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

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Date:	Wed, 15 Jun 2016 12:44:39 +0100
From:	Mark Rutland <mark.rutland@....com>
To:	Alexander Potapenko <glider@...gle.com>
Cc:	linux-arm-kernel@...ts.infradead.org,
	Ard Biesheuvel <ard.biesheuvel@...aro.org>,
	marc.zyngier@....com, Catalin Marinas <catalin.marinas@....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 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?

Thanks,
Mark.