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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
Date: Fri, 30 Aug 2013 11:51:42 -0400	[thread overview]
Message-ID: <20130830115142.1ee4c825@gandalf.local.home> (raw)
In-Reply-To: <5220BC1A.3030108@zytor.com>

On Fri, 30 Aug 2013 08:36:58 -0700
"H. Peter Anvin" <hpa@zytor.com> wrote:

> On 08/23/2013 09:40 AM, Jan Kiszka wrote:
> > Hi all,
> > 
> > 32-bit kernels currently crash/reboot in early microcode loading when
> > non-dynamic function tracing is enabled. Several functions in that path
> > get instrumented with mcount, but its non-dynamic implementation does
> > not work before paging is enabled (it accesses global variables at wrong
> > addresses).
> > 
> > Below some hunks to get it working again - at least in the absence of
> > any microcode in the initrd. Marking all involved functions as __init is
> > another option (as __init implies notrace). But I bet there is more
> > hidden. I see e.g. a pr_warn() in find_cpio_init that should trigger the
> > issue as well if we hit the error it reports (btw. printing at this
> > point of the boot should not work anyway, should it?).
> > 
> > Better ideas?
> > 
> > Jan
> > 
> 
> A better idea would be for the mcount/__fentry__ function to simply
> return until the function tracing stuff is actually ready.
> 

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.

-- Steve

  reply	other threads:[~2013-08-30 15:51 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 [this message]
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
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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