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

[Siddhesh Poyarekar]

On 11/27/20 4:02 PM, Szabolcs Nagy wrote:
> i think that's an opt-in marking. here we need an opt-out
> marking if we want to turn off the effects of the env var.

Right I assumed it to be an opt-in marker and not opt-out.

> or we can introduce an opt-in marking, but it's not clear
> how well the transition works in practice: you have to be
> sure binaries are tagging compatible to mark them and after
> some long time when enough binaries are marked the marking
> becomes useful. the transition with opt-out is clearer i
> think (we can mark binaries as we find issues), but if our
> aim is "on by default" tagging then opt-in will be needed.

The thing with opt-out though is that it's not really opt-out in the 
real sense.  That is, you need to set the tunable to opt in; and then 
the marker is allowed to override it.  If glibc.mem.tagging is enabled 
by default however, then using the marker to override and opt out makes 
sense.

Or maybe I haven't understood your implementation plan correctly and we 
need to talk more about that as HJ suggests, especially since an ABI 
event seems imminent.

> in short this can go in many directions, but if we have
> some insurance (e.g. abi bump mechanism) in place then we
> can make the decision later.

An opt in marker shouldn't need an ABI bump.

Siddhesh