linux-kernel - Re: [PATCHv3 00/24] ILP32 support in ARM64

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Message-ID: <20150212155023.GA25491@e104818-lin.cambridge.arm.com>
Date:	Thu, 12 Feb 2015 15:50:24 +0000
From:	Catalin Marinas <catalin.marinas@....com>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	"H.J. Lu" <hjl.tools@...il.com>, Rich Felker <dalias@...c.org>,
	GNU C Library <libc-alpha@...rceware.org>,
	Andrew Pinski <pinskia@...il.com>, musl@...ts.openwall.com,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Pinski <apinski@...ium.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCHv3 00/24] ILP32 support in ARM64

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:

https://lkml.org/lkml/2011/8/31/244

Couple of more replies from hpa:

https://lkml.org/lkml/2011/8/31/261
https://lkml.org/lkml/2012/2/8/408

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).

-- 
Catalin
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