Messages in this thread | | | Date | Thu, 11 Jan 2018 18:23:03 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH 2/3] objtool: Ignore retpoline alternatives |
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On Thu, Jan 11, 2018 at 05:19:23PM +0000, David Woodhouse wrote: > On Thu, 2018-01-11 at 18:05 +0100, Peter Zijlstra wrote: > > On Thu, Jan 11, 2018 at 06:01:23PM +0100, Jiri Kosina wrote: > > > On Thu, 11 Jan 2018, Josh Poimboeuf wrote: > > > > > > > I think I heard that retpolines won't be ported to anything older than > > > > GCC 4.9, so maybe it's safe to use '%='. I don't remember when it was > > > > introduced into GCC though. > > > > > > I'm afraid we'll have to backport retpolines in some form to 4.3.x at > > > least. I'd be surprised if we'd be the only ones on this planet :) > > > > So upstream code is going to require 4.5 at least, and 4.4 has %=. > > Backport effort will just have to cope or backport more GCC bits, that > > is, if you're backporting retpoline to 4.3 also backport asm-goto. > > Again, the RSB thing is for more than just retpoline; it's needed for > IBRS support too and that *doesn't* necessarily require a newer > compiler at all.
I think the asm-goto was exactly for IBRS, because without that you get to sprinkle LFENCE all over the place.
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