOnce(&super::Scope) -> T + Send,
             T: Send,
         {
+            #[repr(align(8))]
             unsafe fn harness<F, T>(this: *const (), job: *const Job<()>, scope: &super::Scope)
             where
                 F: FnOnce(&super::Scope) -> T + Send,
@@ -1117,6 +1128,7 @@ impl Scope {
 
         let this = SendPtr::new(&raw const *self as *mut Self).unwrap();
         let schedule = move |runnable: Runnable| {
+            #[repr(align(8))]
             unsafe fn harness<T>(this: *const (), job: *const Job<T>, _: &Scope) {
                 let runnable = Runnable::<()>::from_raw(NonNull::new_unchecked(this.cast_mut()));
                 runnable.run();