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From: "H. Peter Anvin" <hpa@zytor.com>
To: Steven Rostedt <rostedt@goodmis.org>
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
Date: Fri, 30 Aug 2013 13:48:55 -0700	[thread overview]
Message-ID: <52210537.2070805@zytor.com> (raw)
In-Reply-To: <20130830130331.1e260e85@gandalf.local.home>

On 08/30/2013 10:03 AM, Steven Rostedt wrote:
> 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 ;-)
> 

Anyway... can we add this to the static tracing code?  It is two
instructions and is only needed on x86-32.  For performance, use dynamic.

	-hpa



  parent reply	other threads:[~2013-08-30 20:49 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-08-23 16:40 x86-32: Early microcode loading stumbles over disabled DYNAMIC_FTRACE Jan Kiszka
2013-08-23 20:17 ` Borislav Petkov
2013-08-26  8:50   ` Jan Kiszka
2013-08-30 15:36 ` H. Peter Anvin
2013-08-30 15:51   ` Steven Rostedt
2013-08-30 16:35     ` H. Peter Anvin
2013-08-30 17:03       ` Steven Rostedt
2013-08-30 17:16         ` H. Peter Anvin
2013-08-30 17:25           ` Steven Rostedt
2013-08-30 17:33             ` Jan Kiszka
2013-08-30 20:48         ` H. Peter Anvin [this message]
2013-08-31  0:17           ` Steven Rostedt
2013-08-31  5:07             ` Borislav Petkov
2013-08-31  5:23               ` Steven Rostedt

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