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Date:   Sat, 23 Apr 2022 12:00:33 +0200
From:   "Jason A. Donenfeld" <Jason@zx2c4.com>
To:     Sandy Harris <sandyinchina@gmail.com>
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Subject: Re: [PATCH v5 11/11] random: insist on random_get_entropy() existing
 in order to simplify
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Hi Sandy,

On Sat, Apr 23, 2022 at 10:24:07AM +0800, Sandy Harris wrote:
> On Sat, Apr 23, 2022 at 6:37 AM Jason A. Donenfeld <Jason@zx2c4.com> wrote:
> >
> > All platforms are now guaranteed to provide some value for
> > random_get_entropy(). In case some bug leads to this not being so, we
> > print a warning, ...
> 
> Would it make sense to test at compile time? If there is no hardware
> RNG nor a cycle counter, then the kernel should be compiled with
> the gcc latent entropy plugin. Generate a warning suggesting that,
> or even an error insisting on it.

Unfortunately, as a last ditch warning safeguard against bugs, I don't
think that's something we can determine at build time. A lot of this
machinery is dynamic. Fortunately a single check at init time brings
with it zero appreciable overhead.

Jason