Messages in this thread | | | Date | Tue, 4 Feb 2014 17:50:33 +0100 | From | Hannes Frederic Sowa <> | Subject | Re: [PATCH 2/5] CPU Jitter RNG: Enable compilation |
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On Tue, Feb 04, 2014 at 05:39:57PM +0100, Hannes Frederic Sowa wrote: > 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 > 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). > > 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?
Quick follow-up:
Maybe you can get some ideas how to stop the compiler from optimizing code from commit fe8c8a126806fe ("crypto: more robust crypto_memneq"). Maybe also volatile could be helpful and OPTIMIZER_HIDE_VAR seems to be a good candidate to use here, too.
Greetings,
Hannes
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