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

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Message-ID: <CAK8P3a2iV7=HkHBVL_puvCQN0DmdKEnVs2aG9MQV_8Q58JSfTA@mail.gmail.com>
Date:   Fri, 21 Jun 2019 11:37:50 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Christian Brauner <christian@...uner.io>
Cc:     Guenter Roeck <linux@...ck-us.net>,
        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>,
        Kees Cook <keescook@...omium.org>,
        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 v3 2/2] arch: wire-up clone3() syscall

On Fri, Jun 21, 2019 at 12:10 AM Christian Brauner <christian@...uner.io> wrote:
> On Thu, Jun 20, 2019 at 11:44:51AM -0700, Guenter Roeck wrote:
> > On Tue, Jun 04, 2019 at 06:09:44PM +0200, Christian Brauner wrote:
>
> clone3() was placed under __ARCH_WANT_SYS_CLONE. Most architectures
> simply define __ARCH_WANT_SYS_CLONE and are done with it.
> Some however, such as nios2 and h8300 don't define it but instead
> provide a sys_clone stub of their own because of architectural
> requirements (or tweaks) and they are mostly written in assembly. (That
> should be left to arch maintainers for sys_clone3.)
>
> The build failures were on my radar already. I hadn't yet replied
> since I haven't pushed the fixup below.
> The solution is to define __ARCH_WANT_SYS_CLONE3 and add a
> cond_syscall(clone3) so we catch all architectures that do not yet
> provide clone3 with a ENOSYS until maintainers have added it.
>
> diff --git a/arch/arm/include/asm/unistd.h b/arch/arm/include/asm/unistd.h
> index 7a39e77984ef..aa35aa5d68dc 100644
> --- a/arch/arm/include/asm/unistd.h
> +++ b/arch/arm/include/asm/unistd.h
> @@ -40,6 +40,7 @@
>  #define __ARCH_WANT_SYS_FORK
>  #define __ARCH_WANT_SYS_VFORK
>  #define __ARCH_WANT_SYS_CLONE
> +#define __ARCH_WANT_SYS_CLONE3

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
coming up with the reverse for clone3 and mark the architectures
that specifically don't want it (if any)?

       Arnd