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Re: [PATCHv3 00/24] ILP32 support in ARM64
- From: "H.J. Lu" <hjl dot tools at gmail dot com>
- To: Catalin Marinas <catalin dot marinas at arm dot com>
- Cc: Andy Lutomirski <luto at amacapital dot net>, Rich Felker <dalias at libc dot org>, 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 08:30:10 -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> <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 7:50 AM, Catalin Marinas
> 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).
Just for the record, tv_nsec/tv_usec can be changed to long
as long as kernel always read them as 32 bits and write them
as 64 bits for both LP64 and ILP32 in 64-bit imespec amd timeval.
In glibc, they can be changed to long without breaking existing binaries.
For x86-32, 64-bit __time_t must be 64-bit aligned. Otherwise, there will
be no padding in 64-bit timespec nor timeval.