linux-kernel - Re: [RFC PATCH 0/4] add support for gcov format introduced in gcc 4.7

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Message-ID: <521B63F7.9050409@linux.vnet.ibm.com>
Date:	Mon, 26 Aug 2013 16:19:35 +0200
From:	Peter Oberparleiter <oberpar@...ux.vnet.ibm.com>
To:	"LF.Tan" <lftan.linux@...il.com>
CC:	Frantisek Hrbata <fhrbata@...hat.com>,
	linux-kernel@...r.kernel.org, jstancek@...hat.com,
	keescook@...omium.org,
	Christophe Guillon <christophe.guillon@...com>,
	rusty@...tcorp.com.au, linux-arch@...r.kernel.org,
	Arnd Bergmann <arnd@...db.de>, mgahagan@...hat.com,
	agospoda@...hat.com
Subject: Re: [RFC PATCH 0/4] add support for gcov format introduced in gcc
 4.7

On 26.08.2013 13:39, LF.Tan wrote:
> Hi all
> 
> I am interested to enable Gcov on my platform (on a target board). I
> have tried to apply the 4 patches submitted by Frantisek Hrbata. But,
> the *.gcda is always empty. Note, I am using GCC 4.7.3.
> 
> I have followed the steps in Documentation/gcov.txt. I've mounted the
> NFS filesystem and it has access to the kernel build directory on host
> machine.The path for the kernel source in host and target are same.
> 
> Let said my kernel module is under drivers/misc,
> drivers/misc/module.ko. Turn on Gcov in drivers/misc/Makefile.
> 
> 1. mount -t debugfs none /sys/kernel/debug/
> 2. insmod <PATH>/module.ko
> 3. Perform some actions to excute code in module.ko
> 4. rmmod <PATH>/module.ko
> 5. Check /sys/kernel/debug/gcov/<PATH>/drivers/misc/. There is a soft
> link of module.gcno (I check the soft link is working), but
> module.gcda is empty.

Are you sure they are empty? .gcda files report a file size of 0 as many
virtual files do, but you can read data from them nevertheless. You could
try running "cat" on them to copy their contents for example.

> Any step is incorrect or missing? Or anyone know how to enable GCOV on
> target board? Please advice.
> I would like to enable GCOV in arch/ code as well.
> Thank you very much.

-- 
Peter Oberparleiter
Linux on System z Development - IBM Germany

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