linux-kernel - Re: [PATCH v2] arm64: allow building with kcov coverage on ARM64

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Date:	Thu, 16 Jun 2016 16:44:12 +0100
From:	Mark Rutland <mark.rutland@....com>
To:	Alexander Potapenko <glider@...gle.com>,
	Catalin Marinas <catalin.marinas@....com>
Cc:	James Morse <james.morse@....com>,
	linux-arm-kernel@...ts.infradead.org,
	Ard Biesheuvel <ard.biesheuvel@...aro.org>,
	marc.zyngier@....com, Will Deacon <will.deacon@....com>,
	LKML <linux-kernel@...r.kernel.org>,
	Quentin Casasnovas <quentin.casasnovas@...cle.com>,
	Kostya Serebryany <kcc@...gle.com>,
	syzkaller <syzkaller@...glegroups.com>,
	Christoffer Dall <christoffer.dall@...aro.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Dmitriy Vyukov <dvyukov@...gle.com>
Subject: Re: [PATCH v2] arm64: allow building with kcov coverage on ARM64

On Thu, Jun 16, 2016 at 05:20:03PM +0200, Alexander Potapenko wrote:
> On Thu, Jun 16, 2016 at 12:47 PM, James Morse <james.morse@....com> wrote:
> > On 15/06/16 15:25, Mark Rutland wrote:
> >> On Wed, Jun 15, 2016 at 01:53:03PM +0200, Alexander Potapenko wrote:
> >>> On Wed, Jun 15, 2016 at 1:44 PM, Mark Rutland <mark.rutland@....com> wrote:
> >>>> On Wed, Jun 15, 2016 at 10:25:10AM +0100, Mark Rutland wrote:
> >>>>> On Tue, Jun 14, 2016 at 08:16:08PM +0200, Alexander Potapenko wrote:
> >>>>>> On Tue, Jun 14, 2016 at 7:55 PM, Mark Rutland <mark.rutland@....com> wrote:
> >>>>>>> I built and booted (via EFI) a kernel with this feature enabled (also
> >>>>>>> with the boot/Makefile change removed). I haven't tested the feature
> >>>>>>> itself as such, as I'm not sure how to do that.
> >>>>>> You can test it by running the test program from Documentation/kcov.txt.
> >>>>>
> >>>>> Ah, I hadn't spotted that. If I get the chance I'll try to give that a
> >>>>> go.
> >>>>
> >>>> I just had a go (with this applied atop of v4.7-rc3), and I get:
> >>>>
> >>>> root@...bensteg:/home/nanook# ./kcov
> >>>> mmap: No such device
> >>>>
> >>>> The device exists (it was able to open the fd, evidently):
> >>>>
> >>>> root@...bensteg:/home/nanook# ls -al /sys/kernel/debug/kcov
> >>>> -rw------- 1 root root 0 Jan  1  1970 /sys/kernel/debug/kcov
> >>>>
> >>>> Strace show me:
> >>>>
> >>>> openat(AT_FDCWD, "/sys/kernel/debug/kcov", O_RDWR) = 3
> >>>> ioctl(3, CHIOMOVE or CM_IOCGATR, 0x10000) = 0
> >>>> mmap(NULL, 524288, PROT_READ|PROT_WRITE, MAP_SHARED, 3, 0) = -1 ENODEV (No such device)
> >>>>
> >>>> It doesn't look like the error paths in kcov_mmap are hitting.
> >>>>
> >>>> Any ideas?
> >>> According to Dmitry (thanks, Dmitry!) this has regressed recently, but
> >>> there's a pending patch that should probably fix the problem:
> >>> http://lkml.iu.edu/hypermail/linux/kernel/1605.2/04379.html
> >>
> >> Thanks for the pointer! With that applied, the program runs.
> >>
> >> However, it looks like I missed a warning from the kernel build system,
> >> and my toolchain doesn't actually support -fsanitize-coverage=trace-pc,
> >> so I'm not going to be able to test that further.
> >
> > I dusted off a compiler that supports this, and ran the sample program under
> > Documentation with the above unproxify patch.
> >
> > Tested-by: James Morse <james.morse@....com>
> I think it's time to ask now :)
> If I receive "Tested-by" or "Acked-by" responses, do I need to send
> out a patch adding them, or should I rely on the maintainer taking the
> patch to the tree?
> The first option reduces the amount of work done by the maintainer,
> while the second one reduces the traffic in the list.
> Sorry, I couldn't find the answer in the manuals.

It's up to the maintainer, so it varies. The best thing to do is to ask
the maintainer what they'd prefer.

>From my experience, Catalin is usually happy to add tags, so I suspect
he'd be happy to do so for this patch (assuming he's happy to pick it
up). I'll leave it for him to say either way.

Thanks,
Mark.