Fix alignment handling for packed structs

chipshort · Jan 26, 2024 · 5c982e9 · 5c982e9
1 parent 5ceb431
commit 5c982e9
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Showing 2 changed files with 12 additions and 8 deletions.
diff --git a/boxify-macro/src/lib.rs b/boxify-macro/src/lib.rs
@@ -215,7 +215,8 @@ fn fill_ptr(ptr: &Expr, value: &Expr) -> proc_macro2::TokenStream {
 
                     quote! {
                         #validate_not_struct
-                        unsafe { #ptr.write(#value); }
+                        // unsafe { #ptr.write(#value); }
+                        unsafe { #ptr.write_unaligned(#value); }
                     }
                 }
             } else {
@@ -226,7 +227,8 @@ fn fill_ptr(ptr: &Expr, value: &Expr) -> proc_macro2::TokenStream {
             // fallback to creating the value on the stack and writing it to
             // the pointer from there
             quote! {
-                unsafe { #ptr.write(#e); }
+                // unsafe { #ptr.write(#e); }
+                unsafe { #ptr.write_unaligned(#e); }
             }
         }
     }
@@ -239,7 +241,7 @@ fn fill_struct_fields(strct_ptr: &Expr, strct: &syn::ExprStruct) -> proc_macro2:
         let expr = &field.expr;
 
         let field_ptr = parse_quote! {
-            core::ptr::addr_of_mut!((*#strct_ptr).#ident)
+            ::core::ptr::addr_of_mut!((*#strct_ptr).#ident)
         };
         fill_ptr(&field_ptr, expr)
     });
@@ -265,7 +267,7 @@ fn fill_tuple(
     let instantiation_codes = elems.iter().enumerate().map(|(index, value)| {
         let index = syn::Index::from(index);
         let field_ptr = parse_quote_spanned! {value.span()=>
-            core::ptr::addr_of_mut!((*#ptr).#index)
+            ::core::ptr::addr_of_mut!((*#ptr).#index)
         };
         fill_ptr(&field_ptr, value)
     });

diff --git a/boxify/src/lib.rs b/boxify/src/lib.rs
@@ -117,13 +117,15 @@ pub unsafe fn fill_array<T: Copy, const SIZE: usize>(array: *mut [T; SIZE], valu
 
     if size_of::<T>() == 1 {
         // in this case, we can use `ptr::write_bytes` instead of `ptr::write`
-        // SAFETY: we just checked that T is 1 byte, so transmuting to u8 is safe
-        let value_byte = core::ptr::addr_of!(value) as *const u8;
-        core::ptr::write_bytes(array, *value_byte, SIZE);
+        // SAFETY: we just checked that T is 1 byte, so casting to *const u8 is valid
+        let value_byte: *const u8 = core::ptr::addr_of!(value) as *const u8;
+        // also casting array to *mut u8 for alignment reasons
+        core::ptr::write_bytes(array as *mut u8, *value_byte, SIZE);
     } else {
         for i in 0..SIZE {
             // write the value to the array
-            array.add(i).write(value);
+            // array.add(i).write(value);
+            array.add(i).write_unaligned(value);
         }
     }
 }