From: Zack Weinberg <zackw-VmQCmMdMyN0AvxtiuMwx3w@public.gmane.org>
To: "Michael Kerrisk (man-pages)"
<mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
Cc: "H.J. Lu" <hjl.tools-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>,
Andreas Schwab <schwab-l3A5Bk7waGM@public.gmane.org>,
libc-alpha <libc-alpha-9JcytcrH/bA+uJoB2kUjGw@public.gmane.org>,
linux-man <linux-man-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
Mike Frysinger <vapier-aBrp7R+bbdUdnm+yROfE0A@public.gmane.org>
Subject: Re: The time(2) man page conflicts with glibc
Date: Wed, 16 Dec 2015 09:50:37 -0500 [thread overview]
Message-ID: <CAKCAbMjrKfsT7P=Q=+1zWC68552aK=ciod0HYk3=HWMvkYW26w@mail.gmail.com> (raw)
In-Reply-To: <56717032.7000007-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
On Wed, Dec 16, 2015 at 9:07 AM, Michael Kerrisk (man-pages)
<mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
>
> Yes, but the raw system call can give us EFAULT. That needs to be
> documented.
>
> By the way, what's the reason that one can't tell if it returns
> an error when time() in libc.a is used?
time() in libc.a assumes that the syscall cannot fail, so it doesn't
set errno. And -EFAULT = (time_t) -14 = 1969-12-31T23:59:46Z is
something that time() could return *without* its being an error. It's
kind of the same problem as strtol() has, except I honestly don't see
any way libc.a could tell the difference.
Given what other people have said about not changing the kernel-level
behavior, here's a new suggestion for the manpages:
RETURN VALUE
Time in seconds since the Epoch.
ERRORS
EFAULT `t` is non-NULL and points outside your accessible
address space (but see BUGS).
On systems where the C library time() wrapper function invokes
an implementation provided by the vdso(7) (so that there is no
trap into the kernel), an invalid address may instead trigger a
SIGSEGV signal. Note that whether vdso(7) is used may depend
on whether a program is statically or dynamically linked.
BUGS
Error returns from this system call are indistinguishable from
successful reports that the time is a few seconds _before_ the
Epoch, so the C library never sets `errno` as a result of this call.
The `t` argument is obsolescent and should always be NULL in
new code. When `t` is NULL, the call cannot fail.
--
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next prev parent reply other threads:[~2015-12-16 14:50 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-12-15 13:58 The time(2) man page conflicts with glibc H.J. Lu
2015-12-15 14:14 ` Zack Weinberg
[not found] ` <CAKCAbMj-X+wLKX3=MDm9z3L9zyikemxCNggu2bfw6=o6K5PGgg-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2015-12-15 14:31 ` Andreas Schwab
2015-12-15 14:55 ` Mike Frysinger
[not found] ` <20151215145517.GR11489-UgUKS2FnFs9+urZeOPWqwQ@public.gmane.org>
2015-12-15 15:19 ` Zack Weinberg
[not found] ` <CAKCAbMh2ysZPQe3oOSjcPsx1_pcnCAQ6yf+gMbv6iDmvfnGXZA-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2015-12-15 18:38 ` Mike Frysinger
2015-12-16 7:08 ` Rich Felker
[not found] ` <20151216070839.GE238-C3MtFaGISjmo6RMmaWD+6Sb1p8zYI1N1@public.gmane.org>
2015-12-16 20:34 ` Mike Frysinger
[not found] ` <20151216203432.GR11489-UgUKS2FnFs9+urZeOPWqwQ@public.gmane.org>
2015-12-16 21:59 ` Rich Felker
[not found] ` <20151216215955.GJ238-C3MtFaGISjmo6RMmaWD+6Sb1p8zYI1N1@public.gmane.org>
2015-12-16 22:27 ` Zack Weinberg
2015-12-16 22:44 ` Rich Felker
[not found] ` <20151216224432.GK238-C3MtFaGISjmo6RMmaWD+6Sb1p8zYI1N1@public.gmane.org>
2015-12-16 22:51 ` Zack Weinberg
2015-12-17 3:15 ` Mike Frysinger
[not found] ` <CAMe9rOoJLk8VzyJKmkOvbmBxhCj4mVA2huYtHJsdxpatbkgJ1g-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2015-12-15 14:16 ` Andreas Schwab
[not found] ` <mvmegen94qs.fsf-8jEJWzg51KSXcDkGTvBoYw@public.gmane.org>
2015-12-15 14:17 ` H.J. Lu
2015-12-16 13:38 ` Michael Kerrisk (man-pages)
[not found] ` <5671696B.3070203-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
2015-12-16 13:53 ` H.J. Lu
[not found] ` <CAMe9rOqsxCEia7OWqzJ-HzZWCra5BTyYqt4japjZTw0pY=fugw-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2015-12-16 14:07 ` Michael Kerrisk (man-pages)
[not found] ` <56717032.7000007-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
2015-12-16 14:50 ` Zack Weinberg [this message]
[not found] ` <CAKCAbMjrKfsT7P=Q=+1zWC68552aK=ciod0HYk3=HWMvkYW26w-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2015-12-16 15:04 ` Michael Kerrisk (man-pages)
2015-12-16 23:05 ` Paul Eggert
[not found] ` <5671EE36.1000402-764C0pRuGfqVc3sceRu5cw@public.gmane.org>
2015-12-17 5:53 ` Michael Kerrisk (man-pages)
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