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

[Arnd Bergmann <arnd at arndb dot de>]

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().

> It also seems that our default value on generic ipc_priv.h
> is not really expressing the kernel ABI.

Right, it should only be set for historic ABIs.

> > 2. semtimedop does not exist on 32-bit ABIs.  They have
> > semtimedop_time64 instead.
> > (I also think that ipc with IPCOP_semtimedop was accidentally made to
> > behave like semtimedop_time64 in 32-bit builds of linux 5.1.  But that
> > would be a kernel bug.)
>
> So it seems we would need to either add an __ASSUME specific for semtimedop
> to just enable wire-up calls if time64 is defined or add another pre-processor
> check to see if __NR_semtimeop is defined as well.

The implementation I expected to see here is to have the
64-bit time_t version of semtimedop() to call the direct semtimedop_time64()
system call, and fall back to the existing implementation if that
returns -ENOSYS and the libc is built to support old kernels.

        Arnd