Re: [PATCH v3 2/2] arch: wire-up clone3() syscall

From: Christian Brauner <christian@brauner.io>
To: Arnd Bergmann <arnd@arndb.de>
Cc: Guenter Roeck <linux@roeck-us.net>,
	Al Viro <viro@zeniv.linux.org.uk>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Jann Horn <jannh@google.com>, Kees Cook <keescook@chromium.org>,
	Florian Weimer <fweimer@redhat.com>,
	Oleg Nesterov <oleg@redhat.com>,
	David Howells <dhowells@redhat.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Adrian Reber <adrian@lisas.de>,
	Linux API <linux-api@vger.kernel.org>,
	linux-arch <linux-arch@vger.kernel.org>,
	the arch/x86 maintainers <x86@kernel.org>,
	Ley Foon Tan <lftan@altera.com>,
	"moderated list:NIOS2 ARCHITECTURE" 
	<nios2-dev@lists.rocketboards.org>
Subject: Re: [PATCH v3 2/2] arch: wire-up clone3() syscall
Date: Fri, 21 Jun 2019 17:30:13 +0200	[thread overview]
Message-ID: <20190621153012.fxwhx25mzmzueqh7@brauner.io> (raw)
In-Reply-To: <CAK8P3a0T1=eg5ONbMFhHi=vmk1K5uogZ+5=wpsXvjVDzn6vS=Q@mail.gmail.com>

On Fri, Jun 21, 2019 at 04:20:15PM +0200, Arnd Bergmann wrote:
> On Fri, Jun 21, 2019 at 1:18 PM Christian Brauner <christian@brauner.io> wrote:
> > On Fri, Jun 21, 2019 at 11:37:50AM +0200, Arnd Bergmann wrote:
> > >
> > > I never really liked having __ARCH_WANT_SYS_CLONE here
> > > because it was the only one that a new architecture needed to
> > > set: all the other __ARCH_WANT_* are for system calls that
> > > are already superseded by newer ones, so a new architecture
> > > would start out with an empty list.
> > >
> > > Since __ARCH_WANT_SYS_CLONE3 replaces
> > > __ARCH_WANT_SYS_CLONE for new architectures, how about
> > > leaving __ARCH_WANT_SYS_CLONE untouched but instead
> >
> > __ARCH_WANT_SYS_CLONE is left untouched. :)
> >
> > > coming up with the reverse for clone3 and mark the architectures
> > > that specifically don't want it (if any)?
> >
> > Afaict, your suggestion is more or less the same thing what is done
> > here. So I'm not sure it buys us anything apart from future
> > architectures not needing to set __ARCH_WANT_SYS_CLONE3.
> >
> > I expect the macro above to be only here temporarily until all arches
> > have caught up and we're sure that they don't require assembly stubs
> > (cf. [1]). A decision I'd leave to the maintainers (since even for
> > nios2 we were kind of on the fence what exactly the sys_clone stub was
> > supposed to do).
> >
> > But I'm happy to take a patch from you if it's equally or more simple
> > than this one right here.
> >
> > In any case, linux-next should be fine on all arches with this fixup
> > now.
> 
> I've looked at bit more closely at the nios2 implementation, and I
> believe this is purely an artifact of this file being copied over
> from m68k, which also has an odd definition. The glibc side
> of nios2 clone() is also odd in other ways, but that appears
> to be unrelated to the kernel ABI.
> 
> I think the best option here would be to not have any special
> cases and just hook up clone3() the same way on all
> architectures, with no #ifdef at all. If it turns out to not work
> on a particular architecture later, they can still disable the
> syscall then.

Hm, if you believe that this is fine and want to "vouch" for it by
whipping up a patch that replaces the wiring up done in [1] I'm happy to
take it. :) Otherwise I'd feel more comfortable not adding all arches at
once.

[1]: https://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux.git/log/?h=clone

Christian