[PATCH] arm: port KCOV to arm

[Mark Rutland]

On Fri, Apr 27, 2018 at 03:51:22PM +0200, Dmitry Vyukov wrote:
> On Fri, Apr 27, 2018 at 3:06 PM, Mark Rutland <mark.rutland at arm.com> wrote:
> > Can you share your kernel config?
> 
> Attached. It's pretty much vexpress_defconfig with few minor
> additions. Here is full description of what I am doing:
> https://github.com/google/syzkaller/blob/master/docs/linux/setup_linux-host_qemu-vm_arm-kernel.md

Cheers!

> FWIW when I do "KCOV_INSTRUMENT_fault.o := n" everything works and I
> see reasonable coverage.

While this may be the case, I think it's papering over a bug rather than
solving it.

[...]

> > I can't reproduce the issue on real hardware atop of v4.17-rc2, when
> > booting and running a standard ARMv7 buildroot userspace. So the kcov
> > mode check seems fine to me.
> 
> It happens after brief fuzzing with syzkaller. So it's both kcov
> opened and some weird syscall workload. Again, here is everything what
> I am doing:
> https://github.com/google/syzkaller/blob/master/docs/linux/setup_linux-host_qemu-vm_arm-kernel.md

I've set this up, and while I see RCU stalls and "no output from test
machine" warnings, I'm not seeing any reports with KCOV splats.

Are you somehow connecting to a VM which failed with no output?

Thanks,
Mark.