From: Andreas Schwab <schwab@linux-m68k.org>
To: Josh Juran <jjuran@gmail.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>,
Geert Uytterhoeven <geert@linux-m68k.org>,
Eugene Syromiatnikov <esyr@redhat.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Linux/m68k <linux-m68k@vger.kernel.org>
Subject: Re: [GIT PULL] siginfo fix for v4.16-rc5
Date: Tue, 03 Apr 2018 19:26:54 +0200 [thread overview]
Message-ID: <87y3i442w1.fsf@linux-m68k.org> (raw)
In-Reply-To: <4A16C7EF-B8B7-457C-B49C-829B44F12FFE@gmail.com> (Josh Juran's message of "Tue, 3 Apr 2018 11:24:58 -0400")
On Apr 03 2018, Josh Juran <jjuran@gmail.com> wrote:
> On Apr 3, 2018, at 10:27 AM, Eric W. Biederman <ebiederm@xmission.com> wrote:
>
>> Geert Uytterhoeven <geert@linux-m68k.org> writes:
>>
>>> On Mon, Apr 2, 2018 at 10:17 PM, Eric W. Biederman <ebiederm@xmission.com> wrote:
>>>
>>>> A 2-byte alignment for 4 byte pointers. That is a new one to me.
>>>
>>> Not just for pointers, also for int and long.
>>
>> The smallest I have seen previously has been 64bit integers having
>> 32bit alignment. 32bit entities having only 16bit alignment on a 32bit
>> arch was simply a surprise. Even when it works there tend to be good
>> reasons not to do that by default.
>
> The 68K architecture began as 16-bit with the 68000. Rather than tightening requirements, the 68020 not only maintained compatibility with 16-bit alignment, but also forgave byte-misaligned data accesses (albeit with a performance penalty). Jumping to an odd address is still an error, though.
The m68k-linux gcc port started as a clone of the Sun3 port, which has a
history dating back to the 68000, which is why it has a maximum of
16-bit alignment. When I implemented ELF support for m68k-linux I
wanted to follow the SVR4 ABI (which has 32-bit alignment), but there
were too many UAPI structures (esp. struct stat) that would have become
incompatible (it would have made it impossible to run ELF binaries on an
a.out kernel or vice-versa), so I had to keep the historical mistake.
Andreas.
--
Andreas Schwab, schwab@linux-m68k.org
GPG Key fingerprint = 58CA 54C7 6D53 942B 1756 01D3 44D5 214B 8276 4ED5
"And now for something completely different."
prev parent reply other threads:[~2018-04-03 17:26 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <87woypy8zc.fsf@xmission.com>
2018-03-31 10:56 ` [GIT PULL] siginfo fix for v4.16-rc5 Eugene Syromiatnikov
2018-04-02 20:17 ` Eric W. Biederman
2018-04-03 7:30 ` Geert Uytterhoeven
2018-04-03 14:27 ` Eric W. Biederman
2018-04-03 15:24 ` Josh Juran
2018-04-03 17:26 ` Andreas Schwab [this message]
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=87y3i442w1.fsf@linux-m68k.org \
--to=schwab@linux-m68k.org \
--cc=ebiederm@xmission.com \
--cc=esyr@redhat.com \
--cc=geert@linux-m68k.org \
--cc=jjuran@gmail.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-m68k@vger.kernel.org \
--cc=torvalds@linux-foundation.org \
/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).