On Fri, Sep 22, 2017 at 11:38 AM, H. Peter Anvin <h...@zytor.com> wrote: > On 09/22/17 09:32, Ingo Molnar wrote: >> >> 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. >> > > We lose EBX on 32 bits, but we don't lose RBX on 64 bits - since x86-64 > has RIP-relative addressing there is no need for a dedicated PIC register. > > I'm somewhat confused how we can have as much as almost 1% overhead. I > suspect that we end up making a GOT and maybe even a PLT for no good reason.
We have a GOT with very few entries, mainly linker script globals that I think we can work to reduce or remove. We have a PLT but it is empty. On latest iteration (not sent yet), modules have PLT32 relocations but no PLT entry. I got rid of mcmodel=large for modules and instead I move the beginning of the module section just after the kernel so relative relocations work. > > -hpa -- Thomas _______________________________________________ Xen-devel mailing list Xen-devel@lists.xen.org https://lists.xen.org/xen-devel
