From: "H. Peter Anvin" <hpa@zytor.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Arnd Bergmann <arnd@arndb.de>,
Christoph Hellwig <hch@infradead.org>,
LKML <linux-kernel@vger.kernel.org>,
"H.J. Lu" <hjl.tools@gmail.com>, Ingo Molnar <mingo@elte.hu>,
Thomas Gleixner <tglx@linutronix.de>,
Richard Kuo <rkuo@codeaurora.org>,
Mark Salter <msalter@redhat.com>, Jonas Bonn <jonas@southpole.se>,
Tobias Klauser <tklauser@distanz.ch>,
"David S. Miller" <davem@davemloft.net>,
"H.J. Lu" <hjl.tools@gmail.com>
Subject: 64-bit time on 32-bit systems
Date: Wed, 08 Feb 2012 13:36:24 -0800 [thread overview]
Message-ID: <4F32EAD8.6020504@zytor.com> (raw)
In-Reply-To: <CA+55aFzEnGb3G2WeVNoS5e2D4poY5O6gJucnVnFRF51NUYkW8A@mail.gmail.com>
Resuming a long-stuck discussion...
On 08/31/2011 10:19 AM, Linus Torvalds wrote:
> On Wed, Aug 31, 2011 at 10:09 AM, H. Peter Anvin <hpa@zytor.com> wrote:
>>>
>>> I suspect only sane solution to this (having thought about it some
>>> more) is to just say "POSIX is f*^&ing wrong".
>>
>> Urk. Someone had the bright idea of defining tv_nsec as "long" in the
>> standard, whereas tv_usec is suseconds_t. F**** brilliant, and more
>> than a little bit stupid.
>
> I think tv_nsec was just overlooked, and people thought "it has no
> legacy users that were 'int', so we'll just leave it at 'long', which
> is guaranteed to be enough for nanoseconds that only needs a range of
> 32 bits".
>
> In contrast, tv_usec probably *does* have legacy users that are "int".
>
> So POSIX almost certainly only looked backwards, and never thought
> about users who would need to make it "long long" for compatibility
> reasons.
>
> The fact that *every*other*related*field* in POSIX/SuS has a typedef
> exactly for these kinds of reasons just shows how stupid that "long
> tv_nsec" thing is.
>
> I suspect that on Linux we can just say "tv_nsec" is suseconds_t too.
> Then we can make time_t and suseconds_t just match, and be "__s64" on
> all new platforms.
>
So I somewhat accidentally stumbled onto what appears to the the reason
for this while cleaning up posix_types.h last night.
The problem at hand seems to be that suseconds_t is 32 bits on SPARC64.
This appears to be the case in both Linux and Solaris, which is
probably why struct timespec has "long" instead of suseconds_t (Sun
always have been prominent on the POSIX committee.)
As such, I don't think we can redefine struct timespec to have
suseconds_t for the nanosecond field, even on Linux. We could define
snseconds_t, or we would have to do something really ugly like define a
padding field when on a 32-bit platform (which the kernel would then
have to ignore when reading from userspace by truncating the 64-bit
value rather than signaling an error if the upper 32 bits are set.)
snseconds_t seems semi-reasonable to me... I guess we'd have to push
that at the POSIX people. Fortunately it shouldn't break anything to
have it be a wider type than is otherwise necessary.
-hpa
--
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel. I don't speak on their behalf.
next prev parent reply other threads:[~2012-02-08 21:37 UTC|newest]
Thread overview: 94+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-08-26 23:00 RFD: x32 ABI system call numbers H. Peter Anvin
2011-08-26 23:13 ` Linus Torvalds
2011-08-26 23:39 ` H. Peter Anvin
2011-08-27 0:36 ` Linus Torvalds
2011-08-27 0:43 ` Linus Torvalds
2011-08-27 0:53 ` H. Peter Anvin
2011-08-27 1:18 ` Linus Torvalds
2011-08-27 1:35 ` H. Peter Anvin
2011-08-27 1:45 ` Linus Torvalds
2011-08-27 1:12 ` H. Peter Anvin
2011-08-27 1:42 ` Linus Torvalds
2011-08-29 19:01 ` Geert Uytterhoeven
2011-08-29 19:03 ` H. Peter Anvin
2011-08-30 1:17 ` Ted Ts'o
2011-08-30 1:48 ` Linus Torvalds
2011-08-30 2:16 ` Kyle Moffett
2011-08-30 4:45 ` H. Peter Anvin
2011-08-30 7:06 ` Geert Uytterhoeven
2011-08-30 12:18 ` Arnd Bergmann
2011-08-30 7:09 ` Andi Kleen
2011-08-30 9:56 ` Alan Cox
2011-08-30 7:00 ` Geert Uytterhoeven
2011-09-20 18:37 ` Jan Engelhardt
2011-09-06 20:40 ` Florian Weimer
2011-08-27 0:57 ` H. Peter Anvin
2011-08-27 4:40 ` Christoph Hellwig
2011-08-29 15:04 ` Arnd Bergmann
2011-08-29 18:31 ` H. Peter Anvin
2011-08-30 12:09 ` Arnd Bergmann
2011-08-30 16:35 ` H. Peter Anvin
2011-08-31 16:14 ` Arnd Bergmann
2011-08-31 16:25 ` H. Peter Anvin
2011-08-31 16:39 ` Arnd Bergmann
2011-08-31 16:48 ` Linus Torvalds
2011-08-31 19:18 ` Arnd Bergmann
2011-08-31 19:44 ` H. Peter Anvin
2011-08-31 19:54 ` Alan Cox
2011-08-31 20:02 ` H. Peter Anvin
2011-08-31 20:55 ` Arnd Bergmann
2011-08-31 20:58 ` H. Peter Anvin
2011-08-31 19:49 ` Geert Uytterhoeven
2011-08-31 16:46 ` Linus Torvalds
2011-08-31 17:05 ` H.J. Lu
2011-09-03 2:56 ` H.J. Lu
2011-09-03 3:04 ` Linus Torvalds
2011-09-03 4:02 ` H.J. Lu
2011-09-03 4:29 ` H. Peter Anvin
2011-09-03 4:44 ` H.J. Lu
2011-09-03 5:16 ` H. Peter Anvin
2011-09-03 14:11 ` H.J. Lu
2011-09-03 5:29 ` H. Peter Anvin
2011-09-03 8:41 ` Arnd Bergmann
2011-09-03 14:04 ` Valdis.Kletnieks
2011-09-03 16:40 ` H. Peter Anvin
2011-09-03 17:16 ` Valdis.Kletnieks
2011-09-03 17:22 ` H.J. Lu
2011-09-03 17:28 ` H. Peter Anvin
2011-09-03 17:27 ` H. Peter Anvin
2011-09-04 13:51 ` Valdis.Kletnieks
2011-09-04 15:17 ` Arnd Bergmann
2011-09-04 17:08 ` Linus Torvalds
2011-09-04 18:40 ` H.J. Lu
2011-09-04 19:06 ` Arnd Bergmann
2011-09-04 19:31 ` H.J. Lu
2011-09-04 21:13 ` Arnd Bergmann
2011-09-04 21:25 ` H.J. Lu
2011-09-04 21:41 ` Arnd Bergmann
2011-09-04 22:13 ` H.J. Lu
2011-09-05 7:48 ` Arnd Bergmann
2011-09-05 15:11 ` H.J. Lu
2011-09-05 17:21 ` Arnd Bergmann
2011-09-05 19:34 ` H.J. Lu
2011-09-05 19:54 ` H.J. Lu
2011-09-05 19:59 ` H. Peter Anvin
2011-09-05 20:27 ` Arnd Bergmann
2011-09-09 21:02 ` H.J. Lu
2011-09-04 20:11 ` H. Peter Anvin
2011-09-04 19:31 ` richard -rw- weinberger
2011-09-04 19:32 ` H.J. Lu
2011-09-03 14:15 ` H.J. Lu
2011-08-31 17:09 ` H. Peter Anvin
2011-08-31 17:19 ` Linus Torvalds
2011-08-31 17:38 ` H. Peter Anvin
2011-09-01 11:35 ` Arnd Bergmann
2011-10-01 19:38 ` Jonas Bonn
2012-02-08 21:36 ` H. Peter Anvin [this message]
2011-09-01 13:30 ` Avi Kivity
2011-09-01 14:13 ` H. Peter Anvin
2011-09-02 0:49 ` Pedro Alves
2011-09-02 1:51 ` H. Peter Anvin
2011-09-02 8:02 ` Arnd Bergmann
2011-09-02 8:42 ` Pedro Alves
2011-09-01 6:08 ` Jonas Bonn
2011-09-02 6:17 ` Andy Lutomirski
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