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SubjectRe: [PATCH v6 13/17] arm64:ilp32: add sys_ilp32.c and a separate table (in entry.S) to use it
Date
On Monday 16 November 2015 10:16:35 Joseph Myers wrote:
> On Sun, 15 Nov 2015, Chris Metcalf wrote:
>
> > I've added Rich, Paul, Joseph, and Mike to the cc's as they are probably
> > a good subset of libc-alpha to help comment on these issues. My sense
> > is that right now, it wouldn't be possible to add a 32-bit architecture
> > with a non-32-bit default for _FILE_OFFSET_BITS. And, obviously, this
> > is why, when I added the tilegx32 APIs to glibc in 2011, I needed to
> > provide _FILE_OFFSET_BITS=32 support.
>
> x32 uses 64-bit off_t only. That's not a problem; the problems are
> tv_nsec not of type long, a bug we should avoid for all new ports (padding
> on tv_nsec is fine; treating that padding as a significant high part of a
> 64-bit value on input to glibc / kernel interfaces isn't), and maybe some
> other types being 64-bit unnecessarily, although as far as I know the
> suggested issues there
> <https://sourceware.org/bugzilla/show_bug.cgi?id=16438> are all
> theoretical.

Let's not get into the tv_nsec discussion today, that is not thankfully
not relevant for arm64 any more at this point. The system call ABI for
arm64/ilp32 is now the same as for any other 32-bit architecture using
the generic ABI, the question we're trying to solve here is only whether it
is ok for new 32-bit glibc ports to only offer a 64-bit off_t as the kernel
currently does (using __kernel_loff_t) or if we still need to support the
_FILE_OFFSET_BITS=32 case.

If I got you right, we can use 64-bit off_t now, so we just need someone
to figure out how to make that the default in glibc for new architectures
while keeping the existing 32-bit architectures unchanged.

Arnd


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