Fedora 28 has GCC 8.1.1 available (currently in ‘updates-testing‘ repo), and I tested this with Kernel 4.17-rc4, to see if there was any improvement in the horde of warnings generated with 8.0.1.

In short, there is no real difference:

....................................
 CC security/keys/request_key.o
arch/x86/kvm/lapic.o: warning: objtool: kvm_lapic_reg_read()+0x126: sibling call from callable instruction with modified stack frame
arch/x86/kvm/lapic.o: warning: objtool: limit_periodic_timer_frequency.part.16()+0x3b: sibling call from callable instruction with modified stack frame
arch/x86/kvm/lapic.o: warning: objtool: kvm_irq_delivery_to_apic_fast()+0x373: sibling call from callable instruction with modified stack frame
arch/x86/kvm/lapic.o: warning: objtool: kvm_intr_is_single_vcpu_fast()+0x286: sibling call from callable instruction with modified stack frame
arch/x86/kvm/lapic.o: warning: objtool: kvm_lapic_set_base()+0xf0: sibling call from callable instruction with modified stack frame
arch/x86/kvm/lapic.o: warning: objtool: kvm_create_lapic()+0x39: sibling call from callable instruction with modified stack frame
arch/x86/kvm/lapic.o: warning: objtool: kvm_lapic_set_base.cold.24()+0x16: sibling call from callable instruction with modified stack frame
..................... etc, etc....................

There were patches proposed for the kernel, for GCC 8, but these would not appear to have made it into mainstream, yet..    There may be some debate over whether the fix is with GCC, or with kernel code…   Older versions of the kernel (tested with 4.9.98) compile more ‘cleanly’..

Robert Gadsdon.    May 7th, 2018.