[PATCH v4 2/2] manual: add architecture specific note on clone and clone3 syscalls

[Yury Khrustalev]

On Wed, Sep 03, 2025 at 11:37:44AM -0400, Rich Felker wrote:
> On Wed, Sep 03, 2025 at 04:53:57PM +0200, Florian Weimer wrote:
> > * Yury Khrustalev:
> > 
> > > On Mon, Sep 01, 2025 at 12:46:11PM -0400, Rich Felker wrote:
> > >> On Mon, Sep 01, 2025 at 06:33:35PM +0200, Florian Weimer wrote:
> > >> > * Yury Khrustalev:
> > >> > 
> > >> > > +@subsection Architecture specific notes on system calls
> > >> > > +
> > >> > > +Because @code{syscall} function does not know anything about what a particular
> > >> > > +system call does or what are the ABI requirements for it, it is important to be
> > >> > > +aware of any additional requirements that the target kernel might have for
> > >> > > +certain system calls.
> > >> > > 
> > >> > > ...
> > >
> > > ** Florian
> > >
> > >> > As this is discussing clone, I think you really should mention that
> > >> > using syscall for clones that are not fork-style (vfork-style, or
> > >> > thread-style) is NOT supported in general.  Not mentioning this
> > >> > important restriction implies support.
> > >
> > > I agree that we should mention this, however, I've looked through the
> > > manual and can't find anything that would imply that clones that are
> > > not fork-style are supported in general. It feels like this important
> > > bit should've been mentioned somewhere else in the manual, e.g. in a
> > > section that describes clone() but we don't seem to have any.
> > 
> > You are adding text that says “if you call clone through syscall, you
> > have to do this extra thing”.  This strongly implies that calling clone
> > through syscall is valid in some cases.  We can instead say that calling
> > clone through syscall is never valid.
> 
> Indeed, and I think this is the right action.


So if I understand this properly, the gist of this thread is that we
don't actually need to describe the actions needed if someone wants to
use SYS_clone or SYS_clone3 via the syscall() function on aarch64.
Instead we should have a patch not related to this SME changed that
would just spell that calling clone (or clone3) via syscall() is not
supported. Is this right?

Thanks,
Yury