On Fri, Apr 09, 2021 at 04:37:41PM -0500, Josh Poimboeuf wrote: > On Fri, Apr 09, 2021 at 01:09:09PM +0100, Mark Rutland wrote: > > Further, I believe all the special cases are assembly functions, and > > most of those are already in special sections to begin with. I reckon > > it'd be simpler and more robust to reject unwinding based on the > > section. If we need to unwind across specific functions in those > > sections, we could opt-in with some metadata. So e.g. we could reject > > all functions in ".entry.text", special casing the EL0 entry functions > > if necessary. > Couldn't this also end up being somewhat fragile? Saying "certain > sections are deemed unreliable" isn't necessarily obvious to somebody > who doesn't already know about it, and it could be overlooked or > forgotten over time. And there's no way to enforce it stays that way. Anything in this area is going to have some opportunity for fragility and missed assumptions somewhere. I do find the idea of using the SYM_CODE annotations that we already have and use for other purposes to flag code that we don't expect to be suitable for reliable unwinding appealing from that point of view. It's pretty clear at the points where they're used that they're needed, even with a pretty surface level review, and the bit actually pushing things into a section is going to be in a single place where the macro is defined. That seems relatively robust as these things go, it seems no worse than our reliance on SYM_FUNC to create BTI annotations. Missing those causes oopses when we try to branch to the function.
Attachment:
signature.asc
Description: PGP signature
