Messages in this thread | | | Date | Tue, 14 Apr 2020 21:48:01 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH V3 5/9] objtool: Add return address unwind hints |
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On Tue, Apr 14, 2020 at 09:27:27PM +0200, Alexandre Chartre wrote: > This provides a generic code to handle any intra-function call. Currently we have > the RSB stuffing ones which are forgotten with the UNWIND_HINT_TYPE_RADDR_DELETE > directive. And for retpoline, they will not return if we have an indirect jump > (JMP_NOSPEC) but they will return if we have an indirect call (CALL_NOSPEC). The > code can handle both cases. For example, if we were to have a CALL_NOSPEC invocation > which is not in an alternative then objtool can now correctly handle it.
The specialness of CALL_NOSPEC goes away with my proposed retpoline rework as well. I really don't think we need something as complicated as this.
Fundamentally validate_branch() will continue after a CALL instruction; so I'm thikning the worst that can happen from not following a (theoretical direct return) is a false-positive unreachable code warning, and we can trivially fix those with exisiting hints.
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