From mboxrd@z Thu Jan  1 00:00:00 1970
From: Florian Weimer <fweimer@redhat.com>
Subject: Re: For review: documentation of clone3() system call
Date: Thu, 07 Nov 2019 17:10:51 +0100
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        Brauner's message of "Thu, 7 Nov 2019 16:19:43 +0100")
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* 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 __f=
lags, 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