My impression is it was mostly a desire to reuse existing x86_64 system calls
as much as possible without modification or additional compat layer work.
The 64-bit time requirement seems to have come from an lkml discussion, which
has quite a bit of interesting background about x32:
https://lkml.org/lkml/2011/8/26/415
https://lkml.org/lkml/2011/8/26/453
On Fri, Dec 14, 2018 at 2:05 PM Andy Lutomirski <l...@amacapital.net> wrote:
>
>
>
> > On Dec 14, 2018, at 8:55 AM, Rich Felker <dal...@libc.org> wrote:
> >
> >> On Fri, Dec 14, 2018 at 05:38:33PM +0100, Florian Weimer wrote:
> >> * Rich Felker:
> >>
> >>> This is all useless (and wrong since tv_nsec is required to have type
> >>> long as part of C and POSIX, regardless of ILP32-vs-LP64; that's a bug
> >>> in glibc's x32).
> >>
> >> We should be able to fix standards if they prove unworkable in practice.
> >> In my opinion, if standards require complex solutions where an obvious
> >> and simple solution exists, then standards are wrong.
> >
> > The requirement doesn't mandate complex solutions. There's nothing
> > complex about tv_nsec being long. long is the smallest type that C
> > guarantees to be large enough to store the range of values, which is
> > forever fixed and can't grow (because the definition of "nano" prefix
> > is fixed :). The type has been long ever since the structure was
> > introduced, and its being long means that there's lots of (correct!)
> > code using %ld (e.g. ".%.9ld" to format results as a decimal without
> > using floating point approximations) to print it. There might also be
> > code taking pointers to it to pass to functions, etc.
> >
> > The only reason a "complex" need arises is that Linux did something
> > horribly wrong here, ignoring the specified type, when introducing an
> > obscure subarch that almost nobody uses. This kind of mistake is
> > becoming a theme in Linux (see also: msghdr). Application authors
> > should not have to pay the price for fixing this by retrofitting yet
> > another silly type like "snseconds_t" or something into programs to
> > accommodate the mistakes of x32.
> >
> >
>
> Does anyone know *why* Linux’s x32 has __kernel_long_t defined as long long?
> I assume that this is where this bug, and most of the other bugs, came from.
>
> This may be silly, but the kernel could plausibly add a x32v2 where long is
> genuinely 32-bit, and then maybe we could drop the old x32 at some point.
> From all the discussion so far, it seems like there really is some demand for
> ILP32, but it’s still not really clear that preserving compatibility with
> existing x32 binaries in the long run is critical.
