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

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Date:	Thu, 16 Jun 2016 11:47:21 +0100
From:	James Morse <james.morse@....com>
To:	Mark Rutland <mark.rutland@....com>,
	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 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>


Thanks,

James