Messages in this thread | | | Date | Mon, 15 Jan 2018 19:12:30 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH 2/4] objtool: Implement jump_assert for _static_cpu_has() |
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On Mon, Jan 15, 2018 at 12:04:05PM -0600, Josh Poimboeuf wrote: > On Mon, Jan 15, 2018 at 05:44:30PM +0100, Peter Zijlstra wrote: > > Unlike the jump_label bits, static_cpu_has is implemented with > > alternatives. Sadly it doesn't readily distinguish itself from any > > other alternatives. > > > > Use a heuristic to guess at it :/ > > > > But like jump_labels, make static_cpu_has set br_static on the > > instructions after the static branch such that we can assert on it. > > This seems a bit heavy handed and fragile, though maybe it is the best > way. Still I wonder if there's a better way to do it. > > Some quick ideas: > > a) Somehow use __jump_table in the _static_cpu_has() macro?
Can do, but adds permanent overhead for the fake table entries, also the alternative in _static_cpu_has is slightly more complex, but it would work I think.
> b) Add another special annotation to tell objtool where > _static_cpu_has() locations are?
Almost did that, but I figured I'd give this a try first. But yes I agree it is somewhat ugly.
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