On Tue, 14 Jul 2020, Josh Poimboeuf wrote: > On Tue, Jul 14, 2020 at 12:56:21PM +0200, Miroslav Benes wrote: > > On Thu, 2 Jul 2020, Josh Poimboeuf wrote: > > > > > On Tue, Jun 23, 2020 at 08:06:07AM -0700, Randy Dunlap wrote: > > > > On 6/22/20 11:28 PM, Stephen Rothwell wrote: > > > > > Hi all, > > > > > > > > > > Changes since 20200622: > > > > > > > > > > > > > on x86_64: > > > > > > > > arch/x86/kernel/cpu/mce/core.o: warning: objtool: mce_timed_out()+0x24: unreachable instruction > > > > kernel/exit.o: warning: objtool: __x64_sys_exit_group()+0x14: unreachable instruction > > > > > > > > Full randconfig file is attached. > > > > > > More livepatch... > > > > Correct. > > > > Both are known and I thought Josh had fixes queued somewhere for both, but > > my memory fails me quite often. See below. > > I did have fixes for some of them in a stash somewhere, but I never > finished them because I decided it's a GCC bug. Same here. > > However, I think it is time to decide how to approach this whole saga. It > > seems that there are not so many places in the kernel in need of > > __noreturn annotation in the end and as jikos argued at least some of > > those should be fixed regardless. > > I would agree that global functions like do_group_exit() deserve a > __noreturn annotation, though it should be in the header file. But > static functions shouldn't need it. Agreed. I'll post the patches for global functions eventually, but see below first. > > Josh, should I prepare proper patches and submit them to relevant > > maintainers to see where this path is going? > > If that's how you want to handle it, ok, but it doesn't seem right to > me, for the static functions at least. > > > It would be much better to fix it in GCC, but it has been like banging > > one's head against a wall so far. Josh, you wanted to create a bug > > for GCC in this respect in the past? Has that happened? > > I didn't open a bug, but I could, if you think that would help. I > haven't had a lot of success with GCC bugs in the past. Understood. > > If I remember correctly, we discussed briefly a possibility to cope with > > that in objtool, but no solution was presented. > > That would also feel like a GCC workaround and might impede objtool's > ability to find bugs like this one, and possibly more serious bugs. > > > Removing -flive-patching is also a possibility. I don't like it much, but > > we discussed it with Petr M. a couple of months ago and it might be a way > > too. > > -flive-patching has many problems which I outlined before. None of them > have been addressed. I still feel the same way, that it should be > reverted until it's ready. Otherwise it's a drain on upstream. > > Also, if the GCC developers won't acknowledge this bug then it doesn't > give me confidence in their ability to keep the feature working as > optimizations are added or changed. I must admit that I've started to share the sentiment recently. And it is probably the main reason for changing my mind about the whole thing. > I still think a potential alternative exists: objtool could be used as a > simple tree-wide object diff tool by generating a checksum for each > function. Then the patch can be applied and built to see exactly which > functions have changed, based on the changed checksums. In which case > this feature would no longer be needed anyway, would you agree? Yes. > I also think that could be a first step for converging our patch > creation processes. Yes again. Petr, would you agree to revert -flive-patching due to reasons above? Is there anything you want to add? Miroslav
