Re: Update kernel-features.h files for Linux 5.1

[Arnd Bergmann <arnd@arndb.de>]

On Thu, May 16, 2019 at 1:15 PM Adhemerval Zanella
<adhemerval.zanella@linaro.org> wrote:
> On 16/05/2019 05:08, Arnd Bergmann wrote:
> > On Fri, May 10, 2019 at 5:07 PM Adhemerval Zanella
> > <adhemerval.zanella@linaro.org> wrote:
> >> On 10/05/2019 07:27, Stepan Golosunov wrote:
> >>> 09.05.2019 в 23:00:37 +0000 Joseph Myers написал:
> >>>> Linux 5.1 adds missing syscalls to the syscall table for many Linux
> >>>> kernel architectures.  This patch updates the kernel-features.h
> >>>> headers accordingly.  I believe the statfs64 structure used by alpha
> >>>> matches what the new kernel syscalls use, but that should be reviewed
> >>>> carefully.
> >>>>
> >>>> Tested with build-many-glibcs.py.
> >>>
> >>> The newly added direct ipc syscalls are different from the old ones:
> >>>
> >>> 1. They do not accept IPC_64.  This means that __IPC_64 should be set
> >>> to zero when new syscalls are used.  And new syscalls can not be used
> >>> for compat functions like __old_semctl.
> >>
> >> So it seems we will need to conditionally set __IPC_64 based on kernel
> >> version.
> >
> > How so? I did not expect to see any libc change here at all, unless
> > you mean after you stop using sys_ipc().
>
> The idea is if user configure a minimum kernel version of v5.1,
> sysvipc would use wire-up syscalls.  So for sys_ipc the affected
> architectures calls with required IPC_64, and for wire-up syscalls
> IPC_64 is redefined accordingly.

Ah, I see. Is there any real advantage in doing this now though?
It seems to save a few cycles for each of those syscalls when building
for linux-5.1+, but the cost is a significant increase in source code
complexity.

      Arnd