From: Bruno Haible <bruno@clisp.org>
To: bug-gnulib@gnu.org
Cc: Paul Eggert <eggert@cs.ucla.edu>
Subject: Re: [PATCH] flexmember: update comment
Date: Sat, 25 May 2019 00:17:11 +0200 [thread overview]
Message-ID: <1616776.HnN4KKd12v@omega> (raw)
In-Reply-To: <20190524220133.31145-1-eggert@cs.ucla.edu>
Hi Paul,
> + Use 'FLEXSIZEOF (struct s, d, N)' to calculate the size in bytes
> + of such a struct containing an N-element array, as both
> + 'sizeof (struct s) + N * sizeof (char)' and
> + 'offsetof (struct s, d) + N * sizeof (char)'
> + might compute a size that can cause malloc to align storage
> + improperly, even in C11.
I'm confused.
1) What is the alignment problem if the array element type is 'char'?
I would understand an alignment problem if it is 'double'. But with 'char'?
'char' has the size 1, and - except on m68k - also the alignment 1.
2) If
(struct s *) malloc (offsetof (struct s, d) + N * sizeof (char))
should be avoided in favour of
(struct s *) malloc (FLEXSIZEOF (struct s, d, N))
don't we need to apply a 'ceil'-like alignment to the malloc result?
Bruno
next prev parent reply other threads:[~2019-05-24 22:17 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-05-24 22:01 [PATCH] flexmember: update comment Paul Eggert
2019-05-24 22:17 ` Bruno Haible [this message]
2019-05-24 22:46 ` Paul Eggert
2019-05-24 23:33 ` Bruno Haible
2019-05-25 0:34 ` Paul Eggert
2019-05-25 13:07 ` Bruno Haible
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
List information: https://lists.gnu.org/mailman/listinfo/bug-gnulib
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=1616776.HnN4KKd12v@omega \
--to=bruno@clisp.org \
--cc=bug-gnulib@gnu.org \
--cc=eggert@cs.ucla.edu \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).