From: Florian Weimer <fw@deneb.enyo.de>
To: Aleksa Sarai <cyphar@cyphar.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>,
Jeff Layton <jlayton@kernel.org>,
"J. Bruce Fields" <bfields@fieldses.org>,
Shuah Khan <shuah@kernel.org>,
dev@opencontainers.org, containers@lists.linux-foundation.org,
linux-api@vger.kernel.org, linux-fsdevel@vger.kernel.org,
linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org
Subject: Re: [PATCH] openat2: switch to __attribute__((packed)) for open_how
Date: Sun, 15 Dec 2019 20:48:24 +0100 [thread overview]
Message-ID: <87o8w9bcaf.fsf@mid.deneb.enyo.de> (raw)
In-Reply-To: <20191213222351.14071-1-cyphar@cyphar.com> (Aleksa Sarai's message of "Sat, 14 Dec 2019 09:23:50 +1100")
* Aleksa Sarai:
> diff --git a/tools/testing/selftests/openat2/helpers.h b/tools/testing/selftests/openat2/helpers.h
> index 43ca5ceab6e3..eb1535c8fa2e 100644
> --- a/tools/testing/selftests/openat2/helpers.h
> +++ b/tools/testing/selftests/openat2/helpers.h
> @@ -32,17 +32,16 @@
> * O_TMPFILE} are set.
> *
> * @flags: O_* flags.
> - * @mode: O_CREAT/O_TMPFILE file mode.
> * @resolve: RESOLVE_* flags.
> + * @mode: O_CREAT/O_TMPFILE file mode.
> */
> struct open_how {
> - __aligned_u64 flags;
> + __u64 flags;
> + __u64 resolve;
> __u16 mode;
> - __u16 __padding[3]; /* must be zeroed */
> - __aligned_u64 resolve;
> -};
> +} __attribute__((packed));
>
> -#define OPEN_HOW_SIZE_VER0 24 /* sizeof first published struct */
> +#define OPEN_HOW_SIZE_VER0 18 /* sizeof first published struct */
> #define OPEN_HOW_SIZE_LATEST OPEN_HOW_SIZE_VER0
A userspace ABI that depends on GCC extensions probably isn't a good
idea. Even with GCC, it will not work well with some future
extensions because it pretty much rules out having arrays or other
members that are access through pointers. Current GCC does not carry
over the packed-ness of the struct to addresses of its members.
next prev parent reply other threads:[~2019-12-15 19:49 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-12-13 22:23 [PATCH] openat2: switch to __attribute__((packed)) for open_how Aleksa Sarai
2019-12-14 22:17 ` Rasmus Villemoes
2019-12-15 12:34 ` Aleksa Sarai
2019-12-16 16:55 ` David Laight
2019-12-17 6:46 ` Aleksa Sarai
2019-12-17 10:14 ` David Laight
2019-12-18 17:31 ` Aleksa Sarai
2019-12-15 19:48 ` Florian Weimer [this message]
2019-12-15 20:55 ` Aleksa Sarai
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
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=87o8w9bcaf.fsf@mid.deneb.enyo.de \
--to=fw@deneb.enyo.de \
--cc=bfields@fieldses.org \
--cc=containers@lists.linux-foundation.org \
--cc=cyphar@cyphar.com \
--cc=dev@opencontainers.org \
--cc=jlayton@kernel.org \
--cc=linux-api@vger.kernel.org \
--cc=linux-fsdevel@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-kselftest@vger.kernel.org \
--cc=shuah@kernel.org \
--cc=viro@zeniv.linux.org.uk \
/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 NNTP newsgroup(s).