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

["H.J. Lu" <hjl dot tools at gmail dot com>]

On Sun, Feb 15, 2015 at 10:05 AM, Rich Felker <dalias@libc.org> wrote:
> On Sun, Feb 15, 2015 at 10:02:23AM -0800, H.J. Lu wrote:
>> 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.
>
> We==who? Every single C programmer in the world should do this because
> x32 has a bug? Note that the above isn't even correct; it assumes

It is a matter of opinion.

> time_t fits in long, which is going to be false when ILP32 archs get

I am referring to casting on value with type time_t, like tv_sec.  You
also need to do casting when printing tv_sec.

> 64-bit time_t. In any case you're not going to have success getting
> the word out to everybody that they "need to" change their code, and
> they shouldn't have to. An O(1) fix (x32) is superior to an O(n) fix
> (every singe C program in the world).
>
> Rich



-- 
H.J.