From 201d17c0d835112bdea5408e6eff4e250f3c238a Mon Sep 17 00:00:00 2001 From: Jakub Jelinek Date: Tue, 13 Feb 2018 21:23:58 +0100 Subject: re PR c/82210 (Having _Alignas in a struct with VLAs causes writing to one array to overwrite another) PR c/82210 * stor-layout.c (place_field): For variable length fields, adjust offset_align afterwards not just based on the field's alignment, but also on the size. * gcc.c-torture/execute/pr82210.c: New test. From-SVN: r257635 --- gcc/stor-layout.c | 24 ++++++++++++++++++++++++ 1 file changed, 24 insertions(+) (limited to 'gcc/stor-layout.c') diff --git a/gcc/stor-layout.c b/gcc/stor-layout.c index 8c415ebb..5fdf81a 100644 --- a/gcc/stor-layout.c +++ b/gcc/stor-layout.c @@ -1622,6 +1622,30 @@ place_field (record_layout_info rli, tree field) = size_binop (PLUS_EXPR, rli->offset, DECL_SIZE_UNIT (field)); rli->bitpos = bitsize_zero_node; rli->offset_align = MIN (rli->offset_align, desired_align); + + if (!multiple_of_p (bitsizetype, DECL_SIZE (field), + bitsize_int (rli->offset_align))) + { + tree type = strip_array_types (TREE_TYPE (field)); + /* The above adjusts offset_align just based on the start of the + field. The field might not have a size that is a multiple of + that offset_align though. If the field is an array of fixed + sized elements, assume there can be any multiple of those + sizes. If it is a variable length aggregate or array of + variable length aggregates, assume worst that the end is + just BITS_PER_UNIT aligned. */ + if (TREE_CODE (TYPE_SIZE (type)) == INTEGER_CST) + { + if (TREE_INT_CST_LOW (TYPE_SIZE (type))) + { + unsigned HOST_WIDE_INT sz + = least_bit_hwi (TREE_INT_CST_LOW (TYPE_SIZE (type))); + rli->offset_align = MIN (rli->offset_align, sz); + } + } + else + rli->offset_align = MIN (rli->offset_align, BITS_PER_UNIT); + } } else if (targetm.ms_bitfield_layout_p (rli->t)) { -- cgit v1.1