linux-kernel - Re: [PATCH] ftrace: powerpc: remove startup functions from tracing

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Message-ID: <alpine.DEB.1.10.0810162100370.20570@gandalf.stny.rr.com>
Date:	Thu, 16 Oct 2008 21:04:51 -0400 (EDT)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
cc:	Josh Boyer <jwboyer@...ux.vnet.ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org, David Miller <davem@...emloft.net>,
	linuxppc-dev@...abs.org, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] ftrace: powerpc: remove startup functions from tracing

On Fri, 17 Oct 2008, Benjamin Herrenschmidt wrote:

> On Thu, 2008-10-16 at 20:48 -0400, Steven Rostedt wrote:
> > 
> > The early init code in PowerPC is not mapped to their final locations
> > and all jumps and memory references must be done with relative jumps
> > and accesses.
> > 
> > The lib files in the powerpc directory are called in early boot, and
> > since mcount will perform direct access to memory, the lib files need
> > not be traced.
> 
> This is annoying though, because that means things like memcpy,
> copy_to_from_user etc... can't be traced. On the other hand a lot
> of that is asm and already doesn't call mcount.

Yeah, I know. I was going to pick and choose which files in there should 
be converted, but then I saw that they were mostly asm, and it seemed to 
be better safe than sorry.

Sure, we could probably bring it down a bit. But I'm a bit paranoid it may 
cause someone else not to boot because of something else being called at 
early boot up.

But don't worry. When we get MCOUNT_RECORD ported to PPC this no longer 
becomes an issue, and we can simply do a
"ifndef CONFIG_FTRACE_MCOUNT_RECORD" around the -pg removal in the 
Makefile. (or what ever the Makefile syntax is for config options)

-- Steve

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