On Mon, May 18, 2026 at 09:36:16AM +0200, Peter Zijlstra wrote: > Anyway, the most contentious part was the whole backwards compat bitmap > crap. When the dynamic linker composes a process of parts that support > IBT and parts that do not, you get to deal with fallout.
Is it acceptable to do all-or-nothing IBT first? And then do a second round of patches with legacy support? Until then, ld.so could: - start with IBT, disable it upon loading incompatible DSO - allow users to manually lock IBT I thought this weak form of IBT is better than nothing at all, if there's a risk that legacy support derails things. Btw, apparently OpenBSD enforces kernel+user IBT. I think the end goal is a user_ibt=force command-line param that locks IBT for all processes on startup. > The IBT spec has this horrid bitmap thing to try and deal with this, and > those early patches exposed that piece of shit to userspace. Then later > patches (suggested by me) used the ARM64/BTI approach of using PROT_BTI. > We'd use a (software) page-table bit, and upon #CP consult that to see > if we should eat the trap or produce a warn/signal whatever. Nice, I'm happy to revive/rebase/test any of this if there's interest. > I think we were near something workable there when Rick got pulled from > this and put onto something more 'important' and things just haven't > moved ever since. > > Anyway, glad to see someone has time to poke at this. Happy to spend whatever time is needed to land IBT. I'm very glad the first reaction wasn't "absolutely no way" :-) Thank you, -Richard
