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Date: Fri, 30 Aug 2013 13:03:31 -0400
From: Steven Rostedt <rostedt@goodmis.org>
To: "H. Peter Anvin" <hpa@zytor.com>
Cc: Jan Kiszka <jan.kiszka@siemens.com>, Fenghua Yu <fenghua.yu@intel.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        x86 <x86@kernel.org>, Ingo Molnar <mingo@elte.hu>,
        Thomas Gleixner <tglx@linutronix.de>
Subject: Re: x86-32: Early microcode loading stumbles over disabled
 DYNAMIC_FTRACE
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On Fri, 30 Aug 2013 09:35:18 -0700
"H. Peter Anvin" <hpa@zytor.com> wrote:

> On 08/30/2013 08:51 AM, Steven Rostedt wrote:
> > 
> > It does when dynamic tracing is enabled. But this issue is with static
> > tracing, there's no code modification, thus all functions call
> > mcount/__fentry__ and we need to look at a variable to determine if we
> > should trace or not.
> > 
> 
> And of course global variables are a no-no without special handling in
> pre-paging mode.  Sigh.
> 
> You *could* bail out of the calling address is < PAGE_OFFSET.
> 

We could do that too, as static tracing already gives us high overhead,
I'm not sure how much more overhead another check like this even
matters.

Who uses static tracing? I only use it to test that it still works ;-)

-- Steve