Re: For review: documentation of clone3() system call

* 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