Re: [PATCH] Add an internal wrapper for clone, clone2 and clone3

[Florian Weimer <fweimer@redhat.com>]

* H. J. Lu via Libc-alpha:

> The clone3 system call provides a superset of the functionality of clone
> and clone2.  It also provides a number of API improve ments, including
> the ability to specify the size of the child's stack area which can be
> used by kernel to compute the shadow stack size when allocating the
> shadow stack.  Add:
>
> extern int __clone_internal (struct clone_args *cl_args, size_t size,
> 			     int (*__fn) (void *__arg), void *__arg);
>
> to provide an abstract interface for clone, clone2 and clone3.
>
> 1. Simplify stack management for clone by passing stack base and size
> to __clone_internal.
> 2. Consolidate clone vs clone2 differences into a single file.
> 3. Use only __clone_internal to clone a thread.  If clone3 returns -1
> with ENOSYS, __clone_internal will fall back to clone or clone2.
> 4. Add the x86-64 clone3 wrapper.
> 5. Enable the public clone3 wrapper in the future after it has been
> added to add targets.

What do you think about providing a clone wrapper which reuses the
caller's stack?  That would be useful for a (v)fork-style clone.  This
variant could also be exported because the callback inherits a
semi-valid TCB in this case.

Thanks,
Florian
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