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Re: [PATCH] off_t: fix register pair calculation for 64-bit case
- From: Yury Norov <ynorov at caviumnetworks dot com>
- To: "H.J. Lu" <hjl dot tools at gmail dot com>
- Cc: GNU C Library <libc-alpha at sourceware dot org>, Mike Frysinger <vapier at gentoo dot org>, "Joseph S. Myers" <joseph at codesourcery dot com>, Chris Metcalf <cmetcalf at tilera dot com>, Andrew Pinski <pinskia at gmail dot com>, <cmetcalf at mellanox dot com>
- Date: Fri, 24 Jun 2016 15:41:13 +0300
- Subject: Re: [PATCH] off_t: fix register pair calculation for 64-bit case
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On Fri, Jun 24, 2016 at 05:30:32AM -0700, H.J. Lu wrote:
> On Fri, Jun 24, 2016 at 5:23 AM, Yury Norov <ynorov@caviumnetworks.com> wrote:
> > There are 3 syscall wrappers under sysdeps/unix/sysv/linux that
> > calculate register pair for off_t like this:
> > __LONG_LONG_PAIR (offset >> 31, offset)
> >
> > While it works for 32-bit off_t, new 32-bit APIs that use 64-bit
> > off_t will be broken with it. This patch redirects affected syscalls
> > to their 64-bit versions. It also saves few instructions and symbols
> > in glibc, as 32-bit syscall wrappers are not generated anymore.
>
> If you have 64-bit register, should you use wordsize-64, like
>
> sysdeps/unix/sysv/linux/wordsize-64
>
> H.J.
Sometimes it's not possible. AARCh64/ILP32 requires to pass 64-bit
parameters as pair. (this is one of two options for ILP32 that is
under discussion)