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Re: [PATCHv3 00/24] ILP32 support in ARM64
- From: "H.J. Lu" <hjl dot tools at gmail dot com>
- To: Rich Felker <dalias at libc dot org>
- Cc: Catalin Marinas <catalin dot marinas at arm dot com>, 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>, LKML <linux-kernel at vger dot kernel dot org>, Andrew Pinski <pinskia at gmail dot com>, musl at lists dot openwall dot com, GNU C Library <libc-alpha at sourceware dot org>
- Date: Wed, 11 Feb 2015 11:57:59 -0800
- Subject: Re: [PATCHv3 00/24] ILP32 support in ARM64
- Authentication-results: sourceware.org; auth=none
- References: <20141002155217 dot GH32147 at e104818-lin dot cambridge dot arm dot com> <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>
>> > 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.