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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: Zack Weinberg <zackw at panix dot com>, GNU C Library <libc-alpha at sourceware dot org>
- Date: Sun, 15 Feb 2015 10:02:23 -0800
- Subject: Re: [PATCHv3 00/24] ILP32 support in ARM64
- Authentication-results: sourceware.org; auth=none
- References: <CAKCAbMiQh2DVjgB_-By8FN2VN01_BkEoVJQunJ9KhWdYM8wJOw at mail dot gmail dot com> <20150215042302 dot GN23507 at brightrain dot aerifal dot cx> <CAKCAbMi8xZ8x3ECwus2LTvaurA66TLA38KgpOj=cAp7k3UwYvQ at mail dot gmail dot com> <20150215160330 dot GP23507 at brightrain dot aerifal dot cx> <CAMe9rOqQM04Lr_RMUBsvA-Y502UQDzXszXA8BUEdsHwZdpRRrA at mail dot gmail dot com> <20150215173155 dot GR23507 at brightrain dot aerifal dot cx>
On Sun, Feb 15, 2015 at 9:31 AM, Rich Felker <firstname.lastname@example.org> wrote:
> On Sun, Feb 15, 2015 at 08:27:33AM -0800, H.J. Lu wrote:
>> On Sun, Feb 15, 2015 at 8:03 AM, Rich Felker <email@example.com> wrote:
>> > On Sun, Feb 15, 2015 at 10:41:36AM -0500, Zack Weinberg wrote:
>> >> On Sat, Feb 14, 2015 at 11:23 PM, Rich Felker <firstname.lastname@example.org> wrote:
>> >> > On Sat, Feb 14, 2015 at 02:18:15PM -0500, Zack Weinberg wrote:
>> >> >> Joseph Myers wrote:
>> >> >> > I believe I made clear in the discussion of 64-bit time interfaces for
>> >> >> > 32-bit systems that the x32 ABI mistake was not one to be repeated - that
>> >> >> > since there is obviously no need for nanoseconds values that cannot fit in
>> >> >> > 32 bits, nanoseconds (and microseconds) values should remain as long in
>> >> >> > accordance with POSIX.
>> >> >>
>> >> >> I have to say that I think tv_nsec (and tv_usec) being specified as
>> >> >> bare 'long' is a spec bug _in and of itself_. The various *_t types
>> >> >> exist precisely to make this sort of problem go away. As such, I am
>> >> >> inclined to think that the _proper_ fix is to file DRs to that effect,
>> >> >> and then invent 'nseconds_t' and use it. Unconditionally - not just
>> >> >> for ILP32-on-64-bit-kernel.
>> >> >
>> >> > POSIX does that nonsense, yes. ISO C, not so much. There's utterly no
>> >> > reason for the type of tv_nsec to be abstract like this,
>> >> If you don't consider this very thread to demonstrate adequate reason
>> >> for the type of tv_nsec to be abstract, then there's probably no point
>> >> me arguing it with you any further, but ...
>> > Bugs in an implementation are not automatically a reason to change a
>> > specification. If you don't understand that there's probably no point
>> > in arguing with you.
>> >> > having it be abstract creates all sorts of additional problems.
>> >> Please state exactly what those problems are.
>> > Lack of a proper format specifier/conversion specifier for use with
>> > printf/scanf family functions. Lack of clarity over which strto*
>> > function you should use with it. Etc.
>> How is it different from time_t?
> time_t is also a pain this way, but it's one of the few such types in
> standard C. POSIX has a lot more that lack macros for their
> printf/scanf specifiers and their min/max values: off_t, uid_t, etc.
> They're of course necessary when you need to support historical
> differences or when future systems may need a larger range of values
> than a particular standard type provides, which is true for time_t.
> It's not true for tv_nsec. There will never be more than 1000000000
> nanoseconds in a second, and LONG_MAX is necessarily larger than
> 1000000000. Forcing all programs that are printing tv_nsec with %ld to
> change to %jd and cast the argument to (intmax_t) is not reasonable.
> It uglifies code and it's a huge burden to fix them all.
We have done it for tv_sec:
posix/tst-regex2.c: printf (": %ld.%09lds\n", (long) stop.tv_sec,
and we should do it for tv_nsec. It works everywhere.