linux-kernel - Re: ftrace breaks sparc64 build

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Message-ID: <alpine.DEB.1.10.0901052104400.16409@gandalf.stny.rr.com>
Date:	Mon, 5 Jan 2009 21:07:05 -0500 (EST)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Heiko Carstens <heiko.carstens@...ibm.com>
cc:	Sam Ravnborg <sam@...nborg.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Steven Rostedt <srostedt@...hat.com>,
	Ingo Molnar <mingo@...e.hu>,
	"David S. Miller" <davem@...emloft.net>,
	sparclinux <sparclinux@...r.kernel.org>
Subject: Re: ftrace breaks sparc64 build


On Tue, 6 Jan 2009, Heiko Carstens wrote:

> On Mon, Jan 05, 2009 at 05:14:22PM -0500, Steven Rostedt wrote:
> > 
> > On Mon, 5 Jan 2009, Sam Ravnborg wrote:
> > 
> > > > Is this all sparc cross compiler?  I'm trying to reproduce it on x86 with 
> > > > no avail :-(
> > > > 
> > > > I would like to test other ways to change the macro, but to do so, I need 
> > > > to get a compiler that will produce the warnings that you see. What 
> > > > version of gcc are you using?
> > > 
> > > I used crosstool to build a 3.4.5 gcc:
> > 
> > Hmm, that's a pretty old compiler. I wonder if it wouldn't just help
> > if we just make the branch tracer dependent on the compiler used. That is.
> > 
> > #if defined(CONFIG_PROFILE_ALL_BRANCHES) && (__GNUC__ >= 4)
> > #define if(cond) ...
> > 
> > Or something :-/
> 
> FWIW, on s390 with gcc 4.3.2 and an allyesconfig I get these:
> 
>   CC      arch/s390/mm/extmem.o
> arch/s390/mm/extmem.c: In function 'segment_modify_shared':
> arch/s390/mm/extmem.c:572: warning: 'end_addr' may be used uninitialized in this function
> arch/s390/mm/extmem.c:572: warning: 'start_addr' may be used uninitialized in this function
> arch/s390/mm/extmem.c: In function 'query_segment_type':
> arch/s390/mm/extmem.c:259: warning: 'vmrc' may be used uninitialized in this function
> 
> Switching off PROFILE_ALL_BRANCHES makes the warnings go away again.

Now that is really interesting. Because end_addr and start_addr are 
initialized via functions:

	if (x)
		init_me(a, &y);
	else
		init_me(b, &y);

Which actually does not make sense why turning off PROFILE_ALL_BRANCHES 
would affect this :-/

-- Steve

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