From d7038020aa0a868c74cddaed5733ad6eeb73406b Mon Sep 17 00:00:00 2001 From: Paul Eggert 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 2e6399e..da0c3ad 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) -- 2.7.4