* 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. Ok, I suspect we can try it, but my preconditions for merging it would be: 1) Linus doesn't NAK it (obviously) 2) we first implement the additional entropy bits that Linus suggested. does this work for you? Thanks, Ingo _______________________________________________ Xen-devel mailing list Xen-devel@lists.xen.org https://lists.xen.org/xen-devel