From owner-cvs-src@FreeBSD.ORG  Wed Jun 13 08:48:01 2007
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Date: Wed, 13 Jun 2007 18:47:58 +1000 (EST)
From: Bruce Evans <brde@optusnet.com.au>
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To: Kip Macy <kip.macy@gmail.com>
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Cc: cvs-src@FreeBSD.org, src-committers@FreeBSD.org,
	Bruce Evans <bde@FreeBSD.org>, cvs-all@FreeBSD.org
Subject: Re: cvs commit: src/sys/libkern mcount.c
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On Tue, 12 Jun 2007, Kip Macy wrote:

> On 6/12/07, Bruce Evans <bde@freebsd.org> wrote:
>> bde         2007-06-13 06:17:48 UTC
>> 
>>   FreeBSD src repository
>> 
>>   Modified files:
>>     sys/libkern          mcount.c
>>   Log:
>>   Unbreak high resolution profiling a little: use dummy asms to prevent
>>   timing loops being optimized away.
>> 
>>   Once apon a time, gcc promised not to optimize away timing loops, but
>>   gcc started optimizing away the call to a null function in the timing
>>   loop here some time between gcc-3.3.3 and gcc-3.4.6, and it started
>>   optimizing away the timing loop itself some time between gcc-3.4.6
>>   and gcc-4.2.
>
> Will this fix the hang on boot that I saw earlier today?

No.  It's unlikely that you even configure profiling.

Bruce