Messages in this thread | | | Date | Tue, 26 May 2020 21:21:57 +0100 | From | Will Deacon <> | Subject | Re: arm64/acpi: NULL dereference reports from UBSAN at boot |
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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.
Will
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