On Fri, Sep 22, 2017 at 9:32 AM, Ingo Molnar <mi...@kernel.org> wrote: > > * Thomas Garnier <thgar...@google.com> wrote: > >> On Thu, Sep 21, 2017 at 8:59 AM, Ingo Molnar <mi...@kernel.org> wrote: >> > >> > ( Sorry about the delay in answering this. I could blame the delay on the >> > merge >> > window, but in reality I've been procrastinating this is due to the >> > permanent, >> > non-trivial impact PIE has on generated C code. ) >> > >> > * Thomas Garnier <thgar...@google.com> wrote: >> > >> >> 1) PIE sometime needs two instructions to represent a single >> >> instruction on mcmodel=kernel. >> > >> > What again is the typical frequency of this occurring in an x86-64 >> > defconfig >> > kernel, with the very latest GCC? >> >> I am not sure what is the best way to measure that. > > If this is the dominant factor then 'sizeof vmlinux' ought to be enough: > >> With ORC: PIE .text is 0.814224% than baseline > > I.e. the overhead is +0.81% in both size and (roughly) in number of > instructions > executed. > > BTW., I think things improved with ORC because with ORC we have RBP as an > extra > register and with PIE we lose RBX - so register pressure in code generation is > lower.
That make sense. > > Ok, I suspect we can try it, but my preconditions for merging it would be: > > 1) Linus doesn't NAK it (obviously) Of course. > 2) we first implement the additional entropy bits that Linus suggested. > > does this work for you? Sure, I can look at how feasible that is. If it is, can I send everything as part of the same patch set? The additional entropy would be enabled for all KASLR but PIE will be off-by-default of course. > > Thanks, > > Ingo -- Thomas _______________________________________________ Xen-devel mailing list Xen-devel@lists.xen.org https://lists.xen.org/xen-devel
