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From: Florian Weimer <fweimer@redhat.com>
To: Christian Brauner <christian.brauner@ubuntu.com>
Cc: "Michael Kerrisk \(man-pages\)" <mtk.manpages@gmail.com>,
	Christian Brauner <christian@brauner.io>,
	lkml <linux-kernel@vger.kernel.org>,
	linux-man <linux-man@vger.kernel.org>,
	Kees Cook <keescook@chromium.org>,
	Oleg Nesterov <oleg@redhat.com>, Arnd Bergmann <arnd@arndb.de>,
	David Howells <dhowells@redhat.com>,
	Pavel Emelyanov <xemul@virtuozzo.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Adrian Reber <adrian@lisas.de>, Andrei Vagin <avagin@gmail.com>,
	Linux API <linux-api@vger.kernel.org>,
	Jann Horn <jannh@google.com>
Subject: Re: For review: documentation of clone3() system call
Date: Thu, 07 Nov 2019 17:10:51 +0100
Message-ID: <87y2wrbras.fsf@oldenburg2.str.redhat.com> (raw)
In-Reply-To: <20191107151941.dw4gtul5lrtax4se@wittgenstein> (Christian Brauner's message of "Thu, 7 Nov 2019 16:19:43 +0100")

* Christian Brauner:

> I've always been confused by the "..." for the glibc wrapper. The glibc
> prototype in bits/sched.h also looks like this:
>
> extern int clone (int (*__fn) (void *__arg), void *__child_stack, int __flags, void *__arg, ...) __THROW;
>
> The additionl args parent_tid, tls, and child_tid are present in _all_
> clone version in the same order. In fact the glibc wrapper here give the
> illusion that it's parent_tid, tls, child_tid. The underlying syscall
> has a different order parent_tidptr, child_tidptr, tls.
>
> Florian, can you advise what prototype we should mention for the glibc
> clone() wrapper here. I'd like it to be as simple as possible and get
> rid of the ...
> Architectural differences are explained in detail below anyway.

Our header has:

/* Clone current process.  */
extern int clone (int (*__fn) (void *__arg), void *__child_stack,
                  int __flags, void *__arg, ...) __THROW;

I have not checked all assembler implementations.  In theory there could
be one that relies on the different calling convention for variadic
functions (e.g., the existence of a parameter save area on POWER).  Or
that swaps arguments in some architecure-specific way. 8-(

I don't have much guidance on this matter, sorry.  I expect that for
clone3, we'll provide a same-stack variant as well (for fork/vfork-like
usage), which will be much closer to the kernel interface.  clone/clone2
doesn't seem very fixable to me at this point.

Thanks,
Florian


  reply index

Thread overview: 30+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-25 16:59 Michael Kerrisk (man-pages)
2019-10-25 17:07 ` Christian Brauner
2019-11-07 12:26   ` Michael Kerrisk (man-pages)
2019-10-26  2:28 ` G. Branden Robinson
2019-10-31  6:06   ` Michael Kerrisk (man-pages)
2019-10-28 15:12 ` Jann Horn
2019-10-28 17:21   ` Christian Brauner
2019-10-28 19:09     ` Jann Horn
2019-10-29 11:27       ` Christian Brauner
2019-10-29 14:26         ` Christian Brauner
2019-10-29 14:36           ` Florian Weimer
2019-10-29 16:04             ` Christian Brauner
2019-10-29 15:20           ` Jann Horn
2019-10-29 16:05             ` Christian Brauner
2019-11-07 15:19 ` Christian Brauner
2019-11-07 16:10   ` Florian Weimer [this message]
2019-11-09  8:09   ` Michael Kerrisk (man-pages)
2019-11-09 16:53     ` Christian Brauner
2019-11-11  9:02       ` Michael Kerrisk (man-pages)
2019-11-11 11:36         ` Christian Brauner
2019-11-11 19:56           ` Michael Kerrisk (man-pages)
2019-11-11 14:55     ` Jann Horn
2019-11-11 16:58       ` Theodore Y. Ts'o
2019-11-11 20:24         ` Jann Horn
2019-11-12 23:03           ` Kees Cook
2019-11-14 12:15       ` Michael Kerrisk (man-pages)
2019-11-14 12:29         ` Christian Brauner
2019-11-11 15:03 ` Florian Weimer
2019-11-11 15:15   ` Jann Horn
2019-11-11 15:20     ` Florian Weimer

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