From: Rich Felker <dalias@libc.org>
To: Catalin Marinas <catalin.marinas@arm.com>
Cc: "libc-alpha@sourceware.org" <libc-alpha@sourceware.org>,
"arnd@arndb.de" <arnd@arndb.de>,
"pinskia@gmail.com" <pinskia@gmail.com>,
"musl@lists.openwall.com" <musl@lists.openwall.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Andrew Pinski <apinski@cavium.com>,
Marcus Shawcroft <Marcus.Shawcroft@arm.com>,
"linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCHv3 00/24] ILP32 support in ARM64
Date: Fri, 13 Feb 2015 13:37:07 -0500 [thread overview]
Message-ID: <20150213183706.GF23507@brightrain.aerifal.cx> (raw)
In-Reply-To: <20150213173345.GA26217@e104818-lin.cambridge.arm.com>
On Fri, Feb 13, 2015 at 05:33:46PM +0000, Catalin Marinas wrote:
> > > > The data structure definition is a little bit fragile, as it depends on
> > > > user space not using the __BIT_ENDIAN symbol in a conflicting way. So
> > > > far we have managed to keep that outside of general purpose headers, but
> > > > it should at least blow up in an obvious way if it does, rather than
> > > > breaking silently.
> > > >
> > > > I still think it's more practical to keep the zeroing in user space though.
> > > > In that case, we keep defining __kernel_timespec64 with a 'typedef long
> > > > long __kernel_snseconds_t', and it's up to the libc to either use
> > > > __kernel_timespec64 as its timespec, or to define a C11-compliant
> > > > timespec itself and zero out the bits before passing the data to the kernel.
> > >
> > > The problem with doing this in user space is syscall(2). If we don't
> > > allow it, then it's fine to do the padding in libc.
> >
> > It's already the case that callers have to tiptoe around syscall(2)
> > usage on a per-arch basis for silly things like the convention for
> > passing 64-bit arguments on 32-bit archs, different arg orders to work
> > around 64-bit alignment and issues with too many args, and various
> > legacy issues. So I think manual use of syscall(2) is a less-critical
> > issue, though of course from a libc perspective I would very much like
> > for the kernel to handle it right.
>
> I think there is another problem with sign-extending tv_nsec in libc.
> The prototype for functions like clock_settime(2) take a const struct
> timespec *. There isn't anything to prevent such structure being in a
> read-only section, even though it is unlikely. So libc would have to
> duplicate the structure rather than just sign-extending tv_nsec in
> place.
Yes, we already have to do this for x32 in musl. I'd rather not have
to do the same for aarch64-ILP32.
Rich
next prev parent reply other threads:[~2015-02-13 18:37 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20141002155217.GH32147@e104818-lin.cambridge.arm.com>
2015-02-10 18:13 ` Rich Felker
2015-02-11 17:39 ` Catalin Marinas
2015-02-11 19:05 ` Szabolcs Nagy
2015-02-11 19:22 ` [musl] " H.J. Lu
2015-02-11 19:50 ` arnd
2015-02-11 20:12 ` Rich Felker
2015-02-11 20:47 ` Jens Gustedt
2015-02-11 21:02 ` arnd
2015-02-11 21:09 ` arnd
2015-02-11 21:37 ` [musl] " Rich Felker
2015-02-16 17:20 ` Arnd Bergmann
2015-02-16 17:51 ` [musl] " Rich Felker
2015-02-16 19:38 ` Arnd Bergmann
2015-02-12 8:12 ` Szabolcs Nagy
2015-02-12 17:07 ` Catalin Marinas
2015-02-11 19:21 ` Rich Felker
2015-02-12 18:17 ` Catalin Marinas
2015-02-12 18:59 ` arnd
2015-02-13 13:33 ` Catalin Marinas
2015-02-13 16:30 ` Rich Felker
2015-02-13 17:33 ` Catalin Marinas
2015-02-13 18:37 ` Rich Felker [this message]
2015-02-16 14:40 ` Arnd Bergmann
2015-02-16 15:38 ` Rich Felker
2015-02-16 16:54 ` Arnd Bergmann
2015-02-11 18:33 ` H.J. Lu
2015-02-11 19:02 ` Rich Felker
2015-02-11 19:16 ` H.J. Lu
2015-02-11 19:25 ` Rich Felker
2015-02-11 19:34 ` H.J. Lu
2015-02-11 19:47 ` Rich Felker
2015-02-11 19:57 ` H.J. Lu
2015-02-11 20:15 ` Andy Lutomirski
2015-02-12 15:50 ` Catalin Marinas
2015-02-12 16:13 ` Rich Felker
2015-02-12 16:30 ` H.J. Lu
2015-02-12 17:00 ` Rich Felker
2015-02-11 21:41 ` Joseph Myers
2015-02-11 19:04 ` Josiah Worcester
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