On Wed, May 27, 2020 at 02:41:04PM +0100, Lorenzo Pieralisi wrote: > On Tue, May 26, 2020 at 09:21:57PM +0100, Will Deacon wrote: > > Hi Lorenzo, Hanjun, [+Nick] > > > > On Thu, May 21, 2020 at 06:37:38PM +0100, Lorenzo Pieralisi wrote: > > > On Thu, May 21, 2020 at 11:09:53AM +0100, Will Deacon wrote: > > > > Hi folks, > > > > > > > > I just tried booting the arm64 for-kernelci branch under QEMU (version > > > > 4.2.50 (v4.2.0-779-g4354edb6dcc7)) with UBSAN enabled, and I see a > > > > couple of NULL pointer dereferences reported at boot. I think they're > > > > both GIC related (log below). I don't see a panic with UBSAN disabled, > > > > so something's fishy here. > > > > > > May I ask you the QEMU command line please - just to make sure I can > > > replicate it. > > > > As it turns out, I'm only able to reproduce this when building with Clang, > > but I don't know whether that's because GCC is missing something of Clang > > is signalling a false positive. You also don't need all of those whacky > > fuzzing options enabled. > > > > Anyway, to reproduce: > > > > $ git checkout for-next/kernelci > > $ make ARCH=arm64 CC=clang CROSS_COMPILE=aarch64-linux-gnu- defconfig > > <then do a menuconfig and enable UBSAN> > > $ make ARCH=arm64 CC=clang CROSS_COMPILE=aarch64-linux-gnu- Image > > > > I throw that at QEMU using: > > > > qemu-system-aarch64 -M virt -machine virtualization=true \ > > -machine virt,gic-version=3 \ > > -cpu max,sve=off -smp 2 -m 4096 \ > > -drive if=pflash,format=raw,file=efi.img,readonly \ > > -drive if=pflash,format=raw,file=varstore.img \ > > -drive if=virtio,format=raw,file=disk.img \ > > -device virtio-scsi-pci,id=scsi0 \ > > -device virtio-rng-pci \ > > -device virtio-net-pci,netdev=net0 \ > > -netdev user,id=net0,hostfwd=tcp::8222-:22 \ > > -nographic \ > > -kernel ~/work/linux/arch/arm64/boot/Image \ > > -append "earlycon root=/dev/vda2" > > > > I built QEMU a while ago according to: > > > > https://mirrors.edge.kernel.org/pub/linux/kernel/people/will/docs/qemu/qemu-arm64-howto.html > > > > and its version 4.2.50 (v4.2.0-779-g4354edb6dcc7). > > > > My clang is version 11.0.1. > > Thanks a lot Will. > > I *think* I was right - it is the ACPI_OFFSET() macro: > > #define ACPI_OFFSET(d, f) ACPI_PTR_DIFF (&(((d *) 0)->f), (void *) 0) > > that triggers the warnings (I suspected it because at least in one of > the warnings I could not see any dereference of any dynamically > allocated data).
Cheers, Lorenzo. > Now on what to do with it - thoughts welcome. Nick -- any idea what to do about the above? The '#define' pasted by Lorenzo is causing a couple of spurious UBSAN splats when compiling with clang 11. Cheers, Will
