Re: [RFC] <sys/tagged-address.h>: An API for tagged address

[Szabolcs Nagy <szabolcs.nagy@arm.com>]

The 02/17/2021 13:58, H.J. Lu via Libc-alpha wrote:
> On Wed, Feb 17, 2021 at 10:43 AM H.J. Lu <hjl.tools@gmail.com> wrote:
> > On Fri, Feb 12, 2021 at 5:06 AM H.J. Lu <hjl.tools@gmail.com> wrote:
> > > On Fri, Feb 12, 2021 at 1:43 AM Florian Weimer <fweimer@redhat.com> wrote:
> > > >
> > > > Do the setters/getters change process or thread properties?
> > >
> > > On x86-64, mask is stored in TCB.   TCB will be updated.  It applies
> > > to all threads.
> 
> Kirill raised a question what should happen when
> 
> /* Set the mask for address bits used in address translation.  Return 0
>    on success.  Return -1 on error.  */
> extern int set_tagged_address_mask (uintptr_t __mask);
> 
> was called in a thread.  It won't work when 2 threads have different address
> masks.  I think set_tagged_address_mask should be disallowed in child
> threads and in parent thread when there are any active child threads.

i think this is the wrong api. currently the libc should set
things up early. api for user code is too late.

user code does not know if it runs single threaded or not
(although we have __libc_single_threaded now, i'm not sure if
we can use that for this purpose)