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Re: [PATCHv3 00/24] ILP32 support in ARM64
- From: Rich Felker <dalias at libc dot org>
- To: Catalin Marinas <catalin dot marinas at arm dot com>
- Cc: Andy Lutomirski <luto at amacapital dot net>, "H.J. Lu" <hjl dot tools at gmail dot com>, GNU C Library <libc-alpha at sourceware dot org>, Andrew Pinski <pinskia at gmail dot com>, musl at lists dot openwall dot com, LKML <linux-kernel at vger dot kernel dot org>, Andrew Pinski <apinski at cavium dot com>, "linux-arm-kernel at lists dot infradead dot org" <linux-arm-kernel at lists dot infradead dot org>
- Date: Thu, 12 Feb 2015 11:13:54 -0500
- Subject: Re: [PATCHv3 00/24] ILP32 support in ARM64
- Authentication-results: sourceware.org; auth=none
- References: <20150210181302 dot GA23886 at brightrain dot aerifal dot cx> <CAMe9rOqX-VpjZ+E-JCusk+e4Kpw1V1tsFq1Kjtai5DR9saKLaA at mail dot gmail dot com> <20150211190252 dot GB23507 at brightrain dot aerifal dot cx> <CAMe9rOoME1fct=Dk1YFeoJbayvhdsaCUBZCY2YD6jK58J7=MkA at mail dot gmail dot com> <20150211192558 dot GE23507 at brightrain dot aerifal dot cx> <CAMe9rOpr6j1siK5gJ_HPLTOfjG_sLOL48TFzaLx+shCS9O8ahA at mail dot gmail dot com> <20150211194741 dot GI23507 at brightrain dot aerifal dot cx> <CAMe9rOrVGFcQN3J1-pkXWd9j4MaQv2QxPrA5cTtLPBPaQ2-zfw at mail dot gmail dot com> <54DBB87C dot 5060901 at amacapital dot net> <20150212155023 dot GA25491 at e104818-lin dot cambridge dot arm dot com>
On Thu, Feb 12, 2015 at 03:50:24PM +0000, Catalin Marinas wrote:
> On Wed, Feb 11, 2015 at 12:15:56PM -0800, Andy Lutomirski wrote:
> > On 02/11/2015 11:57 AM, H.J. Lu wrote:
> > >>>>trivially satisfied if you consider x32 and x86_64 separate
> > >>>>compilation environments, but it's not related to the core issue: that
> > >>>>the definition of timespec violates core (not obscure) requirements of
> > >>>>both POSIX and C11. At the time you were probably unaware of the C11
> > >>>>requirement. Note that it's a LOT harder to effect change in the C
> > >>>>standard, so even if the Austin Group would be amenable to changing
> > >>>>the requirement for timespec to allow something like nseconds_t,
> > >>>>getting WG14 to make this change to work around a Linux/glibc mistake
> > >>>>does not sound practical.
> > >>>
> > >>>That is very unfortunate. I consider it is too late for x32 to change.
> > >>
> > >>Why? It's hardly an incompatible ABI change, as long as the
> > >>kernel/libc fills the upper bits (for old programs that read them
> > >>based on the old headers) when structs are read from the kernel to the
> > >>application, and ignores the upper bits (potentially set or left
> > >>uninitialized by the application) when strings are passed from
> > >>userspace to the kernel. Newly built apps using the struct definition
> > >>with 32-bit tv_nsec would need new libc to ensure that the high bits
> > >>aren't interpreted, but this could be handled by symbol versioning.
> > >>
> > >
> > >We have considered this option. But since kernel wouldn't change
> > >tv_nsec/tv_usec handling just for x32, it wasn't selected.
> > Did anyone *ask* the kernel people (e.g. hpa)?
> It seems so:
> Couple of more replies from hpa:
> It looks like hpa was going to talk the POSIX committee but I don't know
> what the conclusion was and didn't follow the thread (at the time I
> wasn't interested in ARM ILP32).
At this point POSIX committee is not sufficient. ISO C specifies
timespec now, and as Jens Gustedt mentioned (I don't think his reply
made it to the whole CC list; see the musl list archive here:
http://www.openwall.com/lists/musl/2015/02/11/21 ), it seems unlikely
that one could pose a convincing argument for this requirement to be
changed in the C language.