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

From: Arnd Bergmann <arnd@arndb.de>
To: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Rich Felker <dalias@libc.org>,
	"linux-ia64@vger.kernel.org" <linux-ia64@vger.kernel.org>,
	Linux-sh list <linux-sh@vger.kernel.org>,
	Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	Heiko Carstens <heiko.carstens@de.ibm.com>,
	linux-mips@vger.kernel.org, Max Filippov <jcmvbkbc@gmail.com>,
	Network Development <netdev@vger.kernel.org>,
	Deepa Dinamani <deepa.kernel@gmail.com>,
	"H. Peter Anvin" <hpa@zytor.com>,
	sparclinux <sparclinux@vger.kernel.org>,
	linux-arch <linux-arch@vger.kernel.org>,
	linux-s390 <linux-s390@vger.kernel.org>,
	y2038 Mailman List <y2038@lists.linaro.org>,
	Michael Ellerman <mpe@ellerman.id.au>,
	Helge Deller <deller@gmx.de>, X86 ML <x86@kernel.org>,
	Russell King - ARM Linux admin <linux@armlinux.org.uk>,
	Ingo Molnar <mingo@redhat.com>,
	Firoz Khan <firoz.khan@linaro.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Matt Turner <mattst88@gmail.com>,
	Fengh
Subject: Re: [PATCH v2 29/29] y2038: add 64-bit time_t syscalls to all 32-bit architectures
Date: Mon, 21 Jan 2019 20:40:01 +0000	[thread overview]
Message-ID: <CAK8P3a11Pme2d6VbTb2t7fi_vd7UmNuN-yOf2zT59KPzbCT1Lw@mail.gmail.com> (raw)
In-Reply-To: <CAK8P3a04UC2dHVqx1gHXJQzsDw446h1ghLEuRe0xmUyJgrOktw@mail.gmail.com>

On Mon, Jan 21, 2019 at 6:08 PM Arnd Bergmann <arnd@arndb.de> wrote:
> On Mon, Jan 21, 2019 at 9:19 AM Geert Uytterhoeven <geert@linux-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)
