[PATCH v3 2/8] elf: Add a tunable to control use of tagged memory

[Szabolcs Nagy]

The 11/27/2020 06:54, H.J. Lu via Libc-alpha wrote:
> On Fri, Nov 27, 2020 at 4:24 AM Richard Earnshaw
> <Richard.Earnshaw@foss.arm.com> wrote:
> > On 27/11/2020 11:27, Siddhesh Poyarekar wrote:
> > > From a distribution perspective, this could be done in two phases:
> > >
> > > 1. Phase 1 where you ave the tunable which is disabled by default and no
> > > marker present.  This makes tagging available to those who want to opt-in
> > >
> > > 2. Phase 2 is where the tunable is now enabled by default and can be
> > > overridden with an opt-out marker.  Running this opt-out binary on the
> > > older version is safe (and shouldn't need an ABI bump) since tunables
> > > are disabled by default.
> > >
> > > Does that make sense?  If not then I'd really like to see a more
> > > detailed description of how you intend to roll this out.
> > >
> > > Siddhesh
> >
> > Yes, you've captured my thoughts and summarised it better that I was
> > doing myself.  Thank you.
> >
> 
> We need a plan for binary marker first.

if we enable heap tagging in those two phases then the first
phase has no abi commitment (tunables are not abi stable).

heap tagging will not be very useful in phase 1 but at least
users can start testing it and report back issues. (assuming
they have hardware or emulator.)

i was hoping we can have an abi stable env var ui, but i'm
fine with tunables only since that sounds the safest.
(if we wait for the marking design and binutils etc support
then we have less chance to see deployment problems early.)