Hi - On Fri, May 29, 2015 at 03:27:16PM -0500, Josh Poimboeuf wrote: > [...] > > > Also, with the feature missing completely, maybe someone finds a method to > > > introduce it in a maintainable fashion, while with the feature included > > > upstream > > > there's very little pressure to do that. As a bonus we'd also win a > > > workable dwarf > > > unwinder. > > > > Before doing something drastic like this, I think we should get Josh's > > opinion, since I think he's working on a new (?) unwinder. > > I'd definitely like to replace all the asm DWARF CFI annotations with > something more automated and robust. So it doesn't really affect me > whether they're ripped out now or replaced later. > [...] > Then again, I'm not sure how useful or reliable the existing annotations > are anyway, so maybe it doesn't matter much.
In our experience as consumers of this CFI information for years in systemtap, the annotations have been generally correct and reliable. Their presence allows reliable, correct, and efficient kernel->userspace backtracing as used in important systemtap scripts. If the current complaint is primarily about testability, it would be easy to add simple stap-based tests to the kernel to exercise the code and confirm its operation. Perhaps we could extract a specialized self-contained test case (containing an unwinder). I'm not in a position to judge the purported cost savings of removing this code, but there is definitely a negative benefit as a loss of useful functionality, esp. with no replacement in sight. - FChE -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
