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

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Date:	Wed, 11 Feb 2015 11:57:59 -0800
From:	"H.J. Lu" <hjl.tools@...il.com>
To:	Rich Felker <dalias@...c.org>
Cc:	Catalin Marinas <catalin.marinas@....com>,
	Andrew Pinski <apinski@...ium.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Pinski <pinskia@...il.com>, musl@...ts.openwall.com,
	GNU C Library <libc-alpha@...rceware.org>
Subject: Re: [PATCHv3 00/24] ILP32 support in ARM64

>> > 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.



-- 
H.J.
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