linux-kernel - Re: [PATCH 2/5] CPU Jitter RNG: Enable compilation

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Date:	Tue, 04 Feb 2014 17:53:39 +0100
From:	Stephan Mueller <smueller@...onox.de>
To:	Hannes Frederic Sowa <hannes@...essinduktion.org>
Cc:	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Theodore Ts'o <tytso@....edu>,
	Jörn Engel <joern@...fs.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Linux Kernel Developers List <linux-kernel@...r.kernel.org>,
	"Maciej W. Rozycki" <macro@...ux-mips.org>,
	Ralf Baechle <ralf@...ux-mips.org>, dave.taht@...il.com,
	John Crispin <blogic@...nwrt.org>, andrewmcgr@...il.com,
	Thorsten Glaser <tg@...bsd.de>, sandyinchina@...il.com
Subject: Re: [PATCH 2/5] CPU Jitter RNG: Enable compilation

Am Dienstag, 4. Februar 2014, 17:39:57 schrieb Hannes Frederic Sowa:

Hi Hannes,

>On Tue, Feb 04, 2014 at 05:19:52PM +0100, Stephan Mueller wrote:
>> Also, I consider the execution speed of the entropy collection is not
>> really an issue because the RNG delivers random numbers at a
>> comparatively high rate. Any other noise source feeding into random.c
>> delivers data with far less speed.
>
>Compiling the kernel with -O0 could add some other problems, like

I thought with the given flag, I only compile the respective C file 
without optimizations, but not the entire kernel. Am I wrong here?

>e.g. not doing enough constant folding which could result in linking
>errors. I guess it is not a problem currently though, but some of the
>compile time checks depend on this (compiletime_assert and such).

How do you think that my folding code can cause linking errors?
>
>Have you looked into adding compiler barriers into relevant places in
>the loops to stop the compiler from optimizing and spill out the
>values from the registers to their memory locations?

I did not look into that one, let me have a look.
>
>Greetings,
>
>  Hannes


Ciao
Stephan
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