On Tue, Sep 08, 2020 at 11:13:58AM -0700, Linus Torvalds wrote: > Josh, > > On Mon, Sep 7, 2020 at 1:20 AM Petr Mladek <pmladek@xxxxxxxx> wrote: > > > > - Workaround "unreachable instruction" objtool warnings that happen > > with some compiler versions. > > I know I said this fixes things for me, but I just realized it doesn't entirely. > > I wonder how I missed the remaining one: > > arch/x86/kvm/vmx/vmx.o: warning: objtool: > vmx_handle_exit_irqoff()+0x142: unreachable instruction > > so apparently gcc and objtool can still disagree even without that > '-flive-patching'. > > The unreachable code in question is after the call to > handle_external_interrupt_irqoff(), and while that function is a bit > odd, in this case I think it's objtool that is wrong. > > I think that what happens is that the function doesn't have a 'ret' > instruction, and instead returns by doing a tail-call to > __sanitizer_cov_trace_pc with my config. And maybe that is what > confuses objtool. > > This is current tip-of-git of my tree, with a allmodconfig build (but > the actual config will then depend on things like the gcc plugins > being there too, so you may not get exactly the same thing as I do) > > Josh? Am I missing something, and the objtool warning is valid? But > yes, that code is doing some very very special stuff with that thunk > call asm, so it's hard to read the asm. Hm, I don't think I've seen that one. We saw a similar warning in that function before, but it was caused by the combination of CONFIG_UBSAN_ALIGNMENT and CONFIG_UBSAN_TRAP, which I think Kees fixed. Can you share the .o file? At least I can't recreate with GCC 9.3.1, which is all I have at the moment. -- Josh
