netdev - Re: [PATCH v2 29/29] y2038: add 64-bit time_t syscalls to all 32-bit architectures

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Date:   Mon, 21 Jan 2019 21:40:01 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Russell King - ARM Linux admin <linux@...linux.org.uk>,
        Andy Lutomirski <luto@...nel.org>,
        y2038 Mailman List <y2038@...ts.linaro.org>,
        Linux API <linux-api@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        Matt Turner <mattst88@...il.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Tony Luck <tony.luck@...el.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Michal Simek <monstr@...str.eu>,
        Paul Burton <paul.burton@...s.com>,
        Helge Deller <deller@....de>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Rich Felker <dalias@...c.org>,
        "David S. Miller" <davem@...emloft.net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, X86 ML <x86@...nel.org>,
        Max Filippov <jcmvbkbc@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Deepa Dinamani <deepa.kernel@...il.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Firoz Khan <firoz.khan@...aro.org>,
        alpha <linux-alpha@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        "linux-ia64@...r.kernel.org" <linux-ia64@...r.kernel.org>,
        linux-m68k <linux-m68k@...ts.linux-m68k.org>,
        linux-mips@...r.kernel.org,
        Parisc List <linux-parisc@...r.kernel.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        linux-s390 <linux-s390@...r.kernel.org>,
        Linux-sh list <linux-sh@...r.kernel.org>,
        sparclinux <sparclinux@...r.kernel.org>,
        Network Development <netdev@...r.kernel.org>,
        Linux FS Devel <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH v2 29/29] y2038: add 64-bit time_t syscalls to all 32-bit architectures

On Mon, Jan 21, 2019 at 6:08 PM Arnd Bergmann <arnd@...db.de> wrote:
> On Mon, Jan 21, 2019 at 9:19 AM Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
> > Regardless, I'm wondering what to do with the holes marked "room for
> > arch specific calls".
> > When is a syscall really arch-specific, and can it be added there, and
> > when does it turn out (later) that it isn't, breaking the
> > synchronization again?
>
> We've had a bit of that already, with cacheflush(), which exists on
> a couple of architectures, including some that use the first
> 'arch specific' slot (244) of the asm-generic table. I think this
> will be rare enough that we can figure out a solution when we
> get there.
>
> > The pkey syscalls may be a bad example, as AFAIU they can be implemented
> > on some architectures, but not on some others.  Still, I had skipped them
> > when adding new syscalls to m68k.
> >
> > Perhaps we should get rid of the notion of "arch-specific syscalls", and
> > reserve a slot everywhere anyway?
>
> I don't mind calling the hole something else if that helps. Out of
> principle I would already assume that anything we add for x86
> or the generic table should be added everywhere, but we can
> make it broader than that.

Applying this fixup below,

     ARnd

diff --git a/arch/x86/entry/syscalls/syscall_32.tbl
b/arch/x86/entry/syscalls/syscall_32.tbl
index d9c2d2eea044..955ab6a3b61f 100644
--- a/arch/x86/entry/syscalls/syscall_32.tbl
+++ b/arch/x86/entry/syscalls/syscall_32.tbl
@@ -398,7 +398,7 @@
 384    i386    arch_prctl              sys_arch_prctl
 __ia32_compat_sys_arch_prctl
 385    i386    io_pgetevents           sys_io_pgetevents_time32
 __ia32_compat_sys_io_pgetevents
 386    i386    rseq                    sys_rseq
 __ia32_sys_rseq
-# room for arch specific syscalls
+# don't use numbers 387 through 392, add new calls at the end
 393    i386    semget                  sys_semget
 __ia32_sys_semget
 394    i386    semctl                  sys_semctl
 __ia32_compat_sys_semctl
 395    i386    shmget                  sys_shmget
 __ia32_sys_shmget
diff --git a/arch/x86/entry/syscalls/syscall_64.tbl
b/arch/x86/entry/syscalls/syscall_64.tbl
index 43a622aec07e..2ae92fddb6d5 100644
--- a/arch/x86/entry/syscalls/syscall_64.tbl
+++ b/arch/x86/entry/syscalls/syscall_64.tbl
@@ -343,6 +343,8 @@
 332    common  statx                   __x64_sys_statx
 333    common  io_pgetevents           __x64_sys_io_pgetevents
 334    common  rseq                    __x64_sys_rseq
+# don't use numbers 387 through 423, add new calls after the last
+# 'common' entry

 #
 # x32-specific system call numbers start at 512 to avoid cache impact
diff --git a/include/uapi/asm-generic/unistd.h
b/include/uapi/asm-generic/unistd.h
index 53831e4a4c86..acf9a07ab2ff 100644
--- a/include/uapi/asm-generic/unistd.h
+++ b/include/uapi/asm-generic/unistd.h
@@ -740,7 +740,7 @@ __SC_COMP_3264(__NR_io_pgetevents,
sys_io_pgetevents_time32, sys_io_pgetevents,
 __SYSCALL(__NR_rseq, sys_rseq)
 #define __NR_kexec_file_load 294
 __SYSCALL(__NR_kexec_file_load,     sys_kexec_file_load)
-/* 295 through 402 are unassigned to sync up with generic numbers */
+/* 295 through 402 are unassigned to sync up with generic numbers, don't use */
 #if __BITS_PER_LONG == 32
 #define __NR_clock_gettime64 403
 __SYSCALL(__NR_clock_gettime64, sys_clock_gettime)