Re: [PATCH 14/15] arch: add split IPC system calls where needed

Heiko Carstens
2019-01-10T20:32:53Z

On Thu, Jan 10, 2019 at 05:24:34PM +0100, Arnd Bergmann wrote:
> The IPC system call handling is highly inconsistent across architectures,
> some use sys_ipc, some use separate calls, and some use both. We also
> have some architectures that require passing IPC_64 in the flags, and
> others that set it implicitly.
>
> For the additon of a y2083 safe semtimedop() system call, I chose to only
> support the separate entry points, but that requires first supporting
> the regular ones with their own syscall numbers.
>
> The IPC_64 is now implied by the new semctl/shmctl/msgctl system
> calls even on the architectures that require passing it with the ipc()
> multiplexer.
>
> I'm not adding the new semtimedop() or semop() on 32-bit architectures,
> those will get implemented using the new semtimedop_time64() version
> that gets added along with the other time64 calls.
> Three 64-bit architectures (powerpc, s390 and sparc) get semtimedop().
>
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
> One aspect here that might be a bit controversial is the use of
> the same system call numbers across all architectures, synchronizing
> all of them with the x86-32 numbers. With the new syscall.tbl
> files, I hope we can just keep doing that in the future, and no
> longer require the architecture maintainers to assign a number.
>
> This is mainly useful for implementers of the C libraries: if
> we can add future system calls everywhere at the same time, using
> a particular version of the kernel headers also guarantees that
> the system call number macro is visible.

> diff --git a/arch/s390/kernel/syscalls/syscall.tbl b/arch/s390/kernel/syscalls/syscall.tbl
> index 022fc099b628..428cf512a757 100644
> --- a/arch/s390/kernel/syscalls/syscall.tbl
> +++ b/arch/s390/kernel/syscalls/syscall.tbl
> @@ -391,3 +391,15 @@
> 381 common kexec_file_load sys_kexec_file_load compat_sys_kexec_file_load
> 382 common io_pgetevents sys_io_pgetevents compat_sys_io_pgetevents
> 383 common rseq sys_rseq compat_sys_rseq
> +# room for arch specific syscalls
> +392 64 semtimedop sys_semtimedop -
> +393 common semget sys_semget sys_semget
...
> +395 common shmget sys_shmget sys_shmget
...
> +398 common shmdt sys_shmdt sys_shmdt
> +399 common msgget sys_msgget sys_msgget

These four need compat system call wrappers, unfortunately... (well,
actually only shmget and shmdt require them, but let's add them for
all four). See arch/s390/kernel/compat_wrapper.c

I'm afraid this compat special handling will be even more annoying in
the future, since s390 will be the only architecture which requires
this special handling.

_Maybe_ it would make sense to automatically generate a weak compat
system call wrapper for s390 with the SYSCALL_DEFINE macros, but that
probably won't work in all cases.