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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Sun, 25 Mar 2018 20:15:32 -1000
Message-ID: <CA+55aFw8VGnVgaWHVFP-LChMNaoANOwT18jJEWzSCRLFeRGcmA@mail.gmail.com>
Subject: Re: [RFC] new SYSCALL_DEFINE/COMPAT_SYSCALL_DEFINE wrappers
To:     Al Viro <viro@zeniv.linux.org.uk>
Cc:     Ingo Molnar <mingo@kernel.org>,
        Dominik Brodowski <linux@dominikbrodowski.net>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Arnd Bergmann <arnd@arndb.de>,
        linux-arch <linux-arch@vger.kernel.org>,
        Ralf Baechle <ralf@linux-mips.org>,
        James Hogan <jhogan@kernel.org>,
        linux-mips <linux-mips@linux-mips.org>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Michael Ellerman <mpe@ellerman.id.au>,
        ppc-dev <linuxppc-dev@lists.ozlabs.org>,
        Martin Schwidefsky <schwidefsky@de.ibm.com>,
        Heiko Carstens <heiko.carstens@de.ibm.com>,
        linux-s390 <linux-s390@vger.kernel.org>,
        "David S . Miller" <davem@davemloft.net>,
        sparclinux@vger.kernel.org, Ingo Molnar <mingo@redhat.com>,
        Jiri Slaby <jslaby@suse.com>,
        "the arch/x86 maintainers" <x86@kernel.org>
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On Sun, Mar 25, 2018 at 5:47 PM, Al Viro <viro@zeniv.linux.org.uk> wrote:
>
> Linus, Dominik - how do you plan dealing with that fun?

Secretly, I was hoping to kill x32, because it's not being used afaik.

More realistically, I was thinking we'd just use a separate table or
system calls, and generate different versions.

In fact, you can see exactly that in my WIP branch, except it uses the
wrong name.

So see the "WIP-syscall" branch in my normal git kernel repo, and in
particular the patch to <linux/syscalls.h>, which generates
"sys_x64##name" and "sys_i86##name()" inline functions that do that
mapping correcty for native x86-64, and for the (misnamed) x32 cases.

So there are three different cases:

 - native: sys_x64_name() generated by SYSCALL_DEFINEx()

 - compat -bit: compat_sys_i86_name() generated by COMPAT_SYSCALL_DEFINEx()

 - x32: sys_i86_name() generated by SYSCALL_DEFINEx().

and then I actually changed the names in the tables (ie in
arch/x86/entry/syscalls/syscall_64.tbl etc).

HOWEVER.

I didn't actually test any of the compat or x32 ones, and the way I
did it there also was no type-checking or other automated catching of
getting it wrong. So it's almost certainly completely buggy, but the
_intent_ is there and there is a remote possibility that it might even
work.

              Linus