linux-kernel - Re: [PATCH v2] kernel: add kcov code coverage

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Message-ID: <CACT4Y+a1KpzS5RW4U2JY6sgpVxBGmGttYKptMe34bY4AD2ED-g@mail.gmail.com>
Date:	Thu, 14 Jan 2016 10:10:39 +0100
From:	Dmitry Vyukov <dvyukov@...gle.com>
To:	"Kirill A. Shutemov" <kirill@...temov.name>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	David Drysdale <drysdale@...gle.com>,
	Kees Cook <keescook@...gle.com>,
	Quentin Casasnovas <quentin.casasnovas@...cle.com>,
	Sasha Levin <sasha.levin@...cle.com>,
	Vegard Nossum <vegard.nossum@...cle.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Eric Dumazet <edumazet@...gle.com>,
	Tavis Ormandy <taviso@...gle.com>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	syzkaller <syzkaller@...glegroups.com>,
	Kostya Serebryany <kcc@...gle.com>,
	Alexander Potapenko <glider@...gle.com>,
	Andrey Ryabinin <ryabinin.a.a@...il.com>
Subject: Re: [PATCH v2] kernel: add kcov code coverage

On Thu, Jan 14, 2016 at 10:03 AM, Kirill A. Shutemov
<kirill@...temov.name> wrote:
> Hi,
>
> I've tried to build current -next with the patch. It has few reject, but
> nothing major.
>
> Booting the kernel in qemu with CONFIG_KCOV=y has failed. It hangs on
> "smpboot: Total of 3 processors activated (9178.27 BogoMIPS)"
>
> The interesting part is that I have only 2 cpu in this setup!
>
> Huh?
>
> CONFIG_KCOV=n works fine.


Hi Kirill,

Thanks for testing.

I will try to reproduce this if you provide:
 - location of the -next tree
 - gcc revision
 - .config
 - qemu command line

Alternatively, you can try to bulk disable instrumentation of
everything related to boot process (by adding KCOV_INSTRUMENT := n to
the Makefile). Most likely it is due to instrumentation. If it helps,
try to bisect the the guilty files.