gh-151065: Copy fix for memory leak from mimalloc upstream (GH-151066)

ZeroIntensity · web-flow · commit 80f9467434ce · 2026-06-11T18:11:52.000-04:00
Applies microsoft/mimalloc@d7a72c4 to our copy of mimalloc.
diff --git a/Misc/NEWS.d/next/Core_and_Builtins/2026-06-08-05-31-22.gh-issue-151065._o_31F.rst b/Misc/NEWS.d/next/Core_and_Builtins/2026-06-08-05-31-22.gh-issue-151065._o_31F.rst
@@ -0,0 +1 @@
+Fix memory leak when using the :ref:`mimalloc memory allocator <mimalloc>`.
diff --git a/Objects/mimalloc/init.c b/Objects/mimalloc/init.c
@@ -183,9 +183,9 @@ mi_heap_t* _mi_heap_main_get(void) {
 
 // note: in x64 in release build `sizeof(mi_thread_data_t)` is under 4KiB (= OS page size).
 typedef struct mi_thread_data_s {
-  mi_heap_t  heap;  // must come first due to cast in `_mi_heap_done`
+  mi_heap_t  heap;   // must come first due to cast in `_mi_heap_done`
   mi_tld_t   tld;
-  mi_memid_t memid;
+  mi_memid_t memid;  // must come last due to zero'ing
 } mi_thread_data_t;
 
 
@@ -231,7 +231,7 @@ static mi_thread_data_t* mi_thread_data_zalloc(void) {
   }
 
   if (td != NULL && !is_zero) {
-    _mi_memzero_aligned(td, sizeof(*td));
+    _mi_memzero_aligned(td, offsetof(mi_thread_data_t,memid));
   }
   return td;
 }

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1 @@`
	`1`	+Fix memory leak when using the :ref:`mimalloc memory allocator <mimalloc>`.
Original file line number	Diff line number	Diff line change
`@@ -183,9 +183,9 @@ mi_heap_t* _mi_heap_main_get(void) {`
`183`	`183`
`184`	`184`	// note: in x64 in release build `sizeof(mi_thread_data_t)` is under 4KiB (= OS page size).
`185`	`185`	`typedef struct mi_thread_data_s {`
`186`		- mi_heap_t heap; // must come first due to cast in `_mi_heap_done`
	`186`	+ mi_heap_t heap; // must come first due to cast in `_mi_heap_done`
`187`	`187`	`mi_tld_t tld;`
`188`		`- mi_memid_t memid;`
	`188`	`+ mi_memid_t memid; // must come last due to zero'ing`
`189`	`189`	`} mi_thread_data_t;`
`190`	`190`
`191`	`191`
`@@ -231,7 +231,7 @@ static mi_thread_data_t* mi_thread_data_zalloc(void) {`
`231`	`231`	`}`
`232`	`232`
`233`	`233`	`if (td != NULL && !is_zero) {`
`234`		`- _mi_memzero_aligned(td, sizeof(*td));`
	`234`	`+ _mi_memzero_aligned(td, offsetof(mi_thread_data_t,memid));`
`235`	`235`	`}`
`236`	`236`	`return td;`
`237`	`237`	`}`