From d7038020aa0a868c74cddaed5733ad6eeb73406b Mon Sep 17 00:00:00 2001
From: Paul Eggert <eggert@cs.ucla.edu>
Date: Sat, 14 Oct 2017 00:55:25 -0700
Subject: [PATCH] Do not under-align pseudovectors
Problem reported by Fabrice Popineau in:
https://lists.gnu.org/archive/html/emacs-devel/2017-10/msg00357.html
Also see diagnosis by Eli Zaretskii in:
https://lists.gnu.org/archive/html/emacs-devel/2017-10/msg00476.html
* src/alloc.c (vector_alignment):
Now a multiple of alignof (max_align_t).
---
src/alloc.c | 10 +++++++---
1 file changed, 7 insertions(+), 3 deletions(-)
diff --git a/src/alloc.c b/src/alloc.c
index 2e6399e7f8d..da0c3ad4b3e 100644
--- a/src/alloc.c
+++ b/src/alloc.c
@@ -2923,9 +2923,13 @@ set_next_vector (struct Lisp_Vector *v, struct Lisp_Vector *p)
enum
{
- /* Alignment of struct Lisp_Vector objects. */
- vector_alignment = COMMON_MULTIPLE (FLEXALIGNOF (struct Lisp_Vector),
- GCALIGNMENT),
+ /* Alignment of struct Lisp_Vector objects. Because pseudovectors
+ can contain any C type, align at least as strictly as
+ max_align_t. On x86 and x86-64 this can waste up to 8 bytes
+ for typical vectors, since alignof (max_align_t) is 16 but
+ typical vectors need only an alignment of 8. However, it is
+ not worth the hassle to avoid wasting those bytes. */
+ vector_alignment = COMMON_MULTIPLE (alignof (max_align_t), GCALIGNMENT),
/* Vector size requests are a multiple of this. */
roundup_size = COMMON_MULTIPLE (vector_alignment, word_size)
--
2.39.5