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


On Sun, Feb 15, 2015 at 9:31 AM, Rich Felker <dalias@libc.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 <dalias@libc.org> 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 <dalias@libc.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,
(long) stop.tv_nsec);

and we should do  it for tv_nsec.  It works everywhere.

-- 
H.J.


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