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From: Roland McGrath <roland@redhat.com>
To: Ingo Molnar <mingo@elte.hu>
Cc: Priit Laes <plaes@plaes.org>, linux-kernel@vger.kernel.org,
       Thomas Gleixner <tglx@linutronix.de>, Sam Ravnborg <sam@ravnborg.org>
Subject: Re: REGRESSION: x86 vDSO: remove vdso-syms.o
In-Reply-To: Ingo Molnar's message of  Tuesday, 12 February 2008 00:16:35 +0100 <20080211231635.GA27673@elte.hu>
References: <1202769045.10829.12.camel@localhost>
	<20080211225332.2AE2E270191@magilla.localdomain>
	<20080211231635.GA27673@elte.hu>
Message-Id: <20080211232345.A472B270191@magilla.localdomain>
Date: Mon, 11 Feb 2008 15:23:45 -0800 (PST)
Sender: linux-kernel-owner@vger.kernel.org
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> if that file is empty, it might be the effect of a Ctrl-C. I sometimes 
> get that on .o files, if i Ctrl-C a highly parallel make -j at the wrong 
> moment. (is this expected behavior? It's been like this for a long 
> time.)

It is the known situation with the compiler since the dawn of time, yes.
It just writes the file directly, so if it dies in the middle, there's a
file with a fresh date.  For things like this done in makefile commands
with >, it has forever been canonical for the anal to use:

	... > $@.new
	mv -f $@.new $@

which avoids the problem.  The kernel makefiles are entirely haphazard
about places that do this or don't.  It uglifies the commands, but avoids
the problem of freshly-dated but wrong/empty files from botched make runs.
I did not do this in cmd_vdsosym (though I did in cmd_vdso32sym, go figure).


Thanks,
Roland
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