Message-ID: <5220BC1A.3030108@zytor.com>
Date: Fri, 30 Aug 2013 08:36:58 -0700
From: "H. Peter Anvin" <hpa@zytor.com>
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To: Jan Kiszka <jan.kiszka@siemens.com>
CC: Fenghua Yu <fenghua.yu@intel.com>, Steven Rostedt <rostedt@goodmis.org>,
        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
References: <5217908E.2040702@siemens.com>
In-Reply-To: <5217908E.2040702@siemens.com>
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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.

	-hpa


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