fix(profiling): preserve allocation prefix alignment

Author: realFlowControl

profiling/src/allocation/allocation_ge84.rs

@@ -14,7 +14,8 @@ use libc::{c_char, c_uint};
 #[cfg(feature = "debug_stats")]
 use crate::allocation::{ALLOCATION_PROFILING_COUNT, ALLOCATION_PROFILING_SIZE};
 
-const PREFIX_SIZE: usize = core::mem::size_of::<usize>();
+// Preserve the alignment guaranteed by the allocator we wrap.
+const PREFIX_SIZE: usize = core::mem::align_of::<libc::max_align_t>();
 const PREFIX_MAGIC: usize = 0xdd0f_cafe;
 
 #[derive(Copy, Clone)]
@@ -662,6 +663,16 @@ unsafe fn alloc_prof_orig_shutdown(full: bool, silent: bool) {
 mod tests {
     use super::*;
 
+    #[test]
+    fn prefix_preserves_allocator_alignment() {
+        let base = unsafe { libc::malloc(PREFIX_SIZE + 1) };
+        let ptr = unsafe { add_prefix(base) };
+
+        assert_eq!(ptr as usize % PREFIX_SIZE, 0);
+        assert_eq!(unsafe { remove_prefix(ptr) }, base);
+        unsafe { libc::free(base) };
+    }
+
     #[test]
     fn free_handler_tracks_only_when_heap_live_is_enabled() {
         assert_eq!(

profiling/tests/phpt/heap_live_prefix_epoch.phpt

@@ -1,5 +1,5 @@
 --TEST--
-[profiling] heap-live prefix survives object-store and string reallocations
+[profiling] heap-live prefix preserves allocations and alignment
 --SKIPIF--
 <?php
 if (PHP_VERSION_ID < 80400)
@@ -29,8 +29,11 @@ for ($i = 0; $i < 32; $i++) {
 }
 
 unset($objects, $string);
+
+echo hash('xxh3', 'aligned', options: ['seed' => 42]), "\n";
 echo "Done.\n";
 
 ?>
 --EXPECT--
+f2d7e898c1df340a
 Done.