On 02/08/2018 10:07 AM, Christian Borntraeger wrote: > > > On 02/08/2018 09:58 AM, Heiko Carstens wrote: >> On Tue, Feb 06, 2018 at 01:30:28PM +0100, David Hildenbrand wrote: >>> On 06.02.2018 12:21, Christian Borntraeger wrote: >>>> Some old patches refreshed. >>>> >>> >>> Certainly the right thing to do. Especially also interesting due to >>> retpotline (if we get something like that on s390x). If I remember >>> correctly, x86 highly benefits by replacing magic function pointer by >>> switch statements. >> >> If you look at the generated code for the first patch: gcc now generates >> its own jump table which then jumps (indirectly) to a brasl... So it's two >> instead of one branch. >> I'm not saying that this patch is not good, but there seem be a wrong >> assumptions about the benefit here. > > Seems to depend on the compiler. The gcc 7.2 from my Fedora 27 seems to do > the right thing for intercept.o and priv.o. > In the end this will also help the new -mindirect-branch thing as the gcc > support also avoids jump tables if we use thunks. I will update the patch description and focus more on the "let us use the compiler heuristics" and "prepare for thunks".
