Message-ID: <20130827133439.GB2418@localhost.localdomain>
Date:	Tue, 27 Aug 2013 15:34:39 +0200
From:	Frantisek Hrbata <fhrbata@...hat.com>
To:	Peter Oberparleiter <oberpar@...ux.vnet.ibm.com>
Cc:	linux-kernel@...r.kernel.org, jstancek@...hat.com,
	keescook@...omium.org, rusty@...tcorp.com.au,
	linux-arch@...r.kernel.org, arnd@...db.de, mgahagan@...hat.com,
	agospoda@...hat.com
Subject: Re: [RFC PATCH 3/4] gcov: compile specific gcov implementation based
 on gcc version

On Mon, Aug 26, 2013 at 04:14:07PM +0200, Peter Oberparleiter wrote:
> On 24.08.2013 21:44, Frantisek Hrbata wrote:
> > On Fri, Aug 23, 2013 at 05:21:12PM +0200, Peter Oberparleiter wrote:
> >> On 23.08.2013 17:15, Peter Oberparleiter wrote:
> >>> On 23.08.2013 10:39, Frantisek Hrbata wrote:
> >>>> Compile the correct gcov implementation file for a specific gcc version. In
> >>>> the future, if another file is added, the conditions will need to be somehow
> >>>> adjusted to if-elif-else case, but at this point the simple cc-ifversion should
> >>>> be enough.
> >>
> >> As promised, I'm also adding the patch that makes the format-specific part
> >> of gcov-kernel a loadable kernel module:
> >>
> >> ---
> >> kernel: gcov: make format-specific code loadable
> >>
> >> Turn the format-specific part of gcov-kernel into a loadable kernel
> >> module. This enables the use of gcov-kernel with kernel modules
> >> that were compiled with a version of GCC that produces a different
> >> gcov format when compared to the version of GCC that was used to
> >> compile the kernel.
> > 
> > If I understand it correctly, this would mean that you will be able to use only
> > one implementation of gcov format at the time. Meaning you will be able to get
> > coverage data for module, but not for kernel if it was compiled with different
> > gcc(gcda format). This is probably ok if you work only on your module, but I'm
> > not sure this is generally the right approach. In this case I would probably
> > rather see some support for more gcov formats at the same time(e.g. set of
> > callback operations per gcov version). Again I'm probably missing something, but
> > I still cannot see reason why to add such feature. If you want gcov support just
> > compile your kernel and modules with the same gcc version(gcda format). But if
> > this is really needed maybe it would be better to consider some parallel support
> > for more gcov formats based on the gcov_info version.
> 
> The callback approach has other drawbacks (see previous mail).

Agreed, I did not realized these problems for the first time when I was thinking
about the callback approach.
	
> 
> > Would it be possible to add support for the modified gcc 4.7 gcov format and
> > deal with this later? I can incorporate your changes: iter to use buffer,
> > .init_array for modules and possibility to explicitly select the gcda format.
> > In this case we will have at least the basic support in kernel. This is just me
> > thinking out loud.
> 
> I think that's an approach I can live with. Maybe the need for a multi-version
> support will surface again later in a more refined form, but until then there
> should be no reason to delay base GCC 4.7 support any further.

Great. I can incorporate the changes you proposed and post V2. Or do you prefer
to post it by your self? Based on the info and patches you already provided I
guess you already have something ready. Simply what suits you best :).

Many thanks Peter

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

-- 
Frantisek Hrbata
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