Fix aborts due to GC losing pseudovectors

Problem reported by Eli Zaretskii (Bug#41321).
* src/alloc.c (MALLOC_ALIGNMENT_BOUND): New constant.
(LISP_ALIGNMENT): Lower it to avoid crashes on MinGW and similarly
buggy platforms where malloc returns pointers not aligned to
alignof (max_align_t).  But keep it higher on platforms where this
is known to work, as it helps GC performance.
(MALLOC_IS_LISP_ALIGNED): Define in terms of the other two.
* src/alloc.c (stacktop_sentry):
* src/thread.c (run_thread):
Don’t overalign or oversize stack sentries; they need to be
aligned only for pointers and Lisp_Object, not for arbitrary
pseudovector contents.
* src/lisp.h (union emacs_align_type): New type, used for
LISP_ALIGNMENT.

1 files changed, 42 insertions, 1 deletions

diff --git a/src/lisp.h b/src/lisp.h
index 85bdc172b20..937052f6df8 100644
--- a/src/lisp.h
+++ b/src/lisp.h
@@ -277,7 +277,8 @@ error !;
    allocation in a containing union that has GCALIGNED_UNION_MEMBER)
    and does not contain a GC-aligned struct or union, putting
    GCALIGNED_STRUCT after its closing '}' can help the compiler
-   generate better code.
+   generate better code.  Also, such structs should be added to the
+   emacs_align_type union.
 
    Although these macros are reasonably portable, they are not
    guaranteed on non-GCC platforms, as C11 does not require support
@@ -5059,6 +5060,46 @@ maybe_gc (void)
     maybe_garbage_collect ();
 }
 
+/* A type with alignment at least as large as any object that Emacs
+   allocates.  This is not max_align_t because some platforms (e.g.,
+   mingw) have buggy malloc implementations that do not align for
+   max_align_t.  This union contains types of all GCALIGNED_STRUCT
+   components visible here.  */
+union emacs_align_type
+{
+  struct Lisp_Bool_Vector Lisp_Bool_Vector;
+  struct Lisp_Char_Table Lisp_Char_Table;
+  struct Lisp_CondVar Lisp_CondVar;
+  struct Lisp_Finalizer Lisp_Finalizer;
+  struct Lisp_Float Lisp_Float;
+  struct Lisp_Hash_Table Lisp_Hash_Table;
+  struct Lisp_Marker Lisp_Marker;
+  struct Lisp_Misc_Ptr Lisp_Misc_Ptr;
+  struct Lisp_Mutex Lisp_Mutex;
+  struct Lisp_Overlay Lisp_Overlay;
+  struct Lisp_Sub_Char_Table Lisp_Sub_Char_Table;
+  struct Lisp_Subr Lisp_Subr;
+  struct Lisp_User_Ptr Lisp_User_Ptr;
+  struct Lisp_Vector Lisp_Vector;
+  struct thread_state thread_state;
+
+  /* Omit the following since they would require including bignum.h,
+     frame.h etc., and in practice their alignments never exceed that
+     of the structs already listed.  */
+#if 0
+  struct frame frame;
+  struct Lisp_Bignum Lisp_Bignum;
+  struct Lisp_Module_Function Lisp_Module_Function;
+  struct Lisp_Process Lisp_Process;
+  struct save_window_data save_window_data;
+  struct scroll_bar scroll_bar;
+  struct terminal terminal;
+  struct window window;
+  struct xwidget xwidget;
+  struct xwidget_view xwidget_view;
+#endif
+};
+
 INLINE_HEADER_END
 
 #endif /* EMACS_LISP_H */