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

[Adhemerval Zanella <adhemerval.zanella@linaro.org>]

On 15/02/2021 07:44, Florian Weimer via Libc-alpha wrote:
> * 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.
I have this one as a TODO to improve the posix_spawn.