linux-kernel - Re: [PATCH 2/2] arch: wire-up clone6() syscall on x86

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Date:   Mon, 27 May 2019 14:28:33 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Christian Brauner <christian@...uner.io>
Cc:     Al Viro <viro@...iv.linux.org.uk>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Jann Horn <jannh@...gle.com>,
        Florian Weimer <fweimer@...hat.com>,
        Oleg Nesterov <oleg@...hat.com>,
        David Howells <dhowells@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Adrian Reber <adrian@...as.de>,
        Linux API <linux-api@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        "the arch/x86 maintainers" <x86@...nel.org>
Subject: Re: [PATCH 2/2] arch: wire-up clone6() syscall on x86

On Mon, May 27, 2019 at 12:45 PM Christian Brauner <christian@...uner.io> wrote:
> On Mon, May 27, 2019 at 12:02:37PM +0200, Arnd Bergmann wrote:
> > On Sun, May 26, 2019 at 12:27 PM Christian Brauner <christian@...uner.io> wrote:
> > >
> > > Wire up the clone6() call on x86.
> > >
> > > This patch only wires up clone6() on x86. Some of the arches look like they
> > > need special assembly massaging and it is probably smarter if the
> > > appropriate arch maintainers would do the actual wiring.
> >
> > Why do some architectures need special cases here? I'd prefer to have
> > new system calls always get defined in a way that avoids this, and
> > have a common entry point for everyone.
> >
> > Looking at the m68k sys_clone comment in
> > arch/m68k/kernel/process.c, it seems that this was done as an
> > optimization to deal with an inferior ABI. Similar code is present
> > in h8300, ia64, nios2, and sparc. If all of them just do this to
> > shave off a few cycles from the system call entry, I really
> > couldn't care less.
>
> I'm happy to wire all arches up at the same time in the next revision. I
> just wasn't sure why some of them were assemblying the living hell out
> of clone; especially ia64. I really didn't want to bother touching all
> of this just for an initial RFC.

Don't worry about doing all architectures for the RFC, I mainly want this
to be done consistently by the time it gets into linux-next.

One thing to figure out though is whether we need the stack_size argument
that a couple of architectures pass. It's usually hardwired to zero,
but not all the time, and I don't know the history of this.

       Arnd